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by its length gives *28iu. for its breadth, and for that of the bar between the ports also. The exhaust port is double the breadth of the steam port, or *56in. The exhaust edges, E E, of the steam ports are 112in. apart, and that is also the breadth of the cavity of the slide valve, and the length of the cavity is the same as the ports, 2*43in. The "admission " edges, A A, of the steam ports are l'GSin. apart. The travel of the valve is equal to 3} time- the breadth of the steam port, or "980, and its "lap " is one-fifth of that, or lSMiin., and when the valve is laid evenly over the ports its "faces " project -19Gin. bcvond them, so that the total breadth of the valve is 2-072in., say 2 1-KSin. The lead of the valve is one-fifth of the lap) or -039 = about 1-Sain. foil throw.

Fig. 3 will answer as an elevation of the link motion also, the throw of the excentrics is equal to the greatest travel of the valve, or -9yin.; their centres, F and B, are, therefore, *49in. from the centre of the shaft whose diameter I have taken at 1+in., the small side S of the exceutrics I have made {in. wide, and that added to the throw gives l*48iu. for the width of the large sides L, hence the diameter of theexceutricsis3'23in.,and their thickness may bo made lin. I suppose I need not tell Mr. Watson that the mere diameter of the excentria 1ms nothing whatever to do with its throw or excentricity, as the diameter may be increased or reduced without making any alteration in its throw, and the size I have prescribed for it is merely what I should myself consider suitable for his engine.

The "lineal advance" of the excentrics is equal to the sum of the "lap and lead," or *285in.; this link is the same pattern as that in Fig.;), and its length from pin to pin of excentric rods is equal to three throws, or 2'tMin., say Sin. even; the length of the excentric rods is twelve throws, or 11 jin. nearly; the motion at the i

every 4 of magnesia'* used; evaporate to dryness and heat in an iron crucible with metallic sodium.

Testing Gold (4275.1—Dissolve in aqua rcgia. If the solution has a blue or green colour, copper i present; if there is a white residue upon adding water it is alloyed with silver; if there is a precipitate with a bine or green coloration, copper and silver are present together with the gold.

Alabaster Glass (4234).—I am afraid "J." would not be' satisfied with his results if I were to give him a method of glass analysis. I will do so if he particularly wishes it; but I should advise him, if he wishes for correct results, to place i he specimens at once into the hands of a professional analyst.

Effects Of Carbonic Acid (4599).—When carbonic acid is inhaled it produces spasms of the glottis, which prevents the poison from entering the lung's. A candlojwill not barn in a mixture of four volumes of auto one of this gas, and the proportion that will not support combustion will not support life. A candle may burn in a mixture of carbonic acid and air, and yet not support life. Six volumes of air to one of acid would quickly act as a narcotic poison, for if sufficiently diluted it passes the glottis and enters the long*. Picaic Acid (4601).—Picric acid, also called carbarotic and nitrophenisic acid as well as trinitrophenol, being in reality a substitution alcohol, is phenol (carbolic acid) in which three hydrogen atoms have been replaced by uitroxyl; the formula isCsHi (NOjt** O. It may be prepared by acting upou carbolic acid with fuming nitric acid and afterwards purifying the product. If present with colouring matter, tliis latter must be precipitated with snb-ocetato of lead and the aoid taken up with ether. Its solutions are intcnsely yellow. Its lead salt is soluble in water and explodes

ends of this link is -I'sin., and at"its middle it is -502 or 9-lUin.; the lead of the valve when in fnll throw "039in., and when in mid lie gear it is *085in.

If I havo not been sufficiently explicit in the fo ^oing description to enable Mr. Watson to construct a link motion for bis " road-steamer" I shall have much pleasure in answeriu-j any further questions he may


Manager, City Foundry, Limerick.

UNNOTICED QUERIES, Etc. L3U1] Sir,—Having looked over the list of Unnoticed Queries I came across some I had not noticed I therefore send you answers to them.

Magnetic Queries (4232, F. Peel).—The total intensity of a magnet is that force which brings a needle to n position of equilibrium when disturbed. The total intensity is capable of being resolved into the horizontal and vertical intensity. The vertical intensity tends to make the needle dip nnder the influence of the terrestrial magnetism, and when one end of the needle is loaded, the vortical intensity of the north and south end counteract each other. The herizontal intensity tends to make the needle recover its position when displaced from equilibrium under the influence of the earth. The resultant of these two forces is the total intensity, from a knowledge of which the other values can easily bo trigonometricallv determined. .Secular variation is that disturbance which is gradually taking place, and which takes centuries to complete ■ thus, bef ire 1663, the variation at London was to the east; at that year and a few years before it stood at the geographical meridian 0°, from then it gradually went west till 1818, when it stood at W 41"; from then it began steadily to return, and is now about 20° W As regards the magnetic curves, F. Peel can imagine those which occupy the field of a bar-magnet, making allowance for a spherical field, instead of a flat one, as is the case in most illustrations; ho can also compare them with Sabine's chart of isoclinic lines.

Associate In Arts Deobjbk (4269).—Every conilidate is required to satisfy the examiners in — 1, English Grammar, including Analysis; 2, English Composition; 8, Arithmetic; 4, Geography; 5, English History. Questions are set in Faith andReli'"ion • one portion of this section is, however, optional, if any objection is raised on conscientious grounds. The optional subjects are divided into four sections of which the candidate will be required to satisfy' the examiner in two. A, English History, Literature Economy, and Law, with Physical, Political, and Commercial Geography. No candidate will pass if he does not show a fair knowledgo of one division. B, Latin Greek, French, or Gorman, at the option of the candidate; C, Mathematics, Geometry, Mechanics, and Hydrostatics; D, 1, Electricity, Magnetism, Light, and !<'■':•« Chemistry, including practical analysis; 3

on heating. The potassium salt is sparingly soluble iu water and behaves as the above. Pierate of ammonia deflagrates only when heated, and solntions of the acid possess a high yellow colour and an intensely bitter taste.

Fluorine (4g2.ji.—If "E. L. G." will turn to the analysis of bones iu Simon's " Mciical Chemistry," he will find every analysis is marked by the presence of fluorine, and if found in every sample surely it ought to be regarded as a normal constituent. Small quantities, even traces, ought not to be despised; nuclei, which cannot be discerned by the naked eye, determine the crystallization of supersaturated solutions.

Chloride Of Gold (4621).—If the gold is only alloyed with silver, place in a flask.covcr with aqua ro^iit, and digest at a moderate temperature on a water bath; when dissolved, filter and evaporate to dryness (well washing the filter) on a water bath. If the gold is alloyed with copper, dissolve iu aqna rcgia, neutralize with carbonate of soda, and add ferrous sulphate solution. The gold is procipitated as a fine powder, which must be collected and re-dissolved in aqua rcgia and evaporated to dryness on a water bath.

Nitrate Of Silver (4622). —Take the plating solution, evaporate to dryness, mix with carbonate of soda to moderate the action, and heat in a clay crucible, gradually increasing the heat until the silver is completely reduced. Take the silver and dissolve in nitric acid, evaporate to dryness, re-dissolve in water and crystallizo.

South Kensington Examination- Papers (4640). —I shall be most happy to supply your triple subscriber, "J. B. H.," with a set of the above papers if he will write to me through you. They are not yet to be obtained through the publisher.

George E. Davis.

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Animal and Vegetable Physiology; 4. Geology a I -uineralogy. No one passes who does not show a fair knowledge of one of Ihuse divisions. Candidates can also be examined iu Lrawing and Music. No one is admitted over eighteen years of age.

