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is holding le an extra brake, by means of which the engine can be stopped at 10 yards1 notice. He greatest и peed on the high road is 2¡> miles an hour, and in town lu. The coal and water are kept on either side of the boiler. The carriages in construction are just the samo as any other railway carriage, with the exception of the wheels, which are as already described. It is the invention oía gentleman named Lormargot.

Ы. Gabland.


s i H.—Frequent allusion* are made to the different e.m«teTïïtttrrtui of tho heavens both by ancient and modera poets, and this arose not only from the < u torn amongst all nations of making use of figurativo language, bat because the sowing and reaping of corn and airnnnltaral productions depeuded upon a right observation of the rising and mating of particular atara. When, for instance . the sun bad reached the Tropfe«, or turning- poluta, it was necessary to reckon so many days betöre it was advisable to undertake particular work, but in tbe*e times of accurate computation« and *ecronomical observation», the calendar is employed, which is much simpler. Thus, the poet Ik'slndin hi*" Works and Days" makes mention of the Tropics, and tho Roman poet has constant allusions to the signs of the Zodiac.

In order, therefore, to enter into the beauties of these writer« we should have accurate notious of the course of the e»n through the Zodiac, nudlt will beonr business in this letter to show by the globes the longitude and declination of that bright luminary as he proceeds in his round. It is not our purpose now to euter iuto any argument either for or against the Otperuican system, as this bus been amply disunited, but merely to Illustrate certain pbenoincua which can Op explained on either supposition—namely, that the earth moves round the sun, or that the sun moves rouud tho earth, and to illustrate the better, we will make the latter supposition. The figure H a representation of the two outer circles on the wooden horizon of the globe,


and the eclipse may represent the ecliptic on its surface. Tho son's longitude, then, and indeed of any othor celestial «body, i« it« distance from the point Aries « is from this point that the reckoning begin, and it will be found from an inspection of tho figure, that he is at this point on March liO, ho then passes throngh the eigusof the Zodiac as they aro marked in the circle, and reaches thera on the month« immediately sbovo them. Thus the sun eaters Cancer, June 21, and generally speaking he euters a new sign on the 20th of eash month ; that is, apparently enters, for the stars being millious of milos distant from both the earth and the sun, his entrance into them is obvious to the eye only. Concerning the origin ot the names assigned to the signs of the Zodiac, there seems to be some uncertainty, but it is generally supposed that they are intended to denote the peculiarities of the season at ihesc particular times. Thus he entered the sign* of the Kam and tho Bull, when farmers were busy In rearing domestic animals, and at his greatest height, he begins to recede, or, like a crab, to walk backwards. The Lion bei ng a native of the Torrid Zone denotes the beat of the season, the Balances when the days aud nights are again eqnal, the Archer, the bunting season, the Waterbearer, the watery aspect of the clouds, and the Fibhe« that the sea« were open for mans eupply when the ground was hard from frost, and uncultivated. The declination of the sun means his distance north or south of the equator, his Greatest declination being 23£°, when he has reached tlie meridian line on which the angle is measured, which tho ecliptic makes with the equator, and he then shines over the Xorth Foie, and 'Щ° beyond it. But to this subject we shall have afterward« to advert. It, then, we wish to know the sun's longitude by the globe, we have only to look on the wooden horizon for the mouth, aud the corresponding circle beueath will show the sign, and if wo wish to know the declination we have only to bring the sun's place to the brazen meridian, jtut as we find the latitude of a place, and immediately over it is the declination. We may remark that the orbit which the sun makes, or the earth, for it is immaterial for our purpose, is not circular, but elliptical,and those who wish t pursue the subject will do well to study Mr. Proctor ч Maps, published hy Messrs Longman*, •where they wffl find not only the orbit of the earth, but the orbii of all the planets round tbe eun accurately described according to scale. By a study of these maps it will be seen that the sun is iu perigee or nearest to tbe earth In winter, ten days after he haa entered Capricorn. December ;U,when, according to Mr. Proctor's Bcale of measurement, he is 91 millions of miles from the earth, and that he Is in apogee, or at his greatest distance from us, in Midsummer, July 2, when his distance by tbe same scale is millions of miles. Thus we find that we are

nearer to tho sun by 4 millions of miles iu winter than we are In summer, aud,consequently the warmth of our summer arises not from our proximity to the suu, but from the fact of his being longer above the horizon and his rays, owing to his altitude, darting less obliquelv upon the inhabitants of the North Temperate ¿one. These maps show the eituatien of the earth in his orbit for every ten days, as well as what sign of the Zodiac he is In, and should be possessed by tho*e desirous of accurate notions upon this subject. Thus it appears tint the suu's longitude is really the distance which the earth travels in her course round the sun, which, computed in miles, will befouad to bo nure than i3;>,0uiJ miles per hour.

T. S. H. P.S.—Mr. Dyer states the following sonteuce In Letter I. to need correction: "As the globe turuaon i*s axis from west to east, those who live in west longitude, must have their time earlier than those living in east longitude, because they will not come in to the enlightened hemisphere «o soon." He say« tho word "earlier" should be " later." I submit die sentence must stand withont correction. Turn the globe on its axis from west to east, England will come into the enlightened hemisphere sooner than America, which la in west longitude; but the time iu America is earUer than in England, for when it is 12 o'clock at London noon, it Is 7 o'clock in the morning at New York; #o thnt wc come into the enlighteued hemisphere sootur than the Americans^and yet their time is earlier than ours. Tksg in the latter part of the seutence must he connected with the .,..,,*....;■..-< of the sentence.


Sie,—I am glad to flad an improvement in the letter« respecting mills and millering. The remarks of *'C. M." on tho balauclug of «Tones with Clark and Duuhain's patent, I consider good sound reasoning, and I hope we shall hear again from him. Also J. Bottinç'B remarks on the swish in stones, are interesting and true. I having tried the same remedy for similar ovil and corresponding results, ß. Ii. Smith gives us some useful hints betimes. I hope all our du*ty brethren, who have a little useful iniormatiou, will please send it to oar Mechanic for the commou benefit. I will just ask the above, or any other, if they can give me a good remedy for filling up broken joints iu millstones; I havo tried alum aud borax, but cannot make a good job of it.

K. O.

SiH,—I cannot say I am prepared to dispute Mr. Evans' theory that the cause of a stonii's standing and running balances differing is " The balance weight does not coincide with its counteracting object in its radial distance from the centre," but in my blindness I cannot conceive why it should not. Пе asks me if I cannot alter a stone's standiag balance by raising or lowering the weights when runuiug. I have already «aid I have found when a stone's standing and running balance do not coincide, something was wrong, independent of tho balance; but whether it would alter or not if both balances coincided, I am not prepared to say, but to my unenlightened Intellect it seems improbable. But in spite of Mr. Evans' scientific reasons wliy, and my inability to dispute them, some very ugly fact« (to the contrary) sture mo iu tha face. Aud as Mr. E. say* "Facts are stubborn things," I ask both him and Mr. Smith how we managed to balauce our stoues so that they " hummed like a hive of bees," made bran "like л bee's wing," and as good a per centagc before we had the patent balance as wo do uow with it, and why every serious fault that occurred then will now, in spite of balance. And as to despising the standing balance as ''virtually of uo use, and practically non-effective," that idea ha« recently done serious damage. If it be of no use, it is mysterious how we managed to moke our stones work as well without the patent balance a« with it. 1 repeat the fault of a stone's dragging lies either in empty cogs or their pitch circles not meeting, or irons not working parallel with the face, or unlevel bedstone, or faulty face. Of course the running balance will keep a stone from vibratiug (?). I know of stones that have received a good running balauce, but went empty, and on being freed hy the spoutsman, commenced kicking violently, and before tu* mill could be stopped kuocked oil 13 mouths' wear of skirt. Where was the running balauce that it did not keep them steady? What wai the cause of it? And why did it not occur wheu being bolinead? The more uutrue the face. Irons, »be., are, thu greater difference there Is in the two balances—so great M to drag off the skirts when starting and stopping ii the running afana has a ruuuing Instead of a standing halance. If, as Mr. Evans asserts, tbe cause of tbi! difference in the two balauce« Is owing to the unequal specific gravity of tho burrs, or beciuse the balauce weight does not coincide with its counteracting object lu its radial distance from the ceutre, how !■* it we often see parties try the ruuuiug balance of their stones every three or four dressings, and find it differ each tima? Tome it looks very much like a different face to the running «tone.

