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(<t) Reduce *' of lull' a guinea to the fraction of £1 15s . (CP.)

(7.) A house U lot at 50 guineas a year, what amount is due lor 1U weeks 3 days? (CP.)

(f*.) Three phim cakes of equal size are divided equally between seven boys, and (tea of them divide their shares equally with/unr other boys, one of wheat gives his share to tfcree other boys, who divide it equally. What fraction of a plum-cake is received by each boy of the first group of seven, of the second group of four, and of the third group o[ three? If three boys, one from each group, join their portions and sli ire tbem equally, what fraction of a plum cake will each of the three have? (CP.)

4 3

0? > Rednce — of — of a guinea to the fraction of half a 7 6

sovereign. (C.P.)

. - 7

(10.) Find the value of 1—of £16 lis. 0|d. (C.P.) la

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Cias I'hoh Sewagk—Solvent Power Op Pure Water— Colourixq Mktai^Dangers Op Dynamite And NitroGlycerin K An Asbetos Air Kilter—Manganese Some Alloys Of It—Results Of Carbonising Wood In Various; Vapours,

We have at last some information on the method pursued in India to make gas from sewage, a matter which excited u jiood deal of attention some months ago, aad produced Borne wonderful speculations from writers in the daily press. In noticing the subject at the time, wc said flint "the only conceivable mode of obtaining gas from such a material as solid excrement, is by distilling it in a retort just as we do coal." uud such, we see by a letter in the Chemical News from Mr. Hickey, C.E.. of Calcutta, is the method actually pursued. The writer calls his system "a system uf conservancy.'' It is really a system of wauton waste, as bad as our London system. lie destroys all the manurial properties of the filth *iid «ets only a little gas, which can be good for nothing but healing his furnaces to effect the destruction. The plan of

treatment may be described in a few words. The material is carbonised in a retort, and the residue is called " Poudrette coke." This serves to deodorise fresh ordfcre for transport. The mixture of coke and filth is carbonised in a sort of double retort, in one compartment of which the steam from the mixture is made to pass over some coke rendered incandescent, by which hydrogen and carbonic oxide are produced. These gases serve very well for heating theretorts, but have scarcely any illuminating; power. The writer, however, insists " that poudrette coke surcharged with ordure will give a highly luminous gas." a statement we shall believe whew wc see the gas flame. Mr. Hickey should persuade the Hindoos to adopt uis system of cremation along with their ordure, and then he would get an illuminating gas, for, as Sir Thomas Browne says or quotes in his Urn Burial, " from animals sre drawn good burning lights." Mr. Hickey has certainly not solved the sewage difUculty.

The properties of pure water we must believe are at present very little understood. According to M. Becquerel distilled water acts on all metals, even gold and platinnm, and it seemB likely that absolutely pure HaO may really be a very energetic substance.

We have noticed before some processes devised by M. Puscber for giving colours to metals. Finding more precise details we return to the subject, since the invention is likely to interest some of our readers. The process consists, as we have said, in producing a layer of sulphide on the surface of a thickness which must be varied according to Wit colour desired. Tims on brass, according as this layer of sulphides is varied, golden yellow, copper, red, crimson, blue, light blue, or reddish blue shades can ha obtained. The colours, moreover, are very solid, and will take a polish. The preparation by which most ef these effects are given consists of a solution of 45grms. of hyposulphite of soda and 15grma. of acetate of lead in a litre of water. When this solution is heated it decomposes, and sulphide of lead is formed. The object to be coloured, therefore, has onlv to be immersed in the solution maintained at a temperature from 190° to 213° Fah., in order to be coated with the sulphide in shades of colour varying with the duration of the immersioa. A few experiments will teach the exact time required to produce the shade. Iron is always b'ue, tine receives a bronze shade, copper will take the colours named above except the golden yellow. When in the above solution, sulphate of copper is substituted for acetate of lead, brass and imitation golu take first a beautiful red colour, then a green, and finally a rich brown. Marbled effects can by produced by first covering a brass object with a lead solution thickened with gum tragacaoth, drying at 2120, aud afterwards introducing it into the hyposulphite bath. This last we may say keeps unchanged when cold, and can be used many tunes over.

As regards this solution of acetate nf lead and hyposulphite or soda we may say, although Puicher does not mention it, that it constitutes a very good hair dye, slow of course, hut harmless.

A very curious and important fact—if, indeed, it is a factis mentioned by M. Jouglct, who states that nitro-glycerine and dynamite explode in cantact with ozone. Ozone, as our readers are well aware, is only known in the diluted state, and it is highly important to ascertain what proportion of ozone in the air is sufficient to cause these substances to explode. Since they are commonly employed in situations (quarries in the open country, for example) where, according to the meteorologists, ozone is tolerably certain to be found in the air, wc must, unless M. Jouglet is contradicted, look on the use of dynamite even as highly dangerous. If the truth of the statement be established, we have explained the cause of some explosions which have been called "spontaneous."

A very good suggestion for an air filter equally applicable for a ventilator or a respirator is made by M. Wocstyn, who proposes to place in a ventilating shaft a bag of usbestcs. This, like cotton, will arrest auy solid particles floating in the air, and when much soiled the asbetos can be removed and made white hot, by which all organic matters will be destroyed, and it may then be put back in the shaft again. For respirators asbetos would be far preferable to the cotton wool proposed by Dr. Tyndall. It would not hold moisture like the wsol, and would at the same time be most efficacious ns a filter, and made so that the asbetos could be easily removed to be burnt and put back again, they might come into use and be highly recommended. There wonld be no obvious difficulties in the way of effectually ^filtering the air admitted to a large building, but wc agree with M. Dumas in considering that the suggestion of M. Woeatyn is worthy of serious attention.

Manganese, wc fear, will never be a cheap metal, and alone would seem to be susceptible of no useful application j but we learn from the researches of M. Valenciennes that it forms very beautiful and useful alloys with copper. One in particular, containing only 15 per cent, of manganese, is almost white, and in many of its properties greatly resembles steel. Other compounds, we are told, form superb bronzes. Llow far these may be capable of replacing our ordinary bronze it would be premature to speculate in the present undeveloped state of the industry of mauganese. The same metallurgist we have mentioned above has procured pure cobalt, which seems to bo a metal that may some day be usefully appliedPeople sometimes do odd things and arrive at strange and unexpected results. What M. Sidot was driving at when he carbonised wood in the vapour of sulphide of carbon we cannot imagine, but it ended in obtaining charcoal, which when struck in as sonorous as a piece of metal. He then got a bell turned in wood, carbonised it in the same wav, and has an instrument which gives a sound like that of a silver bell. The carbonisation is only superficial, and possibly the bell mey not be very brittle, as it certainly would be if it were complete. Besides sulphide of carbon, the author calcined wood in the vapour of wood spirit, and so obtained a fibrous coke of silky whiteness. This is a very curious result; white coke is a novelty, and it would be interesting to know for certain what does happen when wood is heated to a carbonizing temperature in the vapour of wood spirit.—Media' nic'a Magazine.

