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or aswo say, the total draught to the drawing frame is 216; and these 216 attenua led engine slivers, if the work has been properly done, oompoae a shyer at the last head which for smoothness and regularity In thickness throughout it* length is far superior to the sliver at the engine head. The thickness would be the •tverasre thickness of -216 of the slivers from the engines. I «ay average thickness, because the slivers from the engines not only vary in thickness from each other, but are also unlevel of themselves ; the fibres are in a ruffled, entangled state, being crossed and doubled over each other in all directions.

The object or use of the drawing frame is to double a certain number of slivers together so as to equalise the different thicknesses; to straighten the fibres out warallel to each other, Bo that they will the better twist together in the spinning frames. It will thus bo seen that the drawing and the doubling are necessary to each other, for the drawing could not be carried out to any great extent if there was no doubling, nelthor could there be any doubling without the drawing.

I think very little explanation is required to show to any one at all acquainted with the subject thattliis total draaght of 21rt should not be divided equally between the three heads ; the draught should be easier at the second head than at the third head, and easier at the first head than at the second, because at the first head we have to contend with a rough, uneven Bliver, and if too great a draught were used here we should lose the benefit that should bo derived from the doubling ; the fibres being brought into better order by the draught at the first head, we may Increase the draught in the second head, and so on with the third head. Some spinners take advantage of this fact by also putting more doubling in at the last head than at the first.

The above remarks are offered with a view to a better understanding of '-Factory Lad's" question as to how the draughts should be distributed betweem * lines of rollers lor a total draught of 7 in the drawing frame. There appears to be some misapprehension as to which of the three heads of drawing this question refers. My impression on bending the question was thut this draught was at the last head; I did not for a moment suppose that he would have a draught of 7 In the first head; this, however, seems to have been the impression, judging from the remarks in their replies, of' Harmonious Cotton Spinner" and "Mutual Improvement " (the latter of whom thinks my preparing draughts too keen), and this appears to be the right one according to " Factory Lad's " last communication; If this be so, my advice to "Factory Lad" is that the sooaer he reduces this draught the better, as I am quite satisfied he would find an improvement by so doing. Whatever class of cotton he uses, this draught is, in my opinion, considerably too much at the first head. I really do not see what need he has for 4 lines of roller* at all If he makes no more use of the back line than to get a draupht of 11". or what is the same thing, where the leagth at the first pair of rollers is only increased by l-6th towards a total draught of 7. If this is all the advantage he gets out of the back line, it is worth while to consider whether he would not find it a saving to dispense with that row altogether, and distribute this very small draught between the three lines of rollers—thus, 19 x 3<>S = 6 UO, which are not very materially differeut from the 2 draughts he gives for the 3 rollers.

Assuming that " Factory Lad " has a total draught of 216 in the three beads, and wishes the draught at the last head to be 7,1 should arrange the draughts as follows :—

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The arrangement in the first head is on the supposition that there is a slight draught at the engine head.

The importance of this question to cotton spinners has induced me to enter at this length into the subject; as I hare said in a previous tetter, it is a question on which widely different views are entertained by practical men, and I am sure you will be doing good service to an important industry by allowing it to be freely discussed In the pages of the English M Ech Anic, and I hope that others will not hesitate to follow this with letters giving their views on the matter, knowing as I do that there are large numbers of readers of our journal in these districts who are well qualified to give an opinion on the matter.

E. Slater, Burnley, not only appears to have mystified your readers by his first reply to " Factory Lad's" question, but from bis Becond reply he appears to have got into amuddle himself. 1 cannot conceive how hefcould expect that anvone would gather his meaning tobe25 x 1-69 x 1-67'= 7-055 from the figures 2J + 2$ + 2J = 7, which he calls setting out the draughts equal.

I have no doubt but that the "intelligent old man" who told htm to make his draughts equal knew very well what he was talking about, but at the same time I think the assertion would be qualified when he made it, and this Mr. Slater appears to have lost the end of entirely The figures I gave in a previous letter, as well as those above, are founded on that rule, and it may exeroise the ingenuity of those interested to find out from them what is meant by the phrase of " making the draughts equal."

There is another matter in Mr. Slater's letter on draught* with which he say* he was at one time very much puzzled—that is, where a " given time " Is mentioned as having to be taken into account when findiug the draught between any set of rollers. Time is an element that need not be introduced into the calculation at all, as ft would only make it mora complicated. The draught fs simply, as I have stated before (p. 136), "the ratfo between the surface speeds of the first, or taking in roller, and the last or delivering roller," and this ratio can be found without the trouble of findirg their respecting speeds for any "given time." By putting the speed of the lirwt roller as equal to 1, multiplying and dividing by the figures representing the various wheels and rollers, we get a proportional speed for the delivering roller, which is the draught between the rollers. As an example, take the figures

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Sir,—Our friend "The HarmoniouB Cotton Spinner" has succeeded, as I expected he would do, in finding a mare's nest. He says that " I seem very much disposed to ' pick a fellah up before he's down.'" Ho seems to forget that it was he who kindly undertook to render me that thankless service (see his letter, p. 183).

After what has been said by me and others on the draught between lap and feed rollers, I thought that it would cause him to examine the matter more closely, and thui save both of us from troubling you again with this simple matter.

I am glad lie has now giv^-n the wheels and rollers of the engine* (In which he says there is no draught between feed rollers and lap rollers, a* wc shall now be able to see for ourselves whether there is or is not a draught in hi* engines), and from them 1 think 1 •hall have no difficulty in proving both to the satisfaction of "H. C. S." ana others that there is a draught, and one, too, greater than is required.

He says (p. iBMI, " Let me inform him for his edification that we have at the present about 14«> oarding engine* at work, and if lie can And the sllghest draught in any one of them I dare forfeit the englue lie finds ft In.—Biam., feed rollers, lj|in.; lap roller, 6m.; a 14 wheel on end of feed roller drive* a 48 on lap roller." Looking at this question in a superficial manner, most people might take these figures as "H C. 8." has done, and say that there was no 48 x 1J

draught here, thus, = = 1. But in cotton

14 x 6 spinning, as in all arts and Bciences, It is necessary at times, if we wish to get at the truth, to "penetrate" through the surface, and see if there be any thing below likely to help us in yetting at something near a correct result.

Now, 1 happen to be very well acquainted with the mnke of engine from which these figures are taken, and had they been an exception to the rule I gave, I certainly should not have gone in the face of them by making the statement to which "H. C. S." took exception, as 1 bad -atisrled myself some time ayo that there was a draught between the rollers in engines geared as above.

I will not hold him to the challenge given above, for if I took him at his word he would be very soon minus the whole of the 14" engines now uuder his charge. I do not believe there is an engine working anywhere but what there is a slight draught between the rollers. The lap roller has a smooth surface, and is Otn. diam. The feed rollers are "fluted," and are lifin. dJam. on the tops of the flutes. The flutes are made to work Into each other like ajialrof toothed wheels. The lap in passing between the rollers follows the form of the flutiugs, and being pressed by the tops into the spaces, will deliver as muoh length of lap to the taker-in as plain rollers of about 2in. diam. would do. U "HO. S." doubts this, let him take outthe taker-in, and after turning off with three or four revolutions of the lap roller a certain length of lap, measure the length that has been delivered by tho focd rollers, and report if he find the draught 48x 2

very much different from = 114, which is more

14 x 6 than necessary for keeping the lap stretched. Your correspondent, "B. H., Rochdale, gives (p. 235) one and one-tenth, which is ample for the purpose. I think "H. C. 8." has not tried fluted back top roller* on his drawing frames and other frames, or he would have found out this simple matter long ago.

If " H. C. S." cannot see how a lap can hag without a draught, 1 am not answerable for that. Let him take a cord, and stretch it as tight as he likes between any two points, and he will find it to bag in the middle to a certain extent, and if so with a twisted cord, hew much more with a loose wadding of cotton?

It is not necessary to notice further his remarks about the draw box and delivery rollers, as I do not consider my argument answered by a quibbling over words.

To his inquiry respecting yarn testers, Mr. Samuel Taylor, clock and watch maker, Penn-street, Rochdale, is, or was, the maker of a very good one.

