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"to find tie portion of the power employed which is used in

te P' we have, as above

■in. 0 + <?)

Y = 2Q x --: •

cos. p

Now if P b« the driving pressure on a smooth wedge harm" the same angle, which exerts the same pressure, li, as the rough wedge, we have, iuaju>x f> = 0 m the above

formula,

P = 2(J sin. i.

Dividing the Utter by the former wo obtain

P sin. i cos. i

P' sin. (i + ^j

Example IS—A wrought iron wedge whose angle of cleavage is 7" is forced into a mass of oak. It is required to find what fraction of the driving pressure is consumed by friction, the angle of friction being 31° SO7.

i = 8" 39', t> = 31° 80/
Calculating by the tab-cs we find
p

— = 0 09 nearly, or P' = IIP
P

produce the ns sec that although the efficacy of the wedge is due to friction, still in this, as in every other case, friction diminishes the effects of forces applied to machines.

We shall now pass to the dynamical theory of the action of tic wedge, and snopose lhat the blow is caused by a given weight r falling ihrough a given number of feet h. This weight at the instant of striking the back of the wedge has accumulated in it an amount of work or energy represented by P h, or, if v be the velocity in feet per second of P al the instant of striking the wedge, the number of units of work stored up in it is represented by the well known formulu P x r' »'■"

— since ft = —. Now this energy is expended in over2j 2o"

comiag the tendency of the resisting surfaces to collapse, in overcoming the friction, in compressing lioth the weight itself and the wedge, and in giving motion to each.

Or, representing the useful work gained, which is equal to 5Q x L> E by U, we have

P t» sin. i cos. <p

U = x •

ig sin. l» + $)

Since U = 5Q. x D E. and U is a definite amount of useful work, when 1) E is very small Q will lie very great. This accounts for the enormous resistances which the wedge can overcome when driven by blows.

In the equation

Work employed = P ft,

it is clear that we can increase the work done by increasing P or by increasing ft. that is, by increasing Ilia weight of the hammer, or by increasing its velocity, but it is found in practice that a better result is obtained by incrcasiog the velocity than bv increasing the weight. This has been accounted for by supposing that a rapid blow causes a tremor of the substances, and momenta; ily destroys the friction.

1 shall now conclude this article with the following example:— . , „ , ...

Example 12.—The ends of an iron girder, 30 tons weight, resting on two granite piers, are simultaneously raised hy means of wrought iron wedges, in the form of a right-angled triangle whose height is lin. These wedges are driven home bv 2i blows each of a hummer weighing 1411).. and which is moving at the rate of Hift. per second at the instant of striking the wedge. Find how much work is expended on prejudicial resistances, including friction, Sw.

The number of units of work developed hy one hammer in the 25 blows is equal to

40 x 40

25 x 14 x = 8750

S x 32

Now if there were no prejudicial resistances, this amount or work should have rained a weight of U times tins number of foot pounds, or 1U.VJ00 to the height of lin. (which lathe height the girder is raised), but from the question each wedge onlv raises 15 tuns or o.WUb. to the heiglit1 of one inch, therefore the work lost by triction, &c., is 10500 0 - S3606 = 714001b. raised lin. or li'JM foot pounds, or about ij of the total work expended.

(ToJeconfinued.)

I i

Ex . Express as a decimal .'

Here write down the whole number and numerator as a wlmlenumber,thus5 and 4.counting theuumber otnougldtia he denominator, one. then mark otf cue figure from the right as a decimal, thus, 54. 15

Ex. Express as a decimal.

1000 As above, write 15, tho number of noughts is three, therefore mark off three places from the right. There are, however, only two, and we must prclix a nought, as -015, to make three.

2510013

Ex. Express ■ as a decimal,

1000 2510015 is'he answer, t 36. It will thus be Been that a decimal is simply a fraction with a denomination, 10, or some power of It); this denominator never being written but always understoodAnother fact should also lie noticed, viz., that unlike a wholo number, to add noughts to ilie right of decimals does not

niter their value, thus "1 remains equivalent to — even when

10 written -1O0O0O, but if we aid noughts to the left the value

1 1

is altered, thus '1 = —.but '01 = ——, Sec, Sec.

io liw

fTo Br continued.)

MATHEMATICS. Br C. H. W. Bioos. CHAPTER III.

DECIMALS.

'Continued from page 5 8 Units.

Or, in words, ten times the force required to produce pressure Q is expended in overcoming friction. We thns

j 33. | | | | | | | | . In the number 1111 to tho left

of the vertical line above we observe that as the value of the tens, place tis ten times that of the units, and that of the hundreds ten times that of tens, and so on, conversely tho value of the units' place it one-tenth that of the tens', one-hundredth that of the hundreds', and so on. Now, if we write digits to the right of the units' place, and agree that the law just noticed shall hold for the value represented by them, it is plain that the tirsl to the right of the units will he ouc oiietenth of the unit, the second will be one one-hundredth, and so on—* e., a series of ones written after the units' place will

1 1 1 represent the fraction! one —, one , one . Sic.

