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the ¿с results (forming part of n serios which I obtained by long and laborious calculations) wen» not obtained Ъу Mr. Lockycr himself—not oven inverted commas.

* Bat I repeat, ач respects this parage and threo other far more noteworthy instances, I make no charge n^ainst Mr. Lockyer, save of having forgotten to duly indicate the source whence he had derived hi« information. Had tho complet«- omission of my паши from Ыч book been intentional, the mattor would have been different. As it is, I should not have referred to it at all but for the angry and discourteous note he appended to a paragraph in which 1 had paid him u high but not undeserved compliment.

The fact is, that Professor Pritehard and Mr. Lock•vcr combined their fo.ves to attack roe (apparently for no other reason than that, like them, I work in tho field of popular aetronomical literalnreï. If in self-defence I have faced them, and dealt each a blow " straight from the shoulder," they have themselves only to thank. I am neither (luarrelsunio nor thin-skinned; hut no one shall make nnju-Л and ill-mannered attacks цша iue with impunity. Pacem amo, bellum non timeo. KlCHD. A. Proctob.

WINDMILLS.

;*203] Sib,—In reply to "Derf Errac," page 150, lettoi 152,1 should recommend him, before going to work upon models, to procure Smeatou's work ou tho •• Theory and Construction of both Vertical and Horizontal WiudmillB." Smeaton was the engineer who built the famous lighthouse on the Eddystone rock, near Plymouth.

Ho should also kuow that tho rustic form of Horizontal mill was in nse among the Tartar nations before the timo of the Crusades. Yaliani's plan for the same object may be frequently seen ».et np in the gardens of retired sailors, in the form of four full-rigged ships fixed at the extremities of four arms revolving upon a central pivot, a form that hue been known ever sinco vessels at ьеа were bund able to turn a complete circle with the same wind. All these forms are powerless for effectual work, unless constructed of colossal dimenhions, and then their speed is so slow that formidable trains of wheels and pinions are required in order to perform any useful work

"Dorf Errac" is astounded at the magnitude of the proportions of my horizontal mill, but the arms are only 18ft., whereas in the common vertical they are often 30ft. long. It is true that there is an addition of lift, to the radius for the funnel openings are indispensable for concentration of the wind, without which no useful purpose can be obtained; and it may l»e observed that there being no movable parts, there is no wear and tear.

If "Dorf Krrac " would taku the trouble to construct a model of my machine at the" expense of a few sticks and boine sheet zinc, he will find the immeuse advantage of concentration still greater on the large scale.

A horizontal windmill war» to be seen at tho beginning of the present century at the bouth end of Battersea Bridge, but being constructed on erroneous notions, it was soon done away with. It was in the form of a tower 80ft. high., with no pro vi-.ion for concentration, us may be seen in old views of Battersea Bridge. I was in that mill, however, before it was taken down, and found that it was only driving one pair of stones at a very feeble speed. Hknry W. Revele Y.

averted, if the " agriculturists of England" had exercised their common sense. It is pitiable to find tlmt they do not give a wider meaning to their own proverb of '* making hay whilst the sun shines ;" if they did so, they would '* catch water when it rained," and pro&ervo it in tank« properly protected, which would be sufficient to supply all their wants during the drought.

In conclusion, allow mo to ask "R. P." upon what authority does ho assert that *' clouds passing over us, unless drawn down by gunpowder, empty themselves into the German Ocean?" I feel inclined tu think this is an original idea, and that your correspondent is his own author. Lex.

[205] Stn,—During four years whilst I wa« at Woolwich, when the нку was very cloudy and overcast, whenever the artillery fired upon the Common rain generally ensued. I am inclined to think that a rapid succession of discharges from field gnus would prove more efficacious than a few discharges at intervals from heavy guns.

Oliver Halda Ne Stores, Captain tlate) R.E.

ARTILLERY DISCHARGES AND RAIN*.

[204] Sib,—I am not at all surprised that the Editor of the Time* thought the letter of " R. P." (page ■14») not worth publishing, for had your correspondent been as well informed upon tht* subject he writes opon as he professes to be, ho would have known that the question has often been mooted, but no " right men" nave ever thought it worth taking it up. By tho way, what does " R. P." moan by "right men "? Docs he mean Government olflcials, who might be induced by some "moonsiiiny" theory, to squander tho public money in vague experiments? or does he mean private individuals? If the former, taxpayers would raise a very decided and rational objection. If the latter, I do not think any private individual could bo found foolish enough to spend either tunc or money, for the benefit of a few, in making experiments, the theory of which is pure fiction.

1 maintain that rain is not tho inevitable result of a concussion of the air, for I have -particularly observed the weather after artillery practice on more than one occasion, and as an instance of great concussion of the air which did not result in a fall of rain, I may mention the explosion of tho Lothj Sleigh, in the Mersey, a few years ago. This explosion was so temtic that the noise was actually heard at Birmingham, л distance of about GO miles. But, supposing for the sake of argument, that " R. P.'s" theory be correct, I would ask him of what utility would a continuons discharge of artillery, or a gunpowder explosion, be under a cloudless sky? In cloudy weather it would bo mere labour in vain, ur waste of labour, to cause a concussion of tho air for tho purpose of foreiug rain, inasmuch as a voluntary shower is, in nine cases out of ten, inevitable. Again, allow me to ask "il. P." how many explosions of " Government powder-mills" or continuous "discharges of artillery" would ue necessary to cause one shower of rain over tho whole British area?

I am •' quito at ыа" as to the relevancy "a stone thrown into a pond " has to an explosion of gunpowder, but perhaps there is some deep philosophy in the allusion beyond my poor comprehension. I think the "mythical millions " that a want of raiu has already cost might have been saved, and the "calamity" of a continued drought not only mitigated, bat completely

HOW COD-LIVER OIL IS MADE, AND HOW IT SHOULD BE TAKEN.

[•206] Sib,—As one of oar subscribers has asked some questions about this important oil, I propose, with your permission, to lay before our readers a short account of the oil, and the best manner to administer it.

Ae its name denotes, cod-liver oil is made from the liver of the common cod-fish, and other Rpeeies of Gadas frequenting the seas of Northern Europe and America. The following are the most important species of the oil-yielding fish, in a medical point of view :— Ondú* morrhua or the common cod-fish; Oaduu tallaría* or the dorse; Gadtumolüa, or tin: ling; Gadits carbotiarius, or the coal-fish; and the Gadwt mulanyus, or the whiting. From this list it will be seen that cod-liver oil is the product of many other species of fish besides the common cod.

Tho oil may be extracted from the livers by three different methods :—By exposing them to the sun to undergo a process of fermentation j by boiling them in water for some time ; or by dividing the livers and permitting the oil slowly to drain from them. This method is now employed in the preparation of the best English cod liver oil. The following is the way in which the oil ia made at Messrs. Bell & Co.'s establishment:— Tho livers are collected daily, so that no trace of decomposition may have occurred, carefully examined, in order to remove all traces of blood and impurity, and to separate any inferior livers; they are then sliced and exposed to a temperature not exceeding 180' Fahr, till all the oil has drained from them. This is filtered; afterwards exposed to a temperature of about 50 Fahr., in order to congeal much of the solid fat (margarine), and again filtered and put into bottles well secured from the action of the air.

Three varieties of cod-liver oil occur in commerce, distinguished by their colour—the pale, prepared in England, or elsewhere; besides which are the light brown and dark oil from Norway. Tho difference in colour in tho different oils depends upon the circumstances attending their preparation—as the amount of heat employed, the state of freshness or putridity of the livers, the quantity of decomposed matter present in the oil, and the length of exposure to the atmosphere. The following test is given in Dr. Garrod's "Materia Medica," from which also I have obtained some of the facts as to the preparation, &c., of the oil. When pure cod-liver oil, spread in a thiu layer on a plate, has a drop of oil of vitriol added to it, a beautiful lake or crimson colour is produced, rising from the point of contact of tho oil and acid, and rapidly spreading over the surface. This is probably due to the action of the acid on the biliary principles present in the oil. By this simple test the pure oil is at once detected; for when other oils not of hepatic origin are present, the sulphuric acid^loesnot give the lake colour, or this becomes immediately mixed with and obscured by a dark brown substance from the charring of the oil. Sueh is the case with whale or seal oil, also with olive and other vegetable oils. Somo of my readers may wish to know what cod-liver oil is composed of. It contains oléine, margarine, various biliary principles, also phosphoric ami sulphuric acid, with salts of lime, magnesia, and iron, and a peculiar substance called gaduin—very insoluble in ordinary menstrua, but soluble in sulphuric acid, and giving a blood red colour to tin; solution ; also traces of iodine and bromine ; the proportion of iodine is not more than 0*5 per cent.

