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form an aliquot part of H, we mutt make an allow sue* for It. Suppose, for instance, that the substiler line should Dot be on the line of X., but between I \ and X., we must tin<i how much to allow for it before commencing our reckoning. For the sake of example, suppose the longitude ahoald be 2h. 20n»iu. This, converted into decrees, will be 34°, and using the fame formula—namely, R : sin. 14 : : tau. s .- tan. dlst. —we shall hsve 1° IV. Harlot: measured this distance from the substiler Wne, we must compute the hourarcs by taking it in, and instead of taking tan. 15°. tan. 30°. Ac, we must take tan. 20°, tan. 35°, Ac, adding 5° to each; but ia the morning- hours, by the same process, we fad we must allow 2" 28' from the substiler line to the hour of IX..and instead »f tan. lt°, tan. 30°, Ac, we must add J0°. and compote by tan! is3, tan. 40", &«.; and bv working- tbent out In this way wc shall obtain all tae hour-arc*. In condition, we must remember in all these kinds of di*l» to place the gnomon parallel with the axis ef the world, or point to she poles, and to apply the equation of time when we set our docks and watches by them, and then, like the great run of tb« umWeran, we may always depend upon a* uneratrg guide to direet us to our several duties. T- $. H.

PS. — Tour hiebly-bjatnnrBws eorressjendent "F.R-A.S." whose papers it is • pleamrr* to peruse, recommends "Iloethet on Matbematieal Instrumenu and Dialling Strain," but I venture to sasy that although its contents are most valuable, and Its directions on dialling qui te-sonrdent for those to whom the art is like A B U, yet it at not full enough tor others, nor does it give any dlrcctfens whatever for the n.n simction af declining and reclining dials. The hourarcs may aim be found by that useful rule, the sector, but with much more trouble and far less accuracy than by the method prescribed, which is nothing more than addition and subtraction. In last letter, page 15, in the diagram, for "60°" read "«S<»;" and for the "angle A C B 30» + 90° " read "angle A C11W + 90"."

EXPLANATORY.

Sib,—I cannot aee anything in my letters entitling "K.R.A.S." to suppose I bad him in my thoughts when I referred to what the Gertnsh poet has said about "ftroDrmen." All the same, 1 would submit to him my deabts whether it befits a real lover of science, as he undoubtedly Is, to " eschew discussion ab initio on erery moot point whatever; " nor can I think that the abandonment of "t winning cause" (in itself hardly a commendable thingl would justify the course of dropping an argument when one finds one has made a mistake.

I have brought no charge of either sort, however, against ~F.B_A.8.," for whose scientific attainments and surprising general accuracy (when one considers the wide range of objects be treats of) I have the highest possible respect. It 1 were disposed to do so, I should, be far more inclined to dwell on hta spectrum analysis illustration than on Ms theory respecting object glasses. The latter is a matter ot opinion, the former a question of fact; and any one wlio is desirous as 1 confess I am, of seeing the truth laid as clearly as possible before people, might fairly object to a statement which is opposed, I submit to tne very principles on which spectroscopic analysis depends. J"

_But In praising (as was just) our contributor '."*■ no' ' making a cap; " so that I need

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dwell no farther on a discussion which I also have desired to drop.- Richard A. Pboctoh.

CRIMINAL L1TERATUBE.

•.•S^* clergyman, on the 31st ultimo, wrote under the above beading thus to the Tlmti:"Sir.-Ashort time ago yon recorded the conviction of ,TMT""nunreof immoral prints, noiorttheprosecutlon ot the (joyernment, but ot a society whose successful operations have made them insolvent. To-day you record the words of Mobbs, the murderer:—' I had seen s picture of the man Baker murdering the girl in we hop-gardens.' Week after week the illustrated records! ot crime are circulated over the length and Breadth of the land. In my country parish the Illustrated Potu&A'em has a large circulation. Its pictures represent crime In varied phases; its letter-press is explanatory; but its most damaging part is to be found in Its advertisements. And yet as the law stands 1 much question If it can touch this publication, lias ne M.P, time to consider first and give notice next of a motion upon this subject? Surely crime in England should have its share of consideration with crime in Ireland, and It strikes me that it is somewhat important to protect innocence aa we spread education; but it unhappily appears that while we are squabbling aa to whether leliglon may be taught in our schools, we are permitting vice to be taught everywhere."

Jt such men as Mr. Edward ITenri Todc (who started, and for some time edited that journal), and who afterwards started and edited the >«»ion), and others like him. cannot be induced on moral grounds to forbear from publishing their til thy broadsheets, it is time for the law to interfere. I trust therefore you will allow the*e lew lines to appear, that now, when there seems a chauee of the matter being agitated, we, who are represented by you, may not incur the reproach of having remained silent. Kappa.

TEST OBJECTS.

Sib,—I send yon a few of the tests that have been put upon a telescope in my possession. It is Sin. aperture, 4ft focus, 3 eye-pieces of 35, 60, and 96 diameters. With the lowest power I can discern Jupiter's satellites before sunset, and with the highest power I have observed the transit of the satellites. It shows distinctly -4 stars in the trapezium of Orion, it splits Castor oaeily, shows the. companion of Sirius, also Kigel; Cor Cacoll it show* beautifully with the lowest power; Mizaraleo. 1 have seen the trapezium through a 3*in. and IJiu , and see 6 stars in one, and 6 In the other. Tin; 31n. shows the belts of Jupiter more distinctly than a7gtn. silvered glass reflector. If "K. R.A.K." can give me further test objects, I shall be greatly obliged. William Bagulby.

TURRET CLOCKS.

Sir,—Several correspondents in the last number of the Mechanic ask for more information about the clock 1 described in your pages a short time ago; I will, with your permission, aff<>rd them it. Enclosed is a drawing, showing how the quarter train is discharged and stopped. A is the pin wheel. Three tunes in the hour a pin presses down the lifting piece B, which has two bits of steel rlvetted in it. The locking arm C has also a bit of steel, which comes against the stop on the lifting piece, when it is allowed to fall by the wedVe of hard steel rivettedlntt drop

?ing Into the notch in the cam wheel D, and the detent 'into the notch in the locking plate E. When the end of the lifting frece is pressed by one of the pine, the heavy end rises, and lets one of Its stops slip past the stop on the locking arm C, which moves forward in the direction of the arrow, and comes against the warning stop two or three minutes before the quarter is to be struck. When the end Is free of the pin, the heavy part fall* back Into Its former place, the cam wheel revolves and raises the stops on the lifting piece out of the way of the locking arm, and the num

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ber of strokes is determined by the distance of the notches ia the locking plate, which, in this case, is also the pin plate, and works two levers. The lifting piece B must fall quite dead, or it may fail to stop the train, and therefore the detent F must not touch the bottom of the notch. The hour-discharging mechanism ia the same, only then the locking plate does not work the hammer lever, and the lifting piece end is not pressed down, but raised by the pin in the going part, I said nothing about the dial work, or the way the pointers are driven, because it is not done in the usaat way.

There was an old thirty hour clock, which had been going for nearly two hundred years, and was about worn out, already in the tower; it had only one hand, showing the hours. About three years ago I put machinery to it for striking the quarters. Chaugo wheels were used, and I sent a description, which was published In the English Mechanic. I also put another hand to the clock, showing the minutes. The method was simple, but objectionable, as the minute hand was next the dial, fastened ou a tube. I should prefer to use dial wheels in the usual way; they would be much more costly than change wheels. When I removed the old clock, I found the wheels none the worse for their nearly three years'work. The quarters had been striking at their regular intervals, and I had been well repaid for my labours by hearing their musical sound.

A correspondent asks why I use cast iron wheels in preference to brass ones. Simply because iron wheels cost only about a quarter of the priee of brass ones. No doubt the train is a coarse one, but with weight enough on the barrel it will do its work well. For the going part, 1501b. is hung on a rtin. diam. barrel; that is a great deal, but with a gravity escapcnieut it does not interfere with the time-keeping property of the clock. I believe, from what 1 nave seen of the performance of the clock—and I kept it going in my workshop during the time the hour and quarter pasts were being done—that it will not vary more than a minute In a mouth from mean time, when the pendulum, of varnished steel, is regulated. It takes about half a minute to wind the going part up, and by lifting up a ratchet lever, geared to the third spindle, from below, a maintaining power is kept up. The weight on the barrel of the hour part is 3501b.. and lifts a hammer high enough to bring out the souud well from the tenor bell, weighing, I should say, 16 or 17 cwt. The quarter bells in proportion. I obtained the change wheels of J. Buck, Newgate-street, but Mr. Lloyd, 135, Steelhouse-lane, Birmingham, has sent me his supplementary wheel list, and it appears he can supply many other numbers of teeth besides those I mentioned, amongst others, the 130 tooth wheel I wanted.