B. W. R.

Sin,—Reading your paragraph in la6t week's edition, about the " chart that seems to be going on among us cottonians, I must say that I was at once struck with the force of your remarks. For my own part I shall always strive to let you have a* much of tho grain as possible, but it is sometimes very difficult to keep a little " chaff " from going in with it. With respect to the letter of "Mutual Improvement," the substance of it is just what I am anxiously waiting fc:r myself. Will E. Slater, before he takes up any other subject, kindly give his attention to the following queries, and let us have them in a plain, simple manner. VV"hat does he mean by saying he did not expect "Factory Lad " to have so many replies to his question, and yet to give him a rule which, If correct, not one of tho buiutteds of subscribers can understand, even now he has giveu two explanations V 2. Docs he mean iu his statement of successful spinners that they" Bucceed in spite of the evil of draw-boxes,'" tnoving themtoican evil? 3. Why is a bobbin when leading more taimltt/ pressed than when the flyer leads? 4. Will he kindly allow me to see bis Jack frames

making 6£ hank roviug, tho spindles running 13*i>, and the bobbins leading? 5 Can he run them 13u i per min. and put \ turn per in. in Ula roving—or rather sluubiug-with the bobbin leading? Lastly, will ho explain what he means by "putting tho cart before the horse, If I Intend it to go?" (No chart.) The abovequeries, answered In a clear, definite manner, will please his brother subscribers, be satisfactory to our worthy editor, and will greatly oblige.

The Harmonious Cotton Spinner.

MR. BEARDSLEY'S TRUTH AND TEMPER.

Sir,—Did you realy concieve it possible that yonr readers were alt so "flat "Das to believe that you "believed in free discussion" when you said soinvour remarks on page 210? it realy is of no use try mff n> convince a --stafl"'-bound editor, so I do not attempt ft further; but I will just remind you that the reason why I did not send you my fifth letter last week In the usual course was that I saw plainly that fair play In connection with the English Mechanic; was out of the question, and I thurelore did not think it worth postage. You know you have been guilty of tho grossest partiality, and as such is the case I be- to tell you plainly your conduct shows you neither encourage "free discussion " nor do you appear to have anv desire to keep "your promises," and as a matter of course "redeem them." But yon can inform your' Intimate friend Proctor (B. A. aud I do not know what besides) thatlif there Is "OtherWorlds than Ours," th«ro is also other printing presses than that which turns out the English Mechanic. 1 now take leave of yourself and that trio of sophists you priviledge, bysubscribing myself a disgusted subscriber, but a hater of humbug,

J. ilF.ARDBLET, Langley Mills, Nottingham

[If Mr. Beardsley has lost tho truth, he might have endeavoured to keirp his temper. His reason for not sending hUJifli letter Is not the true one. He did not send it because we did not insert his fourth letter, which we received about three weeks before; and the reason we did not insert it was that everybody, with the exception of Mr. Beardsley, considered that the insertion of such letters was au utter waste of space. Mr. Beardsley's reason for not sending his "fifth" letter is of the same character and quality as his reasons for the earth being a plane aud not a globe. We never promised him unlimited space for the ventilation of his childish theories, aud he ought to be obliged to us for the indulgence we have shown him. He may abuse us to his heart's content, as It will neither ruffl:! our feelings nor disturb our decision.—Ed. E. M.]

[Wo print Mr. Beardsley's letter reriutim el literatttm.]

GEOLOGY.

Sir,—As Mr. Proctor has now concluded his so ably writtenpaporsou " The Earth, its Figure aud Motion"; I should be must happy, with your cunspnt, to wrlcc a series of articles on " The World, it* Formation and Antiquity," in which I would endeavour to impart theelement* of physical geology to thoseof my fellowsubscribers who may be as yet unacquainted with them. I will not here enlarge on tho beauty, or the utility, or the interesting nature of this science; let it surtict? to say, that it is the mo«t practical, rext to chemlsTy, aud the most beautiful aud sublime, next to astronomy, of all the classes of natural knowledge. I think that these recommendations alone, entitle it to have its leading principles more generally known than they are, and, Sir, I know of no more oertain means of arrivingat that desideratum than through the pages of the journal of which your are, without flattery, the head In every sense of the term. It may seem presumptuous on my part to take upon myself to touch this branch of science, when the other branches are represented in your pages by men so much superior to me, both as writers, aud teachers; but believe me it is merely in the absenceof someone else, that I offer my poor pen for the service, conscious, however, that It will shine but feebly In comparison with those of "our " astrouomical, and other authors.

Arthur Underbill.

[We most cheerfully afford Mr. Underbill space for his letters, and particularly at the present season, when what we may term out-door scientific pursuits may be so advantageously followed.—bid. K.M.]

ANGLES AND TANGENTS. Sir—In reading over the pages of the ENO.Lisn Mechanic of the 10th dune, 18J0, I notloed on page 85, " Hugo'*" assertion, without proof, that " angles are not proportional to their tangent*." May 1 beg to ask him is an angle, or corner, at the centre of a circle, the measure of an are of that oirole! and is tho tangent au arc of that circle? If the lesser leg of a right-angled triangle be divided by the other leg of that triangle, the quotient in every case will be the tangent of an arc or angle opposite the lesser leg, as in the following case, by logarithms—viz :—

7-91)8689: unity:: 3 5«7^6i9: 5-6285739* tangent. And iu every case where the given terms have the same ratio as the foregoing we will have the same result, as, 7968689: 7410648466 : : 1 -50103944 0-94299'JO. = 8-769988", as in the other ca*e. And in every case the sine of any angle is to unity as the cosine of the same angle is to the tangent of that aRgle.

Veritas.

THE " PHANTOM" WHEEL.

Sir,—A writer who signs his true name cannot be called upon to reply to anonymous critics, a) such writers may possibly bo presumed to bo either ashamed or afraid to put their real uames to their letters. As Mr. J. A. Mays, however (pane 2.VD, ha* slgued his last communication to the English MeChanic on the subject of my •• volocifL-re," I will be;,' tho favour of a small space for the explanation.

Mr. Mays is perfectly justified In upholding the view* of the " Phantom " Co., but I should very much wish to know the reason why that gentleman has selected my veloci fere for animadversion out of hundreds _ that appear so frequently in yours and other journals, in all

of which high speed i§ impracticable, for at 10 miles an tionr only the legs of the driver would have to make 90 double strokes per minute.

Mr. Maye seem to have »jealousy in regard to speed, but he must himself know that on smooth roads, and all roods are smooth with deep rubber tires, speed can only be limited by the resistance of the atmosphere, very great at Inch velocities, or by the amount of danger in meeting with obstacles. Rubber tires are easily affixed to wheels of any description, und the vulcanised india-rubber rings may be obtained of the proper dimensions and thickness, ready to be put on, л any of the rubber manufactories in town or country.

Rubber tiree were proved at the Great Exhibition of 1851, when a heavy cart wheel so tired was allowed to run over the toes of the bystanders without causin g the slightest'sensation of pain. I have no pecuniary interest whatever in the matter, as my velocifere is not secured by patent rights, to which I bave a most decided objection. The patent laws as they now stand form a lottery from which 09 out of a 100 applicants derive a loss instead of a prize, neither have I any faith in any possible improvements being carried out, for the public is the only Judge of the value of an invention, and no committee, or jury of scientific men can forestall, or anticipate that judgment.

I need scarcely allude to the disagreeable concomitants of even a successful patent—piracy plagiarism, riders, men of straw, and of expensive law auits ihe costs of which must be drawn from the pockets oi the great mass of the public, the consumer.

Hî-nry W. Revelev, Heading.

STEAM LIFEBOAT.

SIR,—Allow me space in your valuable columns for i reply to the objections to the adoption of my in

fir o ved self-righting steam lifeboat enumerated in the etter of Mr. Richard Lewis, which appeared in your number oí the 27th ult. I have fully considered and provided for the necessary requirements, for which purpose I will take the objections in Mr. Lewis's letter ¿eriatim :

"let. That owing to the large quantity of water which must break over lifeboats in heavy surfs, miouatlHg often to three or four tons weight, i( would be difficult to keep the tires from being put out, i Uli at the same time provide sufficient ventilation."