PITOTOGRAPHY IN BOTANY.—To illustrate venation and the nature of the surface of foliage, photography may be turned to good account—far more than la now commonly thought of. A correspondent of the American NuturaJist says lie has seen a photograph from a Bpccimeit of one of the coriaceous-leaved oaks of the Dutch Indies which was truly wonderful in its rendering.


[We do not hold ourselves responsible for the opinion^ of our correspondents. The Editor respectfully requests that all communications should bo drawn up as briefly as possible.]

•»* All communications should be addressed to the Editor of the Km;mhfi Mechanic, 31, Tavielockstreet, Covent Garden, W.C.

AII cheques aud Post Office Orders to be able to J. Passuore Edwards


I would have every one write what he known, an<i as much as be knows, but no mora; and that not in this only, but In all other subjects: For suchapersou may have some particular kuowledge and experience of the nature of such a person or snch a fountain, that, as to other thing?, knows no more than what everybody does, and yet to keep a clutter with this little pittance of Ids, will undertake to write the whole body of physicks: a vice from whence great inconveniences derive their original. —Montaigne'.-* Essays.


Sin,—As Ifhave been requested to scud an example of this notation, which seems to have excited some interest among- such of your murfcal readers who prefer simplicity to complexity, I will shortly send a familiar melody,written mji. I am unable to inform *'Tremolo" where he can purchase music printed on this system. More than twenty years ago, I borrowed Hawkins's instruction book (the only copy he possessed), and until you printed the common chord of C. 1 never again saw a siugle bar in print. Probably Hawkins's instruction book is In the British Museum, and perhaps a copy may be In the stock of some dealer In old and forgotten musio. 1 should be very glad to purchase a copy myself.

I need hardly inform "Tremolo," that he may put the lines of the staff in any position which liketh him belt; Hawkins wrote them perpendicular, and if I remember correctly, read the notes from the bottom upward, just as I have illustrated the system. They may of course be written from top to bottom, or horizontally, from left to right, just as our common notation is; I think this the preferable way, but 1 may be prejudiced from habit in favour of what is familiar to me, for after all we might find the Persian or the Japanese method of reading just as good as our own, if we were used to it. As Charles Dickens would say, " It's all along of our broughtens up." I don't remember my old friend mentioning why he placed his staff perpendicular but 1 have no doubt he could have stated why he did so, for he was pre-eminently a man who could give a reason—satisfactory to himself at least— for every faith within Mm.—N.B.—Some of those faiths were rather odd. to sav the least of them, but for all that he was "a jolly good fellow.'*

To one and ad I beg to say, that I am quite unable to describe Hawkins's notation more lucidly than I have done, so I take the liberty of advising "Flautist," page 304, to mark, on paper, learn, and inwardly digest (not the paper,), but the system, as I have set it forth, not doubting that so astute au ignoramus as be evidently i*, will require no further edification than what lh;it process and a little thought on the subject, will afford him. The labour can hardly be great, for " Tremolo" has succeeded in the attempt at the first trial, a thing which seldom occurs iu works of great difficulty.

How " One and All" can think the tonic sol fa notation simpler than Hawkins's, rather surprises me. It is true, only one sign viz. a letter, is needed for each sound of the diatonic scale, but the system is not convenient for frequent changes of key, aud the notes require adjuncts to indicate their temporal value. This is expressed in Hawkins' by varying the length (only)of the note Itself a pretty yet conclusive proof, which is the least complex of the two."

The Harmonious Blacksmith.



Sir,-i cannot help thinking that "F.K.A.S." is extremely unfortunate in his endeavour to fasten the duty of recomputing the tables of Jupiter's satellites on one of our national scientific establishments. "W, E. P." has denied the propriety of selecting the Nautical Almanac office as the proper place for computations of this nature, and "F.R.A.S." cordially agrees with him, and shifts the responsibility on to* the Royal Observatory, which, I think, is still more inappropriate, as it must be universally admitted that the object for which an observatory is established and maintained is to make observations, or to give the means of forming tables, but not to actually calculate them. But I should advise, since "F.R.A.S." is so extremely anxious to have new tables computed, that he mention the subject to his friend the Astronomer Royal, who, I think I may venture to say, will convince him that the Royal Obseruatory is uot the place for conducting calculations of such a nature.

It must be admitted with pain that this country has never shown Itself ready in too laborious work of computing tables of planets, ice.; and every ephemeris that is provided by the Nautical Almanac Office is calculated from tables compiled by foreigners; and it seems probable that the discussion of the elements of the Jovian system will be left to some distinguished Continental astronomer, unless "F.R.A.S." is willing to undertake the labour himself, and so render himself famous even among others than the readers of your excellent periodical. Omicbon.


Sir,—Allow me to tender my sincere thanks to 'F.R.A.S." for hiareply of the I8th ult. Although 1 believe i am a fair amateur astronomer, yet it is only lately I have been a practical observer, so aia not a fair judge of what is io truth a test for a good speculum. _ .

For instance, theoretically a very fine specimen ol 5|in aperture should divide a double but 77" apart, and give a gllmpso of a •'come" of 12-R ws>nd:ir.l magnitude. Still there may te doubles* but «T apurt and 12 mag. "comes" that the finest 6in. could not master, rendering tests apparently easy practically extremely severe. Ergo, " F.R.A.3." willunderMaijU why doubles, tc, that in truth maybe no »eet, hgui-c in this list.

32 Orionis. n Orionis and Z Bootee, wain, unmistakably divided, each being tried three tinea.

if BoSms, and y Andromeda, both elongated, but vu unable to decide as to the notching of the latter, the definition was not steady.

35 Equulel. 128 Ti Places,4 Lyncis, and 121 Pxx Ursa Major, all clearly divided-the third hardest. and I can hardly think it can be .but 1"-* apart; It seems nearly 1"" apart only.