Cod-liver oil is a remedy which, at the present time, stands in very high estimation; nor does it appear probably that its reputation will he ephemeral. When taken by patients who have become emaciated from any cause, and whose blood is impoverished, it frequently restores the flesh, and, from Dr. Thcophilns Thompson's statements, it appears also to improve the richness of the blood. Under its influence, patients often increase greatly in weight, the inscrease exceeding пишу times the amount of oil consumed during the period. It has been supposed that the iodine and bromine contained in it might produce, the beneficial results, but thisj idea is not tenable, for tho effects of these latter remedies are very different from that of the oil; it would seem probable that it acts simply as an oil, and that it is superior te other oils on account of iU being more readily assimilated. If tho statement of Winkler, prove correct—nameh, that the oléine dilTers from ordinary oléine in not yielding glycerine—

this may in part explain its value; but how it acts is still undetermined.

Some people find the oil unpalatable, from tho manner in which they take it. Thus, some take it upon ale or porter, others upon milk or water. Can it be wondorcd at that such patients cannot "master" the oil? I have always found that the oil can be taken better upon some orange wine, or some mixture containing quinine and sulphuric acid. The acid covers the taste of the oil, and the quinine acts also as л tonic. Some patients cannot even take tho oil when thus mixed with the acid mixture, and for the use of such I recommend tho following:—Take of picked gum Tragacanth Joz., dissolve in 20oz. of boiling water, add sugar according to taste, now pour into this mucilage lOoz. of the best cod-liver oil, shake well; three drops of ев*, lemons, and tho same quantity of ess. almonds should now be added, and if yon wish to keep the mixture for some time add '2oz. of brandy. In this compound the oil combines with tho gum and forms an emulsion of a milky-white colour, which few will know from a well-made custard. The doso of this mixture is just double the quantity of the pare oil. The dose of tho pure oil is from lä. drachm to loz., taken at tho time of a meal or immediately after food. It is often advantageously administered at bed time; and my friend, "A Mechanic," will be able to take his at dinner-time, and so dispense with a pudding.

Patients often find that after they have been taking cod-liver oil for some time they turn from it with disgust. Why is this? I have already remarked that of all oils the cod liver oil is the most easily assimilated by the system. But after a time the intestines refuse to absorb it, and that being the case it passes through them, and is found in an unaltered state in the fa-сев; thus, by a wise provision of nature, directly the oil is of no more use, a dislike is felt for its employment. If, then, peoplo find that after they havetaken cod-liver oil, say for two weeks, it does not agree with them, they should leave it off for about a week or so, then take it again, and so on. By these means the fall benefits oí the oil will be derived. I trust that theee remarks may be of some use to your readers.

С J. H. w.

CARRIAGE WHEELS—THE PHANTOM AND OTHERS.

[207] Sir,—In tho controversy on the relativ* merits of the spider and phantom wheels, which are but differently proportioned examples of Jones's suspension wheel*, modified to render them ton table for light vehicles—modification MiiÍcii maybe taken as representing the most modern forain of the principle of suspending the weight to be carried from the top of the wheel by rods or chains, instead of supporting it on legs or struts, which is just what wheel-spokes are—iu the common way is carried out.

As it is well known that a very much greater weight can be safely supported by an iron or steel rod when that weight is suspended to it than it can safely bear if employed as a column in constant motion, like a wheel spoke, which must not only be incompressible, but also sufficiently rigid not to become bent in use, it follows that so long as it is not employed to communicate the driving forces from its nave to it« periphery—in other words, so long as it is not required to act bike a cogged or toothed wheel, or as part of what is termed "frictional gearing," but as ¡i mere trailing wheel, and its axle is kept nearly horizontal—a wheel to carry with safety a given weight may be constructed on the suspension principio far lighter than in the ordinary manner.

Suspension wheels have the further advantage of being somewhat cheaper than those with spokes, for rod iron or steel is less costly than spokes, even when the latter are formed by automatic tools toot to mention costly hand labour), as in the rase of artillery and waggon wheels constructed for Her Majesty's military service ; but, as ordinarily made, they ore very unfit—from their want of rigidity, in the direction that the driving force is communicated—to act asdrioMfr wheels cither for locomotives or velocipedes. A driving wheel requires rigid arms or spokes, just as a cogged wheel does, and the only practical question is how the needful rigidity may best be obtained without needless increase of weight.

The usual method in the case of locomotive wheels is to construct the spokes of rigid iron, so that they may not sensibly bend when transmitting the thriving force. When this plan is carried out in a velocipede it adds considerably to the weight of the driving wheels, which is a berious objection when it is considered the rider has to Lift his carriage up-hill, which he must do when ascending inclines. The " Phantom" may bo sufficiently rigid, especially if of moderate diameter; but, if I rightly understand, it has the same defect as the " Spider," viz., that each pair of suspending rods are attached to its nave in the tame plane. Now if the rods be short, as in the case of a 36in, or l*2in. wheel, they may, if unnecessarily thick, be rigid enough to perform the function of levers, and transmit the driving force from the axle to the periphery of the wheel, without the weight of the latter being made very great, but it is obvious that if the rods are only strong enough to (safely) suspend the weight of the carriage and its rider, they cannot, when each pair is in the same plane, also be rigid enough to act as lèvera for transmitting the driving force.

To enable a suspension wkeel to become an efficient driving wheel, each pair of rods, instead of being in the same plane, should be attached to its nave at л distance apart equal to tho nave's diameter; that is to say, in nautical language, attached fote and aft.

All the suspension wheels I have seen, until the principle was applied to our hobbies, aliat velocipedes, have been trailing wheels. All cart, omnibus, cab, and railway carriage wheels—excepting the driving wheels of locomotive engines—come under this category ; and for railway carriages whose axes are nearly horizontal— excepting when the wheels are so stupid as to ru n off the metals- I think suspension wheels are specially suited. I have a very strong opinion that when my respected friend Bridges Adams' notions of the advantage of re- ducing the dead weight to be hauled have come to be appreciated as they deserve, suspension wheels, with mild steel rods, of a quality resembling steel music wire, will come into use, not only on account of their much smaller weight but also because of the great facility of repairing them. Weight is of comparatively little importance on level railways; for B wheel, even if it were a solid disc of iron supports its own weight, and therefore that weight does not add to the force of traction required to haul it; but when we encounter gradients of one in twenty or more, all the weight of the train has to be lifted to the summit level, and this requires more coal than to make it follow its leader ou a horizontal line.

It will be understood that I do not propose to make the driving wheels of a locomotive engine on the suspension principle. In them weight causes "bite," and so long as the wheel and rail have to be pressed together it can little matter whether comparatively light wheels are pressed to the rail by a load on their axles or by the weight of the wheels themselves. On the contrary, the heavier the wheel the greater the "bite," irrespective of the load ou its axle ; во if the driving wheels of a locomotive engine were solid castings, like a pair of iron-edge runners (which one of my men called cast-iron grindstones on the same principle that our Mary Ann says she " biles " unclean garments in her *' iron " copper), it would be attended with the advantages of less wear (from diminished pressure in the axle-brasses) and cheapness of construction, for it costs less to cast a heavy disc than to forge a wronght-irou locomotive wheel.

If you think a suspension wheel on the principle I suggest worth engraving I shall be happy to send a drawing. The Harmonious Blacksmith.

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wheels Stiin. ditto; hind axle 7in. long, with 8in. cranks at opposite points. The connecting rods are only \\n. diameter. The two front hanging levers and pedals, as well as the centro framing, is of wood. It steers easily with the two handles firmly fixed to the front axle. It needs no brake, as it is under perfect control by the feet. The muscular exertion is not at all fatiguing, as the muscles of the body are as well supported as if sitting in an arm-chair. There is a steel spring across the point-axle which takes off all concussion. I can get up any moderate incline with it, ■^ц тттНЫпк it would do ten miles in an hour. The distance front axle to axle is 81in.; ditto, between front wheels, 31in. I beg to congratulate y au on the success of your journal. H. Childs.

ANSWERS TO QUESTIONS.

[•2(50] Sir,—When last doing this I forgot to state that "W. T.," who has had very considerable experience in "bushing," i.e., lining with cloth the holes in the butts of pianoforte hammer*, has partly written an article on this subject, which I expect will let more light in on it than anything I can say, who on such mere practical details can only shine by reflected light, i.e., mere moonshine compared to that of the original luminary. May I request that my fellowenquirers will in future adopt the advice of Di Vernon to F. Osbaldiston, Esq, and ask all merely practical questions at him instead of at me. He has promised to answer all such arrears in one batch, and not only reply to Mr. Moffat, No. 26i0, but " correct "— л la tutor—I hope not with a birch rod—Mr. Kemble's odd notions concerning the bushing of pianoforte centres.