Chemical (4270).—Carbonate of soda mixed with finely divided charcoal may be distilled in an iron retort, the neck of which dips under parafflue. Caustic potash may he neutralized with tartaric acid, and the dry salt projected into a red-hot crucible; the black mass is mixed with a small quantity of charcoal and treated as above in the case of sodium. In the case of sodium, Deville recommends the following mixture • —Dry carbonate of soda, 717 parts; charcoal 175 parts; chalk, 10* parts j to be intimately mixed and calcined before placing into the retort. Magnesium may be procured by dissolving the caustic magnesia in hydrochloric acid, and adding 0 parts of salt to

EQUIVALENTS, PAINTING CISTERN, Etc. [382] Sir,—I have not long been a subscriber to this journal, but, by the kindness of an old subscriber, I have for some time been a reader, and desire to say that as such I have derived much useful information aud considerable pleasure, iu return for which, it is my intention to give answers to such questions as I am able. It will also be my pleasure, if requisite, to ask questions of other correspondents. (One I have already asked. 4483, p. 502, to which I hope, if not a complete answer, n partial one will be sent.) I will now endeavonr to answer a few queries.

(4537.)—Equivalents.—The question of " MaO Coj" seems rather out of place. As no doubt you have in some previous number given a full list of elements with their equivalents it would therefore be a folly to reinsert the list. I shall recommend "MaO Co-j" to •jet "The New and Old Notation of Chemistry," by S. W. Rich, price Is., which is a list of elements, and the more important compounds, 217 in all, with their symbols, and equivalents according to both the old and new notation, or any new book on chemistry.

(4500.)—Painting Cistern.—"Cistern "has not stated whether the paint shelled off alone, or whether it was forced off by a scale of the oxide of the iron, which I suspect to be the case. If so, "Cistern " may paint again with safety, it will not shell off. I am. engaged where most of the work done is ironwork, all of which has to be painted. Experience has taught that it is necessary to let tho surface of the iron oxidize first, scrape off tho scale of oxide and then paint. The point will not again shell off. If the water in the cistern is for drinking, it would be much better not to paint at being dangerous to have paints which contain lead in communication with drinking-water.

(4519.)—Tender Feet.—I would advise J. T. Hill to bathe his feet frequently in strong salt aud water if Hca water is not available.

(4492.)—Raisixg Water.—If time permits I will moke a sketch and answer this next week. Psi.

33000 hone-power. The proportion of useful effect to Im cated thns arrived at is usually assumed at 0-5 for t£size of engine, so that the effective power of the leak: thus developed, would be 107*5 x 0*5 = 53*75 hcrses. (Some large boiler manufacturing fln*a& of mj acquaintance wonld call this a 60-horse boiler.)

This (53*75 h.p.) gives per effective horse power [»• hour, 12*4 square feet of effective heating surfac*. 5*151b. of coal, and 38*41b. of steam—results stud* -J actually attained in this case, might be ac-t-ssfert-l sufficiently satisfactory. It is, doubtless, poKabk bt get more work out of this boiler by harder Jin**, az--! indeed, instances are reported, where, with Lu&-.ime boilers of nearly same dimensions, as uach is5-<SU>. of water have been evaporated per sfiart fes of effective heating surface per hour—bars-afe hsweiei. nearly 221b. of coal per square foot <A <ume p-iportioned) grate surface. Such results art n* rtu-i&fcA* iu regular practical boiler working, aiul «-*a*A.1i*-c*cfore, be estimated upon if economy and i&rilhlit-; as objects sought nftor. Indeed, the figure d tTVV- i> twice that of instances of practice in Cora«ll; tk"<. however, balanced by a greater percentage of" d«S' in the engine proper.

It would, doubtless, be a great boon—and 1 tx-sa these few imperfect remarks will lead to its reali-titi'-n —if various correspondents having the oppurtui-i* of experimenting upon the evaporative capacities vi steam boilers of various types, or already, perhaps, in posses-ion of summaries of results—would carry -rat and kindly publish them for the bcuefit of all, and'expecially of those less favoured, in "our" journal, along, with such " notes" of peculiarities of construction, tx. as would enable a fair comparison with each other being made. There is especially wanted a more complete and wide-spread knowledge of the evaporative capacities of a class of boilers now much in demandviz., temi-portablee of the vertical acd horUonial type, consisting of:—1. The vertical and horizontalnre-tobc (multitubular) boilers; 2. The vertical cross -hfsa. tube boilere; and 8. Tho vertical "Field" s> boilers, all with iatrriui! fire-box and grate, and <.ployed now, especially those of the latter clas* ;-* powers up to 80 horses. For fair compariton, howe-n'. with the older and simpler type of boiler—the cylin-ir. cal with hemispherical ends, evaporating about of water per lib. of coal—as the most simple form" •.* start from, the use of the blast nozzle should be discarded, and the usual means of securing the reqni?iv draught—the chimney—aloue employed. For the sacreason cold feed should be used, or if used hot S should be duly accounted for.

On the continent it is usual to allow for Bs portable "Field" boilers with norma/ drauRht br . chimney about 20ft. high, 14} square feet ofheat*: surface, and 0*55 square feet of grate surface r effective horse power; and if this type of boUer V-* repeatedly asserted, is capable of evaporating K* water per foot of heating mrfaeet per hour, witho" tensifying the draught beyond that naturallv aoss able by 20ft. of chimney; the quantity of steam lit raised, and that, too, at a pressnre of 5 to 6 atuiosphcn-. from cero should give out in a good non-ci.udea^iitcngine even a very much larger increment of po-v*rthan me horse. It is evident, therefore, that mart! is' formation is wanted, aud I doubt not but that voci esteemed correspondent Mr. Olrick will be both »fcie and wUling to supply it; at all events, in respe-e* t« r leld boilers—the more so as not only hare the. r, suits at Oxford been (seemingly) nnf avourable as rej-aj-ri this type of boiler, but because there is also not wanti t men, both engineers and others, who utterly deDr«-tri" their employment. Then, again, as to rertUatGo—

tube (multitubular) boilers there is a great discrcpaj; in regard to their stated efficiency. Some E-SsStt makers assume as little as HJ and others a, ma2\

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it is usual ou the Continent to allow 174 «qnoro feet of total heating surface per bor-e power (effective) with steam at a pressure of 0 antl 7 atmosphères from zero. I think, sir—and thin most be my excuse for occupying во mach of year valuable space—that you wül agree with me that there is wanting some practical data npon the evaporative capacities of surfaces, as applied in the various forms of boilers now principally in use ; and I doubt not but that many others would* equally with myself, be much bene A ted by such data being supplied through the medium of your estimable journal. E- W. A.t Cologne.


[334] Sir,—" Т. Л." [271], asks Mr. Proctor to explain what he calls "two curious photographic phenomena." As the gentleman referred to may not happen to be a practical photographer I write hoping to prevent him from seeking a solution of the problems by assuring him thut the first of the "phenomena" uiily exists in imagination, and tlio second, if real only shows that his chemicals decrease rapidly in Hon^itiveness.

"J. W." [282], speaks of a method of accelerating exposure by allowing red light to fall on the plate. Many plans of producing a partial fog and calling it softness have been proposed, and some of them even patented. Among others that of lining the camera with white, and of exposing the plate to a weak light, but they have only served as sources of amusement and wonder.

"Young Photo " (4G31, 4622), had bettor precipitate bis silver with hydrochloric acid, and «ell it to a refiner, who will give him nitrate of silver, if he desires, in exchange for it. If he attempt to evaporate and fuse it he might blow up the neighbourhood, as fulminating silver may easily bo formed in electroplating solutions. He may dissolve his gold in aquaregia (nitric acid, 1 part; hydrochloric acid, 8 parts), and evaporate to dryness on a sand-bath under a chimney, but he will do better to sell his gold and bu}- the chloride; nitrate of silver and chloride of gold, the former especially, being sold for the merest fraction over the intrinsic value of the metal contained.

"Amicus," (4Ü1G) should get Newth*s "Natural Phi losophy." W. E. D.