. 21 Lyncis. (The name 1b almost illegible, so I am not aware whether it is 24 or St.) The first star on "F.K.AS.'s" Hat I have not the B.A. of, neither have I it from Struve's catalogue.

i' Equulel. I always understood this to be n triple of 13" and -8" apart, so sometime back tried to divide the closer, as 1 fancied, of the two. after dividing the wider, but did not succeed, the altitude being low. I noticed, though, a star about 15'' to the right of it nnd belaav. Mr. Norman Lockyer, F.R.S., waa my authority.

14 Lyncis, 145 Leonis. Z Cancri, and c Cygni. Readllv elongated all, strongly notched the first, plainly the second, and te my surprise, gave a clear and distinct pair of discs to Z Cancri (I divided the first with foil aperture). S Cygni, was almost, if not ouite divided; showed a 8pleniliil|atii «f«n#cs.

With regard to light ou ntgatts "Whim the large mirror, with an aperture of jaw oner «u., piol;s up the smallest "comes " to y Orionis, LTk P*x Dclpulni, 15 Honacerotls v (Nu) Ceti, and f Status**, the smaller does the same with »ear.lf Jro. less aperture; with perseverance the MttaUer ifiS aperture) picks up the "comes " to a Lym. v <Jeti* * * lr«iuia. v Orionis, g> Cancri, and „' Orionis. It easily pick" up the triple 0'(Omlcron) Cygni, but I have been almost sure I have seen a fourth, but I find that Smyth and Webb put it down as triple. 0 Or.onis, 5th and 6th star, easily seen. Can '• F.B. A.8." tell me the smallest «-?<*<""■ ""' possible tolsee the 6 with? Mr. Cooke telIs a « of his showed them ; and in GuUleman » Heavens I also find it so stated. T _„„,.,

There Is one point in "F.R.A.S.V letter I cannot make out. He speaks as though a 2tt. mirror were ncc«*sary to see the satellites of Urauus. According to Arago, an 18ln. metallic mirror ia amply large enough, while tbelr exact period of revolution was determined by an 11m. refractor. Moreover, 1 have once or twice thought I glimpsed them in a 10»m. with Browning's mirror used as an Herschellian, or front viewed telescope. Having for the last month been watching Uranus, with two friends, I have paid a Utile attention to It, and one of my friends' 9in. refraclor, I am Informed, shows traces of the largest satellite. However there is a capital test as to the capabilities of a telescope to see them. Between @> and ,i- Capricorn! is a close double, under 3" apart, and of 17 mag. each. Any telescope that with a power of 400 will clearly divide this double is capable of picking up the two largest satellites, number 3 and 4. And I may remark my 10J just divides them with a power of 700, while an llin. Mery will divide them cleanly with a power of 300.

Wul •' Omicron " try as a test u} Bootes, 20 Draoonis, y Corona; Borealls, y Equulel, u Leonis, and 4 Aquarll? a Uas.ic MiKoms.

which be calls "Incomprehensible," arises from bis own vague way of expressing himself, as I am quite certain that any ordinary intellect would be as well able to comprehend what Is meant by the "centre of a journal " as by the " centre of an invention." Would Mr. Evans explain the following sentences in bis first, letter? "All the centres are equal In length and line; it will then be seen fhat the stones can be hung at (in. or 10ln., or any intermediate distance," Ac. Docs he mean that because Che "centres are equal," Ac, that therefore the stones can be hung as stated? I may here state that the "globe-head'r has nearly superseded tho " universal jolut" in all the large mills In Ireland. J. SHABrn.

P.S.—In a recent letter of mine (quoted by Mr. Evans on p. 11) there ia » clerical error. For "foot" read "ends."

Sib,—As tho subject In question Is one in which we are all interested more or less, may I be permitted to make a few remarks thereupon? First, I would respectfully ask Mr. B. K. Smith if wo are to understand him to say that the cross-wind In his bedstone was the cause of the trouble he had with the neck of his spindle?

And, secondly, with all deference to his opinion, I bog leave to dlltcr with bis theory of millstone balance. In answer to " Cumberland Jowhn," he says, '* Put the stone in running balance, nnd the long spindle will make the stone hang steadier." Will It do ao? I trow not. Tho long spindle will cause the stone to hang more sluggish, and the consequent drag on the face will cause the spindle to vibrate, on account of Its Inordinate length, to the detriment of the neck, and even the toe and driving gear. Let " C. J." cut his spindle so as to bring his bearings within the line of gravity. The balance will become thereby more sensitive when the stone Is at its proper velocity. And if the case were mine I would do away with tho crossbar, which is not the best arrangement, on account of the excessive friction of the driver faces, which are also not uufrequontly out of line with the centre bearing, and replace it with a gooi Universal Kynot. And I dare venture to predict that lie would have no further trouble with Was await, and superior work would be the result. Tnos. Evans.

eight rows of spikes or teeth, and making TOO to 400 revolutions per minute; there are also two or tbree rows more of the same kind of teeth, fastened to the cover of the cylinder, and so arranged as to allow the cylinder teeth, when revolving, to pass between them, tuns opening the cotton aud tlit'Mvlug' down tho seeds mud dirt to the bottom, where inert- is a grid for the cotton to strike against, and so free itself from tbeldirt, which passes through the bars of *he grid, the cotton is then passed on to the machine described liy "Gitche Mauito."

I thru*: it would be an advantage to the StcrAsii', if some person would give a description of the machines and processes of tho mrton manufacture, for your paper has a large eircuitftifsn in the district of Stockport, and yet it scarcely ever contains a scrap of matter relating to its staple trade. For myself I shall be glad at any time to answer to the best of my ability any question appertaining to this branch of our Industry. Factor! Lad.

QUESTIONS FOR MILLERS. Sib,—I should be very sorry to strive to deprive Mr. Evans of the credit of being the inventor of the universal joint, bull believe It is a universal fact that flood invented it long before Mr. E. was born. The only portion of It as applied to driving mill stones that he can lay aay claim to is the outward ring, which he supposes originated with himself; but it is quite a common method here of having the stones built round a metal ring for the same purpose, which has the advantage of not occupying any portion of the eye of the stone, as Mr. E.'s does. I have metal boxes let into the eye of my Btones for the bearings to "slide in," which 1 consider an improvement on Mr. E.* "•outward ring," as there is then no necessity for making one of the rings oval. When I read Mr. st.'s description of his invention 1 thought he only referred to the "Oval ring," or I should not have noticed It at all, because I did not consider the "outward rtng" an improvement, but quite the reverse., as the sliding steps are-common ntTempleogue, While the oval ring is confined to myself -, and 1 now see that our motives for adopting the oval shape are •julle lie had to resort to ft in order to have tbe (our journals the same distance from the centre, whl«h is net Tjcsessary for the purpose of making a " trne universal Jotnt." 1 nave seen a hole drilled through tlie"eoek-bead"Of a spindle near the top, and a round pin -driven In, leaving enough of it projecting on both sides of the Bpindle'for the outward rror to rest on, aud it worked as free as if it were the foTfsIre of the outward ring. Bat now, Sir, before giving Mr. Evans the explanation he wants relative to the sentence wbich appears to him "incomprehensible"—namely, that "the centres of all the journals are to the same (vertical) circle"— I think it necessary to refer to his former communication, where he says that "all the centra are equal in length end line,' and to ask him what hemeuus by "centres?" In his laBt letter ho calls tnem "the centres of his invention." from which I conclude that the difficulty be experienced in reconciling the two statements