To prevent the extinction of the fires, I provide the funnels and air-shafts with a cowl of peculiar construction, which, whilst permitting of free draught for the fires, and perfect ventilation, prevents any influx of water by the breakage of a heavy surf over the boat. Nor can these cowls be carried away by the wind, or when struck by the sea, or capsizing of the boat. The second objection made is, that *' the motion of boats under such circumstances Is so great and violent that they sometimes stand almost perpendicular, with either the bow or stern uppermost; that the propellers would work at great disadvantage, and the machinery would perhaps be liable to disarrangement."

1 obviate this objection by providing a screw propeller both at the stem and stern of the vessel. Тпеве propellers being mounted on the same shaft, will always work in unison; and as one at least will always be submerged, there is no fear of the engines "racing." I dispose and secure the boilers and machinery at the bottom of the vessel In such manner that the engines, Ac, could not by any possibility become displaced or disarranged by the motion ot the boat.

■ni. "That the space occupied by the engine, A.c., would make It impossible to use ours if the former should become disabled whilst afloat," &c.

Not only do I leave room to man the usual number of oare without Increasing any of the dimensions of the vessel, but by merely adding one foot to the ordinary length I am enabled to man 12 oars, instead of L0, as usual. Moreover, should the engines be disabled from any cause, the propellers can be immediately unshipped and the vessel propelled by sails or oars alone.

Ith. "That .... such boats .... would require lo have a qualified engineer (engine driver) to keep the machinery In order and work It when afloat," Ac.

I his 1 do uot consider an objection to my invention, a« I am convinced that the increased expense attendant on Increased efficiency In the means of saving life and property will be amply defrayed by the benevolent public, who have already doue so much to further that object.

ith. That "some time would be lost lu lighting the fires and getting- up »team."

By the use" of oil as fuel, steam may be got up in from 10 to 15 minutes, even while the boat is being carried down to the beuch and prepared for launching; so that no time would be lost. Indeed, my boat could set off, if necessary, with throe or four only of her crew, whereas ordinary lifeboats are frequently detained, for want of hands, when every moment is of vital importance.

nth. That "it would be difficult to apply the selfrighting property to such boats; and if they were to remain more than momentarily keel up, the fires would be put out, or they might set the boat on fire."

I provide air chambers of my improved construction ibove the deck, which ensure the righting of the boat; and as the machinery is disposed entirely at the bottom of the vessel, It must increase the self-righting property of the boat. The funnels and air-shafts are provided with self-closing caps, which prevent any influx of water whon the boat capsizes, whilst the boat may bo built of, or lined with, metal, to avoid all chance of its being set on tire.

7th. That "the cases of failure of the present lifeboats are so rare, that the committee of the Institution have not felt called upon to expend largo sums of money on experiments which mightnot afierwardsbe attended with beneficial resulte."

I need hardly refer to the award of £100 made to me to show that the Committee of the Royal National Lifeboat Institution are fully satisfied of the benefits likely to result from the Introduction of my improved steam lifeboat, whilst a reference to the Shipping attd Mercantile Gazette will show that the present service is uot by any means efficient in all cases. Sul That "wherever steam tugs are available, I

think it provable thai steam power cau be advantageously applied through their instrumentality."

In reply со this assertion, I will ouly refer to the number for January 1, 1869, of the Journal of the National Lifeboat Institution, in which appeared an article from the pen of the Rev. J. Gllmore, M.A., of Ramegate, entitled "Saved at Laet: A Tale of the Ramsgate Lifeboat." By this it will be seen that had steam power been applied in the lifeboat itself, instead of depending on the steam tug for assistance, much danger might have been obviated In that case. Besides, the desirability of applying steam power to lifeboats Is fully set forth at page 1 of the same number of the Journal of the Lifeboat Institution above mentioned.

C. W. Petersen, Master Mariner.

STEAM CARRIAGE.

Sih,—I enclose a photograph of a steam-carriage that bas run 1000 miles at the cost of Id. per mile, carrying fourpersous, coal, oil, and toll-gates, making one farthing per mile for each person. It has run 62 milee In 7 hours—that is, from Birmingham to Glou

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cester, abceuding and descending нише of the вtecpes; hills in the Midlnnds; weight löcwt. The engines are driven by gearing 6 to 1; carries water 10 miles, coal for 00 miles can do its 80 miles per day with ease. It has a patent " Field" boiler, 4-horse power; general working pressure 501bs on levels; 90 to 10D up sharp hills; never worked past 1001b. steam.

G. PftKV,

ON THE PIANO.

Sir,—I am sorry that severe pressure of business has prevented me hitherto in forwarding my promised communications on the piano. Pray accept the miserable excuse ef "better late than never," the more especially as my esteemed friend the "Harmonious Blacksmith " has deputed me to reply to several questions addressed to htm in the English Mechanic as being more acquainted, as be is pleased to term it, with practical details than himself, an assertion he cannot prevent me questioning.

My present subject is ou the improvement of the basses and trebles of pianofortes. A German harpsichord maker put additional bass strings to his instruments, which were sounded by pedal keys ; and one of Handera lavourite "concert" harpsichords had this alleged improvement. At a later date a Scotch pianoforte maker used very thick brass and copper strings in a similar way in his grand pianofortes. More recently attempts to reinforce the bass have been made by enlarging the sound boards, as carried out by Gedwin in 1836. and others, including my friend the ■' Harmonious Blacksmith," (see his ra'her costly design for an upright grand cottage piano in No. 235) ; and yet more recently by Mr. Steward, who extends the sounding board to the left of the bass strings at the cost of rendering the instrument yet more unwieldy. In addition, separate pedal pianos have been made by Woolfe, вее his patent of 1*58, No. 1081; and we are soon to have a public performance of Bach's pedal fugues by a celebrated French pianist on one of these Instruments, which, so long as its use is confined to such music, may be pleasing, but hardly so effective as organ performance. If used to give breadth to the bass of legitimate pianoforte music, it ia not only not needed, but la lese suitable for accompaniment than the bass of a good piano of the ordinary construction, usually quite powerful enough without even additional surface of sound-board. Witness any of Broadwood's magnificent concert grands. So I think I am justified in asking the designers of the so-called Improvements, cvi bono?

Many years ago 1 put a set of pedal keys to my piano, and I can testify to their great utility for the mechanical practice of organ music. I found them also capable of greatly assisting the jndicious performer of organ music not written with a separate pedal part,- but whatever convenience they afforded for this purpose, I never required tuem to make more noise than could be done by the finger. I never found any difficulty in making quite noiee enough with the basa of a good pianoforte. Indeed 1 have been too often dligusted by the want of taste exhibited by that class ef performers who во very logically infer that because all music ia sound, the louder the sound, the better the music. 11'such "hammer and tongs" players, and their name is Legion, were entrusted with pedals, not to mention a Woolfe's separate pédalier, no qulet-mlnded person with a musical ear could endure living within three doors of their residences, BUpposlng the party walla to be of the usual thickness, or rather thinness.

As It la far easier to make a piano whose bass overpowers its treble, thau one whose treble is too power