A Stoneman.

[Will some miller, or any one else who may know, tell us how we cau get the names and addresses of the millers «f Great liritaiu and Ireland ?—Ed. E. M.j

Sin,—Having in my letter in this week's issue of the English Mechanic endeavoured to show that a silk bolter must make a better or finer «ample of flour than a wire machine, so that, after showing the advantages of said bolters, 1 will uow describe some of thtdr disadvantages. In the first place, owing to the great leugth they have to be mude to dress from, say, even four pairs of stones is very much again« their adoption in many mills Ьесаиме of their taklog up so much room. and. As they will not, generally speaking, dress more thau from three to five sacks per hour on an average, or abont one-fourth the quantity a good wire machine will dress, causes them to be worked continuously as tbe mill grind», and there I« often fixed over tbe head of the machine a hopper boy or cooler,

to cool the meal before it euters the bolter; it will bo seen by this that a miller cannot keep his ground me&I hy him for two or three days to cool, unless indeed he has extra silks to dress It up with. 3rd. There is another matter tha* is ngaiust them, namely—not being able to change any number of the silk and put another on in a few minute*, according to the stuff that wants dressing and thu time of year, a« of course for damn wheat meal thesilk should be coarser than lor dry foreign wheat meal. To obviate this I have, in conjunction with -Miii.- parties in Manchester, brought out a silk machine that occupies agreatdeal less space thau the present silks, and any bhect may betaken and another put in in a few miuutes. 4th. In dressing With a silk bolter it is impossible to get the bran as clean and bright as by dressing it with a wire machine. Consequently I generally put a small machine to take the bran oat before It entws the silk or after it leaves it, as by that mean« everything fa cleaned up as well as possible. 3th. By dressing with the present silk bolters there Is not more than one-third of tbe silk that actually dr**«ses, as the- rail* or ribs Inside the reel as it revolve« carnV* the head op and drops it ou lo the silk near the bottom at the opposite side of the reel. It Is this that forces iuo*t ofthe floor through Пи"--il-., butltat the same time gl ve> tho silk a sudden twitch, which of course is injurious to 1С

E. Davies.

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9lF,—As this subject has been opened, and is one which, directly or Indirectly, is of vast importance to u« all, it may be as well to say a little more about it, especially because its very vastness involve» the conaeqnenre of very partial views being caught ef it by most mind«; hence it is, that so many, even intelligent people, are captivated by that delusion, "protection to native industry." which i« now set forth under the dbgulsei, but equally delusive, form of "reciprocity," or in other words, refusing to bay cheap what we want, Ъсслнье tho«o from whom we buy bave not sense euough to buy of us, what we offer them cheaper than they can otherwise obtain it. This is the very delusion by which MF. W. M.," page £57, is somewhat afflicted. Ho does not see the whole bearing of what he says. Let us accept at it« worst the result he sots forth. "Our men are compelled to emigrate in large л um!.-г-.' What of that? A temporary suffering to them and others—a resulting unmixed good to them and ;il/ -they leave a country overstocked with labour, where, if tbey cannot produce, they are a burden ou the producers; they go away, and at once become producers to their own great benefit, and large customers to those who remain behind.

Kightly considered, the necessity for emigration is

I a great proof our prosperity, for it means excess of population, but an excess not due to diminished work

| (for any intelligent man knows that the total work of the country is vastly increased every year), but to the rapid ratio of increase of population, and to temporary changes iu the nature of work, which at times throw out whole classes of workmen, who are then unable readily to find fresh work, not from it« deficiency »o much, a« from tbe competition that involve« with those already engaged in it. Now nothing is much more certain In political economy than that a rapid increase of population is a consequence of prosperity. Stagnant nations UL-vur increase—they very commonly deorease in number, and this is only one form of Nature's universal law, that creatures only multiply where there Is food for them. Even one year's bad trade, or disaster, is marked by diminished birth ratea in the next, as well as increased death rates.

Of course it is hard to look beyond the immediate personal action of these laws, aud heneo It is thatso Intelligent a race as the Am^rieaus violate them. Instead of recognising Ihe unlimited advantages Nature gives them, as producers of raw material, they wish to do everything themselves, and s«ek to be manufacturers, whicli those very advantages forbid, by their effect on the labour market. The consequence is, that while a few years ago they were dangerous competitors iu every market, since they adopted their tariff system, we are beating them everywhere, and literally driving their flag off the seas. I quote the following from the "New York shipping aud Commercial List":—"No better commentary upon the decay of American navigation interests cau be had, than is afforded in the fact that the Novelty Iron Work?' have sold off most of the machinery and tools -, the Allaire works are now occupied as astable- the Etna Iron Works have ceased ю make marine engine«; the К»lton Iron Works are for eitle; W. H. Wt-bb'* shipyard is to let; Henry Steer's yard Is empty; the Continental Iron Works are almost deserted t and grass is growing in nearly all of tbe shipyards which a few years ago were filled with workmen,"

It шоу be said, that something similar applies to London, but that is onlv because other English porta are taking the trude. English shipping is superseding American, and there is no other reason than this —America tries to make her own iron, &&., which she cannot, except at high prh-e, instead of buying our« cheap with the corn and other things sho cau really produce well, and thereby indirectly throws away the friendly union with us wltich would result from being mutually necessary to, aud benefactors of, each other.

Sir,—" F. W. M," ftn page 1ЗД seems to hare fallen into the trap that "Soul Kymea" laid. He believes that Enaland is getting drained of her wc«lth, by an outflow о t money siiiflcititit to make our exports balance our imports— a very cjmmonerror. It Is necessary to remember that, with the most insignificant exceptions, trade is barter; the fluctuation in th»amount of gold held by England from yar to year, may be entirely disregarded in examining her trade with the whole world, and this one fact should be steadily kept in sight, that one year with another, tho good« we send out to the foreigner, are consisted by him equal in value to what he sends us la return. Take the oase that I gave, and whicb "V. W. M.** hold* up to ridicule. I send out а сагго, which ooets me here Cie,0Q0, but when it roaches the foreigner, it is worth

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Sib,—I do not quite apprehend Mr. Cunningham'« question, p. 25S. Covered wire in used »imply for convenience of manufacture, but any mode «f keeping the wires out of contact answers. When I first took up the study of electricity, I could get neither books nor material*, and had to study nut things for myself, and discover them aireen, guided only by the knowledee that certain things bad been done. Tbat was in Australia, before the days of gold; it was also before the days of Rbumkorff'o coil, and 1 made to all intents an Induction coil (only without the condenser) without knowing that I had done something new, for my coll gave violent shocks by holding one conductor only. The reason was that I had no covered wire, and invented a substitute, and my wire was exceedingly fine ; lu fact, I laid it very closely and evenly, separali og the turns by a cotton thread, saturating very caretully with an iosulnting varnish, and diviing the layers by silk saturated with the name. But sucha coil, though very well for an amateur experimentalist, would be very troublesome to make, and almost incapable of repair if injured, and consequently would not have been made in any but such exceptional conditions.