SHODDT MANUFACTURE. Sib,—A "willey," a "willow," a "devil "are only different names for the same thlng.and is not a shoddy machine, nor would it answer for one. A willow is the flrst machine that wool (not cotton) passes through far the purpose of opening the wool aud knocking out the dye-stuff. Shoddy does not require thfc operation, and therefore does not go into the willey, but into the "teaxer." A shoddy machine consists merely of a drum or cylinder about 4jft. dla. by 2»iu. wide (working in a frame similar to a large grinding-stone), and a pair of fluted rollers. The cylinder Is made with two metal drum rings, covered with inch thick timl or, on which are screwed or bolted elm lags, about l}ln. thick, and any convenient breadth. These lugs are divided Into spaces about Jin. asunder, and tho teeth are placed alternately in each row. They are steel, and may be any shape—either round, square, or octa

3 gonal They are about —In. thick at the butt, and


taper to a point. They project about ljtn. beyond the timber, and are generally kept in enough from the end of the lag to admit of a Btout Jin. hoop being driven on, which keeps the lags from flying off in case any of the screws should break. When the cylinder is placed in its bearings, a rest should be made fast on the frame, and near enough to the cylinder just to allow the teeth to pass, and then, with a piece of coarse grindstone, grind all the teeth to an equal height While this is doing, the cylinder should be driven the reverse way to the way it Is to work. The burr produced on the top of the teeth by this operation is the principal feature in the machiue's effectiveness. After the machine has worked some time, the burr will get ou the opposite side of the teeth. The cylinder should then be reversed In the frame. The shaft or axis of the cylinder should be long enough to have a driving pulley on each end, or to remove the pulley from one end to the other. The cylinder, when at work, should ge at least 800 revolutions per minute. Across the frame, and as close to tho cylinder as possible, are two fluted rollers, through which the rags pass. These rollers work In a f..ik at each end. The top one is kept down by weighted levers. The smaller these rollers are in diameter, consistent with strength, the better. The rags are laid thin and even on a feed (which I suppose does not require any description). The whole machine la cased in with a provision to take out the shoddy from under tbe machine, and a flue for ventilation. The rollers and feed, which go very slow, are driven from the cylinder shaft. The operallon cannot be called " tearing," as the rugs are "fretted" away, something like the cracker of a whip.

J. Siiarpe, Templeoguo, Co. Dublin

Sir,—On reading this week's number of the'HzChanic, I was struck with "Gitche Manito's" very abrupt remarks on " Scrutator"and the shoddy manufacture, and It occurred to me that it would have been better for "Gitche Mauito," if he bad remembered tho time-honoured proverb "That they who live In gla^s houses," &c.« Now, I have to charge "Gitche Mantto " with tbe same fault that he lays on "Scrutator," viz., that he has jumbled together the wfllowlng and Ecutchlng machines, as applied to cotton manufacture, and also with rushing headlong Into print when he is not thoroughly acquainted with his subject, and I would further Impose upon his memory file first lewwordsof your quotation from Montaigne's Essays: '• I would have every oue write what he knows, and as much as he knows, but no more." 1 see fhat he has consulted one of our best eucyeloBsedlos on tbe Bubject, but it would be best If answers on subjects of manufactures could be given by practical persons.

Now the machine described by " Gitche Mauito is tbe scutcher. The willow Is an entirely different machine, and Is very often termed the devil; It consists of oue large cylinder, containing about

PHOTOGRAPHY. Sir,—I must apologise for not answering " Photo" before this, on the subject of " Toning," but the fact is, I did not receive my English Mechanic, as it went down on -board the unfortunate steamer Normandy.

I presume that " Photo" wants to tone a transparent positive, not negative. He may have been partially led to aay negative through my Baying so in my last. I should have said positive. Now arises another question. Is tho querist going to make now transparencies 1 If so, as they of course will be done at home, he can spare more time, and with that idea, let him develop with pyro, inBtead of iron, giving about three times the length of exposure. TblB generally gives a warm tone and pleasing—like a light chocolate.'Another way is to develop with iron; do not intensify unless very thin, aud after Axing pour over a dilute solution of chl. gold. Ibis will tone rapidly and pleasantly. In some cases a grain of blcblor. mercury added to the gold solution Is good, but for my own working I dispense with mercury, unless for negatives I only want to use once or twice. " Photo" must remember that in all cases a transparency must be fully exposed, certainly rather over than under, in order to get full detail. 1 suppose that be knows how to mount\thera either for tbe stereoscope or screen? If not I will tell him at a future time.

May I ask "Photo" to be a little more explicitWhat sort of house does he mean? Dark room, or studio, or workshop I

Then he says, "He sometimes finds a ring, or more than one solarised place." Ah! I know what that is. I've had it all before now. Listen. These rings (transparent spots of course) are caused by pouring the developer on that portion of the plate where these spots are afterwards produced.

Do not pour the developer on one spot. Sweep it gently over the plate, at the same time tilting the plate by a twist of the wrist so that the developer may pass over the whole. Solarised spots muBt of course be caused by actinic light (white light) touching the negative. Perhaps a small hole in the back or in the camera itself, or it may be some organic substance fallen and so piled up, and reduced the silver during exposure. In all such cases care must be taken to try and ascertain where the fault Ilea. First look at your back (dark slide). If that Is light-tight try the camera. If all right, look to the windows of your dark room, put out of the way all organic matter well clean your glasses (away from the darkToom), and also see that yonr dark slide is clean and works freely. As it is very unlikely that It ia caused by the lens unless that Is struck direct by the sun, why he need not trouble himself about that part of the furniture However, the best shade for the lens Is an instantaneous shutter. If he wants to know how to make one, with your permission, Mr. Editor, 1 will Bhow him how I made mine.