1335] Sib,—Allow me to express my thanks to Mr. Proctor—[257J page 540—for so promptly taking up this question. I very mueh regret that I am not now able to quote the exact words of Mr. Lassoll, my extracts from the "Monthly Notices" being only the snbstance of them. I have notes to the effect that in 1851-2 the positions were as stated on p. 52*2 of the English Mechanic; the apparent ellipse of the orbits being as 8 to tí (Vol. XII.).

In thé papers by Mr. Dawps containing a discussion of Lasself'sandO. Strnve's observations (Vol. VIII.) the major axis of the orbits was assumed to be Роз. 10 J and 190° in Nov., 1817.

I new see that Humboldt refers to " Astr. Nachr." No. 493, for M idler's account of the ullipticity of tho planet.

It would be too much to expect Mr. Proctor to examine these papers for one inquirer only, but if he were induced to do so from his own interest I am not certain that he would not be repaid. I am more certain that he would bo helping an Etudiant.

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mam 1), how can it be said that a picture is produced in that focus, inverted or upside down, seeing that the rays which are so converged do not intersect or cross each other, but merely meet or centre in one spot? Practically I find, however, in order to obtain a clear and distinct picture, it is necessary that the lens or screen, it matters not which, should be shifted so as to increase the distance between the two, as in diagram 1, where C, B, A are the rays received on the screen, some distance beyond the focus F; it can be seen at once, therefore, that these line* having crossed each other, that then, and not until then, does the picture becomo inverted. How can it be said, with respect to the eye and vision, that to see distinctly, or that a distinct picture should fall on the retina, the focus should centre on it, as in diagram No. 2, В? I maintain that it wonld be indistinct, and not inverted; what is meant, therefore, by tho focus falling on the retina, and how can it be reconciled with lung and short sight? Again, if a screen with a small hole permit the rays of light reflected from some distant object, such as a cross A in diagram 3, to pass through it, it will be per

ceived that the lines intersect each other at the opening B, crossing each other and passing on to C. I ask where is the focus? Is it at this opening, or where the pictnro falls on the screen D? Perhaps some of your kind readers will help ш«, with, at the samo time, that indulgence for my ignorance, which is so necessary in answering the inquiries of others. E. O. S.


[8371 Sib,—At tho recent meeting of the British Medical Association at Newcastle, a paper was presented by Dr. John Murray, on the above subject, to which I wish to call the attention of "our" readers. Dr. Richardson, some years ago, in a lecture on tho effects of tobacco-smoking, pointed out that the greater number of the patients in our hospitals for diseases of the chest were non-smokers, and he accounted for this fact, if I remember rightly, by saying that the bronchial membranes of smokers were covered by a coating of mucus, which, he argued, protected those delicate tissues from the effects of our damp atmosphere. Whether this be true or not, Dr. Murray has now come forward as an exponent of the advantages of snufftaking as a preventive of catarrh; and, by a process of inductive reasoning, he arrives at a conclusion that smoking ami snuff-taking are preservatives against, if not cures of, bronchitis and phthisis. Ho states that an habitual smoker seldom or never dies of consumption, and he further declares that he has seen the progress of consumption arrested by practising the habit of snuff-taking. The reasons given by Dr. Murray for this emphatic expression of opinion are as follows :—" By titillating the lining membrane of the nostrils, snuff acts as a powerful derivative and counter-irritant, and its use will tend to preserve the more important and susceptible pulmonary mucous membrane from evil. The sneezing which succeeds the unaccustomed application of the errhine, or agitates even an old and seasoned nose when a new titillant is tried, and the cough which is induced when, by chance, some of the lighter particles get into tho throat, may be of some avail in effecting the elimination of albumenoid matter (the precursor of tubercle) from the lungs—ere it has had time to fill the air-cells and minute bronchi, and coagulate—in like manner as sea-sickness is believed to do. The majority of medical men, when recovering from a common cold, will take a pinch, in order * to speed the going guest.' If good to expedite the departure of a cold, I have no hesitation in affirming that it will be better still as an expedient in altogether preventing the catarrh."

It is believed, that in tobacco and snuff manufactories, the workmen do not suffer from any disease which tobacco can be said to occasion, but, on the contrary, the employés seem to have an immunity from typhus fever, consumption, and cholera. The majority of the State physicians of France agree in believing that employment amongst tobacco is instrumental in preventing consumption, and may even restore consumptives to health. As regards the effects of tobaccosmoking there is still much that requires elucidation. Does the empyreumatic oil or the nicotine affect, in any way, the health of the smokers? Tobacco is supposed to * be repulsive to the uninitiated system because sickness and nausea invariably follow the "first pipe;" but then again so is tho motion of a vessel at 6ea, which generally brings on vomiting. In the one case something may be said to be imbibed (or infumed) into the system; in the other there is nothing of the kind, unless we are to snpposethat tho fresh air is the cause of the sickness. Who, therefore, shall say that tobacco must be injurious because the system repels it at first? Many persons cannot partake of some species of shell-fish without nausea and sickness supervening, and instances are on record where such a simple repast as roast mutton invariably caused "alarming symptoms." But surely no one can say that either mutton or shell-fish is, per te, repulsive to the human stomach? One fact is generally overlooked by the opponents of tobacco in relying tr>o confidently on the supposed antagonism of the system to smoking, as exhibited after the first pipe, viz., that novices do not understand tho method of smoking, and so probably pump the smoke into their stomachs. Of conreo, no habitual smoker ever does that.

It is acknowledged by all smokers that tobaccosmoking acts upon them as a sedative, and enables them to perform heavy mental labour without that nervous prostration which otherwise is its invariable concomitant. Many of our great mathematicians and literary men are, or were, great smokers ; and I know but few hard-working members of the press who are not habitual smokers. Sir Isaac Newton, Charles Dickens, and Mark Lemon were all great smokers, whilst Professor Masson, Mr. Punch, Fun, and others too numerous to mention, are all well-known patrons of the "weed." It is »uid by some anti-tobacco men, that smoking is an insidious poison, weakening the brain and destroying the stomach of its devotees. I ask for proofs. Take the great Teutonic nation, notorious for its inveterate habit of smoking. Are Germans weak, either in brain or body? Do thoy invariably dio young? Or, rather, are thoy not a nation of deep thinkers? No one can say they are deficient in muscle. Of course, smoking carried to excess is a dangerous habit; but then, the same applies to eating, and in fact, to even thing else. What we really want to know is what sort of tobacco is the best, and) what kind of pipe most effectually remove* the poisonous properties which tobacco is said to contain. There can be no harm in removing the nicotine, if possible; though whether it is really absorbed in sufficient quantity to do any harm is

exceedingly doubtful. It is more than probable that cheap tobacco is extensively adulterated, and it ii quite possible that whatever evil effects are laid at the door of the *' fragrant weed," may be traced to the action of the substances with which it is mi\>-d or prepared. Saul Rymka.


[338J Sin,—I have been a diligent reader of " Sigma's " papers on the different kinds of battery, but have not been able to avail myself of the valuable information contained therein to the extent I had hoped for, from my previous ignorance of the eubject. I shall feel much obliged if "Sigma" will, as opportunity offers, explain to me a few difficulties which I will state. 1 don't know how many liquid grains there are in one pint, therefore I have not been able to make np a nitrate of soda solution, which I was anxious to do. In the nitric acid table (p. 2Ö6) the number of atoms in a pound decrease with tho gravity, but in the fourth column the number of atoms appear to increase for the first three flgnres. In the above table aqnafortis is treated as a weak nitric acid.

Does " Sigma " know anything of the article made to be used for all ordinary trade purposes as dipping aquafortis, which is composed of certain proportions of brown oil of vitriol, and nitrous acid, as they call it in the trade? It is a bright brown fuming acid, and a smaller proportion of it is used than of the oil, if I am correctly informed. Would not such an article give worse results than the acid mentioned in the table?