There Is no reason why every village church; if it has a bell, should not have a good public clock. A clever blacksmith, with a lathe and slide rest, could put such a clock as I have described, up in almost any town, for £25, if it only struck the hour, and make very good wages. The bearings for the spindles, I forgot to mention, were fiat bars of iron, screwed to the wooden frames. The pivots work in brasses, rivotted in the bars. The pallets are made of sheet brass, and the 'scape wheel of steel. The pendulum bob is a cylinder of lead, weighing 151b.

Allow me, Sir, In conclusion, to say I like the new shape the English Mechanic has taken, and that I hope it will coutinue to be successful! 1 have subscribed from the first, and have always endeavoured to make it known to my mechanical friends.

Sydney Maddison, Hastings.

P.S.—I have no objection to indicating the place where the clock may be seen; Partney, near Spiisby, is tbe village, and the blacksmith who has charge of the clock would no donbt be glad to show It to any one who found it worth his while to go there.

I was engaged previously in putting up, in the tower of a frieud's church machinery to strike the qnni ters

on four bells, as at Westminster. It can bo done very well with six belliSy if they are in the key of E flat. I should be happy to oVseribe the machinery, together with a novel method on fixing the hammers to the bells. If it would be of Interest to your readers.

THE ILLUIKHCATED PORTION OF THE
JfiwOS'S DISC:

Sir,—I think Mr. Buwdslcyls right in not accepting the explanations already given as exhaustive; for it, when the moon la enly two days old, an imaginary Due be drawn from its centra, seal made te pass through Its surfaas in the eeurre oc the pn>c of the illuminated ant and prolonged*., la wiuluV not cut through ttaenar sit all", but wotuHE be almost at right angles spans Stall luminuiry; bat at Hue dfcawu from the eeattse of the moon, through tluut past* ectho surface whathi is in the centre of the lllaminaxaut halt ((or we ell know that one-half of tbe moon iw subsays to the sun) was prolonged; it would suit thcuiigh the centrethe sun.

.Vow. Mr, when tbe moon is about the end of Che first or third quarter, one-half of the rlltuBdnatedi portion is turned) towards the earth, the other hnH!e£ the illuminated portion is turned away; thorn sore, In this case, the centre of the whole ilurmiaatedt moon, and the centre of tbe iUuiniuared- sdgv aw scent from the earth, coincide; so that fax this part of its orbit the illuminated portion ot the moon's disc- r* fairly directed to the sun, afTiwuancd being made for optical effects. W. F. Swallow.

BREAD-MAKING.

Sir,—I cannot pass over " T. Esteo's" letter without a few words of comment upon it, as I certainly think your correspondent has never tasted good unfermeuted bread. We have used it for 21 years, and scarcely ever failed in having excellent, sweet, moist bread. As to its being injurious to the system, I think it must be far otherwise, as I am myself an invalid of many years' standing, and attribute my present state of health entirely to the use of this Dread, As regards the recipe for baking powder given by "T. K," I think the quantity of rice so large, that any one would fall to make good cakes or pastry with it. Our proportions for baking powder are as follows—viz., tartaric acid, 3oz.; bicarbonate of soda, 4 do.; ground rice, 1 do. As I cannot give tbe mode of operation of making our bread In tne space of a letter, I must refer " T. E." to the FamS.ii Friend of 1850, vol. 2, page 176, where he will had. the full particulars.

The Author Of The Article OS Unferxrhtbd

Bread In Vol. 2 or "familyFriend," 1st

Series.

'sir,—"T. Estee" makes a vital mistake in confounding fermented with uufermented bread. The latter may be kneaded into a kind of raw paste with a little water, while no amount of kneading will effect this change in the former, which, for this reason, sits more lightly on the stomach. Many persons, including the writer, cannot eat uufermenUtd oread. Yeast acts chemically on Hour, " powders " aot mechanically. Buy a shilling treatise on baking of any bookseller for theory, aud whan you have spoiled a few bakings aud brewings you will find out how good sweet Dread is made. If you value this commodity your trouble will not ba lost. Din't try to make good bread out of bad flour. Don't let rice come in contact wltb yeast New Subscriber.

CARB0RETTING GAS.

Sir,—" Adolescens " asks, at p. 645, Vol. X, If he can fit gas burners to his 4in. condenser lanterns 1 and as I have done this for some years past, I am happy to tell him how I fitted them, as " V. W.," page 659, proposes a method which 1 think would prove a very dangerous one, and 1 should like to know if he has actually used the arrangement ho describes. "Adolescens" will have to select very fine hole argand burners (.12 will be required for such powerful Ian terns as he has), and they must be fitted with a conical ring round the outside of the burner, to cause a current of air to impinge upon tbe outside of the flame, aud thus compress the flame to a smaller diameter. I have found with such burners that a common straight chimney gives the best light, but he must fit fine wire gauze under the centre of the burners to obtain a perfectly steady flame. Ordinary ooal-gas will not give a sufficiently powerful or white light tor lanterns, and must be earburetted, as described by " V. W.; " but I advise " Adolesceos " not to attempt to make a vessel inside the lanterns, as, unless be is an experienced hand, he will be very likely to have a dangerous explosion, as the heat of the lanterns in use wtsuld soon cause tbe naphtha in the tin vessel to volatilise too rapidly and burst the vessel, or make a smoky flame from excess of hydrogen vapour. A simpler and cheapor plan is to use a common glass round pickle bottle, which can stand ou the floor or table, on one side of tbe lanterns, out of the way, and the whole affair will not cost 0 1., and yet answers the purpose admirably. Two pieces of compo. pipe, each 6ln. long, must be fitted through a good bung in the mouth of the bottle, the inner end of one being flush with tbe bottom of the bung, and then curved to an elbow. The other must be thrust through the bung about ball way down the inside of the bottle, and the outer end also curved to an elbow. This will be for tbe inlet for the gas. Now tie a sponge or large- sized argand cotton wick to the inner end of the pipe, on which a plug of wood or a cork with a hole through it Is fitted tightly, so as to keep the wick distended, which will then hang down to the bottom of the bottle. Pour In about halt a piut of benzole, not rectified, but what is sold as ordinary benzole by chemists, at about Is. 6d. a pint. Then close tbe bottle, and connect tbe inlet pipe to a gas branch (after taking off the burner), and connect tbe end of the outlet pipe with the pipe leading to both lanterns. This latter connection must not be of india-rubber tubing, but either compo. or flexible tubing (to be got at all gasfitters), as tbe india-rubber

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tube absorbs the benzole sapour very rapidly, and would spoil the effect. The action of inls simple apparatus will be evident, f#r the capillary action will saturate the whole of the cotton wiek or sponge, and as the gas passes from the end of the pipe the presflure will force it through the sponge or wick, and in doing so it will take up the vapour of the benxole, for which it has great affinity. and, passing out of the tattle by the outlet, will burn in the lanterns with a very tine white light, far superior to any oil flame, and also very steady -, but this must be the result of careful experiment, and will depend on the relative length of chimney aud pressure on the gas main. I need hardly add that every joint must be made perfectly tight by cement or sealing-wax, and when done with, the remaining benzole must be emptied into a good stoppered bottle, as it is very volatile. Nothing but very fine hole burners can be used with advantage with such rich gas; and If "Adolescens " flu taps to each burner, he can dissolve without using the ordinary shutter or comb, leaving one burner Just alight, while the other is turned full up. A small hole in each lantern door with a coloured glass In it will enable him to turn on the gas to the proper height; otherwise, he will find a great waste of gas and Bad light.

"V. W." may have used his plan by careful attention, but I am confident ho Wv>uld not get a brighter light and better or more convenient arrangment than what I have described, as I have tested it frequently, and used it constantly In giving lectures, ic, for tho last six years.

Alove is a rough drawing of the bottle, but fear that I have already taken up too much of your valuable space. CDC.

BARIC CHLORATE.

Sib,—As your correspondents "Taffy" and **Pyro" may wish to have some idea as to the sort of baric chlorate they will obtain, by strictly carrying out Mr. Davis's instructions on page 10, 1 append the probable per centage composition of the crystals it will yield. If allowed to eool to 80° C, aud then the crystals collected: — Baric chlorate, 53 percent.; baric chloride, 47 per cent. 1 f allowed to cool down to 00 Centigrade i —Baric chlorate, 47 per cent.; baric chloride, 53 per c*»nt. If allowed to cool to as low as40C. :—Baric chlorate, 41 perceue. ; baric chloride, 50 per cent. If allowed to cool down as low as 20 C:—Baric chlorate, 83 percent.; baric chloride, 67 per cent. Finally, if allowed to, as most probable, cool to 10 Centigrade (50 V.):—Baric chlorate, 27 per rent.; baric chloride, 73 per cent. Therefore, most likely, the Bait obtained, eupposed to be"pure"(?) baric chlorate would consist of a mixture of 1 part of baric chlorate, and Dearly 3 parts of barln chlortde; while, if collected so as to yield the purest salt (i.e., containing only about 60 per cent, of impurities), over 00 per cent of the baric chlorate would be waster! and lost, as the mother liquid would contain from 15 to 70 per cent, of the baric chlorate formed, the exact amount depending on the temperature.