Tho want of Bilver deposit on the lower parts of the face I think I can explain in a few words. "Photo" gets all his light to strike down on the sifter. Is it not ao? If so, let him get a board and cover it with pure white paper, and place it at such nn angle as to reflect the light on to the lower part of tho sitter's face. I think he will find It all right then.

"Photo," and others, are welcome to what lean tell them, for I would not give a " fig" for a mun who "hoards up " what ho knows without telling others, t e., of course, if It's worth knowing. At tbe same time I hold with one of our correspondents, who Bays that people Bhould write what they know, not what they think. Mus.


Sir,—There is an application for letters patent for case-hardening from a Mr. Armitage, of Eirkstall, near Leeds. The following 1b something like the process :—A quantity of pulverised prussiate of potass Is put into a wrought iron retort open at one cud. The retort is put on the Are, and as Boon as thcro is heat enough communicated to make tbe mixture boil, the article to be hardened is plunged Into the boiling mixture, and after it becomes red-hot it is taken out and immersed in cold water, and the process is finished. What I want to know is, whether this is an old or a new process. If the former, then it would be an Injustice to every manufacturer that has to caseharden his Iron by the prussiate of potass process; if new, then the gentleman has a right to biB inventiou.

I for one recollect to have case-hardened by this process 26 years ago, with this exception, that the open end of the retort was sealed up with a luting of clay; and I have often practised this same process since that time. I should take it as a favour if those of your readers who are interested in case-hardening would give an opinion.

I was going to compliment you on the Improved form of our Mechanic, but it would be folly todo so on my part. The recent Issue speaks volumes of Itself, and will carry with U its own recommendation.

St. George.

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Sib,—In No. 248 you illustrated an improved bitchen range. I (tend you herewith drawing* and description of a new oven, lately patented by Mr. Ebeuezer Stevens, of Margate, which seems capable of cooking almost anything. Fig. 1 represente the oven as arranged for roaetiug, if all the space of the oven Is required for that purpose, with the revolving baking plate and dish upon the bottom, showing the door at the back partly opened for basting or other purposes. The hook is turned as required by the knob which is made to turn round for turning the meat on the hook. An ordinary hook or books are used, or the hook or hooks shown in Fig. 11. Fig. 2 represents the oven also arranged for roasting, but with ihe knob or coned or flat rover, top or lid with a hole, circle, or slot formed in the cover thrown back, similar to the lid of a teapot, to enable tho cook to observe more easily the progress of the cooking; this knob, cover, or lid in some cases Is made as shown In Fig. 1, but in this case a straight or arcbed band, rod, or other support, is fixed across an opening at the top of the oven, having in the centre a hole or otherwise to which areattached hooks to revolve, so that the hollow cap, lid, or cover -will lift up on a hinge or hinges to watch the roasting of the meat without beleg suspended to the bottom of the knob itself, and in other cases a slide cover is used instead of a cap or cover to place over the hook or hooks without any hinge, and in other cases a cap or cover without Buy hinge. Fig. 3 represents theovun as best arranged for baking meat with or without pudding and potatoes; the revolving baking plate is now upon the bottom side rims or fluogos of the oven, and the baking dish upon the baking plate, and the revolving baktng dish stand in the, showing the door of the oven partly opened for turniug the dish, and the knob or cover thrown back for looking into the oven to sec the progress of the baking. Fig. 4 represents the oven as arranged for baking pies, puddings, pastry, bread, cakes, or any food required, with two revolviug baking plates upon the side rims or flanges of tho oven, and If it is required with a large oven, more than two shelves can be used, and each shelf or shelves can be used to euit tho ñrc or the food to be baked. The cover or knob and door in this Fig. are both shut. Fig. 5 represents the oven baking dish with the revolving gridironed baking dish stand placed in the dish in an inclined position ;it stands npon the rim, and the legs sideways, forming a small toaster without using the oven for chops and small articles of food. The small cap piece at the top with two hooks drops on and holds fast, and is added if required when the stand is used as a toaster, or an ordinary pot hook or pot hooks double at one end mav be used with this stand without

this cap, or even without any hook or hoolcs at all. Fig. 6 represents a piece of sheet iron, the top or circle part with the edge turned down to hang on the front of tho oven about half the way down or moro if required, when the oven is used for baking bread or

fiastry, to keep the direct heat of the Arc from scorchog the bread. Fig. 7 represents the revolving grldiroued baking dish stand for the oven on Its feet or lega as used for baking purposes. Fig. 8 represents the removable rods or cross bars with the hook, which

goes across the hole or opening at the top of the oven, y which the meat it suspended and turned round as required. This figure belongs to the oven shown in Fig. 2, the lid, cap, or cover of which has a hole or opening in the centre, so that it covers up close all round the knob and the hook, and thus the mea: can be turned whether tîie cover is up or down, whether open or shut. These supports for the meat can be arranged to fit outside or inside of the top of the oven. Fig. 9 represents the baking plate of the oven with revolving plate working on the bottom plate. Fig. 10 represents the revolving adjusting oven stand, worklug on one centre screw, or thoy may be made to slip un and o*jwn In a socket or hollow tube, and fixed by a the side of the socket or tube, or by a centre pin and hollow tube with a hole through each at desired distances, and kept In Its place by a pin. Fig. 11 represents a roasting hook or hooks that can be used with or without the oven if desired. Fig. 12 represents the revolving gridironed oven baking dish stand in an upright or inclined position as it stands in an ordinary plate. Fig. 13 represents the oven In a square or nearly square form on a stand, but not adjusting. In this shape the same kind of hole in the centre at the top with a knob or a bar across and hook, am used, as iu Figs. 1 and 2, but Instead of a cap or cover, as in Fig. 2, the hole Is opened and closed by a eliding cover working on a pivot, having a slotch or opening therein, so shaped as to clear the knob, handle, or ring of the hook In or on the cross bar, and effectually clo?e the opening on the top of tho oven when required. Instead of a revolving baking dish stand, lu this oven the inventor eomotlmcs makes a wire, or other gridironed baking stand, with three or four projections, legs, or catches, either to reet on the rim of the dish, or to stand in the dish; this Fig. shows the arrangement for baking. Thé baking plate or plates revotve as In the D-shaped ovens, the only difference being In the shape of the oven-- Sometimes these square, or nearly square ovens, are made with arched tops, and the sliding cap, cover, or knob, is arranged accordingly; and in some cases, accordlug to the size of the oven, the whole, or nearly tho whole, of the top of the oven is made to lift up. Fig. 14 represents the same oven ae Fig. 13. but with the bakiug stand and baking dish out, and arranged for