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In iig. 14, let the dotted Hues A' B' C represent the position of the wedge ABC after it has received a blow. Now, as the resisting surfaces are supposed to move in a horizontal directum only, if D be the point of application of the mutual rjonnai pressure before the blow, D' must be the corresponding point after, therefore the normal resistance, which we shall call Q, has been overcome through the space D E in its direction, therefore the work expended on Q is equal to Q x DE. Alio, in consequence of the blow, the point Don the wedge has been moved to H (vertically under D), therefore the ■pace passed over by the rubbing surface in the direction in tchtchfrictimartt is equal to E II, but E H = D E cot. i, aince i. 11 U = i, therefore the work expanded on friction is equal to a Q x 1) E cot. i, and neglecting the mutual collision of the weight and wedge, Ac, we must have

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where the nnmber of noughts succeeding the one in the denominator is the same as the number of places to the rijht of the units'place. A. period called the decimal point is placed after the unit's hgure to show tit what point tne Pactional part of the number begins. Thus Wi means one whole number and two tenths plus rive hundredths—i.e., twenty

35 31 five hundredths'. -035 means . Conversely must

1000 100000

751 be represented decimally, thus, •00011, and thus 751,

whence the following rule—

4 34 Toexpressadeciuialfractionintlieformofavulgarfraction. For the numerator set down the digits of the decimal fraction as if thev formed the whole number, and for the denominator set down one followed by as many ciphers as there are places in the decimal.

Ex. K.tpress^'yl us a vulgar fraction.

It must be remembered lhat it whole number is a whole number whether expressed attached to a decimal or uilgar fraction.

Then 1st we have the whole number 2

Ii"nd „ the decimal "51

Which setdown 2il

Underline and write 100

one followed by two noughts, because there arc two places of decimals iu the given number.

3rd. The whole answer being , or 2 .

100 luo

Ex. Express -0010101 as a vulgar fraction.

Here write 1010L us a whole number.

Underline KiUOOOOO
Then write one followed by seen noughts, as above.
Ex. Express o53'U;l as a vulgar fractiou.

< 3

353 = the answer.

100 Ex. Express 55 as a vulgar fraction.

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sin i cos.

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LETTERS TO THE EDITOR.

[Wo do not hold ourselves responsible for the opinions of our correspondents. The Kditob respectfully requests that nil communications should be drawn, up as briefly as possible.] *.* All communications should be addressed to tho

Kditob of the English Mechanic, :u, Tuvlstock

street, t'oveni. Garden, W.C.

All cheques and Post Office Orders to be made payable to J. l'ASSMORE KDWARD9.

I would have every one write what he knows, and as much as lie knows, but no more; nud that not In this only, but In all other subjects: For such a pertou may have some particular knowledge and experience uf the nature of such a persou or such a fountain, that, as to other things, knows no more than what everybody does, and yet to keep a clutter with ihis little pitta'nee of Ms, will undertake to write the wholo body of pliysieks: a vice from whence great inconveniences derive their original. —Montaigne'* Essays.

TURRET CLOCKS.

Sir —The interest manifested by your readers in tho above'subject induces tne lo send you the specification of Jlr. H. W. Cook, of Ovlngtou-equare, London, describing his recent improvements In the construction of turret clocks. Striker.

Tlio object of the invention is to dispense with a large portion of the oidinnry clock-work gearing. with its attendant expense, and, in fact to elimrnate from the clock all the wheels which come before that which nctunlly drives the hands. This gearing in a clock of the ordlnnry construction, but actuated according to this invention, will consist of three wheels — namely. Brat, one which goes round once an hour; second, the escapement wheel; and, third, a wheel connecting the other two. The wheels and driving gear are arranged iu the manner shown in the accompanying drawing, In which Fl^'. 1 represents an elevation of a turret clock constructed according to the Improvements, and provided with striking gear j Fig. ■.' Is a side view of tho same. It will be seen that to the axles of the central wheel o (on the axle of which the hour hand is mounted) is applied a water wheel, which Is driven by a flow of water from a suitable reservoir above. This water wheel inny be of any convenient construction, but the form most suitable for this purpose, und which is shown in the drawings, consists of lour or more pipes, 6 ft, radiating from a centre b\ and furnished with small buckets b> V, at their extremities. These pipes are each provided with a tap or cock, on the solndle of which is mounted a tnppet wheel c c, so arranged that as the arms ot the wheel revolve In the direction of the arrows 11, one of tho arms of the tappet wheel c is brought against a pin d so placed that it will turn on the taps c at a certain point as the wheel goes round in tho direction of the arrows 1, 1. Water will then pass down the i>ipo c from the reservoir above to tho centre 6', and from thnuce up the arm b into the bucket (A The flow of the water down the pipe c into the bucket is stopped as soon as the bucket iu quostlou is full by the tappet wheel c of the tap coming against auothcr pin d' which will turn off the tup and stop the water from flowing into the bucket, iiy this arrungement the splashing of an ordinary water wheel is nvoided, and a very regular pressure is obtained. The hour wheel a gears into a piuion on the axle of tho wheel/. The wheel f gears into a pinion on tho axle of the escapement wheel h. A pinion on the axle b' gears iuto nnd drives the wheel i, on the face of which are plus 2 ^,'whlch ns tho wheel i rotates lift up the tail of a lever j, the other end of which is connected by a wire to one end of a lever 1, which Is connected at its opposite end by a wire to a lever I below, having its fulcrum at 3. As the tell of the lever (Is raised it will draw the catch I Into the position shown by dots, and will (by releasing the pin i on tho lever «) allow me other pin 5 to drop on the back of the catch t. t<oyr when the pin l on the wheel; passes the tall of tho lever j the latter will fall back into the position shown, and tuo pin 5 being released from the catch t will allow the lever u to drop down until stopped by a pin o at the end of the double levor v r>. on which It will rest In the position shown by dots aid by means of the wire «'; this lever » will turn on the tap s, and allow

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water to pass down the pipe «' into tbc arms o and buckets o1 of a second water wheel for actuating the Mr iking part of the mechanism.