A few words as to the selection of an instrument to take the gravity would be very acceptable. At the risk of being thought very dull, I must confess I have not. been able to master as yet the table on page 840; but if " Sigma " will give the quantity of nitrate of soda and of acid, to make, say a pint of solution, and the number of fluid graine in the same, I think, with this additional help I shall succeed.

I certainly should not venture to ask so much, did 1 not recollect that probably there are others whose only source of information on many subjects is our much loved Mechanic, and who, like myself, after honest effort have not reaped all the benefit those papers can afford. H. K.


[33i>] Sin,—I am much obliged to " II. D." (4531) for his kind reply to above query, and find that our views coincide in respect to sections 1 and la of query, i.e., that the pressures iu boiler, when ttated a* in exces» of the atmoepttere, are to be assumed as wholly effective iu aofi-coudensing engines, whilst in condenting engines the force of the vacuum has to be added tu these pressurée. Thus, for a clear understanding of tincase, let the steam pressure in a given boiler be 001b. in excess of the atmosphere (751b. from a vacuum), the gross theoretical horse power of a non-condensing engine ifull pressure throughout the stroke being presumed) will be expressed by either of the following formulae :—

R = fs v


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33000 in which R is tho gross theoretical Н.Г.; /, the cross sectional area of cylinder in square inches; *,the excess force of steam over the atmosphere, per square inch ; *', its total force per square inch from a vacuum; p, the atmospheric pressure per square inch ; and r, the velocity of the piston in feet por minute.

Under same assumptions and values, the gross
theoretic horso power of condensing engines would be
expressed by either of the following formulas :—
R = / (< + p) v

R = f tf_v

In regard to section 3 of query (Compound Engines), the answer of "R. D." is not quite so explicit. Although the reply is satisfactory ам far as it deaU with the question, it does not go to tho full extent of the inquiry, i.e., does not explain how the power of an engine of the given dimensions and data is estimated. I agreo with "R. D." that the ratio ot expansion is as 1 : 4, and that the mean steam pressure is 361b. per square inch in erect* of atmotphere, but I desire to know,—and it is this point upon which I trust to be enlightened,—upon what area» this mean pre$sure take* effect. Does it operate with its mean force upon both the pistons equally per unit of turfacc or only upon one, i.e., upon the largest?

I have noticed in a scientific work, that the power of a compound engine is the same as a tingle cylinder engine of the same dimensions as the loir prêtent* cylinder, and working with the same initial pressure of steam and the same ratio of expansion.

If tbis be so the gross theoretical horse power of engine particularized iu section 3 (see also corrections in No. 2H3, page 543) would be :— (20* x 0-7854) x (36 + 15» x 880 ял _c „ „

ззш "Ä 270''5 HP

It wonld seem to me, however, more correct to deal with rath cylinder xsparatrlf, i.t., calculating the power of each part of the machine for itself, and adding together the two resultants for tho total power. rVrhaps, "R. D." will kindly work ont the example in both waië, by which the correctness or other- Л wise of tho statement as to the siie of low pressure ^

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cylinder forming the basis for estimate ef power, would be demonstrated.

In eonclnsion I would farther take the liberty of inquiring, What percentage of the grant theoretic power obtained on the basis of the foregoing formulas as applied to the three several cla**e* of engines (single-cylindar condensing, single-cylinder non-condeiiHiug, and compound-condensing) may be safely assumed aa effective from off their respective crank-shafts in the form and character of meful available power? Of course good construction and finish рте-supposed.

A Working Engineer.


1340] Sir,—I wish to submit to the scrutiny of the gentlemen who have recently been writing in the English Mechanic on the subject of screws and inclined plane, the following result, which I have arrived at theoretically, as to the most economical angle for the thread of a screw, but which might, at first sight, seem to contradict the commonly-received idea that tho finer the thread of a screw the greater its mechanical power. Now, although if it were possible to to do away with the friction of a screw, there would, theoretically, be no limit to its power, yet as the friction of a screw absorbs a very large proportion of the power applied to turn it round, it becomes a question as to how many times it is necessary to turn it round to produce a certain effect, and as that number of times is dependent on and inversely proportional to the pitch of the screw, the question resolves itself into a consideration of the angle at which the thread of the screw is to be cat to produce the best result.

The simplest possible form in which we can present the screw with a view to this investigation is represented in Fig. 1, where the screw is itself fixed, and the nut with the weight attached is supposed to be moved round by a cord stretched horizontally and falling over a pulley with an experimental weight hung to it. And that is the form that an apparatus for determining this question experimentally would probably assume.

Now for the matter according to theory :—Let angle

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is the same thing, making tan i . cot ( i + ф ) a maximum.

Now, without treating your readers to the differentiation of this small expression, I may statu simply

that the result is that when ¡j is a maximum, then

4 3

or that is to say that the most economical angle for the thread of a screw is 15 ', minus one half of the angle of friction, which depends on the nature of the sul stances composing the screw and nut, and which for (say) a steel screw and wrought-irou or brass nut we may take roughly at 10, so that we get a screw

inclined 45 — — or 40°. 2

As the differentiation mentioned above is a long one, occupying nearly a whole side of letter-paper, and some of the steps being too long to be got into the space, even when written length wise of the sheet, it becomes desirable to adopt the simpler plan of approximation, with the help of a table of tangents, in which way of doing it it comes ont thus:

First suppose 2 = 80 and <p = 10'

then tan i . cot i i ■ vi tan 80' x cot 40
= -577 x 1-19 - *68ti

Next suppose i = 50\ then tan t = 1*19 and cot (i + <t>) =■ '577 which gives the same result as before, so that the proper value uf i probably lies somewhere half-way between the two.

Therefore, lastly, let i = 46°, then

tan i. cot (i + <p) = *889 x -889 = '704 and this seems obviously a maximum without trying any more values, from the consideration that, as the tan and cot vary simultaneously, the largest possible product of the two would certainly bo a square, which this is.

The illustration thut I give above of the probable form an experimental apparatus would assume is by no means a practical one ; in fact I can hardly imagine a case in which it could be applied to any useful purpose; but the usual manner in which the power of a screw is applied is by the screw working through a fixed nut, as in a letter-copying or ordinary house-press, or else as in a smith's vice.

Fig. 8. Take for instance Fig. 8 as a type of the ordinary application of a screw. Not considering the rate or pitch of screw, let us take account of the friction. Now bearing in mind that the amount of friction depends for the same muterial solely on the pressure, and that all the rest of the calculation is a mere matter of leverage, it becomes obvious that the friction on the nnder side of the head of the screw—as it is exerted on an annular plane, whose mean diameter is greater than the mean diameter of the screw thread—takes more power to overcome it than tho friction of the screwthread itself does (unless, indeed, the nut fits the screw very tight, which is considered by workmen to be perfection of work, but is on apar with many otherabsnrd ideas that workmen have), and the broader the collar under the head the more loss through friction. Hence, as it is inevitable that much more than half the power applied to this arrangement, as compared with No. 1, is utterly thrown away, it becomes desirable to reduce the number of times that the screw has to be turned round, or els« to reduce the diameter of the screw and its collar with a view of decreasing the distance from the centre of the screw at which the resistance acts; and thin is done either by retaining the same diameter and increasing the pitch of screw, or else retaining the same pitch and reducing the diameter, which increases the angle of thread, or else a judicious mixture of the two. Also to reduce the friction of collar, make its diameter as small as possible consistently with strength, either making it press on its extremity (pointed if possible), as in a letter copying-press, or by making the collar in the form of grooves as is sometimes done with propeller shafts, recollecting that twenty gooves that tit properly, not tight, have no more friction than one. I believe that there is hardly an application of the screw, except for bolts, in which this plan of very liigh pitch would not tell advantageously, particularly for planing machines, lathes, and screw presses; the velocity of action being modified when necessary by the application of wheels and pinions, as is done in a crab, or crane, or screwing lathe; and I believe there would be much greater economy of power from the less number of times the screw itself would revolve, than there would be loss through the additional gearing. Of course to turn a high-pitched screw round once requires more force or a longer lever than a low-pitched one, but it requires doing so much less frequently.