No doubt Mr. Cunningham's coil acts as he says; the only point is, whether, with the same battery power, much greater effects would not be obtained from the same wire if the interposed material were absent, for the true point to be aimed at is to keep tie wire as close as possible to the magnetic core, as distance baa so great effect is diminishing action; the only limit to this approximation being the necessity for Insulation. The moment this insulation exceeds what is necessary, it is injurious, by weakening the effect; hence the importance of using the very best insulators, and applying them on the best principles. Taking, for illustration, a coil 6in. loug by 3ln. diameter, the aeeondary of which Is an inch in depth, if wo use the common process of working the layers from end to ead, the points of extreme tension are separated only by tbat inch, and it being occupied with a succession of s tages of wire, there la great facility offered for the spark to leap across this space, and wo must resist this by extreme care in insulation; but if, beginning at one end, we work our layers In sections instead of strata, and complete the coil as we go towards the other end, the joints of extreme tension are separated by 6in. Instead of one, and much less perfect insulation is needed. There is, however, a great practical difficulty in the way.and at presenta compromise is effected by the process of dividing the secondary into a series of short independent coils, each complete in itself, and connected to its neighbours.

Tale will reply to Mr. Forbes, No. 3953. The connections are made alternately bypassing an end under the disc to form the commencement of next section, and soldering tbe outer end. The Mercury Break is only needed for very powerful colls.



Sir,—I have lately been making some experiments in dry plate photography, and I think it will not be out of place to give the readers of oui journal a few hints on this subject, which I consider one of the most beautiful and interesting branches of the above art. Within the last two months I have tried three processes, taonln,'Ryley's modified Kothergill, and oollodtoalbumen, but, taking everything into consideration, I prefer the tannin process, as the plates can be prc

Sared very quickly—in fact. I usually prepare two oxen in one night, and allow them to dry In the dark room until morning, when I find them quite dry without the application of artificial heat. 1 have used Maw son's ordinary wet plate collodion, which 1 find an excellent one for the tannin process. I coat the plate and sensitise it in the usual manner, and oa removing the plate from the bath I wash it with about a quart of water (I have tried distilled water, but I find plain water to nuswer quite as well). I then immerse it in a 15 grain solutiou of tannin, and let It remain while another plate is being piepared. It is then taken ont of the tannin, and placed to dry In racks, or reared against the wall. When it le quite dry it la varnished about Jin. all round with ordinary black varnish, laid on with a soft camel hairbrush. It is then ready for exposure, which should be about 12 times as long na for wet plates. I devclope with pyro, '¿grains; citric acid, 1 grain ; water, loz. The picture should be brought out with the least possible Quantity of silver in the developer, and when all the detail is on; it can be intensified in the usual manner. With Ryley'a process 1 had very Httlu success, but with the collodio-albumen procesa I have obtained some very beautiful results; but it is a very troublesome process, and very liable to blisters, «fcc.; so on the whole I prefer the tannin. I usually develope the same evening !take the pictures. I beg to ask " Mus," or some other of your photographic correspondents, if tber will be kind enough to describe to mo the coffee and gum gallic processes, and let me know if they have had any success in them, as I believe they are both very good processes -, but I have not tho formula;. I hare also got an old wedding ring; it weighs just 28 graine. I shall be glad if any of our subscribers can inform me how to convert it into chloride of gold eolation for toning purposes. I have tried "Mu«.'s" toning bath, and find it an excellent one, and should like to have a few more hints from him.

Tannic Acid.


Bib,—After reading In your journal of tho 20th ult. л appeal, on behalf of Capt. Petersen, for subscrip

tions to build a trial steam lifeboat, and among the list of subscribers tmcli corporations and institution* as Lloyd's,the Salvage Institution, the Shipwrecked Mariner«' Society, aud the Royal National Lifeboat Institution, До., I was much surprised to »ее in your impression of the 27th ult. the. letter from Mr. Lewis. secretary to the last-named Institution, raising such objections, many of them ridiculous on the face of them. Surely the several institutions here named, and more particularly tbe Royal National Lifeboat Institution, thoroughly examined the plans, models. an4 drawings, and fully satisfied themselves that Capt. Petersen's invention was not only practicable, but had every chance of success. J doubt not Mr. Lewie raised the same objections at the time his committee was inspecting the invention; and tho explanations given by Capt, Posersen were such tbat they were perfectly satisfied it could be carried out, and exp rested themselves as such by granting £100 (about one-sixth of the amount required) towards building a trial boat.

In order to stow tho absurdity of these objections, I will just quote one. in which he Bays—'■ That the motion of boats, under such circumstances, Is so great and violent, they sometimes standing perpendicular, with either the bow or stern uppermost, that the propeller would work at a great disadvantage, and the machinery be perhaps liable to disarrangement." le self-evident that when this nai<pens, the same objection would apply to the lifeboat now in use, inasmuch as the men in the boats would, under auch circumstances, be placed in an horizontal positiou; but Capt. Petersen's steam lifeboat would have the advantage, for I see by his plans that he carries two more seta of oars than the present boats, in addition to which he has the steam propellers. This advantage is obtained by the difference in the formation and arrangement of tho alr-chnmbers, Ac.

Mr. Lewis must to wrong in saying tbat "most of the p'ans merely aim at putting an engine In one of our lifeboats," for from what I have »een and beard of tho drawings and plans of Capt. t Petersen's eelfrightlng steam lifeboat, I am under'the impression that it is of a very different form, construction, &c, giving us much, if not more, room than those in present use.

I will not trespass further upon your valuable paper, as I have no doubt Capt. Petersen will fully «n s we rail the objections, to the complete satisfaction of the subscribers to the English Mechanic Lifeboat Fund; which fund I hope may be a euccees, and that their boat will bo built in accordance with Capt. Petersen's plans, which I believe are tho very best extant

R. S.


Sir,—I am thinking of rebuilding our church organ: adding a swell and independent pedal organ: and I should like to know what the dimensions of the bellows should be fora liberal supply of wind, and yot no larger than can be helped.

1 should have three Sft. stops, two 4ft., one 2ft. In great organ; two 8ft., two 4ft. In small organ ; one loft, tone (Sit. stopped) in pedal organ. 1 have most of the pipes by me: and the pedal pipes are gedact. with a foot of 31 u. diameter in the aperture for the CCC If any correspondent would give me dimensions for bellows and reservoir I («hall be extremely obliged: also, Is there any real practical advantage in having three feeders worked by a three-throw crank, over the usual two feeders worked by a lever? Theoretically It seems best; but Is It 1

Country Parson.


Sir,—I could hardly believe that Mr. Lockyer had not misread my letter at p. 211 ; but on referring to it I found 1 really had by a lapsus calami spoken of density instead of quantity, lou know how much I have been overtaxed with work lately, and will therefore understand how easily such a slip would occur. Fortunately, however, the text exhibits my real meaning very clearly; and I have written too often and too recently (pee Pop. Se. Eeriew for October, 18(19, In which I have introduced oven a picture of the widened line of hydrogen, as also my " Other Worlds." at p. 46) to a contrary effect for any question to exist as to my knowledge of the fact pointed out by Mr. Lockyer. In the letter he quote*, I was showing that the atmospheric dark linea could not change in thickness as the sun ncared the horizon, notwithstanding the greater range of atmosphere through which the solar rays then pass. No one knows better than Mr. Lockyer that this is the case. A ray from the sun might pass tangentially through the earth's atmosphere fifty times and yet the atraospherlo dark lines would be no'wider than In tho spectrum of the sun in the zenith.

If "T. A.'s" view required further demolition, evidence might be urged which is even clearer than that adduced by Mr. Lockyer. I refer to the existence of dark lines in the spectra of the stars.

I take far too much interest in Mr. Lockycr's work to overlook any of the result*" ho has obtained. Though I do not by any means accept all his conclusions, and indeed consider some of them to be beyond all question erroneous, I none the less appreciate most thoroughly his skill In observation, his ingenuity in devising new modes of research (witness his suggestion in I860 about tho prominence spectrum) and the perseverance aud energy with which ho carries out his purposes. If my haste In writing should ever again lead to a lapsus calami let Mr. Lockyer believe tbe cause of the mistake to be anything rather than forgetfulness of hie work, or of any that is bulng done by our fellow-workere In astronomy.