In applying this iuveutiontothcstrlkingmovement, the advantages are very great, first, because the weight here employed is greater than that required to actuate the clock Itself; and, secondly, because in this case two tralus of wheels are eliminated. The inventor applies the power of a water wheel to tbe cammed wheel n, which consists of three cams, as shown by ditts in Fig. 1, These cams, :ts they are rotated by the action of i he tubular arms oand buckets &', act ou the tail of the lever p, which by the Intervention of the wire D1 lifts the hammer of tbe bell in the turret above. As the water wheel o will only revolve at a steady pace, the regulating fans usually employed In tbc striking gear of ordinary turret clocks may be dispensed with. Thoonly wheel required in this arrangement, with the exception of the cam wheel n for lifting the hammer through the lever p and wire pl i* a ratchet wheel q to drive the lockiHg plate r. The ratchet wheel q line three teeth, and is mounted on the same shaft as the cam wheel », and therefore at every third of a revolution moves the locking plate r one tooth. It will he evident that so long as the arms o of the large water wheel continue to move round they will carry round with them the cam wheel n, and will consequently act on the hammer lever p, as already explained, and also on the ratchet wheel q, which will drive the locking plate r one tooth for every stroke of the hammer ou ihe bell. The strikiug will therefore continue until one of the twelve pint 7 7, on the face of the locking plate r comes against the tail r1 of tbc lever r, on which the lever u rests. The pin 7 as it moves forward will push back the tail vl ef the lever, and thus cause the pin 0 to raise the lever « into the position shown in thedriiwiug.au thus allow the counterbalance lever s2 on the cock * to turn off the water from the arm o and buckets o1, and i hereby stop the cams n and ratchet q until one of the plus - oi (he wheel / comi's round again at the end of the hour and turns on the water again in the pipe ■>'.

When there is any difficulty about introducing a water wheel large enough 10 act in the manner above described, or where complicated movements Buch as chimes are required, the mafu advantages of this system can be obtained by making the weight and drum of any ordinary dock of power sufficient to strike twelve o'clock with its chimed, if any, and then on-auging a small water wheel to wind up the striking movement after every tine that it has octed. Thus, lor instance, in a non-chiming clock, where it is necessary at present to store up power sufficient to

strike 720 times, under this plan only sufficient power is required to strike twelve, thus diminishing the strength and solidity requisite in constructing the clock.

THE SUPPOSED PLANET VULCAN.

Sir.—To the Hat of observers which appeared in the English Mechanic of thelatinst, should be ndricd the names of the Hev. Fred. Howlett, F.K.A S., aud Messrs. Thomas Petty aud W. It. Bland.

The weather has, fortunately, up to the present time, been exceedingly favourable for solar observations. There have been, and ore now, several magnificent groups of spots visible on the sun. Four of these spots have been distinctly visible to the naked eye. At 6h , on March 31, I saw with great distinctness the two groups aud lanrc isolated spot near the W. limb, and am pretty certain that another cluster situated on the

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E. edge of the due was also visible. On ftntreh 2S, at sunrise, 3Ir. H. Ormlsher, of Manchester, discovered three of the croup* without telescopic aid, aud Mr. E. B, Knobel, of Burton-ou-Trent, writes that ou March 25, 26, 27, 28. and 30, he distinctly saw one or more of the spots with the naked eye. It may be appropriate here to give some measures at the size of the largest spot visible. Mr. T. W, Backhouse, of Sunderland, writes that on the 24th March It was 46,000 miles long, and the principal nucleus 19,000. On the 27th It was 45,000 miles long and 3A,ooouiiles wide. It then contained two umbrie,each 8500m, long. On the 1st April it was 4R,000m. long fin a direction nearly parallel with the limb; and 31,000m. wide. Its northern umbra was

BOOOm. long and 7000m. wide. The above spot tra versed the sun's northern hemisphere, and was visible from March 23 to April 4 Inclusive. Several other large spots have been visible. On March 24 Sir. Backhouse measure the largest spot of a cluster in thx* S.E. quadrant, and found It was 36,000m. long.

Observers have noticed several rapid changes in the form of some of the spots. Mr. E. B. Knobel remarked a phenomenon of (bis nature on March 20. He says: —" I begau to observe the sun st about 10.40 a.in., and

ffavo my atteuiion almost entirely to examining the urge spot then visible In the sun's northern hemisphere. I made a sketch of it, which I completed by a few minutes after 11 a.in. At 11.10 a.m. the suu Whs obscured by clouds, which cleared off at 11.15 G-.M.T. I immediately directed my atteution to this spot, and was astonished to observe a change had taken place In tho bridge across the large umbra. A bright pa'.ch seemed to have broken out in the middle of the umbra, which then appeared as in Fig. 2. The moment Iliad the spot in tho field of the telescope It caught my attention, and I felt confident at the time it bad not presented that aapect when it had clouded over five minutes before. I should say the bridge was much brighter than the penumbra. 1 hope other observers hare noticed the same phenomenon.'* The following are the sketches of the spot referred to:— Several other observers have observed somewhat similar phenomena.

No planetary body, or any strange appearance whatever, has been visible on the disc of the suu, or it would have been detected immediately.