With reference to the three apparently coutradic1or/ replies furnished by Mr. Heard, Mr.'G. E. Davis, And " Ernest," concerning hypochlorlo acid, they are "all right and all wrong." U.

AGRICULTURAL IMPLEMENTS—COMSTOCK'S ROTARY SPADER.

Sir,—I am glnd to see that our old friend the EngCibh Mechanic Is so strong and vigorous. As you have lately given the millers a fair portion of your time and attention, perhaps you will be kind enough to pay the like coinplloiont to their brothers the [fanners. In looking over some papers a tew days ago 'which I brought from the Paris Exhibition, 1 found the enclosed, and the thought struck me that perhaps It might be useful to some of your subscribers; it might give some of them a hint which would set their thoughts in the right direction with regard to the improvement of agricultural implements. If you think the spader worth Insertion in your valuable pages you will greatly oblige.

S. Kent, Hastings.

COMSTOCK'S PATENT ROTART SPADER.

The spader Is designed as a substitute for the plough in preparing the ground for seed lu fields that have

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been once broken and the sod rotted. It Is not adapted to breaking prairie or meadow land, nor for land that is not comparatively free from stones, stumps, and roots.

By means of tho lever on the foot board, it Is readily put into position to work or travel, on the larm or road, and is easily controlled by any one capable of driving a team.

The teeth or tines on the fork-bars are about 7iin. apart, and when on the bar constitute what is called "a fork."

The teeth or tines of the fork are east steel, selfsharpeners, of the simplest possible form, -Sin. in length, and are secured to tho bar by a clamp, or stirrup, and wedge, and can be takeu off or pnt on in the field by any person, as each tine and stirrup will fit the fork-bar of any sized spader. Great care has been exercised In determining the strength necessary In these parts; but If broken, and no extras are at hand, may be replaced by any good blacksmith.

A team in ploughing a furrow one foot in width travels 81 miles to each acre (besides turning corners), or 16\ miles in ploughing two acres, which is a good day's work for both team and man, and is not always well done with a furrow of that width; if a narrower one ll turned, the travel 1b Increased. The tlve tine spader works three feet in width; therefore six acres are spaded to 10} miles travelled, or as much aB three pair of horses, three ploughs, and three men will do; and but 275 miles of the team Is required to spade 100 acres; making a gardm bed of the grain-field at less than half the cost of ploughing; and this may be done by any one able to sit on an easy seat and drive the team—no walking or other labour required.

The saving in expense of teams and manual labour alone soon pays the cost of a spader, even to smaller farmers.

Other advantages may be enumerated as of equal. If not greater, importance than the saving of labour and cost.

As the ground can be prepared In much less time, it may be done at the right time—and less time Is given for the soil to settle and pack, and for seeds of weeds te germioate and take root before planting.

The attention of nursery men and market gardeners is invited to the fact that by twice going over lumpy ground with] the spader the soil is better and more cheaply pulverised thaa can be done by any other process.

It will pulverise the soil and leave ft light and mellow when too wet to be worked, without damage by the plough. And on sticky Boiis, where the plough will not scour, it will do its work perfectly.

THE ADVANTAGE OF USING CRUSHED
OATS.

Sir,—The advantage of using oats, beans, peas, Ac, which have been previously crushed and partially ground into a coarse powder, is not as generally known as It should be; I therefore take this opportunity of drawing the attention of thoBe of your readers who are interested In such matters to the following pra ctical Illustration of an important fact, namely, that but little good can be expected from the best descriptions of food unless its mechanical condition 1b also attended to.

Some days ago I procured a small load of horse dung, whlah, being taken from the streets of London, was perfectly free from any loose particle of hay or straw. This manure was put in a heap in my garden, and covered over with a thin layer of earth.

In aboutj a week afterwards I was much surprised to see quite a crop of green shoots coming up on the surface soil, and on making a careful examination at the rootlets, I found that lu each case these shoots proceeded from what had originally been a sound grain of oata.

It would bo interesting to know to what extent, and under what special circumstances, oats and similar cereals are passed off unaffected by the ordinary process of digestion, Ac.

It certainly appears to me very desirable, In order to feed animals with the greatest advantage and profit, that the different kinds of food should be carefully reduced to a fine state of division, then steamed, or at least moistened, after which chaff or similar coarse

material may be mixed in proportion, as we may wish to make a more or leas bulky kind of fodder.

John Hughes, Analyst, 10, Penn-road-villas,
Uolloway, N.

NEW CARRIAGE BRAKE.

Sir,—In your excellent journal of the 28th of January last there appears a notice of a new carriage brake. On reading the description of it, I was much surprised to find that a carriage or cart brake exactly similar in every way to that now patented by Messrs. Parry and Mc Hardy was exhibited at the show of the Highland and Agricultural Society of Scotland held at Dumfries in the summer of 1800, and that to it waa awarded a premium of £10. It attracted great attention, and was universally approved of. It was made and shown by Mr. Tbos. M'Cririck, agricultural implement maker, Old Cumnock, Ayrshire, who has long been well and widely known In the south and west of Scotland for his many useful improvements and LflgflOiOOJ and original inventions In connection with agricultural machinery, but whose diffidence of disposition (which Is so frequently found allied to true and original genius) has hitherto kept him from patenting any of his many inventions; and as he has now considerably passed the allotted span of threescare years and ten his career as an inventor may be said to be over. Still it is right that he shonld not be robbed of any honour which justly belongs to him; and undoubtedly he is bus ariginal inventor of "the new carriage brake" described in your journal of the above date. Messrs. Parry and McHardy may Dot have seen Mr, M'Cririck's brake, and they may have been original inventors also; but even if such has been the case, they have been forestalled in it by Mr. M'Cririck by nearly ten years.

A photograph of the brake, and of the cart to which

it was attached was taken at the time. Could we

have obtalued a spare one, we would have encloaei it;

and we may do so yet, when more of them are taken.

A. B. Todd, Old Cumnock, Ayrshire.

THE SUN.

Sir,—The English MECHANicof the 1st April, 1870, has just come to hand, in whieh I have noticed a letter that bears the initials of "S. B.," who says he was in hopes that some of your "qualified*' correspondents would have answered " Veritas."

"The IDQSMW is a fraction." TWa is not the case, because a fraction Is a part only of a whole. If *'S. B." had stated thnt 1*0869N waB the proportion, ratio, or quotient of two distances or values, he would have been nearer the truth.

Mr. "S.B." has one fundamental error In his calculation of the mean diameter of the sun—namely, he employs the equatorial semi-diameter of the earth, whereas, he ought to have used the mean semi-diameter in order to arrive at a meau value of the sun's diameter.

1 beg to submit the following facts as given by "F.R.A.B." and "8. B.M

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BOOKBINDER'S CUTTING PRESS. Sir,—I send a Bketch of a bookbinder's cutting press, although I firmly believe it will be "LoveTa labour lost," for those whose trade it is to provide bookbinders with cutting presses do not always turn out a good press; but as " Maschll" and others have inquired about the apparatus, I thought it would perhapft be best lor the interests of "our" M EC n A > ic to comply with their wishes. Persons out of the trade seem to form the most erroneous ideas of bookbinding, gilding leather, Ac. I should much like to see some

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tightly fixed, which causes the cheek A to recede from or approach to the cheek B. G O are the heads of the two screws, through which are two holes, about I of an inch in dlam., in which the press-pin, or lever, which is about 20in. long. Is Inserted. H H are two strips of hard wood, placed about IJln. apart, for the plough to traverse in. The cutting press here eaown ii 2ft. between the screws. I I are two guide rods, (irmly fastened in the cheek B, which keep the cheek A in Its proper position. Ab Initio.

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THE '• ENGLISH" VELOCIPEDE ON A NEW

PRINCIPLE, AND OUR ENGLISH BOADS.

Snt,—For many years my attention has been directed

to the subject of velocipedes, both theoretically and

practically ; and when yonr third volume was coming

out I saw it was treated of therein, since which time

1 have been a subscriber.