A screw of 40° rises 8jjin. with a circumference of lOin. or a diameter of 8|in., or say the rise of the thread is about *J' times the outside diameter of the shaft, which appears extravagant, but I have screws of 45 actually in use, so there is no question about their working or sticking. I wonder whether the same would hold good with propellers? I believe it would with 43? J. K. P.


[841] Sir,—Notwithstanding all that has been written on the experience of varions riders, the fact is that the performance of the bicycle can be reduced to a simple sum in arithmetic. The driving wheel seldom reaches 3ft. (¡in. in diameter, but assuming such dimensions, and acknowledging that the driving wheel must inevitably measure the length of road passed over, it must make 560"7 revolutions to accomplish one mile. The action of the crank requires the legs of the driver to make the same number of strokes for the same

distance, and to cover seven miles, seven times that number will be required, und to perform that distance in one hour, 65*1 strokes per minute must be made, or rather more than one full stroke per second. Tin* rate of motion is impossible to many, and very few could keep it up for any length of time. Therefore the statements of 8 or 10 miles an hour as having been performed must be entirely fabulous, or executed on а descent, when no action is required, for we all know, unfortunately, how easy it is to go down hill.

The greatest fallacy of all is the proposal to put more than one driver upon a velocipede, for neither two nor fifty on one machine could increase the speed lin. per honr. Two drivers do not divide the labour, they double it. The only means of giving the velocipede a commercial value is to canse the driving wheeJ or wheels to revolve with a velocity at least fourfold that of the legs of the driver.

Henry W. Rete-ley.


[3421 Sib,—The thought has occurred to me. Would it not be a famous plan to have an " English Меепапк Microscopical Society "? I believe there are a great many more amateurs in this very interesting acienc-than we, perhaps, виррове, all of whom would no doubt be glad of any little help that might to afforded them by better hands if they only knew where to find them; besides which a society ьо formed would be one of the best means of disposing of our duplicate slides. I am not sure that the plan I am about to propose is the be$t, bat I think it a good one. Let all those interested in microscopy send their и a into the editor to be published on the "Micro." page. I then propose that the person whose name stands first, whom I will call A. shall send list of duplicates (bearing his name at top) to B.; at bottom of same sheet A. might write any question he wishee to ask or make known any idea of his own. In not more than two days after receipt of same by В., he shall add another sheet, bearing his name, list of duplicates, answer to A.'s questions, and anything else of interest, and forward same to I '., who will send it to I)., and so on to last member, who will send the whole on to A. A. shall then take away his first sheet and add new one at end. B. to do same, Ac. This list may always be sent from one member to another for a penny by book-post. The best way to fasten sheets together in proper order will be with one of the patent paper fasteners so generally used. A. A.F.


[843] Sir,—I fancy your querist, " Melting Point '* (No. 4586), will find some difficulty in obtaining an exactly correct answer to his query, as the data necessary does not, I believe, exist. Even if it had been obtained for one sample of paraffine melting at 109- Fahr, and IÜ8 Fahr., to all probability-it would differ in another.

To all practical purposes, though, the melting points maybe assumed to be about 115: Fahr., 114 Fabr., and 113: Fahr.

The acid solution of phosphate of lime referred to by Mr. Young in his letter on page 568 is a sulphuric acid solution of phosphate, and is also known as superphosphate.

With reference to the degree of Twaddell'e hydrometer equal to 53- of Baumé's, is, taking Franceour's division, exactly 98°. If it would be of any use to him, I will, if possible, forward to him an approximate rule for converting Baumé's into Twaddell's degrees.

I find " An Exhibitioner at the Royal College of Chemistry" states, on the authority of Professor Huxley, that *' 15 to 20 per cent." of carbonic acid gas "may be breathed without producing any immediate evil effects, provided the quantity of oxygen is increased in a like proportion."

I do not know from whence the above was taken, certainly it may be from some such little work as his "Elementary Physiology," in Macmillan's series; but though I remember casually looking through that work, yet I do not remember any such statement. Perhaps, though, your correspondent, "An Exhibitioner at the Royal College of Chemistry," will state his authority for giving that as Professor Huxley's opinioD. As it stands it is almost too indefinite for even Professor Huxley: for reading it literally and increasing tho oxygen in the same ratio or proportion as the carbonic acid gas has been, we should have to imagine am atmosphere containing some thousands per cent, of oxygen, which is considerably worse than three halves to an whole, and more than I can manage. If we are simply to increase the oxygen only to some 80 per cent., we can hardly be said to have so done, seeing we have increased the carbonic acid some hundredfold. Dr. Taylor, too, has found that a mixture of equal volumes of oxygen and carbonic acid produces death.

Dr. Angus Smith categorically contradicts the assertion that 4 per cent, of pure carbonic acid produces any npparent effects, and that from personal experi • ence ( Proc. Rottal Com., 1864).

That possibly picric acid might be detected by the two extremely simple tests detailed by an " Associate of the Royal School of Mines," on page 578, is undeniable; but that it vould be so done I should hardly care to so gravely affirm. Accordingly I think an "Associate " might have so far exercised his ingenuity as to have at least found some little more decided and certain test than those: acknowledging freely though the difficulty in so doing, due to the тегу small proportion of picric acid present.

The test of "Crow Trees," described on page 573. is a тогу neat little reaction, founded on the production of a picramute; but in its practical value, hardly better than those of an "Associate of the Royal School of Mines," for the тегу infinitesimal amount of picric acid present in beer, and the тегу complex Constitution of that liquid, would render it hardly more trustworthy than as an indication that picric acid might be present.

With all dne courtesy I should command to your energetic correspondent, Mr. Boord, a little care in reading queries; as of course I can but ascribe to his haring very carelessly indeed read a " Young Photo's" query his very incorrect and misleading answer, that might easily cause much annoyance and expense to a "Young Photo." If I am unfortunately wrong in my supposition, and Mr. Boord did read the query with all care and attention, thon I am sure Mr. Boord will accept my apologies, and excuse and kindly pardon my mistake. In that case he will allow me to ásenme the only other supposition, and ascribe his lapse into error to an imperfect acquaintance with the Tarions reactions he writes concerning; so, doubtlessly ho will excuse my setting matters right.

In his answer to "A Young Photo" (462*2), he gravely directs him to precipitate with common salt the silver from his solution of cyanide of silver in cyanide of potassium. Now, as a matter of fact, chloride of sodium produces no precipitate whatever in a solution of the cyanide of silver in cyanide of potassium—a fact that has been known ever since Professor Ittner discovered the salt. If Mr. Boord will refer to any work on chemistry, as Fownes' or Professor Miller's, as he might almost have done before replying, I пате some idea he will find it prominently stated that metallic chlorides prodnce no precipitate in solutions of cyanide of silver in alkaline cyanide. Also, Mr. Boord seems quite unaware that, as Professor Rammelsberg was first to ascertain, chloride of silver is very readily soluble in cyanide of potassium, which of itself would, in my idea, effectually prevent any precipitation. If Mr. Boord would so far oblige by referring to some little work, as Professor Fownes* "Manual," or Dr. Miller's "Elements," I am most decidedly under the impression that he will find the same stated therein, and which, had be, but thought fit to take the trouble to refer to, would have possibly prevented his falling into so flagrant a blunder. Lastly, if I have not already troubled him too much, will he again oblige by referring to some work, and I have some idea that he will find stated therein that chloride of silver is soluble in excess of chloride of sodium.

The consequences of Mr. Boord being, as we must assume, ignorant—no, unaware of these very simple facts, and of his not having seen fit to take the immense trouble to refer to such simple sources as might have enlightened him, is that his answer to "A Young Photo," on p. 578, is erroneous and useless ab initio. That Mr. Boord will regret having written a wrong answer is to be supposed, and that he will regret having given an erroneous reply to your correspondent, "A Young Photo," is certain.