I cannot call to mind where I saw the engraving of the foghorn which " E. A.," No. 3780, desires a copy of, or would have sent it. It is voiced exactly like the reed trumpet pipe of an organ, excepting the proportions of the reed to the pipe, the former being very unusually large in proportion to the length of the latter, anil made stiff enough to bear an enormous pressure of wind.

The Harmonious Blacksmith.

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THE 100TH PSALM, ARRANGED FOR FOUR VOICES, BY GEO. COOPER, SEN., CONTRIBUTED BY THE "HARMONIOUS BLACKSMITH" FOR THE ESPECIAL BEHOOF OF THE TONTO SOL-FAISTS.

[210] Sir,—Rarely indeed do I fail to fulfil a promise, but mine to send a familiar tune in this notation, has remained so long unfulfilled that I am not surprised at an occasional gentle reminder. May I hope this will be received as reply to all demands.

In selecting H All people that on earth do dwell"— not even excepting those savage man-murdering races, the French and German, who have not only ceased to cultivate either social or musical harmonious relations with each other, but have also substituted for them that worst of discords, war—for the purpose of illustrating my old friend's system of musical notation, I have been induced to do so because all people know "All people," and because as almost ¡ all people possess I "All people" in our ordinary complex notation, they i will therefore be' able to compare that with this, and, if wise enough, to admire its beautiful simplicity. If not all people, many people at the least among my fellow-readers, will also be able to compare this with the popular and much vaunted Tonic Sol-Fa system, which, to my crass ignorance, does not appear equally with this to possess the beauty of simplicity, however much of that same article some of the advocates of the Tonic Sol-Fa system may themselves have manifested.

As regards absolute originality, I fear I cannot justly claim for my old friend much more than most other inventors, have exhibited. His notation, when I examined by the light of the experience of those who are accustomed to music by handle, is resolved into a copy of the pins and staples of the barrel of that "organ " made by the said handle to discourse the "sweet music" which drives Babbage to distraction, and compels quiet folk to pay for the privilege of silence, which we then—after this iuflicton—do indeed recognize, in the words of the Chelsea philosopher, to be golden. This copy of these staples and pins, written on two staves of five lines each, is neither more nor less than

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the notation before" в a the reader.

The idea of writing the notes or signs of the sounds uttered when the black keys are depressed on the lines, and those uttered when the white keys are struck in the spaces between the lines, for the purpose of avoiding the necessity of using signs for sharps, flats, and naturals in music, written for keyed instruments, with fixed intervals, is no novelty. If I am not much mistaken, it was done in the notation published by the reverend gentleman, whose name I forget—I think the same person who also anticipated Hawkins in the construction of apparatus which recorded musical performance on keyed instruments. About forty-five years ago I saw this notation engraved in an early vol. of the Phil. Trans., date about 1680.

Anything simpler or more easily impressed on the mind of the intelligent tyro than that all the notes are of the same form, and the fact that the length of any one note in this system expresses its temporal value, it would be difficult to imagine ; but this peculiarity, how

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FRUITLESS LETTERS.

[211] Sir,—Would you have the kindness to inform me through the Mechanic, or by letter, what firm ?« can recommend that makes the best sewing тас&пгс adapted for dress making and general purposes, uri you will greatly oblige me? W. a.

Kearsley, Aug. 2nd, 1870.

(We frequently receive letters like the above, t '■■:-.■. we never on principle give tin- information &¿ked far We think that a publication devoted to scientific esucation, or, in fact, any other kind of education, shed: never recommend the goods of aar particular mane facturer. Weak Journale may, and frequently do sad things "for a consideration;" bat strong joaxo should be, like Carear's wife, M above ¿a^picion." it all events it is useless for any one to write из sotí letters as the one above.—Ed. E. M.J

MAMMOTH.

[313] Sir,—Only two ¿кякЛвшЫШеташшюЕкжМЗФpha» primigeniua, are existing, I think, in maseamsthe mammoth of the Lena,B.t St. PeUtr$b?sg, and the wutmmotk of Lierre, at the Museum of Natural History at Brussels; another specimen was üseoTtred in 1866. near Tomsk in Siberia, and it сопшпздзи has been named by the Academy for the purpose of it» removal Mt St Petersburg. I saw the magnifierai skeleton of the mammoth of Brussels some mouths адо, and & few particulars of its discovery may prove илетезшхц.

In the month of May, 1ЫЮ, when constructing & canal near Lierre (province of Antwerp), the workmen tennd buried in the sands the skeleton of a gigantic animal; this skeleton was lying on the right side, the pu i '. column very much bent ; the head was entire, and there Whs also a task of enormous dimensions ; nearly all the ribs of the left side were missing, and several members were broken, or rather discomposed. Mr. Seoby, % military physician, recognized that it wo» the skeleton of a mammoth. He had all the bones collected, but they had lost their solidity; the head, of an enormous weight, split and separated into numerous ггацшок;*; some other bones also suffered from the extraction an i in the transport.

These ancient remains, deposited ш the museum of Brussels, deteriorated every year until the new direct*. Dr. Dupont—во well known by his investigauoir- in the Belgian grottoes—undertook to restore them. Be was aided in this difficult task by Mr. Dapaun. Ob* of the auxiliaries of the museum, who gave proofs ondei these circumstances of great skill and perseverance- After tea months of laborious exertions the mammoth of Lierre was entirely restored in the action of walking.

The height at the nape is 8m. 60; the height of the* Indian elephant, of which an adult skeleton is also existing at the Museum of Brussels, is only 2m. CO ; the head weighs 250 kilogrammes, and the task measure* 2m. 90, following the curve.

The restoration presented great difficulties ** well as the restoration of the missing bones ; the skull had been reduced into more than 200 СгалввЬ; nearly a third part of the skeleton was wanting. лЫ had to be carved in wood; the humerus, for wbk-4 *¿e museum did not possess all the requisites, could only be restored by the study of another humerus Ье1ои£Ш£ to the University of Ghent; one of the tasks i* arúócial; oue tibia and one rib do not belong to the same animal, but toan individual of the same species, height,and age.

The manner of putting together the mammoth of Lierre deserves special attention. In some zoological galleries the bones are perforated, and are attached.together with iron wire, and so rendered motionless; the mammoth of Brussels has not a single bone perforatedBy means of some adjusting screws every bout can be taken away and examined. The whole of this enormes* skeleton can be taken to pieces in 20 minutes and put up again in less than one hour.

For other particulars on mammoths, especially on that of the Lena, see Intellectual Observer, February, 1867, page 70. Bebnardis.

OUR SIZE AND PRICE.

ГЭ13] Sir, — When about to incorporate the Mkchanic you invited suggestions. I, being her majesty's (self-appointed, if not self-named) suggest" general, then did mine office. One of the said suggestions was to extend the journal to eight pages more, and charge ííd. for it. Considering you have to reject

a good miiny communications, and have undertaken to report the doings of the scientific societies—not to mention renew» and extract« from new books—I cannot Kelp thinking vou could weU occupy more space. It ■toea against the conscience to buy for 2d. what is linnestlv worth 3d.; but, commercially, it might be advantageous to enlarge both number of pages and the price at once. Your present capacity is hardly 1лгяе enough for the journals and their contributors ■which you have absorbed, not to mention one or two others which may be absorbed. So I cannot help thinking that the sooner yon relieve our Tendkr conscience» from the reproach of receiving more than an equivalent for our twopences the better.

The Harmonious Blacksmith.

[Though the "Harmonious Blacksmith" is not the only one who has made a similar suggestion, we think it right to sav that we have no idea whatever of increasing the pnce of the English Mechanic. As to its size we do not know what it may grow to: ranch, however, will depend ou tbo activity of our constituency, of readers and subscribers. It is possible to permanently increase it eight pages without any increase of price. Let us have three subscribers where we have uow got two, and it shall be done.—. Ed. E. SI.]

CHEMICAL, FLORICULTURE. [214] Sir,—The three primary colours, red, blue, and yellow, are not to be found pure in any species of rlower. We have red and bine in fuchsia, but no vellow; yellow and red in the rose, but no blue; blue and yellow in the heartsease, but no red, and so on. I mean, be it understood, decided primar)" colours, and not socondarv. As this seems to be a law of nature that sets the "art of man at defiance, we may expect bine dahlias, yellow geraniums, and scarlet pansies when the circle is squared, but not till then.