1 will be aa brtet and as plain aa I can in what I am about to say, for my aim is the diffusion of clear views of the correct principles of velocipede construction, and to assist In its Inauguration as a really useful machine. I have had several machines made on different principles and designs. One, a three-wheeler, had two driving wheels, between which the rider sat. It could be worked up hill pretty well. Afterwards—thinking that if one were made for two to work, sitting back to back, it would be easier to get up hill, I bad one made for two; and what was the result? Why, the very reverse anticipated! Two could not possibly work it up anything like a bill, and, strange to say, one oould 1 This was about two years ago, since which time 1 have endeavoured 'to trace the reason of this; am! about twelve months sinoe i succeeded In what 1 thought might be Borne explanation of it. Suppose a man had to take two sack-loads of potatoes (weighing, say 5cwt) a mile, and he had before him the choice of a wheelbarrow and a truck (a two-wheel handcart) to take them with; and granting that the truck weighs a* light as the wheelbarrow, which should we suppose he would choose? Common sense would say the truck, because he could balance the load on It, and all he would have to do would be to roll or wheel It along. In the case of a wheelbairow, he would have to lift half the load he! ore tie could wheel the other half. Now, as wheeling a load Is easier than carrying a load, it Is evident that the wheelbarrow is a foolish vehicle where a truck can be used. Let us look again at the above velocipede. We see that the spokes of the driving wheels act similarly to a man's legs in a wheelbarrow, with this difference, that whereas in a wheelbarrow a man's legs have only to overcome the friction of half the load, in this machine the wheels have to be made to overcome the friction of nearly the whole of the load before it can be moved. Again, let us now look at the truck. Its two wheels act as guiding wheels, at the same time bearing the load, and the man's legs act as the spokes of a driving wheel. Now, if a velocipede were made on this principle, the question would be. Would it be easier to propel than the other? I was soon convinced that it would; and having proved It to my own satisfaction, I have laid down this maxim or principle as being the correct one iu the construction of all velocipedes—viz., that no mere weight should be placed on the driving wheel than is actually necossary for driving purposes.

To illustrate this still further, take the case of a luggage train. Suppose that instead of the locomotive drawing Its load of 200 tons behind it, the wholo of the 200 tons were to be placed right over and upon the driving wheels of the engine, what would be the consequence? Why, the power of any ordinary locomotive would most probably fail in endeavouring to overcome the enormous friction caused by the load above. Observing the above principle, I designed the following velocipede, which at a glance will be perceived to be self-adjusting as regards the load on the driving wheel. It also meets every other requirement that is looked for In the velocipede—viz.: 1st. It is light and simple in construction and working. 2nd. It Is perfectly safe, easy to work, and comfortable to ride. 3rd. It is easy to guide, and with all the wheels being free of each other, it turns sharp corners. 4tb. It has a minimum of friction consistent with a maximum of power, as both bands and feet would be used; but I never found it to require more thau the use of one hand with the feet up the fcttep.-st hill, the driving wheels not slipping.

The wheels, as will be seen In the drawing, are rather small, the driving wheel bolng only 2ft. sin . and tho others 2ft. 41n. Some will very likely think they are too small; but those who have made great use of the velocipede on all kinds of roads will never prefer thsm mush larger.

The frame of this velocipede consists of angle Iron bent In the forepart to a curve, as shown. It Is Blled In with wood. They are In four parts. One end of each goes right across a Btrong board, to the under part of which It Is bolted by two bolts. Above this board is the sest, between which is the box, secured by a lock and key. There are no springs, but a good cushion on the seat, and I can atflrin that I have not experienced the slightest unpleasantness as regards jolting, jogging, or shaking (I havo gone over rough roads); Indeed, it Is rather otherwise, for it is truly comfortable to ride, as I havo said above. Another noticeable feature in this machine is the guiding handles being placed at the sldesof the ^eat. This allows the chest more play, and gives greater opportunities of development than when the hand has to reach forward to guide.

This latter remark leads me to refer to the worker of the velocipede. It may be said that the veloclpude will never competo with the railway train as an economlser of time. It may bo so; but It can also be said that the railway train will never compete with the velocipede as a promoter of health. So the velocipede question. In this respect, resolves Itself Into these two points, time or health, not considering the saving of railway fares. Time Is no doubt valuable, but health is still jmore so—It Is Invaluablo; It Is a fortune in Itself. What truly wise man would, for the sake of saving time, always avoid opportunities of promoting his health? As vigorous health means greater capabilities for business, it Is questionable whether the right use of the velocipede is nut more favourable to the attainment of wealth than otherwise.

I will conclude what I have to say on the question in another letter, next week. A Thinker.

EXTRACTS FROM CORRESPONDENCE.

INTERESTING FACTS. —" Pneuma" writes as follows:—" In your number for March 25, page 23, is a small paragraph headed 'Interesting Facts,' among which are two or threo statements which perhaps you will allow me to correct. The German mile Is much more than 1800 ysrds. The Germau short mile is 6859 English yards, and the German long mile 10126 English yards, and the Hanoverian mile 11559.yards (see Kelly's 'Cambist'). The greatest depttrof the sea is more than 4 miles. On the 15th November, 1849, Lie-i tenant (now Captain) Maury, in tho 'Fancy,' let out 5700 fathoms of line (about 61 mile-) without finding a bottom. This was in lat. 31° 69' N. and long. 58° 43' W. This depth exceods the height of Mount Everest, In the Himalaya, by a mile. The statement respecting the English acre Is e7idently wrong. It should read 4810 square yards, being 69yds. 1ft. lOtn. each way."

"J. K. P." also writes:—" Under the above heading, on page 23, you state a Germau mile at 1806 yards. Now a German mile is what they call a 'stunde' or 'hour,' t.e., an hour's walk, and 'Adcnck's Pocket Book' gives 10126 yards, which agrees with * Chambers' Encyclopaedia,' Adcock states the Turkish mile at 1826, while you give 1026, and I havo no means of telling which Is right. A German 'short mile' is 6859 yards according to the I' Imperial Dictionary,' and la quite enough for au hour's walk for me."

DR. USSHER'S ADVICE.—Hy. Good sends us the following.—" Will you allow me to point out one or two errors In'Dr. Ussher a Advice?' First of all, It is not Dr. Ussher's. for I have now before me Cowper'e Poems, in which I pasted a label more than thirty years since, a copy of which I enclose. 1 am quite sure that It Is an oversight of the doctor to say— 'For oft-imparted knowledge doth Diminish learning's store.

You will also observe that the words 'I often lent' should be ' It often lent.' If some of your subscribers would get up a neat label of the above, either in lithography or photography, leaving a spaoe for name, I think they could find a sale for them."

VABNISH1NG THE VIOLIN. — "8t, George" writes:—"I find amber varnish to injure the tone of the violin the least of any that I have tried."

THE ENGLISH MEC HAN 10. —"An Old Subscriber" writes: —" Allow me to congratulate you on the decided improvements recently made In the English MeChanic. Issuing the index with one of the numbers, separating the advertlsementsheets from tho body of the work, giving the contents on the outside page, increasing the: size and at the same time Improving the form of the publication, giving a list of the new patents —these, with what we have had be tore, combined with a greater variety of contents, and, I think, a certain sifting of the Notes and Queries department, make the English Mechanic And Mirror Of Science the principal scientific journal published. You need not stoop to the miserable and deceptive manoeuvre of offering to give away prizes 1 for nothing,' In order to bolster up an artificial circulation; you can stand on your merits."

BENNETT'S DIE CHUCK —Edwin Baker writes :— "Will you allow ms to correct an error in last week's number, with respect to Bennett's die chuck? Mr. Bennett Invented and made that chuck whllo be was In the employ of the Messrs. Holtzapffel, and not Mr. Evans's, as it was given us to understand. I question If Mr. Bennett ever was in the employ of Mr. Evans at all,"

A GOOD BKCIP K FOR HOME-MADE YEAST OR BARM.—Place a quart of malt In some woodon vessel, boll one ounce of hops in three quarts of water one hour; when clear from the vapour arising therefrom your over the malt so as just to scald it. Cover over with thlok flannel or baize till morning, when It should have a frothy (head on; strain. Put halt-aplnt of this liquid to 71b. flour, set your sponge over night. In the morning mix and bake In the ordinary way. This is an excellent recipe, and was given me by the late Sir Charles Napier's cook. Nothing can equal the sweetness of bread made from this.—W. I.

MEDICAL OPINION—Dr. Burdwenll in a letter says:—"I love your Mechanic, but I dislike to see medical questions, and often very absurd ones, asked through It. It Is almost impossible to give an opinion without seeing the patient, and in most cases it would be dangerous to act on good avico given under such circumstances."

NAME OF STAR—"Conjecto" writes:—"Allow me to thank ' Omlcron' (page 656; for the (probable) name of the star which' I saw in conjunction with Venus on the evening of the 3rd Jan. 1 am somewhat surprised that no other mention has been made of this (to me) most Interesting sight. 1 have watched many occupations of stars by the moon but have never been so pleased as with the beautiful appearance presented by Venus and this star, which I watched from the early evening until they disappeared together behind the distant tree-tops. The star was at least as bright aa Jupiter's 3rd satellite, and shone with a steadiness quite remarkable for a fixed star."