Perhaps I have quite mistaken what "An Associate of the Royal School of Mines" intends "A Young Photo" to obtain in his answer to query No. 4622, p. 678; but if your querist, "A Young Photo," thinks he will obtain by it pure nitrate of silver he will be sadly disappointed.

Let "Paddy" (No. 4C76), boil well his precipitate with strong caustic potash, and dissolve as much as possible in dilute nitric acid; dilute with water, filter and precipitate with sodic chloride. Collect and wash well the precipitate, boil with pure strong caustic potash, until converted into a dense black powder. This is to be dissolved in nitric acid and evaporated to dryness in a water bath; dissolve in water and crystallize; ro-dissolve, neutralize with ammonia, and re-crystallize.

Mr. Proctor, I fancy, is explaining a mere supposition and unknown circumstance. Urban.


[814] Fun,-- Not being satisfied with F.R.A.S.V rejection of my views (see pp. 451) and 4!)1), and Mr. Proctor having ignored them altogether, I sent the correspondence to Mr. Alexander Herschel, and I forward you his answer. In the face of so strong an authority will those gentlemen revise their views and criticise my confessedly imperfect mathematics?

T. S. UanoRNK.

"My Dear Ubborne,—If fixed vertically upwards from the earth in vacuo, a projectile would fall westward* from its point of projection.—I remain, yours very truly, Alex. Hkrsciiel.

"Collingwood, Hawkhurst, Aug. 29,1H70."


[845] Snt,—There must be an error in the statement (p. 500) that " the distance from the Boulevard to the enceinte continué averages about 1,1)98 yards." This may be probably the smallest interval anywhere between the Barriéreg (not boulevards) and the enceinte. Thu Barrieres are the very irregular, approximately oval, line of roads at which the shading on p. 564) terminates; including about four times the area of ancient Paris as defined by its Boulevards. These form a far more circular, or rather decagonal circuit, tolerably traceable in the plan, except on the 8.E.; nowhere, I belie v о, so little as two miles behind the outer glacis ; and it is remarkable that they either enclose or touch every monumental or public building of any dignity, with the sole exception of the Arc de l'Etoile, which alone stands

on the line of Barrieres. The zone between these two circuits, known as the Faubourgs, is certainly more densely and, in the northern half, more loftily built, even than the central city, aud more solidly and handsomely on the whole than perhaps any town in the world; but nearly all is private, except a few inferior churches and the railway termini. Thon we must remember the Parisians have far better refuge from bombardment than cellars or sewers; among the bones of their ancestors, in the quarries whence all the noble material of their city has come, undermining its whole southern half. E. L. G.


[346] Sir,—A few of your Bristol subscribers are desirous of emulating the example of some of the other large towns in forming one of the above societies here. We should be glad to receive the names of those readers in Bristol who could join us. W. Johns,

6, Park-row, Bristol.

ELECTRO-MAGNETISM. [ 347] Sir,—Two things appear to have escaped tho thoughts of "Thinker." 1. That the power produced, in any form, heat or motion, by a givon chemical action, has been found always proportional to the number of equivalent» tor what Dalton terms "atom* ") of matter, combined or set free. Now, as the equivalent (or "atomic weight") of carbon is the lowest of any bat that of hydrogen, while that of zinc is rather high, they are held to be as 6 to 32. This would imply that the oxidation of 321b. of zinc in a battery can yield no more power than the burning 61b. of coal. But, secondly, he must have overlooked that every pound of zinc he oxidizes or combines has first had to be deoxidized or set free from combination, by an expenditure of coal, for no zinc is found in a free or com- bined state, as all coal is. The native oxide, or sulphuret of zinc, has first to be decomposed by an equivalent power (yielded by the combination of something else, usually native coal and native oxygen). The zinc has to be separated from those very elements, oxygen or sulphur, one or both, to both of which "Thinker" must recombine it in his battery, its whole poweryielding value to him depending on this previous artificial separation from these elements. He is, therefore, as it were, proposing to compete with an engine by tho power of the water that this very engine has pumped up for him. E. L. G.


[348] Sir,—Since the begining of last month I have been so much occupied by various matters that I have been entirely deprived of the pleasure of reading the English Mechanic, and it is only this day, 5th Sept., that I havo seen in your number of the 5th August, two letters on the flute, one signed by Mr. T. Cridland, and the other by "Flautist," and the latter, addressed to me. I will furnish the information the above two gentlemen ask for. The instruction book that Mr. Cridland wants to know about, is by John Gunn. It is an excellent work, but it is long since out of print, it was published by the author, towards the close of the last century, and I find that the quotation is from Sir J. Reynolds, "Academical Discourses,"A.d. 1776. "Flautist" is quite right in supposing that there is an especial fingering for many of the upper notes on the Siccama flute. I beg to inform him that he can get a printed scale for that instrument of Messrs. С happe 11 л Co., New Bond-street. Henry Chapman.


[349] Sir,—I have an old and vigorous vine that covers the lower half of the back of my house, which faces the west. Last year a few branches turned the corner and ran along the northern wall of my garden, and this year there are several fine bunches of grapes on them, while there are none on the house.

This induces me to encourage its extension along the wall and to check its growth on the house by keeping it topped. The young branches not having been properly attended to, have grown тегу irregularly, some times in clusters of half-a-dozen, an inch apart, and I "would fain lay knife aboard," right and left, but that I fear, without proper advice, to take off the wrong shoots.

The only books on the subject I can refer to deal only in generalities, and do not make the matter clear to me. I therefore appeal to some of your readers to help me; and as it would be difficult to explain my case without drawing, I will begin from the beginning and plant a young shoot from my own or some other vine, and ask for such instruction as will carry me on to the first crop of grapes. This will enable me to treat the old vine properly at the same time.

The wall is 10ft. high, faces due south, and is exposed to the sun from 10 till 3.

What I wish to know is

1st. Will white or black grapes be preferable?

2nd. When should the cuttings be taken and how much of them planted?

3rd. What kind of mould should they be put into at first, and what kind of subsoil should they have to strike down into?

4th. Should they be struck in pots or in the places they are henceforth to occupy?

5th. What should be the future treatment after they are in the ground 7 Is Vino Veritas.


[350] Sut,—If not too late, I will give a little advice to " Cumberland Miner" (p. 307), so that he may avoid the distressing accidents he speaks of. The whole cause is in the use of the pricker, which I had imagined quite obsolete years ago, and all the replies have given palliatives, only they have not gone to the root of the matter. My advice is, throw away the pricker, and use the patent safety fuse—not the gutta-percha fuse, which I grant you, is expensive. The patent safety fuse is only 4Jd. a coil of .eight yards; and if required in damp places, use the fuse with tape wound round the outside, called by us here tape fuse. This is 6d. the coil, but much superior to the ordinary fuse. We have used this fuse at the slate quarries in this neighbourhood for the last twenty years, and have never had an accident in the blasting during that period. The fuse will be found less expensive than the pricker, as the hole left by the latter must be primed with fine sporting powder. The pricker is only fit to be put into a museum as the robe of the dark ages. Wishing the "Cumberland Miner" success with this rose, I beg to subscribe myself, Timothy Burs Tall.


[8511 Sir,—I have no objection to Mr. Proctor enacting the part of scientific policeman, and checking me in statements that appear to him erroneous, if the duty is fairly and courteously executed. It is difficult to judge the motives prompting the acts of others, and I fancied there was more of the spirit of counsel defending a client right or wrong, than was consistent with a philosopher seeking natural truth. It seems from the letter (No. 241, p. 564), that I was mistaken in this surmise, and therefore hope Mr. Proctor will pardon the suspicion. But he is also wrong if he thinks me altogether unacquainted with the writings of other men on the subject of light. I am as well aware as he can be of the discordance between my views and theirs, and will explain to him in a few words the reason of the difference. The prevailing belief is, that the powers and activities of material substances result from the action of properties they inherently possess. This is not my belief, and in dissenting from that doctrine, I think myself able to advance irrefutable proof of, its fallacy. Indeed the questions I have already propounded, both to Mr. Proctor and "F.R.A.S.,"were introduced for the purpose of showing the impossibility of accounting for certain natural phenomena by the prevailing theories, although readily explicable by the theory I have framed, as aüo others still more recondite.