May I venture, however, to point out that the discovery of the influence ot density on the thickness of spectral lines belongs to an earlier date than Mr. Lockyer's alliance with Dr. Franklanrt. I think PlUcker would have something to say en this point as well ав on the influence of temperature. I have a paper before me in which Mr. Huggins says incidentally "it seemed of importance to have proof from experiment that this line of hydrogen, when it becomes broad, expands equally in both directions. 1 made the comparison of tbe narrow line of the vacuum tube with the more ex

panded band which appears when denser hydrogen is employed." This paper is dated April 13, lStVS, and I thiuk it was after the eclipse of lb6b tbat the alliance referred to above was formed. But the discovery ie> older yet. We most not overlook the work of -Miller, Hügeln«, РШскег, Angstrom, Gladstone, and tbe host of other eminent men who have advanced the cause of spectroscopic science.

Richard A. Proctor.


Sir,—The reviewer of my work has treated me so kindly that I hardly liko putting in a word in favour of the view to which he feels compelled to "demur at once." I object, myself, to startling theories unless put forward to explain even more startling facts. This is tbo case aa regards my theory about Jupiter and Saturn.

Any theory which accounts for the apparent advance of a satellite on the disc of Jupiter and its apparent return presently outside the disc (an observation made Independently by three such »etronomera as Smyth, Геагвоп, and Maclear) must, I apprehend, be rather striking. I think mine the ouly available one. In fact, I cannot imagine any other. I by no means assert that the surface of Jupiter was necessarily changed in shape on this occasion. Clouds suspended at a great height in hie atmosphere may have suddenly been dissipated. Again, Saturn's assumption of toe squareshouldered aspect seems to me wholly inexplicable ou any other hypothesis than mine.

Sir John II er s cb ell writes to me of tbfe theory, "Strange aa it seemed to me at first, 1 cannot but admit that the reasons you adduce are not to be lightly set asido."

R. A. Proctor.


Sir,—Sometime since I sent a query to our paper on preventing rust. It was not, I believe, answered. I now send a clipping on this subject, which may be Interesting to others as well as myself :—" Relnsch, of Germany, proposes the amalgamation of the surface* of the Iron as the best protection against r-ist, the only difficulty being to make the mercury adhere to the iron. It is well knowu that iron has no affinity for mercury, and even a perfectly clean surface, when rubbed with metallic mercury, will absorb nono of It. On the other hand, gold, tin, load, and several other metals will take it very readily, and almost all metals quickly become coated with mercury when plunged into a solution of a morcuilal salt; but Iron and steel resist even this treatment, and it is only here and there that some traces of the mercury adhere. Fortunately a method of causing tbe mercury to adhere to the iron has at last been discovered. The iron ia first well cleaned with hydrochloric acid, and then plunged into a very dilute solution of sulphate of copper, mixed with a little hydrochloric acid. It immediately becomes thinly coated with metallic copper, which copper must be removed by means of a. brush, friction with paper, and washing. The iron ia then placed in a very dilute solution of bichloride of mercury, aleo mixed with a little free hydrochloric acid, ft becomes perfectly coated with a layer of mercury, which cannot be removed by friction witb> rough bodies. This mercurial covering protects the iron very well against rusting, especially if after the amalgamation It haa been washed with liquid ammonia. Tho inventor has compared tho action of the air of the laboratory, continually charged, as It Is, with acid vapours, on iron objects, some of which were amalgamated and some not, and found that, while the latter were rapidly eaten up, aa it were, the amalgamated objects did not show a trace of rust ; and he recommends the procesa highly for the working parte of all kinda ot machinery, clocks, engines, Ac. He also proposes to amalgamate the iron parte of suspension and other bridges before covering tbem with paint, in order to eusure a more perfect protection; but, as we know that mercury diminishes considerably the strength of those'.metals, with wblch it easily amalgamates, we think it would be well to teat its action in this respect on iron wire before risking the amalgamation of the wires forming the cables of a suspension bridge."

I may say that I have not practically tested the application of mercury to iron, but I see no reason why this method should not be successful.

J. H. W.


Sir,—Having noticed many queries la onr English Mechanic relative to the lover safety valve, I now offer, for the benefit of my brother readers, the following calculations thereon. Fig. 1 is a diagram of a lever safety valve of the ordinary construction in which L representa the lever, V the valve, and W the weight.

As the words effective prtsjwe will be frequently met with In the following examples, I shall explain tho meaning of this phrase before entering into the calculations.

Suppose the lever of a safety valve of uniform depth and thickness to be 241n. long, 3fn. from the fulcrum to the centre of the valve, and weighing 31b. Now It is tho opinion of many that a lever of this dimensions would only exert a pressure of Sib. on tbe valve. This, I must say, is a great mistake, for such a lever instead of exerting a pressure equal to its own weight, would exert a pressure as great as three times its own weight, or 12lb. on the valve, and this ia what is called the effective pressure.

Role.—If the lever be of uniform depth and thickness the effect of Its weight on the valve is the same aa if it were collected at Its middle, but If the lever is tapered, then Its effective pressure can only be found by disconnecting it and ascertaining what weight ie required to balance it, making the point in a line with the centre of the valve the fulcrum. The result will be the effective pressure of such a lever.

A11 the examples will be worked out by two methods

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21MJ2 Ans. 77 071b. per. sq. in.

Ex. 2. The diameter of a safety valve is 25ln., pressure per square inch 201b., distance from the fulcrum to the centre of the valve 3in-, weight on the end of the lever 40lb., effective pressure of the lever and valve »lb. Required the length of the lever.

Let d reproent the diameter of the valve, e, the decimal -7854, p the effective pressure of the lever and valve, v the weight, « tbe pressnre per pquare inch,/ the distance from A to B, and x the unkuown part A «о С


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Ans. 6 762ln. Ex. 3. The diameter of a safety valve is 3in. distance from the fulcrum to the valve 3in.. effective pressure of the lever and valve 6-25lb. Required the weight to be placed 24in. from the fulcrum to te equal t» 801b. per square inch.

Let d represent the diameter of the valve, e the decimal 7-854, r the ratio ot А С to А В, p the effective preesure of the lever and valve, s the pressure per square inch, and x tbe weight required. Then d1 x e x 8 p

3» x -7854 = 7 0086 area of valve.

60 pressnre per sq. in.


8)559 238


Ans. 69 904751b.

The divisor 8 Is the ratio of А О to А В because 3 : 24 : : 1 : 8

Ex. 4. A safety valve has a lever 67в21п. long, a weight equal to 401b. on its extremity, the pressure per square inch 201b., effective pressure of (the lever and valve 81b., and the diameter of the valve 25in. Kequlred the distance from A to В Let d represent the diameter of the valve, w the wolght, ; the length oí lever, p the pressure per square inch, « the decimal '7854,/ the effective pressure of the valve and lever, and x tbe distance required.


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Ans. 3in. The divisor 90 160 Is obtained by deducting the weight of the valve and lever from the direct pressnre 98161b.

Ex. 5. The lever of a safety-valve is 24in. long, 3in. from tho fulcrum to the centre of the valve, effective weight of tbe valve and lever 6251b., pressure per sq. lu. «nib., weight on the end of lever 69-904751b. Required the diameter of the valve.

Let r represent the ratio of А С to A B, w the weight, p the effective pressure of the valve and lever, S tbe pressure per sq. in. с the decimal 7854, and x the required diameter. Then

w x r + p the area of the a

= valve represented .'. */ — = x

8 by a e

69 90475 weight on lever

8 ratio of А С to А В

6 25 weight of lever and valve.

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difficulty In converting longitude and latitude into right ascension and declination, aud rice rersa.