TO MAKE GOOD BARM.—"T.S. T." says:-" Boil loz of good hops In 2 quarts of water i an hour. When strained and mllkwarm.add 41b. of brown sugar and ilb. of good mealy potatoes previously boiled and squeezed stone jar, and place by the fireside for one day and two ulghts. When it has done working put in a handful of salt, and cork the jar tight and place it In a cool place. This you may use immediately. Keep it closely corked after pouring any out. It is well to add a fresh quantity before the whole is used. It will keep as well tor use when made six months. A' about four o'clock set your barm—that Is, get two or three potatoes (or one good large one), mash them up veiy fine, put them In a sieve and strain about three pints of lukewarm water over them into a crock (throw away the remainder), thon throw tho barm down on tho too of thte, then shake a couple of handfuls of flour on the top of this and cover with a cloth and let stand before the tiro till about 9 o'clock—by this time it will have risen, aud fallen a little again. A regular quiet heat must be kept to it. At that hour throw a little salt through the flour, mix the barm well through the flour, and if too dry add a little warm water. Work it up until quite lit to put into the oven. Next morning, when well risen, divide Into loaves (two quarts of flour to a loaf) After making the loaves, lay them on the board and eover with a cloth for abeut twenty minutes. Do not shake any flour on them at night alter mixing the barm in the evening. About fourteen quarts of flour to this much barm (three pints of made barm) —Buns for breakfast: lib. of flour, whites of two eggs, 2oz. butter, two spoonsful of barm; mix together with milk to a light dough, put at the tire for one hour to rise—five minutes will bake thein. Mix as for a cake."

FREE SCHOOLS OF INDUSTRIAL ART.-A plan Is now before the Massachu9sets State Legislature, U.S., by which every town of a certain size will ho compelled to maintain, in connection with Itt town school system, an evening school for edncation in " the industrial arts." TheBe evening schools will be open two hours on five evenings In the week, with a competent masteror mistress tor every 25 pupils. Travelling loan collections of models audcastsof w>rkB of art ana design are to be formed, the expense of which wUl be borne by the commonwealth. A monthly systoii" examinations Is also proposed, with the exhibit) meritorious works.

REPLIES TO QUERIES.

ZIXC PLAKT. — In reply to "Saul Rymea's" question to me, bis idea of toe rationale is correct. All the descriptions given relate to the lead tree, and of coarse the more lead Bait there is in the water the more vigorous will bo the growth of this specimen of metallie growth. A true zinc tree would require the use of a more oxidisable metal in a zinc solution, and ns the action of such metals as magnesium, sodium-, &c., would probably be too rapid, the metal would be more likely to be thrown down as a non-adherent powder than aa coherent crystals. The process is a true electric one when the "plant" la formed, the electricity acting at the extremities of each deposited particle, and producing there the crystalline deposit. Other metals may bo thus deposited also, ana the nearer alike the affinities of the two metals are for the acl'l holding the one in solution the slower and more perfect thefactien.— Sk;ma.

[17080-HEATING GREENHOUSES BY GAS In reply to " Professional," p. 637,1 bear to say th<it I shall De glad Indeed if ho can point out a plan by which gas nujoe used in the heating of greenhouses, so that it may be done with some degree of economy. He has, however, a much better chance of doing so than I have as with him gas in charged 3s. Gd. per 1000ft, but with me It Is 0s. 3d., in Itself a mighty difference. I have long thought that our gas company t« extortionate, but they maintain that the superior quality of their pas, made from Cannel coal, makes it as cheap to the consumer as gas from other coal at half the price. This reasoning may suit their dividend of 10 per cent, pcrannumjand a bonus besides, but I must acknowledge I don't bellcvein It. "Professional " suggests that it may be the arrangement, and not the material, which onuses the failure with me. I shall endeavour as briefly as I can to explain my apparatus, and then ho may judge for himself. It consists »f a small oopper boiler connected to about 64ft. of 3ln. iron pipe. The boiler Is a cylinder, the under end, as it were, pressed in to form a conoave for the flames to pRy upon. Enveloping the boiler Is an Iron jacket allowing a space of about 2in. between it and boiler. From the top of the iron jacket a 31n. Iron flue Is carried away so as to take off the fumes of the burnt gas, and also to radiate as much heat as possible. This flue Is carried the whole length of the house, and then passed outside The gas is applied at the bottom of the boiler by three of Buusen's burners, so arranged that either one, two, or three may be lighted at one time. I find that in Bevero weather It required the whole to be lighted, and on these occasions, supposing they were lighted at at 4 o'clock in the afternoon, and were kept burning until 8 o'clock next morning—16 hours—it consume! about 100ft. of gas, which cost me 2s. 6d. The apparatus worked well and gave little or no trouble; the only drawbacks were want of heating power, except a very large quantity of gas was consumed, and the injurious effects the fumes had upon the plants. This latter objection could be remedied by keeping the gas entirely out of the house, but this would necessarily entail a certain amount of loss of heat, which could only be made Op by a greater consumption of gas. I suspeot others have come'to the same conclusion as I have done (1 notice the reply ol "J. B.," p. 12, vol II., Ac), bat if "Professional" can produce a plan by which gas may be used with a reasonable cost, and at the same time to give a sufficieacy of heat, I am sure he would confer n favour on several of us amateurs, as there is no doubt that the little attention gas requires gives it in that respect a great advantage ovor other modes of heating—Amateur,

T.f£?)j,t,p02lgla8s roR CHURCH -WINDOWS IS * IKED.—When the windows are painted with the requisite colours, they are placed in an oven much resembling the ordinary bakehouse oven. Around this oven are iron shelves, upon which aro placod'largc iron plates very level; on these plates the glass' from the windows Is placed ; the oven is then very gradually heated The heat is adapted to the nature of the colour required; if the flux is hard the heat is much greater than when soft. This requires great nicety, and perfection can only result from much practice. It sometimes happens that one or two moments of too prolongedan heat, will spoil an entire batch of window panes, turning the colour from what was intended as a bright yellow, to a dirty brown. When the oven is got to the required heat, the calculation Is made by the man who has charge of It as to the duration of the heat; this Is very care-fully watched, then when the glass has had suflldent Are, the oven Is stopped up the bars from the grate drawn out, and the whole is left to cool gradually to prevent cracking. When cool they are then washed with water, the ochre comes off the beautiful stain remains. The heat required Is a little over that of redness. Just approaching a white heat, but modified according to the nature of the colouring materials.—Joseph Leicester.

[1871.J-BLOTCHY FACE.-I have just perused Mr .Johnsona reply as abovo. in answer to a "Sufferer from Blotchy Face." It is certainly good sound advice, but not a remedy for this disagreeable ailment Jour yeare baok, having been troubled with it In a violent form, I was induced to pay a visit to the late L)r. James Seaton Smith, of Liverpool, surgeon of the Skin and Cancer Hospiial in that town, for the purpose of getting a remedy for it. His remedy was the enclosed, coupled with good and plaia diet, which put me to rights in two months. The recipe was dear (£2 2s.), But It was effectual. Let the gentleman Interested give it a trial, and kindly let me know the results through your columns. Sol. arBenlo chlorid ldr.; tinct. Jerri perohlorld. ldr.; tinct. rhu Sdr ■ llg. zarafar 4dr.; aq. pur. Uoz. Ointment—Megt plumb, iodid. lltiu-. ; to be applied outwardly. — FortuNatus.—[A friend of ours, many years since, was troubled with pimples on his face, and particularly under his eyebrows and moustaches, lie consulted several country doctors without deriving any benefit He tried the hydropathic treatment, with the same reBult. He came to London, and consulted one of the physicians of the Cutaneous Hospital, Uriil^e-street Jllackfriars, and was cured in about a fortnight; and

has not suffered from the malady from that day to this.—Ed. E. M ]

[1908.}- ETCHING RAZORS.— For H.SO, read H3S04—F. B. Knox.

[1967.]—PESTLE AND MORTAR.-Sulphurlc acid is the best thing he can use.—A Mechanic.

[1070.]—VARNISH FOR IRON PATTERNS. — "N. L." gives an excellent reply to this query, but he forgot to say that it was raw linseed oil that should be used, brushed on (like paint. Should the pattern be required for almost immediate use, coal tar naphtha is very good, and it dries quickly without heat.—Metal Head.

[2007.] —TEMPERING DRILLS. — Surely your printer must have misread "S. T.'s" answer, which Is exactly the opposite to what he must have meant to state, and which, Bo far from hardening drills, would anneal and soften them. Let me add to my former reply to this query: That for small drills, say to

—in. diameter, a eandle is the most convenient

16

means of letting down the temper, as the mild heat

eauses the colour to change so gradually that the exact

tiut can be obtained with certainty.—J. B.