I shall not now dwell further upon this subject, having at present little leisure to work it out, but I hope shortly to show Mr. Proctor another theory of the cause of the zodiacal light, which I think he will own was not considered in his paper. T. A.


[352] Sib,—I am glad to see that Mr. R. A. Proctor has given Mr. Firth a few words of advice, which I hope he will profit by. Mr. Firth ought to be well acquainted with the fact that it is almost impossible to avoid errors in printing scientific matter, and especially in cases where the writers have not had proofs. Let us hope that your correspondent will see the folly of his recent endeavour to find fault with one who is really deserving of our warmest thanks. In reply to " Young Amateur" (4670), the planet Saturn is situated between Op h ens and Sagittarius. If, on any fine evening, he will look towards the south-west sky, he will not fail to perceive a star shining with a very steady light, and much brighter than any others in its vicinity. The planet will not be high above the horizon.

The solar spots have recently appeared in great numbers. I was much surprised, on examining the disc two or three days ago, to find that there were enormous groups visible in the north hemisphere. It is probable that one or more of these groups has now passed off the disc, but there is no doubt that the sun's photosphere is in a very disturbed state, and we may therefore expect to see numerous large and well defined macula. A Member Of The Obskrvimo Abtrokomical Society.


[353] Sir,—Mr. Coffin [304], p. 567, is quite correct in his idea (which I have frequently stated), that for medical use, the induced current of the primary wire is more valuable than the more intense shocks of the secondary, though these have also their value in some cases. The plan of construction given by me in last volume furnishes both, and carries the current of the primary into the secondary and Becnres a current always in one direction, a matter of great importance.

In reply to the questions. A Rhumkorff coil could be used as suggested, taking care to leave the secondary circuit open, and disconnecting the condenser and providing an additional conductor and screw from the end of the primary within the break, but it would not be a wise process as a special coil is a very simple matter. A certain amount of force would bo absorbed by the secondary wire even when open, but it would be small. I think that the magnetic effect on the core would be increased by increasing the middle layers, but am not certain. At all events, it is unnecessary for medical use, as quite su dictent effect can be obtained from a single cell by even layers. My own coil, made as described, gives action with a single Smee cell, varying from such a carrent m might be passed to stimulate the most sensitive organ, up to one which would set a strong man screaming. Sigma.


[354] Sir,—We see now and then in the papers statements regarding the supply of the rille bearing the above name to the French. The tirst remarks on the subject that came under my notice were about a month ago, to the efiTect that 50,000 of these rifles sent to Fiance in the spring of the vear were so many reasons for Napoleon 111. deciding"tomake war. From the neighbourhood oí Finsbury was stated to be their origin. This morning too, Sept. 3rd, I see in the Timet, in Mr. Muntz's letter, that Count Palikao stated that 40,000 had been sent from this country and more contracted for. I think I can reconcile all these statements thus. A lirni somewhere near Finsbury did have a contract for say 60,000 rifles for the French ; and early this year, when the time was expired for completing the whole order, they had done unlv, say 40,000, and the French Government then told the'ni that they might discontinue making more, as thev thought they had enough. This accounts for the 40,000 delivered, and more said to bo contracted for. This occurred before the second week in March, though how much before I cannot say. It is absurd to suppose that an order for 40,000 rides came over, and was supplied onto/ «tor* since the declaration of war. 1 should think few makers kept in stock many specimens of such a Beestly rifle as a Also the rifles were not wholly made here. The barrels, sword bayonets, and scabbards, came from France; they were " actioned" hero and went home again to be stocked, so that although the French may have and undoubtedly did get a superior quality of workmanship in this small number (a mere fleabite compared with the whole quantity their army carries) yet had these 40,000 been entirely instead of one-hulf made in London, that would have had but small influence on the exact timo when Napoleon III. thought proper to declare war.

The above agrees too with Earl Granville's statement that no rifles have been sent to France tinte war was declared.

A friend of mine in the course of an interview with the Emperor on another subject, three or four years ago, was asked what he thought of the chaseepot, and told H.I.M. that in his opinion the chaisepöt was the worst military arm in Europe except the needle gun. And I am quite of opinion that the Snider is the best, und amply good enough for any eoldiers in the world. I have made breechloaders mvself before now, and studied the matter a little too. J. К P


*.* 1я their answers, Correspondents aro respectfully requested to mention In each Instance the title and number of the query asked.

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KEEPING VARNISH BRUSHES.-A correspondent of the Hub writes: The following method of keeping brushes may be of interest to painters. Should any dirt collect in the brush while varnishing, or the brush drop on the floor, which will happon sometimes, then clean it out well in varnish, and before putting it awav in the keeper fill the brush full of varnish, and in time the dirt and dust will all settle to the bottom Bv cleaning it with turpentine, which is a very volatile substance you will draw aU dust and dirt up to the tin of the' brush, and when using it next time it will all work out and in many cases spoil the job. Every brush should be well dipped in varnish beforo putting it back in the keepor. 1 have used brushes now for eight years and never had them in turpentine.

PARIS GREEN.—A correspondent says:—"Of itself I do not think Paris green is a diflicult paint to manage, but it is of a delicate shade which is easily affected bv outside causes. It is a good and permanent colour but the drawback of its changing, which is so commonly Лxpt',ï1.e.nced^i8geneгвllУ^lш, to the varnish used over it. This can be proved very easily. I have a panel before me which was painted with this green eighteen months ago and varnished, and now it is of a very dark and dirty shade. But by pumicing it until the varnish is removed I find the colour beneath it is still of the original shade almost precisely. As with several other colours the continued beauty of Paris green depends very materially upon the paleness and purity of varnish which is used over it. Paris green needs more than ordinary саго in mixing, from the same reason that its shade is so easily changod. I mix it with white lead, and grin* as stiff as possible in oil and a little japan gold size. As it quickly settles it Bhould be stirred frequently during application, and should be worked as rapidly as possible, the whole panel being laid on and not touched again, otherwise it will give a streaky appearance.' J IT

[S942.]-MAKINe BUTTER.-8ee, under the heading OI • Useful Notes," page 28, present volume.—SebuiUs.

[8949.]—"GUAYANA," OR GUIANA.—I find I have misconstrued what "Bernardin" said; I therefore apologize. In answer to " E. L. G.," who points out mv error in omitting the a, I cannot acknowledge that such is an error, since greater authorities do not uso it. I must certainly say, in my opinion, that the word is lomi, not «jorf, a« introducing such a letter would make it. The Rev. Thomas Milner. M.A., in his "GaUerv of Geography, writes it as Guiana, and Stielen " Hand Atlas" gives Ouj/naa, so Iwrotoit both ways, although I do not myself think the substitution of i instead of » correct. The word, as the Rev. Thomas Milner says, " is derived from the aboriginal tribe Guayanoct— a form of Waiini a small tributary of the Orinoco." There does not exist nt the present time any republic, but I find that such territory has merged into the Venezuelan Republic as spoken of by your correspondent " E. L. G." While' in Brazil last year, I mado enquiries respecting these three dependencies, and was informed that Don Joao (Quinto had given them to the three Powers after which they are named for some service«, but for what my informant did not say. No one who has been residing in Brazil, or on the South'Amoriean Continent near the equator, can say it is healthy for Eeropeans.—J. G. [4002.] -MUSLIN.-Aquilla (my better half) informs nie that some colours may be restored to muslins or cashmeres vory easily by simply washing them in buttermilk,— Aquillus.