Dan Rosen.

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THE SYMBOL тт. CONIC SECTIONS, ETC.

[216] Sib,—" Gimel " should have told us he wrote *' to argue," and not for information. "He knows all about the matter," he now says. Apparently, however, he does not know that a ratio is but an abstract quantity. Todhunter is quite right, of course. *' Gimel " might as well say that the symbol 8 does not invariably represent the number three, because it also represents the number of angles in a triangle.

I should regard "the section produced by a plane passing through the vertex of a cone" as either two intersecting right lines, or oue right line, or a point (according to the position of the plane), not о» a hyperbola. One may, if one so chooses, speak of a circle as an ellipse, whose eccentricity is zero; of two intersecting lines as a hyperbola, whose axis is zero; of aright Hue (or rather two coincident right Hues) a» a parabola, whose tahie rectum is zero, and so on: but I do not нее the sense of it myself. Richard A. Proctor.

P.S.*—Todhunter and the Symbol тт.—Todhunter is right, of conree.

MOTIVE POWER FOR VELOCIPEDE.

[217] Sir,—I cordially join with Thos. Stanhope in hoping that some of your talented correspondents will be able to design a useful, safe, and moderately priced steam velocipede. I have read with the greatest uttention and interest every new description of bicycle and velocipede which has appeared in your journal, each one profossing to be the easiest and best ever invented ; btill I am as much at a loss as ever as to a selection of the most practically usefnl machine for а mau who is too old to care either for the excitement of a little danger, or for too much physical labour, but who would gladly make use of some means of locomotion for his daily journey to business, rather swifter than his own feet, and rather less costly than a quadruped. Is it too much to look forward to the time when every road will be a tramway, anil when steam carriages will run on them without any danger or inconvenience? and can we not " educate" the public in thÍ3 direction by a "pioneer " steam velocipede? R. M.

WALL DECORATION.—FRESCO AND STEREOCHROM Y.

[2181 Sir,—Your esteemed correspond,mt " Subbas" has given a very good aud short description of fresco painting ; however, there is a more simple method not generally known. It is this: When the rough cast is dry.

the second coat, " intonaco," is floated all over the wall, about 3-bin. thick, firmly pressed down with the trowel only; it is then left to dry. When perfectly dry the face of this last coat is rubbed down with sandstone to remove the thin skin which has formed on the surface; this thin skin removed will leave the wall quite porous, and now the painting may begin, by first saturating with soft water as much of the surface as can be painted in a day ; it is also well to keep the edges wet for the next «lay, when the same is repeated until the whole wall is finished.

lu this method the joins are avoided. But painting in fresco is now superseded by stereochromic painting, also sometimes called water-glass painting, a method which ¡jives the artist perfect control aud freedom over his material. One may work a painting over and over again until the desired effect is produced. An artist who is used to fresco, to body colour, or distemper painting, can master the details at once ; besides the work is more durable than fresco; the two large pictures in the House of Lords are executed in water-glass medium.

The method is this: After the wall is covered with the second coat of mortar—one lime and two line washed sand—the wall is left to dry perfectly. The colours are ground in pure water only, and applied with no other vehicle than water; the same colours are used as in fresco, no vegetable colour is admissible; when painting, the surface is first wetted to displace the air from the pores, the colours are worked into each other; when all is finished, the colours are only on the surface and will not bear to be touched; the whole painting is now fixed with water-glass solution in a diluted state, the solution is applied with a syringe for the fust time, after it is done with the brush.

The above is only an outline of the method, but if required, and with permission of our kind Editor, a detailed accouut will follow. The Welsh Shepherd.

CURIOUS SENTENCE.

[2191 Sir,—I am attracted to this topic (p. 423, letter 92; and p. 469, letter 104), by my having a different reading. The central letter, as I always knew the passage, was not R, but N : Sator arepo tenet opera rotas. Meaning, (gator) the sower (arepo) of mischief (tenet) keeps {opera) his works (rotas) on wheels, or a-going. It was, in old times, the schoolboy tradition amo» g my comrades that Arepo signified of mischief ; the same word occurs in the (venerable I) uur&ery rhyme:

One-ery, two-ery, six-ery, seven,

Arepo, craoknbo, ten and eleven;

Pin, pan, musky-dan,

Twiddle dum, twaddledum, twenty-one.

Arepo is probably a bogie word ; it is of Syriac cut, and of eastern origin. The Mohammedans have agrea deal about Araf, the partition between hell and paradise, see the Koran, heading of chapter vii,; Araf being much the same as Erebus; thus arepo might possibly mean deeds of darkness or mischief. We must not be too severe on the classical Latiuity of the like ; the passage affects to be an iambic trimeter verse, but it is merely a monkish amnsement. The best known is: Roma tibi subito motibus ibit amor, i.e., Rome, on thee suddenly with its emotions shall come love. This is by Sidouius Apollinaris, a Christian writer, л.п. 442. A medieval toy of the kind was : Sacrsm pingue dabouon macrum sacrificabo, which is an hexameter, meaning : I will give a fat victim, I will not offer a lean sacrifice—alluding to Abel. But the same read backwards by words is Cain's offering: I will sacrifice the lean, I will not give a fat victim; and this is a pentameter. Such a quaint conceit was called the Palindrome, or Sotadic verse. The latest play »f the sort I know is that Mr. P. G. Hamerton writes capital letters from abroad to the Globe newspaper, and signs his name G. P. Notremah. Gimel.

THE INDUCTORIUM.

[220] Sir,—I will, with your permission, make а few critical remarks on this subject, also with référence to the ingenious method of construction given by your correspondent "Indnctorium." First, the tension of the electricity or length of spark depends on the number of windings of tho secondary wires (eateri* paribus). In my opinion, if tension is required, the induction coil should be made longer, keeping the diameter constant. By this method, the number of windings and length of spark would be proportional to the length of wires. To obviate the inconveniences of spools of great length, large coils might be divided into sections, and combined iu a compact form. As an instance of low tension, considering the length of wires used (viz., 150 miles), I may cite the coil at the Polytechnic Institution, which with full battery power gives only 26in. sparks. A spark 4in. in length, has been obtained;from three miles of secondary wire; therefore, if the diameter of such a coil were kept constant, and 150 miles of wire used, sparks of ltîft. in length would be obtained. The following, I think, proves the correctness of the above reasoning. If two coils giving 4in. sparks be combined, and the current of the battery be kept constant, the combination will give 8in. sparks. If any of your readers detect a flaw in the above reasoning, I should be glad to have it pointed out, and also to have their opinion (perhaps I may include "Sigma ") on the subject.

May I ask "Inductorium," whose method of construction I like, if he has tried the effect of 5 or 6 cells on his coil? which, I have no doubt, would give interesting results as to length of spurk; also, did he succeed in winding the wire in regular layers in so confined a space as ¿iu. between the discs.

S. T. Preston.

THE MICROSCOPIC INVESTIGATION OF MALARIA.

[221] Sir,—I need scarcely say that I have been very much interested in the articles on zymotics which have recently appeared in the Enolish Mechanic, and, as a further contribution on the same subject, 1 send an account of a discussion at a recent meeting of the Polytechnic Club of the American Institute.

Dr. Vauderweyde introduced the subjeot by showing and explaining the device, as applied to his own microscope, for conducting the examination. Firstly, the liquid was placed in a cell, not such as is ordinarily used in microscopic investigations, but set in a perpendicular position, so that the light may be passed through it in a horizontal direction; the light from the cell is refracted and reflected by means of a prism up the tube of the microscope, and then, by another refraction and reflection, direct through the eye-piece in a horizontal line to the eye. This is very convenient, and saves many annoyances of former methods. Formerly, doctors had little faith in the revelations of the microscope, and scouted the idea that some diseases were originated by animalcula—as the itch and some others.

The researches of Hallier, the great microscopic of Jena, were referred to, and his conclusions with regard to the. germs found in the bile of cattle dying of tho Texan cattle disease stated at some length. This Texan cattle distemper answers to the yellow fever in the human system. In the bile taken from these cattle were found germs which not only lived, but grew and increased after the manner of thoee in yeast. Tho course of growth in tho yeast plant was then traced, and the resemblance of the other germs pointed out. In regard to those found in the bile, it was etated, and illustrated by fine drawings, that their development was very largely influenced by the circumstances in which they were placed, one form being found when the growth was in carbonaceous substances, and another very different one when in substances containing nitrogen. Another interesting fact was then stated, showing a very close resemblance between the highest developed form of these plants or germs and thoee found ш syphilitic diseases. Further developments resulting from close study of these germs may throw light upon the development theory, as well as the different relation* of animals. All animals, during their development, go through the forms of all classes of animals below them—the impression of the parent alone deciding how far this development shall proceed.