I find, on observing the sun this morning with my tin. metallic reflector, that an immense group of spots hnvc just appeared on the E.N.E. edge of the disc. The photosphere in the region ol this group is greatly disturbed, aud there are numerous faculae visible. From the present appearance of this cluster, 1 Imagine it will be of greater almenslons than any other group recently visible. If the weather continues favourable, 1 will forward you sketches of the appearanco of this group, aud will duly send you particulars of further observations.

William F. Denning, lion. Sec. Observing Astronomical Society Ashley-road, Bristol, April 5.

SHAND'S IMPROVEMENTS IN STEAM

PUMPING AND FIKE ENGINES. Sir,—The following description of Shand's recent improvements in steam pumping aud fire engines may not prove uninteresting:— Mr. Shand claims that they enable him to obtain by

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simple and direct means an uniform action In hU pump and perfect equilibrium of all the parts In motion, that le to say, he obtained a continuous flow through suction inlets and delivery outlets, very desirable when used as a steam fire engine, and In effect resembling ■ rotary action. Greater thoroughfares through the valves wre also obtained than can be by the uduai means in equal areas of barrel and bucket. The steam pumping engine is composed of three steam cylinders arranged in line with each other, and the pistons or each attached through its rod directly to a ram aud bucket, each of which works in one of three pump barrels, also in line opposite the cylinder;*. In the attachments of the pi-ton rods to their respective rams a slot is formed, or what is generally known as a slotted crosshead, into which work the journals of a three-throw or equilateral crank, the shaft of which having three eccentrics fitted thereto, each actuating a slid- valve to admit and discharge tbesteara working the pistons, nil the working parts are thus made to balance each other. For compactness the three-throw crank may I<c worked by means of slotted cross heads, but ordinary connecting rods may bo used for this purpura. Kach pump barrel is connected at bottom to out? suction chamber, and at rnp to one pump head, by which the aupclv and the delivery is made common to all three pumps, producing the uniformity before named, rendering the action aoft, unaccompanied by the violent thud nnd vibration produced by *he ordinary reciprocating pump when speedily driven. The steam and exhaust pipes of the cylinders are also connected each Into one, thus constituting but one engine and pump, with continuous instead of the jerking and intermittent action usual in the ordinary pumps. The suction and delivery valves are usually composed of a number of vulcanised Indfa-rubber discs fixed over as many gratings, the outline of each grating being circular, these being formed in a fiat plate (also a disc) and forming the foot valve or bucket, and of suitable diameter to the barrels. The size of the rubber disc is by this arrangement limited, as being circles within the boundary of a larger circle the valves can be made no larger than to touch each other.

The seats are of a pyramidal fonn, the Inclined faces of which allow of larger circular gratings than can be obtained In the flat valve seat of dlse form before described. By these means the thoroughfares through the gratings are increased and r.u increased flow of water through the suction and delivery valves is obtained.

^eT-1 i« a front elevation, In whlc!i are ahown the slotted crnsa head ami the connecting rod arrangements. Fig. 2 is an end elevation with the frame broken away to show the arrangement of cross head; and Fig. 3 Is an end elevation, partly in section, showing the arraugemeut of couuectlng jod and the pyramidal valve seats.

A are the steam cylinders, the pistons of which are connected directly to the rams 11 by the two piston rods C In the connecting rod arrangement, and by the single piston rod D and the foot piece £ in the slotted •POM bead arrangement. The couuectlng rods F or the slotted croas heads G transmit motion to the threethrow or equilateral cranka II, producing a rotary

motion of the crank shaft I, on which are fixed the

three eccentrics J for working the steam slide vales.

Attached to the ram B U the bucket K, in which the gratings of the pyramidal valve seats are shown, also

the India-rubber valves In section with their guards. L is one of tho foot valves, ahown In section, also of thcpyramidal form aud fitted to the bottom of <nch pump barrel; M the inlet to motion chamber N from which each pump la supplied; <> the pump barrels; P the pump head receiving the delivery of each pump; Qthe discharge outlets, of which there mav be one or several, as required. Fireman.

TUB TELESCUrE, Ac.

Sib,—A 4ln. object glass which will show the nth Star in the trapezium of (_)' Orlouis needs no encomium oi mlue to m 'ke the owner most legitimately proud of it. I can only tell Mr. Alston (p. 40), that had he paid Dullmeyer (whom I take to bo our first living object glass maker). BO guineas for a 41 n. objective, it could not have possibly doue more than his " Wray." I scarcely know n more severe test In the whole Heavens than Lhe rtth Star in the trapezium of Uriou for an instrument of the size he refets to.

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I can give " G *' (2271), p. 45. littlo or no Information as to what has become of Kitchener's instruments; which are scattered all over the country. It may. however, nsslst him in tracing the "Beauclerc" telescope, if I tell him that It was advertised for sale for £130, by the Kev. A. F. Fadley, of Lincoln, In the Tunes for February 9th, 1861; who bought It, or whether It was ever disposed of at all, I cannot say.

Mr. J. H. Ward (2275), same page, will find glas* of a very dark neutral tint, or ol that hu<? known to Opticians, as " Louden Smoke," the most pleasant to 086 aa an eye-cap in viewing the Sun. He must be careful, though, either to employ the "Holgson" reflector (english 31 ecu Ante. Vol. IX , p. 180), or to constrict the aperture of hli telescope to 2Iu., or less. Otherwise he will find hi* dark glass crack at once.

"\V. H. 1*. " (2287) can do nothing with his telescope Lenses are not like trained Boldiers, they wou't stand fire.