In the accompanying figure, у is the first point of Aries, and E у and Q у the ecliptic and equator respectively. Consequently

А у is tbe right ascension = a


С У is the longitude ='

S A is the declination = <5


S С is the latitude = \

»y Q Is the obliquity of the ecliptic = ы
Sy A = ?>

S is the place of tho star. And we will suppose that 0i fi and ш are given to determine I and \. Of course the reverse problem is precisely similar. Join S у = Г with tho arc of n great circle, then

tan. с cos. P = cos. a, cos. ¿, and tan. S у A = .

sin. a Then

»in. X = sin. F. «in. (p — w)

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cos. a. This t« not the same formula as was given on the page alluded to by G. Firth, but the one can be deduced from the other. I will give him the formulae properly corrected, and which I think Is as easy a method as any other of altering co-ordinates.

tan. Ö"

= tan. В

sin. a


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Сов. В tan. A sin. / = tan. \. If O. Firth wishes an example worked out in figure* I shall be most happy to send it, or to give him any aasistance. Omicron.

(Illustrated abate.)

Sir,—The ring principle on all instruments of the flute genns, is the same, it gives the power of closing two or more holes by the action of one finger only. The invention of this system belongs to a Captain Gordon, who conceived the idea in Paris, abont thirty years ago ; the application of it, however, i* Böehm'e a professor of Munich. I think a little work •' The Flute in its Transition State," by the Hon. and Rev. H. Skefflngton, would interest "Another Flautist." Hatchard, or Skefflmrton Piccadilly, are the publishers. As a soloist I am acquainted with nearly every form of flute. For the Böei.m ri uto Í cannot say much; it is an expensive instrument; tbe faults I find with are, the constantly-recurring difficulties in executing rapid and continuous passages, especially in the third octave, arising from the cross and back fingerings. To illustrate this, the В flat, which U produced naturally and easily on the lSlcbolson flute, ia fingered on the Böehm by placing the third finger ot tbe left hand on the ring of the G hole, and F »harp is fingered by pressing down the ring of the E hole; these are very awkward and unnatural fin a eringe, added to which, the quality of tone In the third octave is thin, weak, and the notes bear very sharp (in tbe old flute they bear .¿at*), and it Is almost imposable for an amateur to blow them in tune. This arises from the fundamental holes being made too large, and without due attention to tbe part they are required to take aa rent holes in the production of tbe notes in the third octave. But should "Another Flautist" desire still to hear more of the ВбеЬш , I shall be happy to give him information. Tune, tone, and facility, are the things sought for by flute players of all classes, and with your permission 1 will now describe as briefly as I can, a flute in which these qualities are combined to the fullest possible extent As a professor of the flute, having no pecuniary interest in flute manufacture, I continued to use the Böhm because its powers and capabilities wire so great, notwithstanding the toil It imposed upon the performer,e specially with the open G sharp key. Nearly eight years ago, the late Mr. John Clinton showed me his flute, called tbo "Equiaooant," a vast improvement on the Böhm, which I have used ever since, I subjoin n sketch of it, with an explanation In tbe BÖehm the thumb key makes С natural, in this flute that key makefl both В flat and С natural. There is a small open key at a (the С natural key), which is keptsAïrfby the thumb key, and when the latter is oponed for В flat iu tbe usual manner of fingering this note, tho С natural key is kept closed by the second finger of the left band pressing down the ring surrounding the A hole. There is also an open F sharp k*;y at 6, which is ahnt by the second finger of the right baud pressing on the F natural hole ring, the third finger of the same band closes It in making D and F natural, for which latter note the " fork fingering" Is used in all rugged aud difficult passages. The F natural key (short) remains. At с there Is a lever for acting rapidly upon either the В flat or С natural keys. At d is a lever for the D shake key e. Your correspondent kuowe not what he asks; the mechautsm of flutea has been a vexed and most intricate question.



Sir,—I shall be glad If you will allow me, through the medium of your pages, to ask some of your able correspondents, the following questions, which are important to many in the same circumstances as myself. It is well known that the Post-Office baa lately acquired the telegraph*, and a great many postmasters have to waste hours daily In watching tbe inetrumen ts, and therefore 1 wish to know whether it is possible to fix a bell, or otber apparatus, to the existing single needle Instrument, in such a manner, that we shall have warning without the watching now tedious to

A Poor Postmaster.


Lock Stitch. (Continvrd from page 232.) Sir,—Spools, or metallic bobbins, require illustration to show what has been attempted in the way oí

.mprovemcnt.*_The Wheeler and Wilson epool Ul —in.

l(i 5 diam., and —In. thick outside, and holds 18} yards of

No. 21 cotton, «nd the Elliptic holde Hj yards, the

1 7

«'nam. being l—in., and the outside thickness —in.

16 S3

Wheeler and V* ilson's spool Is represented at Fig. 1,

a front view, and Fig. 2 a section. It 1ч formed of a

pair of thin steel dines, a b, fixed on a brass axis C,

with a hole through it, which fits on the «haft of the

machine to receive a rotary motion for winding on the

thread, and in the space between the double convex

spooL А тегу slight variation of tension may be

given by winding on the thread more or less tightly,

bot it is too limited to be of much use. To provide a

tension on a spool, the following plan has been

adopted. A pair of flat dines, with the thread wound

on the axl*. which also has a hole through it, is

placed within a case or shell, having an axis to retain

tbe «pool in place, and to allow it to unwind freely.

In the rim of tbe case or shell, holes were made for

the thread from the »pool to pass through, to give

tension In the same manner as in 'Ihomas's shnttle.

There are machines of different makers working this

kind of spool, but they are not successful compared

with other machines, although it may be wrong to

trace the failure to the spool only. In some machines,

the spool was applied horizontally, as illustrated in

Vlg. 3, a plan, and Fig. 4 a sectional elevation; a is

the spool, composed of two flat dives on an axis, with

л hole through it. The shell or case A, has a rentre

pin, on which the spool a revolves. The thrend pannes

/rom it to the holes C, and is passed through out' or

more to obtain the tension required. The framed d

ol the -Machine, is bored large enough to contain tbe

spool, and a rotating book e secured to the pinion f .