The cell that causes the fever and ague has certain necessities of growth, as stillness of air and certain conditions of soil. This cell, or germ, when taken up with the breath, produces the fever. It does not rise any great distance from the ground, and hence the greater danger of sitting than standing in places where it abounds. The state of the body has much to do with the effect of the germ upon the system. When, after a full meal and in good health, exposure takes place, the danger is much lefts than when the stomach is empty and the system tired and exhausted. It will probably be proved that all contagious diseases have a common origin.

The use of the spectroscope has done much for science in the analysis of liquids. The two absorption lines of blood, in spectrum analysis, give us the means of distinguishing blood from any other substance, and showing the presouce of any foreign body in the same, as they are never confounded with any others; no two bodies ever producing the same spectrum. In typhus fever the blood discs appear broken up, sometimes flattened and a disc half gone, as though cut in two. We find some poisons useful in disease, and their action may be attributed to their destroying these cells, or their arresting action, an, for instance, carbolic acid in small-pox, where, properly administered both externally and internally, it completely breaks up the disease. The effects of arsenic eating are possibly due to tho destruction of orgauic growths in the syetem, rather than its arresting waste.

For small-pox Mr. Nash considered warmth, catmint tea, and Saratoga water abont the best things; and Mr. Edwards said that one of the great errors of society is that people think that two sets of facts cannot be true at the same time, when both of them are true ; for example, we are prono to think that either the chemical, the electrical, or the germ theory of disease is the trne one, and the others false, yet they may all be correct. In the fearful epidemics of 1453, he found that at first the strong and healthy were attacked, and those that had been sick, or were just recovering, were the ones that escaped. As the disease extended, all were attacked, and finally the negroes, who had always braved malaria, both iu Africa and in the South, fell victims to it. Those who recovered always had been under such treatment as would keep them from getting out of a perspiration ; and it was tho old nurses and négresses that understood this treatment, and weiu successful, while the faculty failed.

In the course of the discussion upon the several theories of disease, Mr. Root enunciated his theory of the circulation of the blood and the power of the muscles, which was, briefly, that they acted through the pressure of the blood within them dilating, and so shortening them. Dr. Vauderweyde considered that this was disproved by several well-known facts, as the elasticity of the arteries, which, by their expansion and contraction with the beating of the heart, prevented the transmission of power in this way; also the fact that the blood was only transmitted through the walls of the capillaries by eudymosis, and not by pressure.

I enclose the account as it has reached me, believing that it will bo interesting to oar readers in general, and those interested iu microscopical examinations in particular. J« T. W.

GAS.

[221] Hii:,—I had no intention of being discourteous to "C. D. C," bnt when any one attacks other people, even though they are united in the form of a " Company"—which is too commonly regarded an a legitimate object of plunder and abused—he mibt expect to get attacked in return : and when any one picks up a foolish and most unfounded charge, and supports it by instances equally unfounded, I, for one, scarcely think it is discourtesy to mm his readers that his knowledge of the subject is too scant to justify them in accepting; his statements, for he invites* this Insetting forth these unsound remarks. For myself, I have not the least personal interest in the matter, 'as "C. D. C." supposes, but I do know what is the truth; and I do know, from years of acquaintance with gas engineers and gas directors, that as full a sense of right and as thorough a desire to do justice to their customers pervades that class as is to bo found in any commercial body or individual; and having watched many of the squabbles got up by interested parties. I know that the cry against the companies is pure claptrap.

As to the manufacturing part of the question, I spent three years, not long ago, in one of the largest Loudon works, with the intention of taking charge of a works; therefore, I am fully able to assure your readers that the notions set forth by "C. D. C." (taken up as they are from people who know remarkably little of the matter, though making much noise) are entirely erroneous. He says (p. 4481, I am bound to

Srove this assertion, and I proceed to meet his esire. The point at issue is tho alleged removal of illuminating hydrocarbons from the gas, beeanse tho companies "find it expedient"—a phrase whica certainly implies that they do so for reasons not covered by the necessities of manufactories.

Now it is not even true that the illuminating power is reduced thereby, for the simple fact is, that the gas, as it leaves the retorts, is totally unfit for combustion as it light-giving agent. It burns with a lurid, smokv flame, and is heavily charged with sulphur and ammonia, both of which the companies are bound bv law, under heavy penalties, to remove. There is no known process for removing these which does not also remove some of the light-giving materials; thorefore, any reduction of the real illuminating power belonging to the gas, after the tar and condensable vapours are allowed to condense (which they must do, or they would choke all the pipes) is imposed on the companies by law to their great loss, for a little common sense will tell any one that it is their interest to koep in the gas all the power possible.

Following down "C. D. C.'s" letter, I do not class Letheby, Franklaud, and the others named as "gas quacks;" nor do they join iu the senseless gabble the real qnacks utter. They watch and endeavour to keep down those irregularities of manufacture dne to the inferiority of materials and carelessness of men met with in all manufactures, and which the gas managers themselves are as desirous as any one to d minish.

Next, as to the dividends, I must point out how "C. D. C." betrays his real miucquaiutauc with the subject and the source of his supposed facts. The companies arc limited to dividends varying from 7 to 10 per cent. Will any one say tins is too much for a trading profit when any day some new improvement might even supersede gas and destroy the capital invested? Remembering also that for very many years the companies scarcely had any dividend at all till improved manufacture—notably the use of clay retorts, and common-sense business arrangement's limiting ruiuous competition—were adopted. But "C. D. C." says, and "the bonus in addition, to avoid the letter of the law "—again an imputation of dishonesty. Now the simple fact is, no company can declare a bonus, and any ono can stop their dividend by showing to a court of law that it is in excess; bnt the law permits them if iu any years they do not make their full dividend in any subsequent year within six to make up that deficiency, and some of the companies have been able to do this, not as a bonus to evade the law, but openly and legally as arrears given them by the fair.

As to carlmretting, I have not the slightest intention of disputing about a matter which scores of patentees have tried at. By all means lot any one try it who likes—as I have, and many others. The simple fact remains, as pointed out by another coutribntor, that after a great flourish of trumpets, and many statistics showing the great profit of the process as used in the city lamps, it u-at abandoned; and the general public steadily declines to patron.ze the many patented plans, and giving my opinion simply as my opinion, I consider it does so very wisely.

I find I have omitted one argument, which, as it i.-. based on truth, must not pass. It is quite true that jig to the mode of working a larger quantity may be obtained from the coals but of inferior quality. This is just one of the questions of manufacture aiid cost—the best way to obtain a gas of the power required by law. If the heat is very high or prolonged, more, but poorer, gas is obtained; and to compensate for this a certain proportion of rich and costly cannel coal must be used. Whut has this to do with the public, or how are they wronged? The company is bound to give them 1'2-candle gas, making it how it. plcazet.. As a fact, tho companies do supply 18 and 14-candle gas, as Messrs. Lethobv and Franklaud show by their reports; and this is tiio way the " public suffer." Siujia.

EXTEAOTS EBOM OOBBESPONDENCE.

Filters filled with black oxide of iron are said to be very effectual iu removing organic matter from uupure water.

BRASS INSTRUMENTS.—J. Samuel says-—"In almost every public work in tho United Kingdom there is a brass band, and there are generally some members who are mechanic-, and most of thorn take in tho EXOT.ISH Mechanic. Now, I think it would be a great boon to them,as well as me, if some well-learned brother reader would write a treatise on all the different kind, of brass instruments and best makers; something similar to what Mr. Hermann Smith is writing about the harmonium."

GAS BY A NEW PROCESS (p. 474.1.185).-" Gimel" says:—"Let me add my earnest trust that this maybe described in a practical way, so that it may be tried. To say nothing of gas light, I can tostify that ono of the most delightful comforts is the gas fire, which you can have blazing, or low, or out, at pleasure; but il is very expensive."

SETTING OF VALVES.-" Paul Pry" says:-"Although the editor has not formally given Mr. Baskerville leave to contribute a scries of papers on the setting of valves, I hope he (Mr. Baskerville) will do so, nevertheless. Such a contribution, especially from the pen of Mr. BaskerviUe, would greatly enhance the value of the Exombh Mechanic to a very large section of its readers. In the mean time, I should be very glad to see a letter on the subject of the expansion valve as an auxiliary to the slide valve, explaining its action, and the method of setting it."