[201:t.]-MULTITUBULAR BOILERS.—Tubes ia boilers of this kind should have a ring on one end, say |ln. thick; the ring may bo put iu the end of the boiler first, and caulked. In ordering the tubes, he could order them bulged at the factory, about l-16in. The advantage of the ring is that if the tubes should scale they cau be knocked out from one end. — Millv.

[2043,]—PILLS.—Not only pills, but (that most nauseous form of medicine) powders may be taken by any one without the least difficulty. Buy at any coufectlonors asheet of the wafer that they use lor ratifees, costing one halfpenny. This is 8 or 9in. sq, and is to De broken up Into squares of an loch arid half or two inches. Take one of these, dip it in water, and lay it ou the palm of the hand, where it Instantly becomes as limp aB a rag and as slippery as an oyster. Lay your one or more pills, or your powders, in the oeiitre, and fold the wafer over It, put It on the tongue where It lies flat, like an oyster, and a sup of watctakes It down without taste or trouble. This method Ib always practised In Germany, and has been in use in my house for twenty years, and, strange to say, I have never met any person, medical man, or druggist in England who seemed to have ever heard or it. ft Is perfectly effective, within reach of the poorest, and ought to be more generally known.—G. Nash, S. Michael's Vicarage, Louth.

[2044.J-REPOLISHING STEEL WATCH CHAIN. —" H.B.M." should rub his chain between his hands, dusting them with fine flour of emery from time to time; he will soon get it tolerably bright, then fasten it to his bunch of keys which be carries in his pocket, and the chain will soon become burnished. Proved.

[2055.]—COIN OR COUNTER.—My statement on p. 20 is incorrect; as stated by Mr. Batty, the pieces referred to are certainly weights.—Hrnry W. Henfbxv. M.N S.. Ac., Ac.

[2050.J-CEMENT FOR AQUARIUM.-l Indiarubber, 12 mineral naphtha or coal tar heated together, add 20 of pounded shellac. When required to be used heat to about 260".—Blue Ruin.

[2062.]—SODA WATER BOTTLING MACHINE. —Seeing no one answer T Harding, 1 will endeavour to do so myself. In the first place his leathers are loo thin, and the hole in the washsr should not be smaller than the cone where the corks are put In; again, have them screwed up tight. I have been in the habit of buying a soldier's belt (an old one), and making tbem myself. One lasts mo nearly two years. Since I have used them, now nearly ten years, I have never had the bother T. H. complains of If he wants any further information, I shall be glad to give It—J. T. Bailey.

[2058.]-CONTENT OF IRON PANS.-In auswer to "J. R.; W," taking the depth of the pan as A, diameter as </. and V as cubia.il content of pau, v - 3-1416.

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Blue Ruin. [2084.]—GRANITIC PAINT.-" S. T," In his reply lu your last weck't* number, is in error as to this paint. He states that the menstruum employed In it is silicate of potash, to harden and combine it with the pigment with which it is admixed. The granitic paint of the Silicate Zoplssa Composition and Granitic Paint Company, of 3»a, King William-street, City, contains no silicate of potash, and is well known to dry and harden in a manner superior to any paint yet manufactured. The statement of "S. T," if uncontradicted, might do us great injury.—Thomas Child, Manager.

[2093.]-BRAZING CAST IRON.-The only method of brazing cast iron is to fit the broken parts exactly together in moulding Band, then pour melted iron over the parts to be Joined, and when cool chip off the superfluous Iron. If properly done the joints will be diffi-ult to detect—blue Ruin.

[20!>».]-SUBMARINE LAMP, Ac—I send the following reply to the second question of •• A Diver" under this heading, viz., to find the solid contents of'a vessel with semicircular ends:—

Lot I = Full length of vessel
d = Diameter „ „
t = Solidity „
Then ""

t = d> x -2018 (3 I - rf),
Or, in words:

From three times the total length of vessel subtract its diameter, multiply the result by the square of the diameter and by -2618 for the solidity.

If I = 10ft., and d = 4ft., we have
a = 16 x -2618 (:)0 - 4)
= 16 x -2018 y. 2tS
= 10S9088 cubic feet.

The content may also be found bv obtaining the solidity of the middle cylindrical part, then that »f the semicircular ends, and adding the two results together; but I think "A Diver" will find the rule given above more concise. — William Moor, Jan., Hetton Colliery.

[2097.J-STAINING WOOD BLACK.—Boll lib. of chip logwood in 2 quarts of water, add loz. of imrl-a-u, and apply it hot to the work with a brush. Then take 41b. of logwood, boll it aa before In 2 quarts of water, and add joz. of verdigris, and ioz of copperas; strain It off. put in Jib. of rusty steel filings, with this go over the work a second time. Oil of vitriol diluted with water and applied with a brush makes a good black atain.— Guillaume.

[2098 ]—DISCONNECTING STEAM PIPES.—Putting brown paper between tho flanges and the indiarubber washer will keep it from adhering to the iron. I have found this to answer well.—Aberdeen MeChanic.

[209S.]-DISCON\ECTING STEAM PIPES.-Canvas steeped in red lead is frequently used instead of India rubber; or if the flanges have been faced, a little plain red lead will do. Another way.—Steep plaited gasket in whitelead, and by working it in the hand It may be used several times; or, Instead of whitelead mix blacklead with boiling oil into a paste and work well Into the gasket; if the flanges are rough or uneven, equal parts of redload and whitelead with fine metal borings. In using gasket, canvas, Ac, care should be taken that the cuds do not overlap, but meet nicely. —Blue Ruin.

[2110.]—TO REMOVE RUST.—Plunge the hooks into a bath of diluted hydroehlorie (muriatic) acid, say 1 pint of acid to 1 quart of water. Leave them there for twenty-four hours, then take them out and rut) them well with a scrubbing brush. The oxide will come off like dirt under the action of soap. Shoult any rust still remain, aB It Is likely In thetcorroded parts, return the hooks to the bath a few hours more, and repeat scrubbing. Afterwards well wash In plum water several times and thoroughly dry before a fire. Lastly, a little rubblngwlth oil and fine emery pswder will restore the polish. Should grease have mingled with the rust, It is necessary to remove it wi-li a hot solution of soda, before submitting the metal to the acid.—Guillaume.

[2116.]-WATER POWER.-I find that my answer to this question last week had reference to 200 cubic feet of water per minute falling from a height of 30ft.. whereas the question was: What would be the power of 200 gallons per minute falling from that height? The answer skould have been 1] h p., reduced to a useful effect of 1 — b,p.—C. S. 6 [2117.]-CEMENT FOR IRON ROOM.—" T. S. H." will lind tho following to auswer his ^urpeae: 1 bushel of sand, 41b. of red lead, lib. of whiting; mix up with boiled linseed oil and a little boiling water.—Sweep Ho.

r2119.]-CLEANlNG PIANO KEYS AND TEETH. —If the discolouration docs not extend much below the surface, the Ivory may be scraped till something like its original condition is obtained, then smoothed with very fmo glass paper, aud finally polished with a leather buff and whiting. As to teeth. If " Ilex " means natural ones, which have simply obeyed the laws of nature, 1 with him should be glad to know of any means to restore their pristine whiteness without injury to their present or future usefulness, bu*such a remedy I fear, will be as easily obtained as a mill for grinding old age Into youth.—F. F. C.

[212l.]-BOILER TAP.-Had "Glider" followed the suggestion of some of our correspondents, adding "proved," he could not have recommended emery and oil. It will not stop the leaking, but mako the tap useless. Let" R A."pound apiece of freestone, and sifr it through a piece of coarse pack«hev-t. Mix this with water and grind it, adding n» sand, but keeping the plug wet for five minutes before drying the plug and bill. This, if properly dune, will make the tap perfectly tight. Proved—Conical Plug.

[2121.J-BOILER TAP.—I should advise "R A." to take his tap out—he may do so with a hammer and chisel—and apply to J. Blakuborough for a patent tap^ which ho may fix himself. It will not leak for years; and then it can be made good without taking it oil. Address J. Blakeborough, Commercial Brassworks, Brlghouse. Yorkshire.—Sweep Ho.

[2126.]^J0INING WIRE.—"K. H. B." will make the best connection by first cleaning or scrapmcr with an old knife three or four inches of the wire ends; cross them at right angles, hold firm with a pair of pliers, and twist the ends tight around each other; then solder with rosin.—Sweep Ho.

[2131.]—PUMPS.-Inrcplyto * Plumber,"although this does not seem to mo to bo plumber's work, a turbine may be made to receive a supplv of from 40 to 50 gallons per minute (say 45) with a fall of 8ft, and to deliver water at a height of 70ft. above it at the rate of .Igalious per minute. This Is a small quantity, but it is as much as can be dono with the power and under the circumstances named, A water ram would be a more suitable appliance, and would cost less. It would deliver about the uui; quantity—C. 8.