bating bread and pastry. This oven ie shown without the stand and with an arched top. Fig. 15 represente the sliding1 cap or cover for oven 13 and 14, with the bar, knob, and hook. Fig-. 16 represents the wire baking dish stand for ovens 1¿ and 14, standing on ite legs as for baking, placed in a dish or plate; it will Btaud upright or in an inclined position, similar to baking dish stand Fig. 12. Fig. 17 represen« thebaking plate for ovens. Figs. IS and 14. Fig. 18 represents the circular baking plate with pivot, ta work In the centre hole of the baking plate. Fig. 17. Fig. 19 represente the toaster for chops or steaks before the fire; the band or bridge across the dish may be a fixture or made to slide on the dish. The hooks turn round separately, and the frame works round on a pivot. Fig. 20 represents the .'revolvinggridiron, the reservoir is all round below the bars, and the bars arc slightly arched and fluted, or otherwise; the bars may be properly formed aud attached to the reservoir itself, singly or otherwise, as a fixture, or fastened to end pieces and clipped fast to the reservoir by tho two ends turned up and ovor of the under cross; band or bar, into or upon which the handle is made to work the gridiron round upon. Bon Vivant.


Sir,—Fig. 1 is i sketch of water gauge for steamboilers which I suggest as an improvement that, in my estimation, will please many of my brother readers, and Fig. 2 is a sketch of gauge cock which cannot fail to prove acure to leakage and broken cocks.

The water gange, as may be seen by the declivity

f;iven in the bottom part of the gauge, obvlatee the edging of sand. Section 1 represents the internal appearance i a a Is a plug valve and seat in the bottom part, which is provided with a flange to bolt it to the boiler witb four pins; this plug valve ie fixed as seen on the end of a smooth 3-10th Inch rod, which passe» through a gland g, which can be packed at any time by drawing up the plug, which the pressure will keepup tightly providing the cock n be shut, which cock ia provided with a gland, as seen, and the '«"vicing pin has Its tightening surface broken by ocl >*a« pabsagehole, the course being in through Ui* bottom, and out at the side; it ie evident no sand can find rest in this gauge, but should there be auy oily or other matter floauug on the water, it may be blown out by turningthe pin of the cock n until Its course Is equal with the vent bole *, thus, by the pressure from the bottom, the glass is cleared; It may also be seen that the gaugeglass is protected and made tight by a shield, the sameas the "Aston" gauge, differing only by being1 lightened by the box nut m, which, when screwed down tipht, is followed down on a little hemp and red I lead, tight to prévaut escape through the threads wffb back nut. By drawing up the plug valve occasionally by the handle e and taming it as ybu pull. you rub off the, crustration; thus the engineer is provided with a water gauge that will tell no untruth through leakage and stoppage, because eucb cannot wed exist, and the durability is more than doubled.

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Much trouble baB been experienced by the leakage acd breaking of the gauge cocka as well as the leaking and breaking of ibe bottom cocka ol the glass water gauge, but such la entirely prevented by my construction, aa seen. Fig. 2, and by section 2 of m Internal appearance, which is timplvthe bottom part of the water gauge, horizontally fixed by a back nut

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Sin,—Some little time ago I was erecting anew front gate, and laboured under the following requirements:—1st, that the gate should swing free until coming to rest; 2ndly, that it should only open one way. After some little trouble I hit upon the invention I herewith send you a drawing or. It is just possible that some of your readers may find themselves at some time or other under fimilar "r" and by the use of this arrangement receive similar relief. In the drawings one is supposed to be standing in the gateway facing the post, the black spot representing the swinging pin fixed on the gate—Fig. 1. The gate is at rest; the pin of course can neither pass to the right or the left. Fig. 2. ()u the handle being lifted up or pressed down, according as the aide happens to come, the lefthand jaw is depressed, and the stud or gate pin can only pass out to the left. On the handle being released it falls back upon the stud underneath, which both enpportsit and prevents the'right-hand jaw from being depressed, and the latch assume* the position in Fig. 1. The gate now being left to swing, the pin, on approaching the jaws, strikes whichever one it first meets, depresses it as it falls under the blow, the connecting link passea down the slot in the handle, carrying with it the other jaw. the connecting links being joined on either side by the slot, the weight on the end of the right jaw bringing both juws immediately back into their former position; the same thing is repeated on each swing of the gate, until finally it comes to rest with its pin between the jaws, as In Fig. 1.


the passing gate pin down to a minimum. The handle also remains at rest during the whole time of the gate's swinging, and from these two reasons wear and tear—which are always heavy items against swinging latches—aro very greatly reduced.

I may add that mine, which is quite a success, was forged by my village blacksmith, and finished by myself, F- that it is quite a simple affair.

Percival A. Fothebgill, B.A., F.R.A.S.,
Watford, Rugby.


Sir,—I am pleased to see your attention called once more to the principle of rotary engines, as they T

I think, even supposing the particular requirements were out of the case, that this is a good kind of swing latch, chiefly for this reason—that the weight on the right jaw can be so adjusted as to bring the blow of


great favourites of mine, I having made several. The first one was made about 10 years niro, very similar to the engraving sent by Edwin E. 11 ill, page 656, Vol. X. Subsequently I made a triangular one,with three wheels revolving together, of which I send i-ketch. The Fame, amouut of driving force acting on all the three buckota together make it altogether a powerful machine and much superior to the couple of wheels. A = a tub on the top of the machine, into which the driving medium is admitted, acting against the buckets {B) of the three wheels revolving together, bucket to bucket and allowing of noescapc between till forced asunder by the steam or water. The whole is in an air-tight box, and the three wheels geared together with a pair of mitre wheels fixed ou the main shaft outside the case. I enclose a horizontal Dlan of the machine John .ui-sckovl, Kendal.


Sin,—I some three weeks ago sent a note for insertion in our valuable journal, requiring information Id reference to a method for the eradication and prevention of incrustation In a multitubular boiler, but as yet I have failed to see anything In reference to it In print, whilst I see numbers of questions of far Icbb moment to your varied subscribers, such as Astronomy, Equation*, and others of very little intercut to onehalf of the workmen such, as I opine, support our journal.

I seejone, *' Vlvus Bperandum," mentions Irish moss. That 1 have tried, but it has not answered. I thought of trying sulphuric acid mixed with it. Perhaps if tho question Is thoroughly ventilated, some of our brother correspondents may be able to give me the desired Inlormation.

Flood, Charles-street, Hanley, Staffordshire.