"Astronomer " f2S15), p. 4fi, is delightfully vague In the absence of any details as to aperture, &c., I can

only conceive that his little telescope is a very good O'le, aud his bigger Instrument an exceedingly bad* one.

"II. A.C. " (2347), alKo on p. 4fi. Is apparently speaking of a reflecting telescope, albeit he says nothing directly to Indicate that such Is the case. He further omits to state whether It has a vertical motion upon trunnion*, or in fact (save by an ambiguous reference to its being "raised or lowered bv means of two nuts") whether it has any vertical motion at all. ABsumiug, however, pro hoc vice, that he can move it in a truly vertical direction, he must stretch a perpendicular spider line across the centre of the field of his eye-piece; and then obtaining his exact local time, calculate In the way exemplified on p. 2, the precise time of trausit of any star near the horizon. He must then bisect this star by his wire, just before Its culmination, aud, moving tho whole instrument bodily after it. stop at the calculated In-ntant of its appulse to the Meridian. His telescope vrill be then as nearly due North and South as ever he is likely to get It, and he may now lower It aud Bee what terrestrial object forms a meridian mark.

To set the Instrument east and west, he may describe a circle on the ground, having the longest leg of his triangle as a ceutre. and the distance between ft and either of the others for a radius. If now be wilt notice where this shorterleg touches the o'rttra when the instrument Is In the Meridian, aud will covet round i he exact quarter of the circle from such pusitiou, he will have obviously shifted the telescope, cither iuto an easterly or westerly position, according to the direction in which he has travelled round the circle.

As for his device for looking at the sun, it 1b nothing In the world but the " Hodgson" reflector referred to above. It is the best aud sutest way Juere is of examining solar detail.

His third query, albeit very indirectly a telescopic one. I may a« well answer here by saying that N. 1*. D. may be converted Info declination as follows. When it does not exceed 03°, subtract it from 9u°, and tha remainder will bo North Declination ; when it does exceed l»0°, subtract 0U° from it, the remainder will be South Declination.

For example the N. P. T>. of a star is 47° 10', what is its declination? U0° - 47° 10' = 42- 50' Dec. North.

Or. what Is the Declination of a star whose N. F. D. Is 105° 12'/, 105° I*'- 00° = l.V 12'Dec South.

An unexpected fine night has enabled me to redeem my promise to lo.>k at t, Ursa; Majoris w.th Alcor and their neighbours. In preceding column is a sketch of the field of view of a 4Jln. telescope with a power of 74, when directed to Mizar. I mu?t, however, exprYssly caution "Jupiter.** or any one else, not to accept the apparent magnitude* of the small stars indicated as correct I do not think that yonr engraver could possibly cut some of them without making tho punctures so minute as to till with ink In the process of printing. My querist must therefore regard ray diagram merely as an eye map of the positlou of tho points of light which were visible when I mads it.

With regard to the letter of "« Ursa Mlnoris" (n. 59), I --'m just in this difficulty, that ray T<Uh Vol. of the English Mechanic Is now in the binder's baud* So that I have no means of referring to the reply to him to which he adverts. Ou this account his reference to "24 Lyncis'Ms a puzzle to me; 4 and 14 Lyncls are both pretty test objects, each about V apart, but 24 and 31 are unlcnowu to mo as doubles. What "the first Star on 'F.R.A.S.'s' list" was, I have not the most distant conception cither, in the absence of such list from the cause specified. Your correspondent ought certainly to divide the closer pair t Equulel with the Optical means he possesses ; its components are now just over 1* fiom each other. The Star '• about IS' (roally 11") to the right nnd below' ■ it is the third component of the triple asterism.

The list of object* resolved by "a Ursa; Mlnoris," is creditable to his instrument, albeit it contains some of various values as tests

Apropos of the flih Star in the trapezium of $ Orionis, 1 am disposed, as I have before stated in your columns,|to put a fin. Achromatic as the smallest instrument with which, under the mo»t favourable circumstances, this exceedingly difficult object cau be glimpsed. If however .Mr. Cooke's 3fin. did show it, such telescope must have been unique as a production of its manufacturer. I should perhaps add, in fairness that suspicion exists of this Star's variability.

I never Intended to indicate that tho Satellites of Uranus were invisible In anything less than a aft. mirror. Some one whose lottor bore internal evidence that he was iu possession of a 3in object glass, or something of that sort, asked what maynifging power was necessary to observe these mourn 1' t jestingly inquired in return if he had a In. mirror, that he put tho question? I am quite familiar with all that Arago has written pa the subject, and know the story •f Lamont aud the llio. Merz refractor, probably very nearly as well as "o Visa" himself. 1 will try and be more serious for the future.

Mr. Baguley, p. 63, asks me for some tests for a Sin. refractor. He may try y Leonls, 19 Leonis, J Ureae Majoris, u Leonis, 127 P.XIII Virginia or i liobtis, for separating power. All these are easy objects. He will find more dioVult ones in 156 P. XIII Ursse Majoris, 70P.X1V tjibra;, v5 Scorpil, or X Ophiucb). For a trial of his light-grasping power he can look at 13 P.V1II Caucrl.ef P.V1I1 Cancri, 15Hydra, t Ursse Majoris, 0 HydrtEor y JJrsa: Majoris. The comes toy Crateris will be just beyond his capability. He may also attempt the resolution of that gorgeous mass of stars 13 M Uerculis. 1 shall De happy to learn what success he has had iu the resolution of these few' objects; and shall be glad to supply hiin with a supplementary list, should he be successful with tho one I now give him.