[2139]-BOILER.—If John Jones willstato. through the Mechanic, the length and diameter of the boiler ho Intends to put down, and what is the greatest height be can put his water-tank from his steam boiler, and the pressure r.f steam at its highest point, I wilt send him a rough sketch of a self-acting feed that I have at work at present on two boilers workiug at l.'lb. per square Inch Anti-egyptian.

[2143.]-SOFTENING CAST IRON—" G. B. K. eanuot soften cast iron. But by chipping off the surface or skin with a chisel he will flud it easier to cut —Blue Ruin.

[2152.]-PAINT ON BICYCLES.-Grind tho drv colour; thicken with good pale copal varulsh, then thin with turpentine; lay on evenly with commou paint brush. ThlB should have very dull appearance, and dry very hard. When thoroughly dry, varnish with go«d pale copal (or carriage) varulsh; put In a watio.

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plae*, and away from dut (afler varnishing), until thoroughly dry.—W. H.

piieo] -PRESSURE ON COLUMNS.—If" W. R. E.-' will give the length of columns, and state whether tteyare compose i of cast or wrought iron, I shall be happy to answer htm—Blob Ruin.

noo]—PRESSURE ON COLUMNS.—This questloii cannot be completely answered In its present form as the weight of the columns t» not given. 1 he following figures, from the " Engineer's Pocket Cook. may, perhaps, suffice:— Solid cast-iron columns, 3{iu. diameter, will each bear— Heifftu In feet | 6 I

10 I 12

Load in cwta. I 282 1 214 I 191 I 173 I 158 I 136 -J. 11.

[•M60]—PRESSURE ON COLUMNS.—According to Molesworth, the breaklug-losd distributed equally on jr« 3i all four columns = 59 6 whereby L is the length

L of a column, assuming L to be greater than 15 times the diameter of the column. The calculation is easily carried out by means of logarithms.—A. Tolhausen.

[2162.]—SEAMSOFHACKINTOSH.-IfG. W D." will refer to reply 1777, page 613, Vol. X., he will find that 1 there stated that I found " Kay's Coagullne" (Kay, Bros., Stockport, 6d. per bottle) answer my purpose inmendingthe seamsofmymackintosh,which statement I confirm.—W. H. I. P.

12102.]—SEAMS OF MACINTOSH.—Nothing is better than India rubber dissolved In naphtha.—J. B.

[2169.]—PROBLEM.—Through A draw A F parallel

[graphic]

to B C, and equal to the difference between A C and A B. Join O and F, and produce C F and A B to meet In Q. Bisect b C in II, and join G H by a line cnttlng A C In K Through E draw D K I parallel to B C, and L> K is the required line. For sinco AF = AC-AB, and the triangles A C F and BCI are similar, as also A I) E and ABC, KI=KC-DB. But since B 11 = II C, and D I Is parallel tn B C .-. D E = E I. Then D E = K C - 1) IS as required.— T. Brown.

[2170.1—AN UNANSWERED QUERY.—I beg to inform " (litcue Manlto" that I replied to this question uue time ago. It is tue opinion of the best numismatists that copper soma should be left alone, or at most simply washed with soap and water. Cleaned or coloured copper coins arc quite worthless.--henry W. Henphev, M.N.S., &c, Jtc, Markuun House, Brighton. (21711J-UWANSWEBED QUERY-Dissolve small quantity of corrosive sublimate in vinegar; dip or place copper coins therein; wipe dry, and finish with bUcklead, using common stove brush.—W. II.

[2176.]—BLAST FAN.—The proportions I sent '• Fan Blast "if. 583, Vol. X.) are suitable for a smith's forge. Let •' C. T." look at them, and If he cannot get on with them I shall be very glad to help him all that I can.—John W. Bedford.

[.•173.]—CIRCULAR DISC.-Areas of ciroles vary as the squares of their radii: as, therefore, 86 is the square of 61n. (the radios of the given circle), theradluB of the disc which Is to cover half the area must be the square root of 18, or4-24264071u.—J. B.

[217a]—CIRCULAR DISC-If "Indagator".' will inscribe a square in a circle of the diameter of the orifice— viz., 1ft, the side of the sqnare will be the diameter of the required discs = 81853ln. Or. if he will square the diameter of the orifice, lain, x 12in = 144 ; take half the product 721n., extract its square root = 8'4853in. because the areas of circles are to each other as the squares of their diameter. —S. B.

[21S0.]-E.HGINEER1NG IN GERMANY.—There are several engineering colleges — Polytechalsc he Sehnlen—on the Continent that have attained a worldwide famo. In these colleges very little knowledge of mathematics is required to pass the examination in the preliminary course—Voraehule—and in four or five years' study the studont can have gone through the various branches of engineering, theoretically and practically, the latter shown by excursions, if steady and diligent. Age required. 17; and yearly school-fee, PA. Establishments of this kind exist in Berlin, Karlsruhe, Hanover, Munich, Stuttgart, Vienna, Zurich, Ac. Should any young gentleman entertain the idea of studying there, I can give him further information. Lastly, the x area of the sector is = 450 squaro feet.—A Tolhausen, 18, Waterloo-road, Manchester.

[2182.J-COXSTRUCTING COILS.—" Nemo" will require about 40 yards of No. 1ft primary wire; but for a coll the size he purposes makiug it would be better to use No. 12. Tho number of sheets of foil to the pound of course depends upon its thickness; the best foil, however, runs about 00 sheets lit squaro to sbe pouud. If the coil is well constructed the maximum spark will be about 6in. long. The number of bottle batteries requstte will depend on the surface of carbon exposed: he will probably require five or six colls. The secondary wire should be first covered with silk and have some insulating material, in a fluid state, brushed over each layer as it is wound on the coil. 1'h in paper saturated with paraffin wax may be substituted tor gutta-percha tissue. The silk used for covering wire differs from ordinary silk in not being twisted.—J. D. M.

[2183.1 — TAXIDERMY. — The Taxidermist's Manual," Ac. by CupL Thomas Brown, F.L.8., published by A. FullartonaudCo., London. Price 3s. 6d.

I).—WlLLlNU.

[2183.]—TAXIDKRMY.—There area few chapters on the above, as well as on skinning nnd preserving birds, reptiles, fishes, 4sc at the end of "Beeton's Book of Birds." which may bo ordered through any bookseller.—Vivis Sperandum.

[21840 — SULPHATE OF LEAD BATTERY.— Some time ago I decided to fit up my house with some half a dozen electric bells. I got all the apparatus 1 required from a firm at Halifax, except the battery, but took some time to consider this matter, as I wanted one which would fulfil two conditions—cheapness and constancy. I at last decided upon a sulphate of lead, one which I must say has answered perfectly both. 1 made it up myself as follows:—I obtained 6 glass

Sickle jars and 6 porous cells, I then made 6 cyliners of thick sheet zinc to go easily into tha glass cells. I got sooso No. 8 copper wire and wound intospirala to fit loosely into the porous pots. After placing them all in their proper places I mixed up some sulphate of lead with water and nearly filled eaoh porous pot. I then filled each glass cell within an inch and a half of the top with clean water, adding some crystals of Tillman's sea salt, and after connecting the copper spirals of the one cell to the sloe cylinders «f the next all through the series, leaving a zino unconnected at ono end and a copper unconnected at the other end, it was all ready for use. I placed it upon a shell' at the top of my cellar and connected the wires communicating with my six rooms and bells. It is now nine months since It was set going and appears as good now as at first. It cost me for material about 15s,, the cells are quart size, I am very proud of my handiwork, and believo it quite as goad and far cheaper than tho trade would have supplied me.—A Gooo Bor.

[2188.]—VELOCIPEDES, Ac. — In every case a driving wheel above 361n. becomes a disadvantage; the greater the diameter of the wheel above 361n. the greater the disadvantage. Treading is the best mode of driving, for when tho foot Is pressed on the treadle the weight of body then ceases to be the load and becomes the propelling power. As a crank 6lo. In depth Is quite sufficient for working the.foot, so adriving wheel more than o61n. will be too great a leverage for that crank; and what is gained by a larger wheel down an incline is lost with more when on a bad road or ascending a hill. Sit as close to the driving wheel as possible, that tho pressure may be on it; enough pressure ou tho guiding wheel to steady it is sufficient. Regulate the height of your seat according to the depth of your treadle, so that when you are on your seat, and your legs straightened down, tho loot may just fairly reach the treadle when it is at its extreme downwards. I would use two oonneotlng rods—one on each side. Let them be your treadles, pivot them to the crank of the driving wheel (the hind oae), also to the crank through the frame between the wheels. Let each crank be of equal length that the treadles may work in unison—oue handle to guide with, another for the brake; also a projecting bit close by the brake handle to steady yourself with (this is for driving the hind wheel). Perhaps you may glean something from these suggestions. I think we may yet improve the veloce. I have been a velocipedlst more than 20 years, and I consider as yet it has been altered and not Improved. The bicycle Is fit for none but those who aro fond of dangerous sports. Driving the front wheel of a tricycle, sitting so far lroin It, and dragging two behind. It Is a mistake. Driving by levers pivoted near tho front wheel Is a mistake. A four-wheeled veloco Is the best.—N. G. Lamdorne.