ful for Its basa, aa Sam Weiler would «ay, "I should verry much like to hear one "; but I have very little hope, or rather I quite deapair of doing so. I have yet to learn the advantage, except in a commercial sense, ot making an independeut pédalier -in other words, of making tiro baaaes to one treble In one piano, for this la exactly what it amounts to. That the independent pedaller can be made with a very wide scale, extremely heavy hammers, for;what Mr. Merman Smith terms "foot touch" ia powerful, unusually thick strings and an immense sounding-board, and that it may, and probably doee produce magnificent sounds in conaequence of ita extraordinarily great proper tiona, ia quite true. Ita employment aa a sole instrument, or tor the accompaniment ot a large number of voicea would probably be very effective, though I suspect it never can rival the organ, or even a large harmonium, for such a purpose. When employed as an addition to genuine pianoforte music, it must, just in proportion to Ita overpowering loudness, destroy lie true musical effect by drowning the melody. Another proposed method of increasing theloudnes* of pianos, is by cauaing one aet of atrlnga to put tw n or more sounding-boards into vibration. I believe this was employed in some of the earlier harpsichords, and ia successfully carried out In the violin. Its application to the piano was patented by Broad wood in 1783. 1 have but little hope of its success when applied to the trebte of a piano, however much it might improve the tenor and bas-«. In the violin the vibrations of the string* are maintained by the bow, which is not only a powerful instrument for impulsion compared with any amount of reatatance to motion which a fiddle-Btring is capable of, but the fact that the vibrations can be Maintained for any length of time at the pleaaure of tbe performer, completely altera the conditions. Were the treble strings of a piano urged by a powerful bow, it ia тегу probable their vibrations, being maintained, might be communicated to many sound-boards placed above and below the one to which the bridge upoa which the strings reat ia attached. TVe maintenance of their vibrations would afford time for them to be communicated to the several soundboards, just as they are to tbe back of a violin through Its belly ami its sound-poet: but the vlbratlonaof pianoforte treble strings endure so short a time (when struck by hammers only) that they ceaae before they can be communicated to many soundboards, therefore we can hardly expect to obtain additional tone from those additional sound-boards. 1 firmly believe one good properly-made aound-board u better than many, although more than one may probably be of uae in the middle and ba#a of a grand whose sound-board (from Its narrowness at the tail end) la often too small for Its baas strings, whose vibrations endure во long, that there Is ample time for tbem to be communicated to at least two other soundboards placed one above, and the other below the normal one. But I greatly doubt if there is any practical advantage to be obtained by usiDg more than one, which may not be better realised by enlarging the single sound-board commonly employed. Room for doing this la easily obtained by widen lag the usually too narrow tall of the case at its right hand or treble aide, to the great Improvement of its tone aa welt aa appearance. In upright instrument*, the aound-board muy be made of any desired width without widening the case ; Indeed It may be made to extend over the whole surface of the back. Erard'a do this, but after all it ia improving the treble and not the baas, which is the thing required.

If inatead of trying to do what every pianoforte maker who understands hie buainesa can do easily, my lrlend the "Harmonious Blacksmith" and aome of my fellow-readers «ho aie more practical in their crotchets than he is, would exert their Ingenuity to increase the power and purity of the treble, I should have no need to ask cut bono f It baa been attempted, but I have seen none yet decidedly successful. One method If to enlarge the sound-board beyond the bridge; but this in the two specimens I saw, though most elaborate in every respect, resulted In failure. Extending the aound-board within the bridge seems more promising. Erom the time ef Dodd, Goodwin. Noeworthy, and A. Wornum, to the late design of Steward we have had repeated attempts to carry out the idea; but I have yet to aee it carried out successfully ao far ae increasing the power of the treble is concerned.

Another and more promising mode of increaeing power in the treble is doing there what the Independent pédalier does for the basa, viz., ueing two pianoa instead of one, in the same caae, the whole of tbe strings of the said (literally) two pianos being actuated by one actianor mechaniam, In No. 208 "J. J." proposes this plan, and in No. 278 the "Harmonious Blackaraith " has offered aome euggestions of a more practical character than many of hie crotchets for carrying it out. "J. J.a" design la not Intended to increase the loudness of the sounds uttered by any given atring in the treble ; but it really ie what I have before stated it to be, viz., two treble pianna.in one case. It is true, there is but one Bounding-board common to both, but each string or set of strings has its separate pair of bridgea, although one bridge of each pair ia on the same sounding-board, and each of the other pair is on the same intermediate metal bar. Each etriug also has us own hammer, though they are both on one shank, and move on one centre. I feel, therefore, quite juatified in terming '* J. J.V design two treble pianos placed above each other in one caae. We all know two pianoee, sounded together, are louder than one.

The chief objectlone to this plan are the difficulties of construction (perhaps the "Harmonloua Black smi th'a" design for carrying it out might be cheapened and simplified) : also the unavoidable increased height of the Instrument. To me personally this latter ta no oLjeclioa at all. X much prefer a Rix leet cabinet to , four feet cottage; but commercially It don't pay tmake р1апйа moro than 4ft. 4ln. at the utmost. People don't know icktit is good for them, and won't buy tall instruments with plenty length oi string for producing basses of flue quality. If " J J.'e." planfwcre carried out as far down as the compile as pitch C, it would add something like two feet to ¿he height, thue makiug a four feet cottage as tall нв л four feet cabinet. I fear only the few who prefer mnsic to furniture would become purchaser?.

I fancy that the difficulty of tuning ench an instrument would be considerable, and J know from experience that the majority of pianoforte tu пег с are neither careful nor Intelligent enough to turneither this or any other instrument requiring unusual care' or Intelligence. The pitches of the upper and lower etringe must be altered, but very little at one time, or a large proportion of the whole tensile force of the strings would be resolved on the intermediate metal bar which carries the two bridges. To avoid this evil will require an amount of care and caution that tuners who are accustomed to "pullup" string* a whole tone or more at once can hardly be expected to exercise—but perhaps, like the Tory party, they might be "educated.'* Some difficulty might "be experienced in adjusting the upper hammers to strike their strings at the same instant, and with the same force, that the lower hammers strike their etringe, but it can be done if the workman's head is screwed on the right way. No one who works only hv •' the rule of thumb" should be entrusted to do it. I know I could do it myself; indeed, after more than thirty years practical and extensive experience—not to mention the тплну, many long months I have been engaged during my spare hours in carrying out no end of what I may term the "curiosities " of pianoforte making, for my friend the "Harmonious Blacksmith,*' there is literally nothing 1 should be afraid ta uudertake. If originality «f idea ¡.unfeund in the Patent Office records), occasionally even to me appearing to verge into absurdity—utter disregard for the ordinary usages ond practices of the trad-', which has caused many a wrangle between us, and his persistent determination, to test to the very last, the pros and cons of his ideas at any cost, cannot fail to give a man experience in hie trade, I ought to confess to myself under deep obligations to him. I have not only learned more theoretically from him, a mere amateur, than any manin the trade could have taught me, except I had access to the knowledge locked up in the archives of such firms as Broad wood, Си I lard, and Krard. which only oozes out. by driblets In their productions ; even then it is only visible to those with brains to appreciate—but 1 bavu learned in the pleasantest possible way—viz., by being well paid for my time. We must all pay for our fads, and he is no exception to the rule that "Children must be paid for."

In my next, with your permission, I will replv to a few questious by "Harmonious BlacksmiLh's" desire, though addressed to him.

W. T., Pianoforte Tuner and Repairer.

ROBERTS' GALVANIC BATTEBV. Sir,—ft gave me pleasure fo read In your English

MECHANICAL FINGERS.

Sir,—1 have just invented a very useful mechanical contrivance, a photo of which I enclose. Three weeks ago, I had a machinist apply for au arm amputated a [few inches from the shoulder, and she wanted nmongst a number of appliances, an instrument that would hold the work like the natural fingers, to enable her to hem, stitch, and tack her work for the machine,

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purpose, as I mentioned the use for which I required it, when getting it from Mesera. Smith aod Beck.

Will any reader kindly assist me by suggesting a remedy for the above defect, or if this cannot be done, would he recommend any cheap form of condeuser with a longer focal length.

X. Y. Z.

THK AIR PUMP.—THE HIGHEST VACUUM.