I suspect that" Neptune" (2436), p. 70, is merely laughing at me. He has, according to his own showing, ^ot hold of a flint disc of abnormally high dispersive power, but what its exact index is of course 1 must be ignorant. He tells me the focal length of the crown, and that of tho whole combination, and he professes to have such stupendous faith iu my mathematical juggling as to suppose that I can from this compute the curves he requires "in a few lines.'' I do not know whether "Neptune" has ever calculated the curves for an object glass himself ; but I cun assure him that I have, af> initio, and 1 made a vow when I had finished, that 1 would never voluntarily wade through such a dreary waste of figures again. To get out accurately, the four surfaces of an achromatic combiuut ion of the size of your correspondent's, would involve, imprimis, the most accurate knowledge of tho refractive and ilispersive indices of the materials to be employed; and then amass of elaborate calcul a tiou which 1 really have neither the time nor the inclination to face. It is not like a terrestrial telescope, or other small instrument, in which Sir John Herschel's simple formula can be employed: it Is a serious undertaking, as " Neptune " may satisfy himself by reference to any standard book on optics. A Fellow Of The Koyal Astronomical Societt.

TIME

Sir,—" Not a F.R. A.S." (2425), p. 70 is slightly confusing two different things. All lie has to do is to calculate his own local mean time accurately, and then by adding 8m. 7s. to it he will obtain the Greenwich mean time at that instant. Tho addition of 13Is. is to the apparent Klght Ascension of the Suu at his local mean noon, be;'use the Karth turns from West to East, and In the interval between tho Greenwich Meridian coming uuder the Sun. and the arrival of that of yonr correspondent there, the Sun himself will have travelled a little way in the Ecliptic, and have increased his Might Ascension by the 133s.

Au example scarcely seems necessary, but for perspicuity 1 give one. worked out at length. What will be the Greenwich .Moan Time nt 6h. 11m. 50-39s. Local Sideral time in Longitude 8m. 7s. W., on the 15 April? Turning first to p. 63 of the "Nautical Almanac," wo find

h. m. s. Sidereal time at Greenwich .Mean Noon 1 30 40 06 Add proportional part of 1)8565 1"33

Sidereal time at local Mean Noon 1 33 47 30 h. in. s. Then from 0 14 50-39 take.. .. 1 33 47 39

There remains 4 41 3 00 Tho Sidereal hours, minutes, aud seconds, since Mean Noon.

Converting this into Solar time, by the aid of the table atp. 506, thus :—

h. in. s. h. m. s.
4 = 3 09 2n (1.918

41 = 40 68-2831

3 = 21)018

I have assumed that my querist's longitude is 8m. 7s. in Mean Time west of Greenwich. If it be 8m. 7s. sidereal time, he must convert this into mean time, which he will fins' to be Sin. 57s., and add that.

I can only reply to Mr. W. F. Swallow (2301), p. 68. that 1 have nothing to explain, modify or retract with reference to what I wrote with regard to tho gnomon (/oc. cit.), in your list volume. Mr. Swallow asserts that the length of the shadow of a gnomon at the time of the equinox is not au arithmetical mean between the two lengths of the same shadow at the Solstices; and I say that it is. Utrum horum mavis accipe. A Fellow or The Royal Astronomical Society.

. Wo get 4 40 10-9507 Local Mean

h. m. s. time, and finally If to this 4 40 16-90 we add 8 7 00

we obtain 4 48 23 90 the Greenwich Mean Time at our supposed place of observation at the assumed Sideral Time on the day specified.

PERSONAL.

Sin, I lower my sword to Sir. Proctor. I see the force of his objection with reference to ray determination not to argue under any circumstances whatever; and can quite conceive that too rigid' an adherence to such determination may often render me liable to misconstruction. Pro hoc rice then, I candidly admit that my spectroscopic illustration was a most unfortunate one, and my use of the words "a vrioti," where I Bhould have said, and only mettnt, "at the first blush," certaiuly calculated to couvey the impression that I was enunciating, what I bolleved to be, a scientific truth. There is less excuse for me, because I was familar with thy form iu which the Astronomer Royal bad stated his difficulty, and the immediate and convincing reply that was given to him; but I wauted au illustration and, it seems,could only furnish one iu this slipshod lorni. I should be very sorry that it should go forth to the world that 1 believed that the dispersiou of tho two dissimilar spectra, might have theoretically been expected togo ou, paripaxsu. although on reading may own words over (litera scripta manet), they certainly appear to couvey that idea.

There is agentleman signing himself "Veritas,"who has hououredine with a considerable amou ut of attention for some w^oks pa*X. It may perhaps save him the expenditure of a greal deal of paper and Injft if J refer him again to the article " Veuus on the iota's Face," which ho* formnd the text from which he has been preachlug. If he will honour nap by reading' it once more, he will find that I absolutely reEudlate rigid accuracy in my figures, niy aole object avlng been to render apprehensible, in the most popular form that I could devise, the priucipte on which the measurements described, are made. To have gone into all the details and refinements of calculation would have been to have ^expanded what filled some 0 or 7 columns of the English Mechanic. into a thin octavo volume. Onco for all, then, I u>ed round numbers everywhere, aud it is of no use "Veritas "foundiug any theory upon them.