[2195.]—SMOKELESS LAMPS.—I beg to Inform "Practical " that the cone must be made to fit the lamp; that is to say, it is to stand upon the gallery and reaoh up to that part of the wick just going to burn, leaving an air passage at top about i free, as shown In my section, page 458. It must, moreover, bo adjusted to each lamp so as to produce the best effect. The ball should be about the diameter of the round wick, also adjustable as to height for best effect. Hollow balls of brass or Iron may bo got of the proper size at any metal shop. Tho cone prevents tho air passing through the pierced bottom of tho gallery getting into tho gloss globe, and must not therefore be pierced, r or raising and lowering the wiek, ' Practical" must look at any well make round wick colza lamp, or, argand burner. Upon the whole, as " Practical " does not seem to be well acquainted with this subject, 1 should advise him to apply to a practical lamp manufacturer who will at once understand my section.— Henry W. Keveley, Reading.

[2200.] -STEAM LAUNCH.-An engine working np to 8-horse would be about the power required for the boat mentioned by " Solicitor." I should recommend a vertical boiler for two reasons. Firstly, they are much more convenient to get at for cleaning and repairs—a most Important point where salt water only is used and, secondly, the tubes are not so likely to be un covered by the water lu consequence of the pltohlngof the boat in arough sea. The boiler should be made of the best material and capable of standing at least 801b. working pressure. The engines should have double cylinders and be fitted with reversing gear. Is not Oft. beam rather to much for n boat only 30ft. long .» About 7ft.,I should say. would be a better proposition. I shall be happy to give " Solicitor " any further information should he require It.—Canon.

[2204.]—PROBLEM—If "W. B. S." considers h Is problem, ho will see that it resolves Itself into finding the height of a cylindor of water weighing 25 lb., and standing on a circular base 121n. diameter. I think he can work this. With regard to his second question (2205), the atmospheric pressuro per inch which sustains 301n. of mercury In the barometer Is tbe weight of 30 cubic inches of mercury. A table of specific gravittos will inform him that a cubic foot of mercury weighs about 13G00oz. From this he can calculate the pressure required.—Pneuma.

[2208.]—CERAMIC MANUFACTURE.—The treatise on porcelain in Lardner's "Cyclopedia," which may generally be bought at bookstalls for about 2s. 6d., contains an account of the colours used lu painting aud priutiug. There arc several editions of Brongniart, but no cheap one. Tho way 1 pick up my books at a low price is by reading the :atalogues of dealers In secondhand books, or Bale catalogues; although I

have sometimes to wait a oon«iderable time, I generally manage to get What I am in search oL—H. B. Miller.

i2215.]-BRONZINGBRASS.—Some time since, I asked through these columns bow to bronze tbe ferrules of fishing rods, without eliciting any reply, I fortunately found a tradesman who kindly told me, and I succeeded perfectly In glrrng the brass an appearance of real bronze. The recipe is. Id. of oxide of Iron (rust), Id. of arsenic, mixed tn 4 a pint of hydrochloric aold. Clean the brass well to get rid of lacquer or grease, and apply with a brash until the desired colour is obtained. Stop the process by oiling well, whon it may be varnished or clear lacquered.—Vivis Sperandum.

[2218.J-GEOMETRY.—Theor.: three circles being given, the lines respectively tangent to 2 of them have their intersections ou the same straight line. "X. X." asks a geometrical proof: perhaps the foliowlag might satisfy him Draw a plane through the 2 centres ; on each side of this plane wc can construct one tangent to the 3 spheres constructed on theelrclcs; these 2 symmetrical planes will cut the plane of the centres on the same line. Now, supposing 3 cones respectively tangent to 2 adheres, those 3 cones will be langent to the 2 planes, and have their vertices on their line of Intersection, and those vertices are the Intersections of the tangents to the circles. Other demonstration. Analytic, r. Salmon, "Conic Sections," No. 117 — Bernardin.

[2220 ]—SOLDERING—File the end of tho Iron pipe bright, then see that the soldering iron (which should be as large a one as can be got, so that It may carry a great amount of heat) is well tinned ; this is important in all soldering operations. When the Iron has been in use some time after tinning, or when it has been made too hot, the solder and the copper become melted together and the solder seems to eat holes In the copper, lu this state the Iron is not fit for use, but must be filed down smooth and re-tinned. Having the iron ready, and as hot as it will bear, take ana wet tbe part to be tinned with a little spirits of salt that has had as much zinc chippings put in It as it will dissolve, then apply the solder with tbe iron, bearing in mind that the pipe will have to bo very hot with the iron before it will tin; it would be as well to tin the iron pipe with a little block tin or pewter, If available. If any difficulty is found in tinning tbe Iron pipe a little powdered salammonisc might be sprinkled over it when very hot, which would assist the tinning; this done, the lead pipe must be widened out so as to form a lip all round the Iron pipe, and soldered round with line solder,taking oaro to keep the heat of the Iron on the iron pipe rather than the lead, or what is called a plumber's joint may be mode by pouring on a quantity of plumbers' solder from a ladle, and wiping off the superfluous solder with a greased cloth. For an amateur the first plan will be the most simple.—

SlGISMUND,

[2221.]—BOILER.—In reply to Inquiries from "Ono in a Fix" respecting the use of Carrigeen moss to prevent the Incrustation of boilers, I was recommended to use It by an inspector of boilers. I do not see any reason why It should not bo put in feed cistern and drawn directly to boiler, provided there is no overflow from cistern that would carry off the moss as waste. The quantity I would recommend for 60-horse boiler would be a stone weight per week (the present cost of the moss is about £10 per ton hero in Ireland). I cannot speak of Its merits as a purgative of a very foul boiler, as 1 never allow a scale to get on mine -, but I do think from using It that it prevents the formation, nnd I am certain that It is a very harmless article.— Vivis Sperandum.

[2225.]—VACUUM IN CYLINDER.—The exhaust steam leaving a high pressure cylinder csuses no vacuum, but, on the contrary, should the passage be too small it often causes back prefsuie and compression on tne return stroke by not fully and easily exhausting.—H. Sumner.

[2227.]—LIFE PKESiiRVERS.— Thn life preservers found on all sea-going vessels are composed of siloes of cork, neatly arranged and compressed together so as to form a zone 30" in diameter. 0' in width, an* 4' in thickness ; it contains about 121b. of cork, is generally covered with painted canvas, and will support 6 persons. Inflated belts are liable to get punctured, and Bo tendered useless.—Vivia Sperandum.

[22.7.]—LIFE-BELT.—" Avslonensis" would find "the buoyant waistcoat" made by tho "Aquatio Safety Company "better for boating than any of the ordinary life belts. My friends say thoy are the best and most portable things of the kind yet out.— W. U. I. P.

[2228] — ADDRESSES WANTED. — If "Foreign Correspondent" will got the "Mineral Statistics of Great Britain and Ireland," by Robert Hunt, F.R.S.,

Eublished by Longmans, Oraen. Reader, and Dyer, and y Stanford, Charlngcross, price 2s., he will find the name of every colliery in the United Kingdom and where situated, and owner's name, besides a quantity at other useful information.—S. W. T.

[2233.J — STAINED GLASS. —A small treatise on "Olass 'Is contained In Vol. 115 of Lardner's "Cabinet Cyclopaedia:" after this, study the works of the late Charles Winston, to whom every glass painter is deeply indebted for the untiring attention bestowed oa this art, from 1830 until his lameutod death iu 1884. They prlncipally consist of "An Introduction to the Study of Painted Glass, with Remarks on Modern Glass Painting" 184u Parker; ".Memoirs Illustrative of the Art of Glass Painting," 1665, Murray; "An Inquiry into the Difference of Style Observable In Ancient Glass Paintings, especially in England, with Uiuts on Glass Painting," 2ud edition, 2 parts, 1867, Parker and Co. "Proba est materia, si probuni adulbeas artifleem.''— Erasmus. I trust this reply may not prevent Mr. Leicester from rendering his highly-valued assistance. —H. B. Miller.

[22340-FROM "JUPITER."—My 3In. glass >as got from 8. and B. Solomon's, 39, Albemarlc-street, London; price, on pillarand claw-stanf, «5. It has one day eyepiece abaut 40 power, and one night-power 100 bat 1 have addod several othors stn-e—20, DO, 75, (100 dayoyo piece), isoaud 275. The latter works very

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