Sir,—A common exhausting syringe will produce a vacuum sufficient for the experiments mentioned by "Induetorium." p. 252, but at the expense of much labour. Certainly " Inductorium's " air-pump ehould do the work well. If, however, he requires stratification, the case is very different. I have never been able to produce it with adouble-barr?Hed pump, but a small pump which I have, on Yates' plan, gives me very good results. The form is shown in sketch, omitting unnecessary details. There are valves at A and Al openiug out wards, but none between the barrel

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borne by Mr. II. Chapman to the great nrtv.111t.141s of the galvauic battery which I In теп ted 111 ls.i-j. Permit nie to say that the cost of the battery (which he properly etates ¡ft greii t wheu platinum is used as- ;i negative plate) i» reduced fourfold by substituting graphite for platinum, aurt the battery is not much diminished in power by auch change. I have used my battery for electric light, and "for fusing iridium many successive hours with undiminished force. I used ioug draiu pipes (stopped at bottom) to contain the exciting liquid. These pipes were about 36ln. long. The plates being Din..were hung at the top: thus, 1, 1, graphite, or platinum -, 2, the line plates. The vessel was then filled with dilute nitric acid, sp. gr. 1240». The action is as follows :— l'art of the oxygen of the arid combines with the tin, forming metastannic acid, which, being comparatively insoluble, falls away from the surface of the tin plate to the bottom of the deep vessel. The surface of the plate is thus kept clean, and the exciting liquid is not encumbered with any opnosing metallic solution (an evil in all other batteries). Further, the metastannic acid falls down as a hydrate .thus carrying with it an equivalent of water, which tends to maintain the eupernateut liquid Dearly at its full strength. Again, the product of the battery, after obtaining Hie electric force, is a marketable ■ commodity, mttastaunic add being used in calico works. We sent more than a ton weight of this product of the batterv to Manchester, and sold it n't a price which paid nearly for the cost of work-iug the battery liut thocompetition by Voting's process of making metastanulc acid direct from the ores of tin kept the price down, otherwise we should have had our electric power for nothing. I would veuture to observe that this is the end to which experimenters in electricity should direct their attention viz., to make the product of the battery pay for the plates and exciting fluid As the nitric acid gave 1111 part of it» oxygen only to the tin, nitrous acid fumes were given off abundantly ; but these fumes were collected Into a peculiar kind of reservoir, iu which they were condensed, and part of the acid thus recovered. Circumstances directed my attention to other matters, and I have not followed out this matter as I ought to nave done.

I cannot refrain from bearing testimony to the exceeding usefulness 0/ your publication and the excellent spirit in which it is conducted.

Лаптгк Roberts. Pendarrow House, near
Crickhowell

After many trials Г succeeded, and so successful is the appliauce, and simple, that in a short time she was enabled to stitch and hold the liuest or coarsest tabrlc. with almost as much ease as with the natural lingers.

The instrument is fixed in the witst, and is removed, as you see, instantly on touching the spring. There are three rods corresponding to the thumb and the first and second linger; the two under rods are fixed; the top one,over which the work is drawn, is movable in any direction, and bound to the other two by a vulcanised rubber baud; this baud according to its tension keeps the work. On to each rod is a piece of brass tube, which revolves when the work is drawn. Over the two under tubes is slid a piece of vulcanised rubber pipe. The work is placed in the instrument precisely as it is in over the index finger, the vulcanised rubber holds the work just like the soft cushions ol the lingers ;tis the person stitches she can draw the work, the rollet s revolve, and thus they can hem, and stitch st any length. Ladies wins have lost an arm at the shoulder, aboveor belowelbow, may now by the use of this instrument follow Mieir favourite employment, which through their loss they may have long been deprived of

J. GlLLINGIIAM.

and the receiver to be exhausted, so that the rarefied air has no work to do In lifting valves. The pump Is hard to work at first, but beomeseasy as the exhaustion proceeds. Were "Induetorium" not so Will acquainted with the subject, I ehould suppose that the joints of his apparatus were not air-tight, but that. I suppose, is impossible, and therefore 1 cannot account for his failure. If "Induetorium" will furnish details of his coil giving 4In. sparks with a single small cell, and having oulylin. of secondary, hewill much oblige.

J. V.

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nearly to the bottom. Wheu the apparatus is at rest the water remains below the diaphragm, as shown iu Fig. 1 ; but when air ir* blown in, it gradually rises through the pipe to the position eliowu in Fig. 2. The water as it descends prenses out the air iu a uteady stream at the nozzle; a valve prevents it from returning into the bellows.

CtTIIKERT.

MICROSCOPIC CONDENSER.

Sin,—I have a Kclluer eyepiece which I am desirous of mounting as a condenser, but I find that the focal distance is so short (about Jin.}, that when it is placed under the stage the upper surface of the eyepiece interferes with the movement of the mechanical stage. I have tried the mirror with both surfaces, aud have used both ends of the eyepice uppermost. I presume that the eyepiece is (he proper one for the

SALADS.

Sir,—On page 150 of our Mechanic, "Beta"' appears strongly to advocate the use of dandelion as a salad. Iïuthe forgets to consider that mankind in •jeuerul do not relish the taste of this herb as a salad, and hence it is rejected by almost everybody, at least in this country, nor will any commendations of its good qualities, which it assuredly possesses, induce people to use it, knowing, as they well do, that there are other herbs as good, aud even superior when used

as -■!!:■ ]-.

Dandelion is most effective in diseases of the liver. It may, iu fact, be considered, particularly the roots of the herb, as almost a panacea for ailments of that organ. Un the kidueys, too, it acts beneficially, and no doubt on the spleen as well. But dandelion as a salad is most unpalatable, and even when blanched it is anything but agreeable. I have tried all kinds of salaos, aud there is nothing, in my opinion, to excel our old friend watercress. It is always welcome, and always wholesome, and can scarcely be sufficiently praised. We ought to eat a good deal more of it than we do. It seems to be universally liked, and, like plantain, seems to follow man wherever he goes; I have seen ft growing profusely near the Falls of Niagara, and t believe in the neighbourhood of Montreal and other places. In "Beta's" list of salads, I observe the word "beer." this, of course, is a misprint, and should read "beet." I am rather surprised that this gentleman has not included mustard in his list, for it is well liked and largely eateu mixed with cress, nor has he mentioned young onions, which are much consumed iu the spring time of the year.

I may add that the leaves of Indian creas (the common nasturtium) Jare a good salad. They are not as hot ¡is horse radish nor as cool as a cucumber, but agreeably piquant, and far preferable, I think, to dandelion leaves. On the Continent this cress is, one may say, in general use, but here in England we do not seem tocare about ¡tas asalad.andouly admire it for ibsgay and variegated flower, aud for the great ease with which it isgrown. I cannot agree with " Beta" lu his remark that through ignorauce or prejudice many of tho salads mentioned by him are at present despised by mankind. They are not despised, but simply unused, mankind having discovered other salads more a preeable to their tastes.

Tautau.

ORTHOTOPTICS.

Sir,— Your esteemed correspondent "The Welsh Shepherd," at page ^57 calls attention to a subject which has been frequently discussed among physiologists—nsmely, the rectitude or inversion of vision. Now, to begin. We are periectly acquainted with the anatomy and mechanism of the organs which subserve that sense, and we know that, in contradistinction to all our other senses, a perfect fixture, though very small, and inverted, is actually produced on a convenient part of each of these organs. But there our knowledge censes to assist ua as to theleftect produced upon the so-called uiuorum, and this, in all likelihood, will remain a mystery so long as we are in the flesh. As for conjecture, there has Do n plenty of that, but none of it can be of much utility. If I understand the "W. S.'s" communication rightly, the gist of his argument is that monocular vision v/ould present objects in an inverted position to the mind, while binocular visiou would produce tho sensation of erection. In other words, that two upside downs are equivalent to one right-side-upwards. In attempting to show this. he adduces the case of a little boy who was afflicted with disease, and perhaps congenital deficiency. But this case unfortunately, proves too much; for it le said that, in drawing the picture of a house, for instance, he drew it wrong side upwards; but then, if he had done that, his delineation, like everything else, would also have been inverted to him, and, consequently, seemed to him what would be right side upwards to us, and so, wrong side upwards to him. It w*ould appear, then, that he was merely endeavouring to hoax the bystanders. This would seem th« more probable, for we are assured that " the very rudiments

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f'Tthe optic nerve on the left side '•• pre wanting.'' Now, If this description be accurate, it wouM Imply a very extensive deficiency of the bruin, reaching back . « far a* to what ia called the cctenml genicular body, and would excite Do wonder at a perversion of intellect, for the malformation would probably not be confined to that tract. The aspect of a fungous growth at the bottom of the eye is not crystalline, but metallic, and was well described some time ago in your columns by Dr. Uaaher, whoso good-tempered articles we have r^rently mi.-sod. It is easy for anybody to try whether njonocular vision inverts the impression on the cenM>rium by simply closing one eye, or, if that will not ►ati-fy the " Welsh Shepherd "we have no end of case* of moat extensive lesions of the brain on one side only to aid Ub. His theory about the decussation of nerve fibres in the optic commissure will not hold water for one instant, the fact being that the crossing merely produces a distribution of right hand fibres to the right hand Bide of both eyes, and rice versa, thus securing a consentaneous action of the two Bides. Wo Lave a most remarkable case on record bearing on this subject narrated by Locke, I think, in his essay "On the Human Understanding" The question wan propounded to him by the celehrnted Mr. Boyle, whether, supposing a person to be born blind and to have his sight afterwards given to him, he would, by mere inspection, be able to distinguish a cube from a sphere. Locke, after some reflection, replied that he would not, and shortly afterwards an opportunity presented itself of testing this, for one of our great surgeons, Mr. Cheselden, encountered a young man si years of age, who was born blind, and remained so, having congenital cataract. Mr. Cheselden operated on him, and he recoverrdhis sight He was not able to tell a cube from a sphere without manipulation; he »aw onjectsin their upright position, but everything appeared painfully close to his eyes. After a period hu saw like other people.