an axis, o. passes through the pinion. The top end of

tbe axis'forms the bed on which the spool aud case

rests, and tbe lower end is secured to the frame of the

machine. The plnion/is driven by a rack motion in

some machines, in others the hook receives a direct

circular movement Tbe action is as follows: —the

nscent of the needle la the needle slot, throws off the

loop, the book takes ft in its rotation, or its vibratory

movement, and opens It, when on the back end of the

hook, then carries it more than halfway around the

spool case ; here tbe needle pul le the thread off the hook,

which returns ready for the next stroke or stitch. In

machines which make a complete rotation of the hook,

the needle thread is lc.-s liable to break, and more

easily slips off tbe book. When tbe needle thread has

been passed around the spool case and released, it has

to be palled up through the needle plate at a great

velocity—for every stitch from 2in. to 31n of thread

must so pass. The is usually done by a spring above

the needle, and the least accident to so delicate au

instrument, puts tbe machine out of order. A thin

fabric, stitched by a shuttle, compared with one

stitched by a spool machine, shows in practice what

may be expected from theory—viz., tbe less quantity

of thread passed through the fabric, the better tbe

stitch, aud the longer tbe loop passed through the

fabric, the more uneven it must appear, laying below

the surface on tbe upper side, or d>awn too deeply

luto it, and forming too thick a ridge on the lower

tilde. The spool machines are not made or soM

because of this quality, but because of certain other

merits they possess. All the best qualities In the

various machines bare not been combined in any

machine yet xmide, nor are they Itkeiy to be. This

thought should humble some of the members of the

sewing machine family, who are given to overmuch

boaeting. Little remains to be noticed about the

various instruments employed in the formation of the

lock stitch, until the machine.- are described and


(Jitter contrivances have been patented, or proposed, but not of sufficient practical value to describe tbem; and some of these here noticed, serve to show the many ways proposed to do the same thing, and to point out that the impracticable may become the stepping stone to the useful; or to »how iuventors what has been already done, or attempted, and to save them the trouble of re-inventliigand rc-patenting. This has been done to a large extent, and many years' experience in searching the patents, and making new machines, and experiments for inventors, leads me, a* a matter of duty, to warn those who are fond of new ideas to b« careful. One of the most unsuccessful attempts to form tbe lock stitch, and oue often attempted, is to use a large reel of thread below in a spool, shuttle, or its equivalent, Mo that it will last as long as the needle thread, and require no re-winding. One of tbe most likely plans to do this, was to place the reel In a large* spool case, having an external ■crew, which, by rotating, carried the needle thread from its front to its back end, the holder and driver being arranged to let the thread pass over it without obstruction. The arrangement wan so far practical, bat it Involved long needle loops. More time is lost In pulling up long needle loops iban lu rewinding spool» or shuttle reels. The spool, layingVm its flatbed, and having a horizontal moving hook, is not so well adapted to work as one vertically placed. In the for roer the book in taking the thread from the needle pulls it oat of Its slot horizontally, and thus bends or breaks It The vertical pull of the hook is a far better arrangement, the needle being less liable to strain or breaking; and the thread pulled more In one direction only, or chiefly downward instead of across thenotdle: A vertically oscillating bo"k has been applied to carry the thread around the ip< ol, ¡he hook being curved to nearly match the circumference of the spool or holder. AU such contfirnnees are more complicated than direct circular motion, and the complicated in mechanism is nearly always leading to failure ; the simple, giving less trouble to learn, or keep iu order, leads to success.

It is not advisable to do more than allude to other inventions for making the lock stitch, Shuttle maebines are made to work with waxed thread, kept beated by ели ; in some the loop of the ueedle thread is kt rt opcu by a hook, so that the shuttle passes through without dragging on the thread. Iu on« machine storking leather the shuttle la made to work

above, instead of under It. Leather machine bands, ship sails, heavy carpets, and every kind of sewing, from the heaviest to the lightest. Is done by the shuttle. Oue of the earliest attempts at a lock stitch machine was to use a double-pointed needle with Its eye In the middle, arranged to go through the fabric, and back; being pulled by mechanical fingers, and using one thread, and pulling it tight at each stitch, as in hand sewing wa.* once thought the best way. Another inventor proposed usiug a long needle, and to gather the fabric on it, then pull it through, and draw out the gathers until the thread was tightened; this simple but limited appliance Is often revived and sold.

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The revival, and abandonment of inventions and Imitation* is abundantly illustrated in the history of the sewing machine. A museum containing one machine made to work from each invention, would be very interesting to the mechanic; it would be a very iarge collection, and show euch link which connects together the extremen of difference. How uulike, at first night, appears the Howe, and tbe Wheeler and Wilson machines! If they were taken to pieces, and then mixed together, we should only hud a resemblance in their needles, all the other parts being dissimilar, yet adapted In a difft rent manner to make the lock stitch The Instruments tor making the lock stitch, already described in these pages, connect linkby link, with slight shades of difference, the extremen of form aud action. Some of these contrivances never came in, or noon went out of une, and only served to teach what could not be done, or to suggest ideas for better Inventions. Itls strange to find in "the development of ypecies," and the Jcvetupment of invention, there in a resemblance. The sewing machine was not a perfect aud complete invention at the commencement, but was developed by successive stages of improvement; the strong and useful predominate, the weak and useless die out. Selection of the right stitch in the first thing to do by those who desire to make a sewing machine, then to copy the best mochan leal contrivance to produce the stitch, to study in detail the formation of tbe stitch, and working of the thread. The workmanship should be good, but it is of less importance than correct principle and proportion. There should be harmony of movement; needle and shuttle must be in time, and work smoothly. Further particulars will be given when the machines are completely illustrated, and at this stage many may be tempted to make sewing machines without having first paid sufficient attention to the formation of the stitch.

Let such be warnod in time, "a stitch in time saves nine."

A Practical Man. r.S.—" Jacquard," 3848. Notes and Queries, is advised not to be iu a hurry to begin making a sewing machine. His questions show great discernment, but involve too many considerations to be answered in л brief reply to do him service. What he requires Is partly explained at page 232, and the rest will be fully dealt with when the subject Is sufficiently advanced. Machines of different classes will be fully Illustrated and their qualities compared, so that *' Jacquard " and others may know how to proceed. No. 1. Some machines drive the shuttle by a crank, others by a enmwlth a paase. The form of cam depends on tbe other parts of the machines. 2. Buy a shuttle the size you wish. The shell la stamped to shape, and the ends brazed In. X The stroke is longer than shuttle from

— to Jin., according to tbe machine and size emir,

ployed. 4. The needle to raise about Ain. nnd then pause while tbe shuttle passes through the loop.


Sir,—The best system of shorthand is, I believe. Mr. Pitman's (of hath); It is not hard to learn, and any one with an hour's dally practice, should be able to write at the end of twelvemonths, sixty wolds per minute.

G. Gregory.


Sir,—In answer to" Hermit," p. 255, Pitman's system Is decidedly the most popular, and I think the simplest nnd most comprehensive. At one timo I learnt Odell's, but did not somehow think very much of it. It Is of course very difficult to say which le preferable from actual experience, as to learn one system thoroughly is not an easy task, while to mix that with others would lead to a glorious confueion. The ease with which Pitman's system is attained speaks well for It. I received from Mr. Pitman two courses of lessons, which, of course, greatly facilitates the acquirement of the art, and can only say I was much pleased with the simplicity upon which the system is based. I would by allmvans recommend " Hermit" to join a class takeu by tho above gentleman, when he would see for himself how surprisingly easy it is to learn. It is perhaps scarcely necessary to add that all depends upon the time devoted, and the regularity when practicing.

Harrv G. Xewton.


Sir, Much as has been written in this valuable journal on electricity, chiefly in relation to experiments, or to the scienco Itself ал a recreation, very little has been advanced on galvanism as a medical agent.

This subject appears to me of such vital importance, compared with many subject* discussed in your paper, such as electrical bells, magnetic engines. 4c., Ac, that I think It Is high time that the subject of medical galvanism should be better understood, and more frequently discussed than it has yet been.

I have been iuduced to address you because I believe there is no other journal In this conn try which is better fitted to deal wiih this branch of electricity thau the English WtCHAHic, botii in its practical aud theoretical bearings. Some of your correspondents have, I believe, objected to medical subjects being discussed, and so taras physic itself is concerned, I should saj that the inquirers themselves are not likely to suffer much in constitution by remaining In ignorance of some of the Irrational prescriptions which are often suggested to them. But when a subject like the present falls within the domain of physical science, and when it is remembered that electricity is both an external and an internal remedy, which can alleviate pain and arrest disease, and this, too. tw the most rational inexpensive, and simple manner, and when the patient himself may adiniaister the remedy without fear of adulteration or empiricsm. Its importance becomes secondary to no other branch of electrical or experimental science, and Its generation and application demands the attentiou of any jourual which is competent to deal with the subject, and professing the advancement and well-being of Its readers. It i* true thnt electricity as a remedial agent has worked ft-way but very slowly, but it would not be difficult to show, did space permit, how this lias happened. I believe there are still inauy intelligent physicians who regard galvanism lu disease as empirical simply, as I take It, because they do not see or understand why or wherefore it, being n thing intangible, and as immaterial as a shadow, should have any effect upon the nervous economy. Ou tbe other baud, others have gone so far as to believe this mysterious fluid to be the nervous influence itself. Hut whatever doctrine i is right, it is sufficient for our purpose to know that electricity is a surprising stimulant to the nervous system; and, moreover, that it would appear to have the power of preparing, repairing, and replenishing the shattered telegraph wires of the body wit hpenuaneut additional energy.