Thanks.—Permit me to thank Messrs. " Saul Rymea " and G. E. Crick, p. 44, for their kindness iu so promptly answering my question as to engraving on slate. 1 have further t ■• thank Sir. Leicester for the trouble he has taken to reply to me ou p. 60. 1 rather fear, though, that the process which he describes is beyond the reach of a mere amateur. A Fellow Of Thc Royal Astronomical Society.

THE SUN'S DISTANCE FROM THE EARTH.

Sip,—The following information I copy from Vol. LllI, page 1,of thc Phil. Trims, lor the year 17di, with comment, for the notice of your correspondent, "S. 15.," in your number lor April 1st, 1S7U, p. 38 : —

"Of the Sun's Distance from the Earth, deduced from Mr. Short's Observations relating to the Horizontal Parallax of tho Sun. Bv Peter Daval, Esq., V.P. of R.S. To James Barrow, V.P, of It.S.

According to Mr. Short, tho mean horizontal parallax of the sun is 8* 05. Now, this parallax 1b the angle which the semi-diameter of the earth subtends, as seon from the sun. Therefore, as S"05 is to 360" (the whole periphery of a circle), so is the semi-dismoterof the earth to the periphery of the earth round the sun. Hut as 8'05 is very nearly the 149820th part of SOU", as may be easily proved by division, according to the latest observations, the mean semi-diameter of the earth is 3958 English miles, which being multiplied by 149,830, produces 59.5.011,308 miles for the circumference of the orbit of the earth. The distance of the earth from the sun is the semi-diameter of this orbit; and the periphery o! tlio circle is to its scmidiameter very nearly as <>,«3,18o to 1, Therefore, If we divide 593,011,308 by 0,383,180, the quotient, which is very nearly 94.380,08.5, will give tho mean distance of the earth from the suu In iiugllsh miles.

As the orbit of the earth is au elli pse, not a circle, the distance of the earth from the suu will bo greater in its aphelion, aud less iu its perihelion, than here assigned.

The result obtained will depend, of course, upon the true valuo of theimoan horizontal parallax. R. 11.

THE COLOURS OF JUPITER. Sin,—I beg to reply to Mr. Purklss's letter in your last issue; at the same time I may be permitted tol:iforin him that 1 have not the slightest wish to enter Into a long discussion on the points iu question. If I have erred In making it a question of colour iustcad of relative brightness, I am quite willing to stand corlectcd. I cannot agree with Air. Purkiss that large apertures and high powers do not enable us to discriminate delicate gradations of light aud shade as well as of colour. The fact that this is tlio case is abundantly proved by the detail shown iu a corroct drawing of the planet with a large aperture of either object glass or speculum, and by the utter absence of such detail in drawings made with small telescopes. The simple explanation of the fact that tho belts actually appear darker in a small than in a large telescope is that in a large instrument we get sufficient pow^r to perceivo the belts diversified with many irregularities of light aud shade, nod hence they do not appear to be such a dense dark nmss as when viewed in an instrument iu which thero is uot sufficient power to reveal these details, aud which conse

quently simply shows the belts as dark dense bands across the planet's disc.

Mr. Purkiss dissents from tho opinion that no pigments or materials with which we are acquainted cau be made to accurately represent tho differences which really exist, but such is really the case, and, as au instance of this kind of difficulty as applied to the delineation of terrestrial objects, we may mention that an artist who introduced a Illy Into one of bis pictures" was compelled to represent It in different depths of grey, but still preserved the relative purity of the flower in question, although it would obviously be untruthful to call a lily grey, aud the requisite force of contrast was only obtained by sacrificing truth to effcyct, by unduly darkening the rest of the picture.

Mr. Purkiss thinks I am in error in stating that Mr. Browning's drawing is over-ooloured, and adds his own opinion that the error lays in the other direction, for, aceordiug to his humble opinion, the colour was eveu more vivid than shown in the drawing. This is in direct contradiction to Mr Browning's own words, quoted iu Mr. Denning's letter, where he distinctly Bays.—" Tlio coloured print taken from my drawing is decidedly over-coloured, the yellow aud red are too bright, nnd the ashy blue, or firey, far too dark." And Mr. Purkiss, in thanking Mr. Denning for h's reply, says :— "It is concise and appropriate, and every tiling which could be desired." Surely such evident contradictions in the writings of a gentleman of his eminence iu optics and astronomy deserve explanation.

On another point I need some little enlightenment. Whero can we see paintings which n«t only equal, but surpass Nature herself?—In which there is preserved throughout such a glowing luminosity as to far exceed the brightest tints of thc landscape? I do uot profess to be a judge of paintings, but I have spent many a happy hour iu contemplating scenes of beauty portrayed un cuuvas with marvellous fidelity, but could not venture to assert that the gorgeous sunset of the artist equalled, much less exceeded, the real beauty with which tie great orfe of day gilds tho western heavens as be slowly sinks to rest ou a bed of clouds.

Mr. Purkiss complains that tor skilful draughtsmen practice astronomy, and an jdifhcuiticB are made of things which ought to be comparatively easy. Now if celestial drawing is so easy, why uot favour us with Bome deliuoatlooB of obiects observed with mirrors of his own manufacture, aince lie states their definition to be excellent, anal I have no reasou to doubt for one moment their superior quality. It would, however, bean additional a?itisfactiou to read the testimony of some other observers who are working with his'specula. Charles Gbover.

COVERING THE KEYS OF TIANOFORTES, ORGANS, AND HARMONIUMS.