There arc, then, no means of ascertaining in what position we see objects, or. indeed, if we all see tbcm in like manner, because their relative positions and magnitudes are similar in all cases; it does not, however, follow that because the picture is inverted at the fundus of the eye, it should be so carried to the ?<"n'orium, for it may be there presented horizontally Willi the base forward, and if so there would bo a solntiou of the question.

But we are not to suppose that people always know whether they are looking at an object right or wrong side upwards, for if we go to the palace at Hampton Court, wo shall find the visiters looking at the pictures on the ceilings from all parts of the rooms. Few may be aware of it, but such, notwithstanding, is the fact, thitt the large majority of persons contract a Iwibit of using but one eye, to the detriment of the other, that the unused eye loses, partly or entirely, the faculty of focussing and adapting itself to see at different disiance*; auu this may be perceived if we take a book and attempt to read first with one eye alone, then with the other, also alone. This should be attended to by those who have to wear spectacles, as it frequently happens that glasses of different locuses are required for the two eyes. We cannot, as just observed, lell how others sec, as we have uo means oi instituting a comparison, aud, for aught we know, one person, may see as though he looked through the small end of an opera glass, aud another as through the large end. The impressions produced by colours may also be widely different.

Io conclude,—it 1b of little consequence to us whether objects are presented to us upright or inverted, as all know who arc iu the habit of using the microscope, for here the bottom appears to be the top, aud the right hand size the left, and ?i« versa, but our experience soon enables us to supply the correction.

F.R.CS.

PECULIARITY IN EYESIGHT.

Sib,—For about two years my eyesight has been failing me out of doors (to correct which I use concave glasses). For reading it Is as good as ever. In looking at. say, a flagstaff with the left eye, I am favoured with three images thereof—namely, the flagstaff proper, and an linage parallel thereto like a sbadow at each side. With the right eye, and with both eyes at once, there is ouly one shadow—to the right. Ib looking at a pretty clrl thlspcculiaritvls agreeable enough (my wife here pulled my ears), but it detracts very much from the appearance of a landscape, &c. I suppose it is caused through the irregular flattening of the eye lens through natural decay, perhaps accelerated by following my daily avocation in a too glaring light. I have a wiudow In front or inc and one to iny left. Thus, my work is in the light, while the light also falls upon my eyes. Now, it seems tome that this disposition of the light will cause the pupils to contract Irregularly, and that the centre will flatten by age and use j but that the outer edge (irregularly protected) will be preserved iu its original convexity, thus causing two or more foci iu the same eye. What strengthens me In this opinion is, that at dusk, while other people can see easily, everything is a blur to me, and when it becomes dark, by the greater dilation of the pupils, the focus of the outer edge becomes the principal one, and so I can se« toleraoly well again. Should any of my brother readers confirm me in this opinion, I will take steps to remove the cause. An «pinion will oblige.

BLACKBonN Amateur.

effect? Mr. Reveley. however, probably has good reasons for supplying the air from above, and I. for one, would be mosi happy to have further information respecting hi* novel plan. He also refers to the benefits arising from the carrying off of the products of gas combustion by means Independent of the general ventilation. A proof of what may be easily effected ia this way lately came under my observation. An old house, having rather a low ceiling, was fitted up with gas, but the air always became very oppressive when the gas was burning. The occupant being an ingenious man, had a tinaed iron funnel constructed, some 10 or 12in. diameter, and suspended over the burner; the funnel terminatedjin a tube about an inch in diameter, through which all the products of gas were carried into the house flue. After the adoption of this plan the air ia the room remained cool and fresh.

J. HABTIlfCS.

SIMULTANEOUS EQUATIONS. (Continued.) Sir,—To continue :— (7.) (1) 7 w - 13: = 87 (2) 10ji - 3x = 11 (8) 8 w + 14 x = 57 (4) 3x - 11 c = 50

Multiply ill and (3) by 3 and 7 respectively, subtracting products.

21 w - m r = 261 U « + 9* x = 399 Multiply (4) by 49,addlog to to) (5) - 98 x - 39 r = - 1.18 98 X - 539 z = 2450

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VENTILATION OF BUILDINGS. Sm>—I have read with much interest Mr. Henry » . Keveley's letter (No. s«9> on the ventilation of builil'[>IT>. Seeing that the enjoyment of health so much "epends on the proper supply of pure air, especially to ',welling-houscs,thu importanceof this subject cannot, 1 think, be over-estimated. Mr. Keveley's plan is to Mipply the fresh air from above, through the ceilinp. and expel the bad air through the Hour. Would it not l>e better to reverse this plan, and supply the pure :ilr from beneath, while the lmourc wa*i expelled from above, seeing that the heat and breath of the body and the products of combustion have all a tendency to :»cood—at least there exists a general belief to that

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SPECTUUJi ANALYSIS.

Sin,—Iob*e»-ve a correspondent, H- W. Bishop, (J<KM),, asks that another series of articles shall be given upon spectrum analysis. Allow me to support till** suggestion, and arid that no doubt there are many who like myself possess a small laboratory for experimental chemical iuvesrigation.and who would be glad to ad I to their stock a spectroscopic apparatus if it could be provided at a not too great cost.

My own case is this :— I have a good practical knowledge of analytical work, and desire to acquire an equally practical kuowleag^of spectrum,analysis. At present I know little more than the name, and io make my laboratory more complete and useful, to add a spectroscope for chemical purposes. Therefore any information conveyed through your columns to assist, in either makiug, arrangiug, or where to purchase and work the necessary apparatus will be duly appreciated.

W. B. TRADE AND COMMERCE.

Sir,—The second paragraph of "F. W. M.s" letter on page 257, expresses a very common belief, but one so pernicious, that the error caunot be expressed too often. He thinks that we ought to refuse to buy cheap goods from the foreigner if he refuses to buy cheap goods from us, " because if we did so buy them we should be paying the wagefl of the foreign workman who made them, and therefore there woald be just so much less (money) for our own workmen/' who are thesefore compelled to emigrate. "It is pretty plain that for each foreign, workman we support in this manner, one English workman is compelled to leave his country or to become a pauper."

As all this Is heresy of the blackest hue in the eyes of all orthodox true believers in political economy, 1 thought I might safely leave this portion of " F.W. M. V letter to other and more competent writers ; aud therefore confined myself last week to vindicating my first letter, which "F.W. M. "somewhat cruelly held up to ridicule. Having a most salutary horror of encroaching on your space I intend to state principles without any of the qualifictitious they require ia practice.

I will start with two axioms.

1 A conutry that imports goods, pays for them by its own exported products.

Z. Wages are paid out of the accumulated wealth of a country.

In these questions one part of the transaction is obvious, the other, the compensating one, requires some attention to find out. When I buy a foreign-made article,"F. W. M."even sees, that part of the money I pay for It, goes to support the foreign workman who made it. What he does not see Is, that some foreign gentleman pays an equivalent sum lor some English article that strikes his fancy, aud that part of his money goes to support an English workmen, for taking the whole of one nation's trado with auotber, the one transaction cannot happen unless the other happens too.

Therefore, when we havegot only thus far, we find that the Knglish workmau is eqmihj supported whether I buy a British or a foreign made article. Let us now go one step further. If 1 buy a foreign article In preference to an Knglish one, It must be, because It is, rarterisparibus, cheaper than the English one. Let us suppose, for iustauce, that 1 get ibr £10 a foreign article ; whereas If 1 bought a similar English one 1 should have to pay £20 for it. No one can deny that I am £1" richer for my intelligent preference, and have that extra £10 to lay out on another article; for no sane peraoanow puts away his savings in an old stocking, he invests it somehow or other, therefore, I shall still lay out £20, on industrial products—English or foreign makes no dillerence to the English workman, as we bavc^iound above. The result is that I am richer by £10for choosing the foreign product; that irt to say, that the fund from which wages are paid is increased by that sum; which, in the long run is guid for the working classes; ert/o, buying a dear

English product when you en a get л foreign one «i wsJfor less money lea dead loss to thc'conmiuuity.