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Sir,—I am glad to sec a letter in the English MeChanic on tho subject of ■' Violin Varnish." I almost despair of the secret of the old varnish being discovered. I, fllke many otharB, till lately thought it was made with oil, but now iTem of opinion that the gum, whatever it was, was dissolved in spirits of some kind. Ne doubt the Italian makers paid *he greatest attention to everything connected with the manufacture of violins, and that is the reason why their instruments surpass all others. In these days everything gives way to cheapness, and itdoeanot pay a maker to construct instruments of accurate proportions. Most of the French copies have the back and belly of the aame thickness throughout; of Coomb a violin so made Is cheaper, and takes less time to "finish than an accurately-proportioned one, and then it is covered with a varnish that looks tolerably well, but injures the tone. I believe that very few violins are made in England now, as the cost of labour is so much Iesw on the Continent, consequently English makers do not trouble themselves about varnish. B,

( of water, cream, or bottles of beer or wine may be placed in the cylinder. Tho wine, not requiring to be frozen, may remain only a short time, and then be replaced by a second or third edition, till the gas is completely condensed.

It is best to use the stove supplied with the machine, as it prevents the boiler getting burnt.

I have only heard of one accident, and that was from carelessness. A person in Australia had let the machine lie for some time In the hot sun, and then placed it on the fire; of course, the "steam," so to speak, was already up, and the consequence was a blow up.

The solution lasts, theoretically, for ever—In practice it lasts many years. The boiler can be filled again, but it is a very troublesome operation, ;i> the moment a soldering iron Is brought near the aperture, the gas begins to escape; still ft has been often done.

These machines are not so expensive as Mr. Yonge says, but still they are too dear, and in consequence are almost exclusively nsed In hot countries.

They afford the easiest*and cheapest way of making ice, leaving tho firat cost out of consideration, as no chemicals whatever are required, only a charcoal or coke fire;; other fuel will do, but is said not to be so good.

There is nn agent In London, but the machines are only advertised in tho particular papers which go to hot countries.

I have unfortunately lost the drawings, or would ■end one for you to engrave.

W. £. bTAM,F.Y, 443, Hackney-road.

Including bronchitis, it is well known that medicines are of very little use, being merely palliatives. There Is usually something wrong in the ptyle of living or in the air that is breathed. By carrying out the above instructions our Buffering friend might derive considerable relief; but if, unfortunately, that should not be the case, he may pursue the following plan :— Take of pure croton oil one drop only, and apply It to the surface of the throat, rubbing It against the organ affected. Do this every day, and the oil, which is very powerful, will toon produce an eruption, which, as it progresses, will, in all probability, restore the voice to its full tone and vigour. 1 v i Tal

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Si R,—I am sorry that Mr. Purkiss is at a Iocs to know what I meant by the question I asked^hlm (page 600, Vol.X.) I will, however, try to put it as plain as I can.

It has been found that a truly spherical mirror does not reflect all the rays which strike its surface to one focal point; the rays from those parts of the mirror near the circumference being reflected to points nearer the mirror than the rays from the more central part, consequently to make a mirror which shall reflect to one focus, the surface near the circumference must be rubbed away or depressed. Sir W. Herschol says, "That the total thickness to be abraded from the edge of a spherical speculum 48in. in. diameter, and 40ft. locus, to convert it into a paraboloid, is only 131333rd part of an inch." I copy this diagram from Mr. Browning's "Plea for Reflectors." Tho dotted line represents the spherical curve of the mirror when the polishing Is begun, and the continuous line the parabolic curve it assumes when the polishing process


is finished. It will be, of course, understood that in the diagram these curves are enosmously exaggerated. Vow, It-will easily be seen that to convert the spherical surface a b, into the parabolic one c d, the mirror must be rubbed away more at the circumference a c and h </, and gradually less as the centre t is approached. At page 358, Mr. Purkiss says, "The parabollsing Is effected not by depressing or rubbing away the edges ef the disc, as in the old method, but by depressing the centre.

I suppose by the word disc, Mr. Purkiss means the mirror. Mow, I cannot understand how the parabolic curve is formed by depressing the centre ; if it had been tho opposite/ that is, by depressing tho ports away from the centre or towards the circumference, I could have understood It. I am sorry indeed to give Mr. I'urkiss trouble, but I hope he will forgive me for doing so, and putting mc right on this point, I shall feel oblJgod. Novice.


Sir,—Your readers may perhaps like a fuller description of Carre's ice machine than is given by Mr. Yonge, in No. 261, March 25th.

The "Domestic" machine is made of best iron boiler tubes, procured from England, and tested to 2001b. pressure. It consists of an upright boiler partly rilled with very strong ammoniacal solution, so strong that a glass bottle of it held iu the hand at once gives off bubbles or gaB. From the top of this rises a tube to about the same height as the boiler. This tube ends In a smaller one, which bendB down to level of top of the boiler, and Is inserted into a cylindrical vessel kept at a distance of about a foot and a half from the boiler. This cylinder has a smaller one rlvetted Into it. In which the tin containing the water to bo frozen is Inserted.

The whole of the machine is hermetically closed, so as to allow no escape of the gas. The boiler is pnt on a charcoal fire, aud when a thermometer shows the temperature to have risen to the proper point the solution is converted into gas at a great pressure. The boiler Js removed from the fire, and placed in a tub of cold water ■, tho tin of liquid to be frozen is

?laced in the cylinder, and the gas begins to condense, n a certain time, according to the coolness of the water In the tub, such a great degree oi cold is produced by tho condensation that tho contents of the tin are frozen solid.

In hot countries the water in the tub must be changed two or three times as it gets worm. Instead