[4263.]-TRANSPARENCIES.—For the,, prints c.a a close thin even-surfaced paper should be selected Colour on the right side of the picture with moitt irate r colonrs,apply strong even washes and use the "stipple" as sparingly as possible. As the pictures are to be se» i by transmitted light, they will require deeper eukmriuTo determine the exact depth will require practice. Ski, s should be kept very clear. Prepare a solution of l anada balsam (not too thick) in rectified oil of turpentine, coat the face of the coloured picture rapidlv аш! evenly with this cement, taking care that no part» are left untonched by the brush, and immediately apply it to the glass which must be scrupulously clean, press it closely and carefully, expel ail air bubble* or the work will be irrecoverably spoiled When the ccmout 1ms become hard anddry (about thirtv hoars will suffice tor this) varnish with the best picture copal. Flat camelhair tools should be employed for the cement and

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AN AMERICAN SALT-MINE.-Thc Patriot, of San Jose, California, gives tho following account of the great mine, or rather plain, of salt which lies about eighty miles N.W. of Austin, in Nevada territory, and not far distant from the railway. The mine is thirtv miles long by about twelve or thirteen miles broad without any break orinterruption. The surface presenté the appearance of a frozen lako with a light eprinkling of snow over it; the first etratum of salt is from twelve to fourteen inches m thickness, beneath which is a laver of argillaceous mud of a uniform depth of two feet; and under this again is the principal layer of salt, the thickness of which has not been ascertained, although a shaft has iieen sunk to the depth of several yards. The salt of this main etratum is described as being hard asonar! 7

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[4208.]-ADULTE RATION.-Thia query of J. Moody, if consigned to the limbo of the " unnoticed," will be sô for tho contrary reasons to the usual ones; in fact bocause too important, and too continually cropping up nn every side. He must remember not onlv Mr. Brighfs eternally memorable dictum that adultération, taise weights, and measures, and so forth are •' a form of competition; but (as is plainly implied) thev form that particular sort of competition by which Mr. Bright's "nation" (or tho two mobs that we dignifv with that name) have resolved to try the experiment of living. The world Is, m this century, to be enlightened on the possibility of thus living; and so grand an experiment must not be interrupted. Mankind must see it carried out a outrance. A querist put exactly J. Moody's question last year, ш July, in Public Opinion, and I, happening to see it, replied to this effect, that there neither is nor ought to be any means of detecting or publishing names of such traders as he and J. Moodv complain of. It would bo unjust if there were, for they are not offenders. 1 hey do but act as we force them. If there be wrong-doers, it is not they who adulterate tea by putting in what ought not to be in tea; but those who adulterate mankind nad the "nation," by creating therein classes of beings that ought not to be. It is not shopkeepers, but the shopkeeper-maA-tr» that are answerable. Perhaps I hardly make this clear, but enough for tho querist to rejoin immediately that when he '• wrote the other day on our commercial ¡умет, it was not with a view to complain of it as a whole," and so we parted. He may (or may not) have understood tho fact, that he and oach one of us must either attack and tight it <u о whole (in what way, I will readily explain if any one wishes to know) or accept it at a whole,—with adulteration, short weight, cheating of tho blind, and all its other features Let none dream there can be any neutral here He mut bo the system's soldier or its enemy. It is because this begins to be seei. by many, I think, that we hear less and less of querists like J. Moody. They see, and silently choose their side.—E. L. G.

[4209.]-WATER-WHEEL.-This cannot be answered without knowing approximately the qunntitv of water falling per minute. "J. Itoyd " might see from statements repeated in olinost every number of the Em.lisu Mechanic that to yield a horse-power, the weight falling 6,t¿mJTMtb»»."001b.(or ftboot 660 gallons) per minute"

[4282]-UNNOTICED QUERIES ON MAGNETISM — ihe horizontal intensity is that of the directive forcé in a common compass-needle—i.e., one balanced after being magnetized-its tendency to swing back when disturbed horizontally. Vertical intensity is that wherewith a dipping needle, or one that was balanced on a norizontal axis before being magnetized, returns to the local angleof dip, when disturbed therefrom in a vertical plane, up or down. Both are measured, or their strength at different places compared, by counting at each place the oscillations made per minute by the same needlejust as local amounts of gravity are compared bv thé numbers of oscillations per day of the same pondalum The needle shows the magnetic forces to vary over the globe like gravity, but to far greater extent and very irregularly. The horizontal force vanishes at tho earth's magnetic poles, the compass there having no directive power; but the vertical thero a maximum, as also the dip. Secular variation is the change observed in any of these data in a century; or the term expresses merely luie variation as distinguished from that of locality. Four kinds, at least, of magnetic curves exist all over the globe, and arc slowly changing. l,t. Those through places of like declination (or direction of the compass relatively to the meridian l, and these roughly resemble meridians. 2nd. Those of equal horizontal force. 3rd. Of equal inclination (or dip). And 4th Of equa. vertical force. And of the three latter all resemble wavy parallels of latitude.^E. L. G.

[424G.]-GLYCERINE FOR COD-LIVER 0IL.-V7e have many better substitutes for ood-livcr oil Although patients increase in weight while taking it, they rapidly fall back if it is discontinued for only a short time.—


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umber, burnt sienna, brown pink. Prussian blue. All shades of purple may be mode with the madders and blue, also in green with the yellows and blue, and blue and the browna. The madders may be enriched bv adding little burnt sienna as in draperies, 4c, in which case, shade with madder mixed with burnt nmber. Vandyke brown is a useful colour in transparent painting Use a little ox-gall with the water iu colouring, and avoid gum and dust.—Sable.

[42S8.]— FORCE-PUMP FOR IRRIGATION.—Small portable force-pumps are made by most pump-maker". They are very useful for watering flower or kitchengardens. They will throw from 30 to 40«, Price about 80s. Names of makers can bo fourni in "The Directory"

and in tho advertisement pages of " our" journal. Seks


[4381.]—METHYLATED SPIRIT.—Ibeg leave to contradict most emphatically the statement of "T. L. H." that " as a rule all the tinctures now sold in chemists" shops are prepared with the methylated spirit, and many of such tinctures are for internal application." There could bo no greater mis-statement, or greater display ol ignorance on the part of "T. L. H." than this. So respectable chemist would ever dream of making tinctures for internal use from methylated spirit, and if he did so he would find them unsaleable. Moreover tho use of methylated spirit is now strictly prohibited in the manufacture of any medicine for internal use, except ether and chloroform. This is on account of "cleaned spirit " having been sold by some unscrupulous drascist among the poorer classes as a stimulant, under various names. Methylated spirit may be used for linimeuts, Ac., for external use, and where cheapness is an object with the purchaser there can be no objection.—Hesey James, Pharmaceutist, Woolwiei.

[4883.]—THREE COINS—Though 1 am no judge ot coins, I fear there is a misprint in W. J. Eggleston's reply to "Hastings." Should not " London" (first word, fourth line) be "Londonderry " :> "John Ervin at ye ferry of Londonderry."—AqciLLOS.

[4298.]—MILLERS.—In reply to the query of " J. S. H.," I beg to eend the following description of Howes, Rabcock, & Co.'s " Eureka Smut and Separating Machine," one of which we have been using for some time, and find it far surpasses any other machines which we have hitherto tried for cleaning GMrka or other kinds of wheat. Cut No. 1 is a perspective riew, one section of

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the outer easing being removed. It represents, on the right, the screenings dropping from the separator, and on the left, at tho bottom of the machine, the discharging of grain. No. 2 is a sectional view, showing an internai arrangement of the machine. The direction of the arrows represents currents of air, created by the action of the fan through the separators and different parts of the machine, for separating the grain, collecting the dust and other impurities, and discharging them out of the mill. On tho left showier? the wheat entering:

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