H ER UK RT.

DESIGNS FOR TUE LATHE.

SiH,—In your very interesting- paper I have noticed Boric letters inquiring aboi\t the best mode of trying iiud recording designs executed in the lathe. The common method of doing this, by a paper on tbe chuck and a pencil in the elide rest, is at best so very inconvenient aud unsuccessful, that many amateur turners among your readers will doubtless be glad to learn a much superior proof. That you may be able to judge of the result obtained, I enclose a couple of samples; and these are selected on account of their ¿»«perfections, that you may see what arc tbe difficulties to avoid.

The card is common enamelled or ivory faced cardboard, such as may be bought in sheets of any card maker, and cut to lit the chuck. This cardboard, after belog cut, is brushed over with Indian ink, two or more coats in opposite directions, until a jet black surface is obtained. This must be done quickly, with a litbt hand, so as not to soak up the enamel; and the Ink must be goed and rubbed smooth, free Irom lumps, as the least knot on the paper injures tho design. Then- 4*nrds are held upon any flat chuck by а narrow brass rim; the rim is fastened down by a catch on each side of the chuck.

The tool isa needle-point, which is preyed forward by a spring; Its penetration Is regulated by un adjustable shield, as the card will never lio perfectly Hat.

The lines, being white upon a blat-k ground, will be distinctly .visible nowever fine they may bo drawn ; and there is scarcely a limit to the delicacy of the work which may be executed in this way. The cards may be easily preserved, and the "sittings" noted upon the back of each for future reference. If the designs are wanted tor publication, any photographer cau copy them, enlarged or diminished, if required; aud they ore much more effective than the patterns printed from blocks, on account of the greater distinctness and delicacy of the lines.

Should any of your readers whft are turners desire it, I will scud a drawing of my tool; I do not now do so because I am not л good draughtsman, and am, moreover, not certain of the favourable reception of my suggestion. Still I wished to chare with my ft-J low ítmateura an invention which has given me much amusement and much pleasure to m:»uy friends.

V.,;New York.

[The specimen* enclosed by our New York correspondent are exquisitely executed. We should be glad to give, for tbe benefit nf our readers, an illustrated description of his lathe.—[Ed. K.M.]

TUE " GERM THEORY."

Sir,—Will you allow me to say that, while- agreeing with *' J M—-о" in a great deal that he says,

(p. 2.V4.1 cannot imagine that the "building "bespeaks of would be ef the («lightest use in curing consumption. 1 do not think 1'rof. Tyudall is quite sure himself what the molecules floating in air really are; for although when the stream of aír wat- passed through a red heat the molecules "were destroyed," similar

Ehenomena occurred when a tin case containing bofl>g water was held underneath; so the molecules may be organic or inorganic for all that has been prwett at present.

That persons living at high altitudes randy if ever Buffer from consumption I imagine arise* from the air being ** lighter" as well as purer. Thus the lungs would take deeper inspirations, and become fully inflated and, no to speak, iterated. lu other words, beCuum* tbe pressure of the atmosphère is not so great on a high mou m ain it becomes necessary to obtain the rt quälte amount of oxygen to breathe meredeeplv, and toexpand the chest moro fully, and consequently the lungs. For myself, I do not believe tuberculous

matter can exist in well-aerated luugs. "J

M о" say» that "airof great tenuity\?> will not

suspend the «?ermw mechauically and carry them about." finely, there ie мме mistake here.

But I should like to hear Dr. (issuer's opinion on the whole subject.

Saul Uymka.

TOURISTS' TRIP3.-IRELAND.

Sir,—The great number of inquiries resulting from my note on the "Midland aad We-tern Districts of Ireland" fully proves that a tour through that romantic part is not without great interest, but as I cannot answer ail inquirers individually, I hnpo you will again do шс a favour by inserting the following remark*, 4c, for the benefit of those numerous kind friends who, by their letters, evince u great desire to visit the Irish. 1st. I. would address myself to those who have oulya week at their disposal, л circular tour through the county Wicklow they would tind very Interesting. We take tbe train from Weetlaud-row station, Dublin, for Kingstown, a sixpenny rrle, and then proceed on foot through the pretty towns of Dalkey and KilHney, where having obtained permission to щи-end a mount, formerly belonging to John Mappas, Esq., we view a splendid panorama oí many fquare miles in extent stretched out before us. A little farther on lies Bray, with its celebrated promontory stretching out into the sea. called the Head of Bray. Here we must stay ti day or two to vMt the "Seren Churches." th.. "Devil's Glen," and the "Dorgle." The legends attaching to these places told by the carmen in their own vernacular, are droll In the extreme. This glen of the Dargle is the most beautiful spot in tbe country. The rugged and precipitous side* rise on either hand to tho terrific height of +00 or 5'Oft., and are covered with the most luxuriant vegetation, among which are several families of splendid ferne; at the bottom wind* the stream from which it takes its name. The sublime scene and the mu»ic of the waters as thev ru»h along over the rocky bed cast a spell over the lover of nature which euelulu* him to tho spot; but we pass on ihr,.» 'U densely-wooded lavlnes, uutil we reach Enni-kerrv, where we must also stay a day or two to explore.

About ó mfles from here, past the Sugar Loaf Mountain, lie the domains of the Earl of Powiscourt, and by the courtesy of his park keeper, Mr. Hopkins, we were permitted to view the Deer Park Falls by moonlight, a scene that will evor bo photographed on our memory. \Ye retrace our stcpe to Enniskerry, and find comfortable quarters and an obliging landlord at the Hotel Royale; then, again taking the road, post Lough Bray, we visit some genuine Irish cabins on the hill side, containing, as usual, the pig that pays the rent, all tho poultry, very little crockery and furniture, and a great deal of peat smoke. One tiling you are sure of. and that Is a hearty welcome to share their meal, which chiefly consists of potatoes (cooked with the bone in them), and milk. A more generous people I never met with; they aro ever ready to asdst and wish you " God speed." Hut we travel on past the Reformatory of ülcu Cree, containing about 700 inmates, under the paternal supervision of Father Fox, to Round Town, through Rathmines and Rathcar, into Dublin, aud what time wo have we may spend profitably bv visiting Phoenix Park, the Cathedral, and many interesting places in the old city. And now— aud. To those who have a fortnight's leisure. We take the excursion from Blackatone Statiou, Dublin, to Galway (all particulars of the Midland Great Western trains may be bad by writing to the courteous traffic manager, Mr. Skipworth), a distance of 130 miles, passing en route Maynooth College, Mullingar, Ballansloe, and other interesting places. The old town of Galway is thoroughly Iri-h ; the women are seen in droves, dressed In the old red cloaks, and without shoes and stockings, carrying fish and turf. Visiting Queen's College, the famous salmon fishery, and the curious colony called the Claddaugh. and tho pretty suburban town of Salthill, we book ourselves as passengers by the steamer that plies daily between Galway and Coug, the fare Is. 6d., a distance of about 50 miles. This is a pleasant little trip on tho fresh waters of Lough Corrib ; numerous islandsjare dotted here and there, and feeding on *.he shore we saw flocks of cormorants. Passing the residence of Captain Blake, and several dilapidated und deserted uunuor les. wo reach Cong, and by the kind permission of Sir A. Guinness we are permitted to roam over the spacious domain. About ¡U miles distant aro i he waters of Lough Mask, flowing into Lough Oorrib through a subterranean passage formed in tho limestone, which has suuk in many places, forming immense caves. The inhabitants of Cong light them up with straw whenever visited by stranger*. From here wo pass through Ma'am {past Lynch's Hotel, a most re mai kable structure, the front of the place being, as the Irish express it. all at the back ; the front part facing the road certaluly has neither door, window, nor siga, and it is only by passing round that we discover signs of life), ou to Clifden, from here to К y lern ore, and through the pass, visiting the castle of Sir. Henry, oue of the benefactors of Ireland, especially in the west, through Lctterfract and Lenane, two charming places, from there to Westport, spend two or three days hero, ascend Croagh Patrick and feast our eyes with the scenery around the Bay of Westport, then take the train aud pass to Foxford, from hero by road to Ballina, a town numbering about ¿000 souls ; hero we see the quaint old Irish stylo of travelling, tho wife riding behind the husband on the samo horse, and holding by the tail of the animal with one baud and clasping her husband with tho other, from here we take the public car and travel comfortably to Sligo, the extremity of our tour, aud hero you may pass several days, as the neighbourhood is extremely Interesting alike to tho botauist, geologist, and the pleasureseeker. Trips jiiv arranged on Lough (¡ill most days. We now leave Sligo and return by train through Ballymole aud Long fo id to Dublin, aud thus ends an excursion throughadistrictexceedinglybeautiful, but thinly populated, capable of being far more extensively cultivated thau at preseut. Apologizing for the length of this letter, 1 bhall be happy to answer further inquiries.