Itefore 1 close allow me to state more particularly my object. It is to ask your correspondents to take this subject up. Amongst the mauy thousands of subscribers to the English Mechanic there will ever be a vast percentage who receive these pages every week, sufferers from some bodily derangement or disease, and who might receive incalculable benefit from a proper application of galvanism. Many, doubtless, ate poor and unable to purchase the costly and often worthless apparatus, as sold nl the instrument makers. Many do not understand the modus operandi of the same. It would not be necessary to plunge into the theory of the nervous effects of electricity, but to point out the most desirable, easy, cheap, and efficient way of constructing apparatus suitable lor medical use. What is wanted, then, are plain drawings and directions with advice as to the proper administration of the current. An ordinary coil, I believe, is not suitable, the objections beiu» that where there is more than one continued wire the current is completed in one, while in the secondary ■wire another current is induced which completely destroys the power as a remedial agent.

.Since writing the above I have received so many answers respecting Medical Coil (" Wanted ") as per advertisement in No. 270, that I am moro strongly convinced than ever that the apparatus and application generally are totally uosuitedto the purpose. The chief error seems to be in using" intense battery power as though the living economy were to bo relieved of pain by additional torture. Moat ot the eoils are primary and secondary wires, and most likely have no guide to the uninitiated as to which is the negatiue ami which the positive pole. It is manifest that this latter is of the greatest importance, since In many liisoasesthe current from the positive element should flow with the natural stream through the system, whilst in others thocurrent is reversed.

W. A.


Sir,—In a letter addressed to the astronomical readers of the journal in general, H. W. Bishop state* that 1 said " that the light of D'Arrest's comet was to be 0126." 1 think Imny venture to say that I never said anything of the kind. What I said Whs, probably, that the intensity of the light of the comet would be represented by that fraction.

The intensity of light of a heavenly body not eelf1 luminous is proportioned to , R and D represent

ing respectively the radius vector and the distance from the earth. At the time mentioned this fraction 1

was equal to 0-126. At the time that the comet

R2 Di

b< camo invisible to Maclear, at the Cape of Good Hope, at the last apparition, the Intensity was equal to u 190, the probability was therefore that at the date 1 mentioned, the comet would be slightly fainter than wheu lout sight of by Maclear. So far as 1 know at present, the comet has not been discovered.



Sir, — Since the appearance In the English Mechanic of the description of the Saltaire Lathe, 1 have beeu troubled with a wish which I have had many a time during the last two or three years; and that is to improve the lathe in my possession, or make a new onp; I have been a subscriber from the first number, and have carefully read all the articles on the lathe, but I am undecided on many of tho different points ofa perfect amateur's lathe. Could Mr. Smith be induced to give us working drawings of an amateurs lathe, drawings to scale, say the gantry, so as to give height from floor, and a section of do., length he would recommend gantry to be, drawings of the two heads, and height of centres, together with the form and diameter of spindle of fust head—in fact, all drawings and dimensions to enable an intelligent workman to construct one, always bearing in mind all to be made so that the other tools, chucks, slides, and the different cutting apparatus belonging to a complete lathe could be added to at the inclination or convenience of the workman -, I think it would bo a very interesting subject, and one very popular. If the height of the centres given did uotsuit every one, they could enlarge or reduce the dimensions to their own. That the subject is of interest I see by the inquiries of No. 3866 and 3867 in this week's number. Some time since we had two or three promises from different parties to give us specimens, Ac, which I am sure would give pleasure to more than myself, and alBO Mr. Hunt promised drawings of his chucks. 1 am sure they will excuse me reminding them—the reason is, I am anxiously expecting them.

^" II.


SiR,—I f any of your contributors would kindly afford information upon the following points In connection with achromatic telescope object glasses, it would be highly esteemed. In Brewster's and other works upon optics, the secondary spectrum is described as being of a wine, claret, purple, or lilac colour, on one side, and of a green colour on the other side of the focus. Now, I have had opportunities of examining object glasses by some of our best makers, and the outstanding colours in all of them, were (to my eyes) blue and yellow. Am I to infer from this difference, that the tint ot such oustandtng colours is chiefly influenced by the colours of the two rays selected for correction, and that the extreme red and violet ones (as mentioned in the works alluded to), are no longer (as a rule) adopted for that purpose ; or is such difference attributable to the irrationality of the glass now employed! It has struck me, upon comparing one or two glasses which have come under my notice, giving a dark outstanding colour, resembling the claret, or other colour referred to, with one in the blue state of correction, that tho formor was incomparably superior in defining fine black lines, which I attributed to the contrast botwe3n black and white being much better preserved under the influence of a dark colour, than a pale bright one. The dark colour also appeared to be much less in quantity than the blue, which latter seemed to form a cloud before the object, and a wide fringe around it, while no such obstruction was perceptible or appreciable in the case of the claret or deeper-toned colour. I should like some of your readers to make the experiment upon a white enamelled watch face, at a distance not exceeding thirty or forty yards, in full sunshine, under a high power. Other states of achromatism may, by uniting more luminous rays, appear, theoretically, to offer an advantage in the shape of Increased intensity, but is it not proimble that a paramount disadvantage may accrue from the uncorrected colour being both paler and thicker, or of greater breadth, whereby the advantage which would otherwise necessarily follow the increased amount of light, would be coun

terbalanced? If the experiment suggested be made, it will be observed that uuder tho blue correction, black letters will appear absolutely blue, whereas iu the other case, the black will remain unimpaired. I should also be glad to know what effect over and under correction have apon the definition, and wh ether object glasses, in which the extreme red and violet rays are united, can now be procured, and of whom?

O. G.


Sir,— The deposits of limestone pass-d over by your correspondent " F. Harwood," p. 25?, is that known to geologists as the Mountain Limestone, and occurs as the middle group iu the Carboniferous system immediately underlying the true coal measures. This formation and the carboniferous slates are widely developed in Ireland, and give to the scenery of that country some ol its peculiar and special features. J he characteristic fossils of the mountain limestone *re corals, and enermites, especially the latter, which very often mako up the entire mass of the stone; from this circumstance it is aptly termed "cuerruital limestone." The enermite, or "stone lily," so called from its elegant shape, is an animal, and belongs to the class Rualata; it Is, in fact, a star-fish set upon a flexible and jointed stalk. It is of marine habitat, and wherever fouud as fossils indicates the strata to be of marine origin. Until recently the race of Ori no ideal were thought to be extinct, and only a dozen kinds are now known to exist, one of tho dozen being dredged up by Professor Forbes iu Dublin Bay. The separated discs of which the stems of these creatures were composed being naturally perforated, were thus easily strung upon strings and used as rosaries; they were likewise called wheel-stones, and St. Cuthbert's beads, by the English peasantry, St. Cuthbert being credited with their production. Sir Walter Scott refers to this circumstance ia Marmion :—

"On a rock by Lindisfarn
St. Cuthbert sits and toils to frame
The sea-born beads that bear his name."

H. H.


Sir,—I am pleased to find Bo good an authority as J. Norman Lockyer endeavouring to remove my difficulties regarding the origin of the dark lines in tUe solar spectrum. In returning thanks, may I assure him the evidence afforded by the phenomenon referred to had beeu duly considered before 1 ventured to write the letter on p. 114; but I arrived at the conclusion that tho want of chemical power in the light of the solar prominences was the cause of some of the lines changing from dark to bright.

I cannot agree with Air. Proctor In considering Kirchhoff right in ignoring crepuscular evidence. Neither, iu my opinion, are the conditions wanting in the upper atmosphere for the chemical combination with oxygen of iiou, magnesium, &c. He is, however, undoubtedly correct in considering that employing one'stelf about photographic mauipulations does not necessarily teach anythlug concerning i he nature of light. That depends upon the character of the operator. lie may be an excellent photographer, although a poor philosopher.

In dismissing this subject, I wish to add a few wordB respecting the motive for its introduction. In the hands of the astronomer (Jut spectroscope has proved t»t great service. In the hands of the meteorologist it wouid be equally as useful. 1 hope thishiut will uqi be disregarded.