Sir,—tiuch is the tltlootf a book recently published, and referred to by " FJK.A.S." ifi his article on*' Transits," in your journal of last week. "F.R.A.S." says he has never -soou the book. I have, and rhall be glad to gtve him and your readers In general some information about It, so that in stating my opinion I may compare notes with any other of your readers who, like myself, have been captivated by its title and become the possessor of a copy. The result of a diligent study of It has been to me one of disappointment. In theory the plan suggested 1b a capital one, but beyond theory, impracticable. No doubt the labour oT •the author in produoing tables of the places of 350 stars has been very great, and In this respect great credit iedue to him. Hie (plan Is to fix a small telescope permanently, so that It shall always point to a zone of the Heavens extending from 60° to.53°N.P.D.t and of course pointing an near as possible to the meridian. So far, so good. By this means the telescope, pointing so near to the zenith, the chance of error is reduced almost to a minimum, and the error when once discovered will be the same for every observation and always, and the observation corrected with the greatest ease. But now comes the funniest part of the affair. The author says in hie title page that his "tables are arranged to show, by the use of a little arithmetic, the mean solar time," Ac, and at p. 8, he says, "The tables have been so arranged so as to be nadily used by those who are not astronomers, and whose acquaintance with mathematics is limited to the knowledge of a little arithmetic." Will it be believed, after such a statement, that the 350 stars whose places are glvin are most of them stars not visible to the naked eye, being stars ef the 7 th and 8th magnitudes, some of the 6th, a few of the 3rd and 4th, and only one of the first? Even if these 350 were all the stars known In tbat zone of the Heavens to pass the meridian in the course of 24 hours, when two or three happen to crosB the wire within one or two minutes of each other, how can It be known which is each star, especially if, owing to the state of the sky, a glimpse of the transit of one only Is obtained? For instance, under 23h. It.A., I find one star's pi ace given as 43m. 29s.; the next, 47m. 45s.; the next, 48m. 15s.; and the next. 49m. 22s. If your clock were accurate, you might argue from the clock to the star, and know what particular star was on the wire; but you could not argue from the star to the clock as to its correctness. But in.-tead ef the number of stars Included In that zone being limited to 350, it contains more than 12000, at least 2000 of which are visible In a small telescope. How, then, can even an astronomer know what particular star is on the wire at any instant, unlesB he argues from his clock to the star? whereas the desigu of this book is to enable anyone "not an astronomer" to argue from the star to the clock! I carmot see how the book can be very useful for transit purposes, even to accomplished astronomers. As to persons who are not astronomers, the idea is out of the question. 1 beg respectfully to enter my protest against the misleading statement I have quoted. Luke The Labouber.


Sib,—I wish, with your permission, to offer a few remarks to "A Three Years' Sufferer *' from this distressing disease. In the first place he should at once change his diet, avoiding much animal food, and living principally upon eggs and farinaceous food. He should partake largely of pearl barley and groats well boiled In chicken broth or In mutton broth, skimming the latter carefully, and taking it entirety free from fat. Gruel, carefully made, and sweetened with honey, should be taken every evening Instead of supper. This may be occasionally varied by eating roasted apples, of good quality, slightly sweetened. Drink three times every day aud three hours after every meal, ateocupful of tho infusion of the common bore hound. Keep warmly clad, and shun late hours and dissipation. Above all, keep the feet warm and dry. and wear next to the skin a flannel shirt. Do not wear my filers, but gradually leave them off, and keep the chest warm by Buttoning the coat up to the neck. This should always be done in severe weather. Ventilation fhonId be particularly attended to, especially that of the bed-room. There are many ways of doing this without causing any draught, and it is as well to observe that if this important matter be not attended to, any other remedies will be almost useless, since It is through the afflicted organs (the bronchi) that the air is carried on to the lungs. In some diseases,

Sib,—The Inst kind of sun-dial necessary to tie

noticed is that known by the name of reclining dial, and it is such as may be made upon a plane which reclines or leans back, like, for instance, the roof of a house or church. If tho plane exactly faces the 8., and merely reclines from the zenith, the calculation Is easy, as well as the structure; the only thins; neceasary to de is to find how many degrees it reclines from the zenith, and to make it like a vertical dial of a different latitude. So many degrees' as the plane reclines must be added to the latitude, and then the dial made for that latitude. Thus, supposing the plane reclines 10° from the zenith, the latitude must be reckoned as 1(j° more—namely, «J1° 3?—and then the dial mods-like a vertical sou ah dial; but if the plane declines ns well aa reclines, Jhe calculation and the structure require more care, aud for This reason we seldom if ever see a dial of this kind. It may, however, bo of service to know how to masse one- The first thing to do is to find the recllnatlon of the plane, roof. or slanting .'wall, and this may be done'toy applying a carpenter s rule to the slant, and opening ii till the other leg is on a level with the horizon, winch may be known by a common level. The angle may then be easily [measured. The declination may be found by a magnetic needle, as directed page 460. We will suppose, for the soke of showing how the problem may be solved, that the recllnatlon from the zenith Is 20°, and the declination to be from the S. towards the E. 30°. Our object must be to find live things: (1) the latitude and longitude of the place where it would be a horizontal dial, (2) the distance of our 12 o'clock line from the perpendicular, (3) the distance of the meridian of the plane from our 12 o'clock lino, (4) the elevation of the style, (5) the hour-arcs. "We may find the latitude and longitude of the place by the terrestrial globe. If we elevate the X. pole to our latitude 61s°, we must then screw the quadrant of altitude over the zenith 38^° from the pole, and bring the end of It to the decree of the plane's declination, which in this case is 30° from the S. towards the E. We must then bring the meridian of Greenwich to the brazen meridian, and count upwards from the wooden horizon en the quadrant of altitude 20°, which is the recHnation of the plane from the zenith. Having made a mark on this part of the globe, we mutt bring it to the brazen meridian, We shall then know the latitude aud longitude, which is 14° S. and 30° E. Now, since the elevation of the style must always be equal to the latitude, we shall by this means know to what height to raise it. We shall also know the difference of time between this place aud London—namely, 2 hours— which we shall afterwurds make use of in finding the width ef the hour-arcs. Again, since the plane en which we suppose our dial to be made reollnes from the zenith, the 12 o'clock line will not be the perpendicular, as in declining dials, but a little distance from it; and in order to Ascertain this distance, wtj shall find it convenient to work it out by the formula in Spherical Trigonometry*- In Fig. 1 let A be«0« C = 30°, the declination. A C = 90°, the recllnatlon. Here, then, we have two angles and a side, and we can find A B, the distance of the 12 o'clock line from the perpendicular:—Thus, K : sin. AC:: tan, C: tan A B which is 11° lu'. Again, by the globe wc find that the place where the dial would be a horizontal one is lu Africa, 14° S. and 30° E. This, converted Into time by dividing by 15, gives 2 hours' difference; and we may therefore find the distance of the meridian of the plane from our 12 o'clock line by tho some formula —namely, B : sin. 1st. 14° : :tan. 30°: tan. dlst, which is equal to 7° 57'; and this, added to the former n° lo' - r.f 7'. is the distance of the substller line from the perpendicular. The last thing to do is to find the hour-arcs; and the simplest way of doing this is to use the same formula as the preceding, which we also use to compute the hour-arcs on a horizontal dial; and where the time is an aliquot part of 12, the process is easy. We must take the meridian or substller line as the beginning of the reckoning, and having marked all the distances on the dial, we

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