F. Iiabwood, 33, Newark-street, Leicester.

[We should be slad to insert other letters containing reliable information for tourists, and particularly about localities which moro or less abound with beautiful scenery or objects of scientific interest. Information on railway aud steamboat fares, hotel charges, &a, would also be appreciated, and no doubt received with thanks.—Ed. E. M.]

DRY PLATE PHOTOGRAPHY. Sir,—I strongly recommend '' Tannic Acid" to try the g urn gallic process in preference to the tannin. He will And it inore certain and better in every respect. For full details [ must refer him to the "Year Book of Photography for 1B70," price Is , as to give them here would require un unfair amount of space; but I cau briefly state it thus :—To make the preservative, dissolve separately, gallic acid, iigre.; water, edrchms.; andguin nrabic, 20grs.; sugar caudy, 5ггв : water, Aire hing. These are to be mixed and filtered Just before u.-e. The plate having beeu coated with a suitable collodion, is excited and washed as usual, flooded with the preservative, aud drained and dried. It may be developed with pyrogallio acid, but Mr. Gordon recommends the following iron solution ¡—Gelatine, lgr. ; glacial acetic acid, lj minims; protosulph. iron. 20 to :i0grs.; water, loz: a few drops oí silver solution to be added ЬсГто using. The exposure is about from four to six times lunger than for wet plates.

D.E DAL US.

good recommendation; but if, iu addition to this, the letters are not grey, but bUcl; It proves beyond all question that there can be uo false light, consequently uo aberration, and therefore all tbe rays unite in one precise focus. I certainly incline to tho opinion that very small letterpress constitutes not only one of the readiest, but one of the finest tests for any telescope, while the far greater immunity from atmospheric disturbance which such terrestrial tests possess renders them much more handy than celestial objects for severe scrutiny. I dare say " Optical Bricklayer " will get still better definition with a properly, constructed eyepiece.

W. PURKIBH.

FOCAL LENGTH OF CONCAVE LENS.

Sir,—It may perhaps interest "A Fellow of tho Royal Astronomical Society," page 251, and his querist "Scorpio," to know that on page 19 of '* Smith's Optics," there is given n method of Unding tho focal length of a concave lens by experiment, it consists in covering the lens with a piece of paper, in which a few pin holes have been made. Tho focal length may then bo discovered by holding the lens in the suu's rays at such a distance before a sheet of paper that the distance of any two holes ou the sheet of paper may be double the distance from each ether of the two correspondí ¡g holes in the paper on the lens. The distance of the leus from the sheet of paper will then be e<iual to its focal length. The experiment may be somewhat varied by placing apiece of cardboard with a single circular hole in It in contact with the lens aud a sheet of paper on which a circle has been drawn of twice the diaiaeter of this hole at such a distance behind it thai the dliïuied circle of light from the leas may just till the circle. The distance from the lens to the paper Is iu Cocal length, as before. If the lens be ground on its edge, iL may be sufficient simply to hold it before a sheet of paper on which a circle twice in diameter has been drawn.

H EHRT T Vi VI AK

A CUMBERLAND MINER'S APPEAL

Sir,—Having witnessed a very serious accident today, by which a comrade has lost hie eyesight for ever, I seek the assistance of my fellow-subscribers for the means to prevent such accidouU.

In blastinc Iron ore we use a tool called a'pricker," и is of various lengths, ranging from Itf. to 4ft.: it is made of fjin. b<*st nail rod iron (borne shoo), and drawn to a point. Tbe use of this tool is, that during the process of charging it is kept in the hole so that wheu withdrawn it leaves a space iu the "stemming" down to tho powder, into which we Introduce the straw. The straws we use are corn straws dried aud tilled with very fine powder. As all our work Is by contract, we never use tho pitent gutta percha fuze, except in very wet places, because we cau not afford it. The danger of the " pricker " is that during the process of pulling down among the powder it ignites, and, of course, tho powder is blasted in the man's face. We have made the prickers of copper, but they do not answer, as we flatten them whilst '* stemming," and then we cauuot withdraw them.

Ari such accidents are of almost daily occurrence, it would be a blessing to us poor miners could there bo something mveuted to protect us.

A Cumberland Miner.

PERFORMANCE OF SPECULUM.

Sir,—Your correspondent, "Optical Bricklayer," in soliciting my opinion on the performance uf his 7 5-l6ths in. mirror, has, so far as I can judge, accomplished a decided success. He does not. however, givo the number of the Mechanic in which the engraving referred to is to be found; but if the lines of letterpress are smaller thau the ordinary correwpuHdencecolumns, such would, at a distance of loo yards, be a sulllcittitly «evero test for any ordinary aperture The tr«i»',ilitv of such small type at the above distance is of itself a

ELECTRICAL DISCOVERIES.

Sir.—I was not a little surprised, I may even say electrified, to read in the last number of your excellent magazine an account of the so-called "discoveries" in friotlonal. or high tension electricity, purporting to have been mad« by Mr. J. N. Hearder, F.C.S., of Plymouth, and exhibited under what he consider* to be a new form uf instrument, and term* the Electric Fulgnrator. Permit me to say that these very dncoveries. in air their identity, and in the very uieaus employed in their elucidation, were made by me threeanu-twenty years ago, fact for fact, and almost letter for letter, and word for word! These discoveries formed the substance of a paper which I forwarded to tbe Royal Society in 1M7, and which was road before that learned body ai Somerset House, in January or February, 1.4*3. The Literary Gazette, of that period, gives a report of the paper, and will furnish the exact date. See also Proceedings »f the Royal Society for l.s-18. In May, dune, and July of the saino year I delivered a series of lectures at the Royal Polytechnic Institution, on "The Phenomena ot Thunder h tortus, and the Cause of Lightning,1'Ac, aud 1 exhibited the powerful effects of my discoveries by producing loud aud dense flashes of concentrated lightning through an uninterrupted interval of air three ieet in length. I use the word concentrated, as referring to quantity, which was here combined with intensity. I employed 12 immense Leyduu jars, having a coated surface of upwards of U'O square feet, aud rapidly charged to the utmost by the hydj;»-electrlc machine of the institution. The flashes weresometimt-s straight, but generally zigzag, or like a long lineof WW's, slightly bent, in the form of an irregular curve from tho earth, aud they were so powerful that any one of them was capable of destroying life. Each jar was insulated upon a stout varnished glass pillar, 3ft high, and the series were conuected together by a framework of levers, so that when charged, they could be suddeuly thrown Into striking positon, to determine the disruption of the fla-h. Singularly enough, two-and-twenty veers afterwards, this self-same discovery and this sell-same arrangement, even to the system of levers and the guias insulatora, exactly 3ft. high, are brought forward a* novelties by Mr. Hearder. I tried at the time, however, to carry the thing further, aud make u far more imposing demonstration than that above named. I

[)roposed to the directors of the institution to produce, >y such n combination of jars in their large theatre, a fla^h of lightning through an uninterrupted interval of 12 or 2oft. of air, which I could easily have accomplished, and without danger, but they were afraid of the occurrence of seine fatal acrldeur, aud for this reason aloue my proposed demonstration was abandoned. In proof of the facts above stated, I refer to

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