IA note offering space was appended by tho editor to Mr. Baskerville's last letter, but, was omitted in mistake by the printer. Mr. Baskerville lias since been written to, and he will in all probability contribute tho offered papers.—Ed. E. M.]

SPEED OF CIRCULAR SAWS.-A correspondent of tho Scientific Amrriran says:— "It is laid down in mechanics that the speed of a circular saw should be. about two miles per minute—that is, the periphery of the saw shonld run 9,000, or a little over that number of feet per minute. Having had much experience in tho building and the running of saw mills. I have found that a greater speed could be used with safety, of which I will give an example, a mill that I finished and put in operation about eight months ago. I was iu nowise trammelled, and everything was left to my direction, which gave me an opportunity of testing a very high speed, together with a heavy feed on a large saw. The size of the building was Sift, y 100ft.. and two stories high. Size of engine. 15ft. x 30ft. x 82ft., with 83 revolutions per minute. Throe cylinder boilers, 861n. diameter - 30ft. long. Flywheel, 20in. face s 12ft. diameter: weight,8.00111b. From the flywheel, with a20in. belt, is driven a 4iu. counter shaft."with a 4ft. pulley. A (Uft. pulley on counter shaft, with a 16in. belt to a 2ft. pulley on saw mandrel, drives the saw, which is (Win. diameter, running 800 revolutions per minute— 14.lXH.irt. per minute—which is about 5.000ft. per minute oyer the standard. With this very high speed the saw cuts Sin. to the revolution, making a Sin. feed, and in one day of twelve hours, 97 logs, producing over 84,000ft.. were cut."

PREVENTING THE CLOGGING OF BOLTING CLOTHS.—" An Old Miller," writing from one of the agricultural states of America, says :—" A good method of preventing the clogging of bolting cloths consists In thoroughly cleaning them, inside and nut, as well as the l«lting chest, and then passing the flame of burning alcohol rapidly under the whole cloth. Extreme care should be taken to avoid damping the cloth."

THE RIGI RAILWAY.—A correspondent of the Engineer, writing from Fitznau, thus describes this novelty in railways:—"Immediately after leaving tho station-yard the ascent is commenced, and in about 100 or 150 yards tho inclino of 1 in 4 begins, and will, I believe, terminate only at tho summit. Tho rails, which are very light, aro laid down to what appears the ordinary gauge; in the middle is a wrought-iron rack rail of about 4in. or 5in. pitch: the rails are laid on transverse sleepers, and outside the rails, longitudinal beams are bolted to tho sleepers. The locomotive, " Stadt Luzern" by name, has (when on the incline of 1 In 4) a vertical boiler, the cylinders are lljin. diameter, aud 16in. stroke; they are outside, and are parallel to the rails. Tho valve motion is of the straight link kind, the exceutrics being outside the crank pin. As is very often seen on the Continent, tho machine Is supported on four wheels: their diameter is, I should think, Hbout 2ft. 4in.; they are loose on their axles, the rack wheels are keyed on iii the middle, and one axle is driven by the engine bv spur gearing, the engine making three' revolutions to'one of the rack-wheels; the axle which is not worked by the engine has two friction wheels keyed on it for the brakes to press on, and the brake on the only truck I saw was of the same sort." The writer saw a truck containing about 41 tons "pushed "up the incline at the rate of four or five miles an hour.

EYE-LOTIONS.—A correspondent of the lancet calls Attention to tho dangerous practice of would-be philanthropists giving away eye-water to all applicants without reference to the real nature of the particular disease. He thinks, however, where it is confined to tho sulphate of zinc lotion little harm is done. "Tho old family recipe for eve-water, if inefficient, is generally very inoffensive : it is strong of the water: and if it does no good it does no harm to anyone, and produce* little visible effect. It contains neither lead nor belladonna. In ninety-nine cases out of a hundred it, is a very dilute solution of sulphate of zinc (white vitriol, so called). Water, alone, for the eyes is an excellent sanatory appliance, as frequently, perhaps, as it is for generarpurposes of health. But as simple conjunctivitis or catarrhal ophthalmia is the most frequent of eye complaints, a little snlphate of zinc is thrown in on speculation. It sometimes does good, it is very cheap, and it manifests its presence even in so great a quantity of water. We generally use too much water iu our collyria. It was a valuable bint to me some time ago, when n distinguished foreigner observed that our strongest (he was speaking of sulphate of zinc—two grains to the ounce of water) was only the strength of their weakest lotion. But, if one did not know when to prescribe or to omit sulphate of zinc, or sulphate of atropine, or othor common lotions, one could only be safe by great dilution, and aide perhaps by combinations of different remedies."

EEPLTES TO QUEEIE3.

*♦* Is their answers, Correspondents aw rttpor ■ requested to mention in each instance tat uu, number of the qnory asked.

[So87.] — DUSTING BRASS MOULD8.-I la?-. mit the following :—For light wort face vwV' with the following: 3 parts new sand, and 1 pi,. mix it up as you would facing *and and tact K- . with pea-meal. For heavy castings nut Zfa.-", sand, 1 part old, and 1 part dried low. •.' your pattern with, and face your nioald vri , meal. For dry-sand work use S' parts drr I Ji.; , new sninl; and for facing your dry-sand meekly 'jwith, use lime; mix it in water the same *v t . would black-wash. If " Ironfounder" win ti-, . Instructions, he will find that "X. L..," whoui.-^,, * query, is quite wrong. If " N. L..," has bcena**! -" casting, he must know that coal du»t Is note.»~. brass work. In the first place, lira* U ltj, searching nature that it would eat its way ton, casting would be vl.it we call struck afljj- fc if he used black-wash for his cores andd*-.* brass would fetch it all off and leave it ta a-1,. castings, as black-wash cannot withstand**., brass on its surface. Lime is the onlrafja-rj withstand the action of brass; and la*tly,dMfa or blacking are used for brass work, it DUa> look a nasty black colour, almost the &aa -W. J. W.

[275H.1-LAMENESS IN HORSES—H«r „.lameness in horses I take to be no new mru, during 1868-91 obtained from feotne exten«ivt e:~s that were making a few miles cast of Louio... other things, a quantity of horse shoes 5.*vsolid aud heavy, similar to the one figured in n , cnAKie of July 29 (which from the depth ti>s found at must have lain there several hundn-1-r which if usod for lameness, then the one figure*.-., bo an invention, only a revival. I have aboutt»r..i of early horse-shoes, all very different from tW in use; also some old bits and spore. To any ra* tercstcd in these things I shall have much "pieus in showing them,—A Cieiosiit Cotizcroa.

(2756.)-LAMF.N'ESS IN HORSES.-"Country Trt . in reply to J. C. Dutfryn, advise, bleeding in Ibe attiw stages of Laminitit (fever ia Ike feel 1. Intbeinij.nl' of cases the disease consists ol congestion of tbe emir? venous circulation of the toot, and it may remain in thai state for days without taking <<d infiiuuiiation. 3fv treatment is to remove tbe (.rdin&rv shoes, and immediately apply tho bpecial Omi, not' seated, or beviiled, but bearing the whole width on Vb* stle u on the win. unless tho sole happens from being pared to oettm. Give aldose of from :i to G dram* mot otmc« as *inu-l according to sizeof animal, which must "be eompeBedt' take exercise on soft or wet ground If available. *v-i times daily. Should the case be a very acute oat 1-4 water may bo applied during the intervals nl <ierc» and also ten drops of Fleming's tincture of scoafc^ be given every hour until the animal is relieved. "■ aloes may lie repeated in about three days, if asr~or any lameness remains. The majority ef * • arc relieved in two or three days. I neverbka--stage of the disease.—T. D. Broad.

[3766.1 — TO CLEAN, AND FILL IB t~S BAROMETERS.— Buv a glass tunc chwas** S4in. long, small or largo bore as, reqnjaW? with a fine rod with rag or tho small l*m«*^ pipes (tobacco, to he had at any cigar shop. ra*S'-' mercury at any wholesale druggist's, pric« *k«i** crown per pound. Makea funnel of clean wjfcacvs*and pour tho mercury through repcatetTskte^ -' or vessel, until quite clean; tkouiusei-t'aclea=ts»papcr with a line hole into the tube, puv »'£ quarter of an inch of the top; take a chun to ■■''■ and stop up with the finger, reverse and topE" the air bubble up an.l down till clear of sp«>- .J L then fill up. Buy a boxwood cistern (orl-evt"^yourself). and fit it on the tube before with nine und if too loose, nnscrew the end with tho shecp-i^ » and till np, theu screw on, and the tithe is made > looking at the cistern of any mercuriiU baromctfi idea is soon got hold of. Adjust by a youd rule, Im good barometer of a friend or public instituu'ett. ''■ work may be made to fancy. A Bcrew at the bott-'E^ enable the mercury to rise to the top, Mo as to be cmabout without risk. My advice to amateurs uk *• make many, as tho fumes of mercury «re very ui1 a* —far better purchase.—GnonoE Mackak.