T. A.


Sir,- As a rule, I do not care to call In question the replies given in good faith by your correspondents, but in your present number 1 find "Anti-Egyptian" gives a reply which is very likely, from its vagueness. to mislead many of our fellow-readers. His first remark, that it is useless to test a boiler uuless the plates and stams are visible, is quite correct; but after that he states that a single rivet ted boiler cannot be worked at a higher pressure thau 151b. on the square inch. Now, from old age or imperfect construction, it may be that his engineer forbids hfm to work his own boilers at a higher pressure, yet the statement that no boiler can be worked beyond 151b. unless it is double rivetted, is certainly a long way from the truth. I can assure him that we have three Cornish boilers constantly at work, from year's end to year's end, at a pressure varying between 351b. and 401b.. and yet they are all single rivetted. How can tho two statements be reconciled?

T. S. Conibbee.


Sir,—'* Zeta's" query (No. 3037) is very simple. The weight of one litre of nitrous oxide at 0C. and 760 metre of mercury is 19712 grammes. 200 grammes, then, must measure 101-401 littes, and as one litro equals 61-028 cubic inches, that is equivalent to a volume of 6101 065 cubic inches. He can readily obtain the weight in grammes of one litre of any gas at 0 C. and 76 metres of mercury, by multiplying '0806 by the atomic weight of the gas, and divide by its volume: as for nitrous acids

■0806 x 44

= 1*0712 grammes.

2 Mr. Murray (No. 3961) should use gelatine as a cement for bisulphide prisms, it is the easiest, if not the best, as I can personally testify.



Sir,—A correspondent, "Another Flautist," requires the composition of German silver. I offer the following :—1st, copper, 40pts.; zinc. 2ft, and nickel, 31pts. 2nd, copper, lupts. ; zinc, t>, and nickel, ipts. The first is a good metal, which takes a high polish, and tho second is the white copper of the Chinese.

Query 8850.—" Thermo " may perhaps «oiw war -caercury iu his thermometer by giving It a aertes «f •rta.-^i jerks. See also other correspondents' acs^-r* ie "Gitcho Maui to," some time since.

Query 3975 (" Gratus ").— Bleaching powtfcer Is tmmds by placing lime (moist) in a chamber, npon p*rtwra*cr. shelves, and submitting it to the action of ehiarine. evolved by the action of hydrochloric acM ^pon ^m black oxide of manganese. Refer t*> correspofvi^^" answer- on the subject in a recent volume

Manufacture or Oxygen (3SS3.— ** M. P. O SO Oxygen may be prepared from manganate of heating it to a certain temperature in a retort -wh connected with a steam boiler, and a pump while' plies air. The retort containing the m&ngai first heated, and the tap from the steam boiler i on, when the following change takes place :—

(Naa MnU4), + (H/>1, = (NaHOH + Un aO, + <k The oxygen being liberated, is passed on to the *>:*■»_. When this part of the operation is over, the *t*e-aa * shut off, and superheated air pumped over tho sa lure in the retort for about a quarter of an hour, asm It is again ready to undergo the first operation. las air must be freed from carbonic acid by passing K through caustic soda solution before being rinmnafl over the spent manganate. The m angaria te may he made In large quantities by heating to redness mature of black oxide of manganese, carbonate asi nitrate of soda, the heat being continued for «*wat time, In order t,> decompose the sodium nitrate, whim is at first formed.

Query 3887.—The Utilisation Of SrwAOE.—* "On the Utilisation of Sewage by Irrigation and H fration," by C. E. Austin, Mem. Inst. C,E.; rt&Mau Latham's "Inaugural Address," published by >tn. and Baron Lleblg's letter on the utilisation ofti* metropolitan sewage, published by Allnutt There > plenty of Information on the subject to be font4 scattered through the Engineer* Building A'cws, *&d Gardener's Chronicle.

Water Analysis.—("Aqua" 3886).—If "AquaIs not accustomed to make analyses of different articles, and water more particularly, he should tu* Nicholson's process, which is admirably described m the Quarterly Journal of the Chemical Sorictit for December, le6"i. The apparatus required would be 2 burette*. SO cbc., divided into 500 parts, with an ErdmarjzTs float. The burettes must be provided with a gins* stopcock iu lieu of the indiaruober tube, and Mobr's clip; several small stoppered flasks, to hold about 100 cbc.; porcelain and glass evaporating basins, a few beakers, and a litre measuring flask. Solutions required are:—Standard lime solution: Dissolve o 172 grm, of selenite iu a litre of water. Soap solution; The eapo mollis of the Pharmacopoeia ia to be dissolved in a mixture of equil volumes of distilled water and methylated spirit, to be of snch a strength that ?S divisions of the burette ara required to produce * permanent lather with SO cbc. of the standard lime solution. Barium nitrate solution: 0*26 grm. in a litre of distilled water. Silver nitrate solution: *5 grms. in a litre of water. Ammonium oxalate, 0'^oa grm. la a litre ot distilled water. Chameleon eolation: Ulasolve 0159 grm. of potassityn permanganate in a litreof water. These are the standard solutions required; but for the analytical process 1 must refer " Aqua" to Nicholson's paper, the December part of tho Journal of the Chemical Society for 1802, as it would occupy too much time and space to give it In detail.

Volume or Gas (Query 3937).—" Zota" can calculate the volume of gas thus :—11 16 litres ef hydrogen weigh 1 gramme; and as the density of nitrous oxide is 'll, that is half the molecular weight, u 16 litres or that gas measured at 0°C. and ?60mra. would weteh S2 grammes. Now. as we know that ±2 gram Mips occapy 11-16 litreB, we can easily find the volume occupied by 200 grammes:— 1110 x 200

= 101-454 litres at 0°C. and 760mm.


Weight Of Gas (3956).— R. Terset can, by lollovIng the method here detailed, find the weight of a*v volume of gas. Ftr*t, methyl gas la known by the

formula J [j{j3 therefore, the density would be IS.

Now. a litre of hydrogen at 0°C. and 760mm. weigh-* 0i hvm grm.; consequently, a litre of methyl wouid weigh 1-344 grms. at the same temperature and pressure. But the temperature is 20°C, whilst the pressure remains unaltered. A litre at 0°C. would become 10?:i3at20oC.bytheequationl+ atorl +(0*003665x20;. We can now easily get the weight of 1 litre, for we have found that 1.0733 litres of methyl at 2o°C. weigh 1344 grammes; what will a litre weigh? By the 1344

equation: = 1*862 grms., or the weight of a

10733 litre of methyl gas 26°C. and 760mm. Aa regards the second part of tho question, bow to prepare acetic acid from the substances mentioned, he may prepare it thus:—First flack the lime with water, and boil it with sodium carbonate to form sodium hydrate. Tills must be obtained in the solid state by evaporation.;

Na,C03 + Ca(HO)3 = (NaHO)i + CaC03. The ethyl iodide Is then acted upon by the eauitic soda, and the resulting alcohol distilled off :—

CjUM + NaHO = C,H«0 + Nal The alcohol is then heated with sulphuric acid and potassium chromate, when aldehyde is formed :—

C?HcO + O = Cjfli O + HaO and this aldehyde, when fu^ed with caustic soda, forms the sodium salt of the acid, from which salt the acid ia liberated by sulphuric acid :—

aH.O + NaHO = C2H, Na02 + H3

and (tViiNal*-,), + H5SO4 = ((.^HiO.^ + Na2R0t

I hope I have made the process plain enough fur R.

Terset, and shall be most happy to help him on tbc

road to knowledge whenever he chooses to ask.

G r.oRGK E. Davis.


Sir,—Would you kindly insert the enclosed in your valuable journal; it will, I think, interest a. large number ot your readers. Aviatok.

In the proceedings of the Royal Institution of

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