(3815.}—EMERY WHEELS.—The expressed oil-!. seed, like several other vegetable oils, but in a jrr. ■ ■ degree, is capable by exposure of absorbing a !■'amount of oxygen. It is this property of linww! which renders it so valuable for mixing with pipnw:' as it is this gradual absorption of oxygen -which"k-t <■' the oil, aud produces the pheniomenou of drying ii * paint. For this purpose linseed oil is put through :t process of boiling with litherage aud oxide> of lead, :rwhich it absorbs so much oxygen as to promote it--If ing properties. In this condition it is styled " bnuVJ!" seed oil." This peculiar property of Unseed oil rcnJt it very valuable in certain arts, as bycontinningtheen tion by prolonged exposureto the fttniosphere it assaias tho appearance and character of India rubber, bta very tenacious and durable, which any one can pem-.i in tho durable qualities of ordinary wax-cloth. The1 emery wheels are formed of clean emery componv., with just a sufficient amount of boiled linseed oil. t'-> mixture being agitated for a sufficient period under f' posnre to a considerable temperature and a tree nfi-i". of atmospheric air, or some still more powerful ovi.ii. ing agent, can be made to assume the necessary de>^ of tenacity, and whilst warm, being exposed to h>d-*s lie pressure iu a suitable mould, and subsequent Vfrji" in a stove, the emery wheel is complete.—Mateix.

[3851.]—HARNESS.—"Saddler's" reply would but been valuablo some years back. I will eive in advice and experience. If you use a " comp«>siti.n your harness will require constant applications of oil an dye, and scraping—tbe former to keep it supple nr. black, the latter to take away the cracky app^arai.0 I find Clarke's harness blacking far preferable to an. r. ccipt I over tried, and I am told it contains tho right pr. portions of oil, dye, and polish.—Not A Saddle*.

ra949.]—GUYANA OR GUIANA.—These are three colonie*, belonging to the British, Dutch, and French, of tbis name. They lire situated between longitude R1-- 30r and Gl west, and latitudes 1 to 8" 30' north. "Venezuela lies between longitude 6U ■ to 73; weet, and latitude 2 to IIя north. Your correspondent "Bernar«liii" i« mistaken in saying they are to north of Vcnezueln, such being impossible, since the Carribean Sea

\\ .; -.11.-s the shores of Venezuela un the north. The estímete here is very unhealthy for Europeans. Demorara

i •-. iiiR the capital of British Guiana, the most westerly

:unl adjoining Venezuela.—J. G.

tílí>52.1— LOAM PANS.—Having been troubled the ваше as " Inquirer," I discovered that there was too much clay inthe loam,and after the mould was black•waeue»! and smoothed over, I came over it all with barm, or very stale beer, put on with a very Uno brush ; this Ъая the doublo effect of staying it from reining, and the blackwashfrom scaling.—N. L.

Г89в2.]—SOAP-MAKING.—Some valuable information on this subject is to be found in Dr. Ure'á " Dictionary of Arts and Manufactures."—Bkta.

[39в2.] —WORKS ON SOAP-MAKING,—" Campbell "Meruit on Soap and Candios," cost about £2; "Ott ou Soap, making," cost about 10s. 6d.; " Kurten on Soap-making," «•oetuuknown. All tobe got through Trübner & Co. The -two first are the highest authorities on the subject, and «re .''Ji¡4¡-ii'.r and well illustrated; the last is good and -practical, but the translation (from the German) is lanltv, many errors in substauees, mensuro s and weights, which would puzzle a uuvice, though not diftl<!ult of correction by a practical hand at the trade.—D. G.

[4020.]—WOULFFE'S BOTTLE.—Let " M. P. C. S." •ohuck a piece of ordinary brass tube in a lathe (say) Sin. or Sin. long, and its external diameter slightly less than the internal diameter of the neck; now, whilst the tube is in rapid motion, press the part requiring to be cut out gently against the end, using emery and oil, or Hue sand and water, as n cut ting or abraiding medium. It will bo found a great advantage if he can manage to apply the pressure through the medium of a piece of india-rubber hold agaiust the Inside of the bottle; this will cut it out quite clean. The same pian is applicable to cuttiug the central hole in oli < s Ac. A very neat applica

tion of it is to cut opening opposite to the winding centres of shade-covered ;these openings can Inprotected by inserting 'a' small bra^s bn*h от ilet with a little white lead, a threat brass plug being used to keep out dust. Under those circumstances the shade never requires to be lifted,as the winding, &c, can be effected by the application of a suitable key.—Matrix.

Г4022.] — TUNING BELLOWS FOB HARMONIUM. —See "EleveV letter, p. 180, ante.Saul Rymea.

[4042.1— MAGNET.—Nos. 16 or 18 would answer.— Sigma.

14044.]— AIR GUN.—The drawing represent* the lock and breech screwed together. A A lock, В spring, С trigger, D tumbler, F. sear, F F push piu, G trigger spring, H sear spring, III scats for the upper plate, "removed to show the construction. The trigger and sear work on studs riveted into the plate, and prolongod through the upper plate, screwed down by a single screw, whieh also serves to check the motion of the sear. J section of breech, К valve, L brass tube. The valve rod within this tube has a spiral spring along its length to keep the valve to its seat ; the valve is best made of bnllock's hoof. The lock is represented ready to be discharged. The barrel—not shown—is on the other side of the'

chief merits are—first, a complete scale; second, a single sound to each key, whether drawn out or compressed, thereby dispensing with tho the thumb-bellows of German concertinas. I have heard very difficult music excellently performed on those instruments by Mr. W, H. Birch, of Reading, who is, I believe, musical editor for Boosey & Co., Hollos-street.—J. Nash.

[4096.]— SODA WATER.—TO '• P. C. S."—Tell me if two strong-hooped barrels would stand the pressure; and what material the bottling and corking apparatus should bo made of; and what length, <■( time it would take to impregnate the water with the gas ; and what be m«ans by a washing vessel between ?'Лцу information he can give will bo thaukfuUv received. Ï tried tho onslacked lime, and it was quite a failure, which I knew it would be.—D. W. L.

[4102.] —GALVANISM.—Dr. Altbans's work is,perhaps the best on medical electricity, pace 15s., obtainable through any bookseller. My next paper will deal with the galvanometer question.—BxoUA.

[4121.] —BOTTLING FBUIT.—Take any quantity of fruit that is Bound and fresh ; fill your bottles ; till a copper nearly full with cold water, with a bnard at the bottom: put tho bottles in. up to their necks in the water; put it ou the Üre, and let tho boat get up to 150 degrees; let them staud at that heat for twenty minutes, then take them out, and All tho bottles with boiling water; thou bang them, and tie with a bladder, and they will keep any length of time if kept air-tight. —P. W. L.

[4136.]—EGG-HATCHING MACHINE.—" P. G. M.," who asks for information in detail on this subject, will find an illustration of Pinchen*« Incubator on p. 108, Vol. X., of our Mechanic. It has, I believe, been found successful. According to M. Reaumur, all that is required is a heat of 96 ' Fahr. Eggs kept at that temperature for the requisite number of days will produce chickens. Mr. Cántelo, however, wbosomo years ago exhibited what he called a hydro-incubator, asserts that the proper temperature is lUo^Fahr.; and if this heat is sustained chickens will sometimes appear on the eighteenth or nineteenth day. His machine was capable of hatching from 100 to 600 "eggs; and its principle consisted in allowing warm water to flow along plates of glass placed over the eggs. The Egyptian and Chinese systems are much the simplest, as in these the eggs aro merely placed in trays of sand or bran, and kept in ovens or on heated iron plates. It is vory doubtful whether any system can be made profitable in this country.—Saul Rymea.

[4141.1—FIRECLAY BAKING.—The raw fireclay is usually mixed with one-third its weight of burnt fireclay termed "grog," or powder of old glass pots from which all the clinker, &c, has first been carefully removed. Sometimes a certain proportion of sand is added, or clays, other than Stourbridge, according to circumstances and the purposes to which the clay is to be applied. This mixture is moistened, kneaded, and let stand for some time; often a fortnight or three weeks, receiving occasional kueadings in tho meantimey the longer you can let it stand and tho more thorough!. it is mixed the better the clay. When tho articles are made they are allowed to dry gradually in a warm rdomt when they are very thick, three months aro often allowed (for; this operation; they are then transferred to an oven and raised to redness. The more tdowly this drying and baking takes place tho leas the liability to crack. In somo cases fireclay crucibles are not previously burnt or baked before use. Inthe oase of pots used for casting steel it is found that if tho pots are burnt with the mouth downwards thoy do

from only semi-double flowers, and will forward " Saul Rymea" some it heVillgive me his address. It w ts saved from ft few simUe that grew with нише а* пае double опез as any one could wish to Sop having spikes of flowers from 9iu. to 12iu. long, beeidet a mass of siJe branches; they are what we in Sussex call tho Giant stuck.—

No KM A.

[4273.]—SPLITTING WHALEBONE.-The blades previous to cutting aro softened by boiling for a couple of hours in a long copper. They are then fastened edge upwards in an ordinary wooden bench vice, and plaued by the subjoined tool. А В arc two handles, С D is an iron plate, with a guide-notch E ; F is a semicircular knife, screwed firmly at each end to the iron plate С D, having its cutting edge adjusted in a piano so much lower than the bottom of the notch E as the thickness

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of tho whalebone is intended to bo ; Tor different thicknesses tho knife may bo set by the scrows at different levels. Tho workman holding tho tool by the handles applies tho notch E at the end of tho whalebone blado furthest from him, and pulls it gently along so a* to shave off a slice in the direction of tho fibres, care being taken not to cut aoross any of them. Those slips are afterwards dried, and planed level, and are polished with ground pumice, felt, and water. I do not know whero "Enquirer" can obtain whalebone; but it is brought from Greenland in pieces containing ten or twelve blades. Thebladosare sometimos separated aud cleaned by the sailors of the whalii*g ships. The price varies from £50 to £150 per ton.—H. U.

[4379.]—GAS METERS.—Asa maker both of wet and dry meters, I, with all duo deference to Mr. H. Newton, prefer tho former for exactitude and durability. Not to extend unnecessarily my letter, I will quote Clegg's work, (no mean authority) :—u The opinions of gas engineers continuo to be divided as to the relativo merits of dry and wet meters; but for accuracy of registration, when tho water is at the proper level, tho wet meter is not surpassed, if it bo equaled, by auy other."—E. Wellard, Bordeaux.

[4314.]—RULE WANTED,—lib. of cast iron contain* 3-81 cubic inches; hence the cubic contents of any cast body in inches, divided by 8-H4, will give its weight. Elucidation of example:—60 x 3'«1 « 230-40 cubic inches in the block and i> x 14*8 = 1B0*6; hence the cubic contents 2:10*40 -h 130-5 «■ 1-78551 + inches thick. —W. Driscoll.

[4316.]— A DIFFCÜLT QUESTION.—I do not sac that there can be any doubt about there being first tho inside tube 12' diameter, gripped by a second tube, hoop, or ring, 18" diameter, ami this second one gripped, in its turn by a third, with an eit;ht tou grip.—Unit.

[4322.]—SEWING MACHINES.—It is rather difficult to say exactly what tho cause of **H. W.'s trouble is, as the effect ho describes may be caused in one or two ways. There may not be auffloient tension ou the top thread or the little brush is not properly adjusted agaiust the hook.—Unit.

I [4356.]—SOFTENING SKINS.—If flowers of sulphur be mixed in a little milk, and after standing an hour or

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plate A A ; it is of brass, carefully bored and polished. In constructing an air cane, be sure the reservoir is sufficiently stout, and made of copper, that the brass cottar iulo which tho breech screws fits accurately, and is well soldered. Tho butt end should be brassed up, not tinned. Further details if requested.—T. A.

[4072.] - HARMONIUM QUERY.—As "Elevo" is doubtless too busy to answer queries just vet, I am sure he will pardon mo for treading on his ground, especially as I shall merely toll "Valve" what I have been told by "Eleve." Tho reed holes for 8ft. tone should be Hin. by 5-16in. at baso; and 9-lfiin. by 3-lGiu. at treble. The pallet holes should be lin. by fin. at base, and Jin. by З-llïin. at treble, of course graduated us regards length all the way; and tho pallet holes should be Jin. wide to all but tho top octave—i.e., thirteen notes.—Savj.

Buck*.

[4076.] -NATURAL SELECTION.—This doctrine, which is gaining general acceptance among the leading minds, is that the many varied species of plants and animals are gradually developed from a few simpler forms by natural processes; that tho surrounding conditions of good climate, &c, produce mollifications and those are perpotuatcd which suit the varied conditions. The idea really is that nature doesjust what man does when he produces new varieties. How far tho process is to be considered to extend is doubtful; some people are terribly afraid of tho doctrine, under the idea that it doe? away with creative action; whereas, it really means that the creative power is everywhere present, always active now and for ever, instead of acting once for all. Vi hen fully developed and rightly understood, it will bo found to teach as the Great Teacher taught, that the Sparrow falls not to the ground unheeded by its Father and ours; that each springing seed, each blade of waving grass, and the humblest insect, whose life is but A summer day, is part of a great whole pervaded by the uni venal life, of whieh these different forms are the actions and development.—Smsu.

[40Э2.1—THE ENGLISH CONCE «TINA.—Since no one else replies to "Lost," allow mo to say that the English concertina is really a good instrument. Its

not crack, but if л\ itb the mouth upwards, they do The " grog "or burnt fireclay is added to form a sort of skeleton, as it were, aud thus prevent the tendency to crack.—An Associate Of The Royal School of Mines.

[43060 — CHROMATIC FAIRY FOUNTAIN,— "Q. Q. R." evidently does not understand Prof. Tyndall's experiment. Wheu a ray of light, passing from water into air, strikes the snrface at an angle greater than what is called the "limiting angle of refraction"—viz., about 48° 27'. it is •• totally reflected;" but this does not occur when the angle of incidence is less. In the falling stream the ray is continually reflected in this mauiier along tho stream, thus (see Fig. 1); but, inthe

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arrangement proposed by " Q. Q. R.," the ray would evidently vory soon strike the surface at a much less angle, or, indeed, perpendicularly, and would accordingly pasa through iuto tho air without reflection: the falling water could not, therefore, be illumined,—Ionohant

lit 1 SUMAN.

[422G.J—DOUBLE STOCKS.—In my humble opinion (although only an amateur) the beet plan to get seed for double stocks is to pick off from the single ones every flower that has only lour petals, saving only those with five and six petal-,on what я florist would call semidonblc, which will produce seed that will come nearly all double. I havo now got somo seed nearly ripe, saved

two the milk (without disturbing tho sulphur) be rubbed into the skin it will keep it soft. Care should be taken not to prepare it too long before using, as tho milk is apt to becomo putrefied. Perhaps the above mixturo may uot answer " Country Vet.'s " purpose, as it is used to soften the skin (human) and improve tho complexion. Yet he can give it a trial if he chooses, as its cost will be very small.—Kansas.

Z[4359.1 —AMBER BEADS.—Amber beads maybe repoli shed with whiteuing and water, or rottenstonc and oil, finishing in cither case with friction alone. Amber may be known from mcllite (honey-stonot and copal, both of which are sometimes substituted for it, by the agreeable odour it emits when burning, and by the greater electrical power it possesses after friction; melliteis infusible by heat.—T. W. Uooijd.

[4361.]—METHYLATED SPIRIT.—"T. L. H.M is in error when he savs turpentine is added to spirit, to form methylated spirit.—An Associate Of The Royal School Of Minks.

[4361.]— METHYLATED SPIRIT.—This is a mixturo of <R) parts of spirit of wine (S.G. 830), duty Jrtet and 1U parts of wood spirit (methyl, alcohol, or carbinol). It cannot be used for medicinal purposes or beverages on account of its repulsivo taste and odour; but for many of the purposes for which pure spirit of wine was formerly used, such as the preparation of varni-dies, polishes, chemicals, the preservation of museum specimens, Ac, it forms an efficient and cheap substitute.— Beta.

143C3.] — LIMEWASH ON MASONRY. — " Agent" should use a weak mixture of spirits of salts, or muriatic acid, and water.—Beta.

[4364.J— DRYING SMALL WHEELS.—A small room or cupboard heated by a gas stove would be the most economical, though I should imagine that any quick process would be apt to cause tbeai to twist.—T. W. Boo it D.

Г4866.]— INDICATOR DIAGRAMS.—"Fireman," In order to calculate indicator diagrams, must divide them into at least ten equal parts by lines drawn at right

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