Sia,—" Progress," No. 2342, inquires if his worn harmonium keys can be laced—i.e., re-covered with enamel. Many patents for covering tho keys of musical iustruments with glass and enamel, have been taken out, but tboBe materials have never como into general use, and almost every one prefers ivory for the purpose.

Re-covering keys with natural ivory is a daily practice aud auy keyinakor will do it for "Progress," and a suitable cousideratiou. Perhaps " Progress '* would progress fastest if he sent his keys to Messrs. Urooks, supposing he would be satisfied with natural ivory. I don't think he will find any one who will undertake to cover them with enamel.

Artificial ivory has been made of tolerable quality by the French, but by far the best specimens 1 have seen were the productions of Mr. 11. J. Brown, who although best known as a public writer and poet, was by hereditary descent a comb maker, lie made excellent combs of his artificial ivory, the composition of which he kept secret, but 1 think a chemise might give a shrewd guess at its component parts.

lieucy iirowu was the mau tlio late W. J. Fox alluded to iu his article iu the Westminster Review on "The Poets of the People." After mentioning Ebenezer Elliot, he wrote of Henry Brown :— 'There is a man who makes combs in Whitechaple," and compared him to Crabbo, giving deserved praise to his teally beautiful pecni " Sunday." which, with his " Mechanic's Saturday Night," and his "Saint Monday," graphically portrayed tho working mau of that period. Of course "yo working man" is now quite a dilfercnt being, he having oeen educated into a civilised, refined, intellectual, and moral Christian, who is quite iuneccnt of " Old Tom," nnd unacquainted, practically, with the meauiug of the words " pot of beer."

The Hahmomous Blacksmith.

COMFORT FOR TRAVELLERS BY RAILROAD AND STEAMER IN AMERICA.

Sir,—English railway directors are not greatly celebrated lor tho care they exhibit for the comfort of passengers; perhaps if they exhibited more care for their passengers' comfort than thoy do it would hardly be appreciated by thc majority of travellers, especially if it were accompanied by an increase iu tbe lares, lor however Britons may wish u> be wellserved for nothing, they, as a rule, prefer being served badly without paymuut, to being well served and paying a fair price for it, and this rule holds good not only in the mutter of railway travelling, but also in the administration of justice (1 shoild have written lam. They ore not invariably identical, or our great uupaid, which is only another name for our "reatly inefficient, would not be so popular with that "numerous class who fancy that a thing which costs nothing must necessarily be cheap, which is usually tho reverse ol true.) *

Ou some Eugllsh railways first-class passengers can obmlu tbe luxury of foot warmers in winter; but as our climate-tho experience of the last six mouths i.otwithstuinliug-is not quite so extreme as those of Sweden aud North America, of course it don't matter

the mass of travellers who, as they go second and third class, do travel with cold toes, tor the feelln"s of such •• common poople " cant be of much importance, uotwithstaudtug that their fares arc, perhaps in

inoct Instance*, the only owes which yieM a pn»flt ; for\ it is the opinion of Home experienced traffic manageis that first-class passengers are often carried at a Ions*. On American railways the practice of heating the cars In winter Is universal, Mo not only can tbo passenger* warm their noses (and their toesrs, as the Frenchman designated his pedal extremities), but if I am rightly informed the cars are now also cooled insnmmer.tt i* stated, by allowing solid carbonic acid to evaporate, and considering that a temperature of 90° in the shade is uot uncommon in the Southern States, this must be a great luxury for travellers, nor will It in future be confined to those who travel on land, for it in stilted in the Food Journal that it is to be extended to those who go down to the pea In (steam* ship?.

A steamer trading between New York and Galveston, is fitted with apparatus'for condensing carbonic acid, and in a recent experiment, its cabin, (SC>tx, long. ;l3ft. wide, and l'Jft. high, had its temperature reduced fxonnS F. to 2i> below zero iu eight minutes. It U not mated if any living beings remained in the cabin during this experiment, but I fear if they did the effect would have been to Induce couia, for it'ie obvious they would have been compelled to iwhale an atmosphere containing an abnormal proportion of carbonic acid, and this, however conducive to sleep and anaesthesia, is hardly conducive to longevity. That carbonic arid in the gaseous state might be employed economically in the treatment of paupers au<t criminals may be quite true, as I stated in my former communication on the " relief" of the poor and the ratepayers, but it is quite uusuitable for those who can "pay their way," and may be expected to pay their way iu their fares more than once, for it would render tnew quite incapable of paying twice, which is just the thing traffic maunders desire, and term development of passenger traffic.

SVe have imported several American inventions to our advantage, and I think the present is pre-eminently the tirao to Import this refreshing, or rather refrigerating, one, for it raight be applied most advantageously at the present time to further the progress of national education by cooling that religious fervour which, strange to »;iyt exhibits itself In a Christian laud by preventing little children from being taught the three It's, political cconemy, and their duties to their neighbour*, of course if we continue to bring tbem up in ignorance we continue to manufacture thieves and paupers, whether we intend It or not We can hardly ex[»ect to gather grapes from thistles, for in moral* as iu horticulture, verily a* ye sow so shall ye reap. The Harmonious Islacksmitu.

TO MILLERS.

Sib,—It gives me groat pleasure to find that so many of our dusty tribe are becoming readers of the Kmjusii Mechanic, and that a few of them are alxo correspondent*. I should rejoice greatly to see the latter multiplied. Lt would be the means in an indirect way of promoting Its circulation among the former, a class of men to which a scientific paper hud no charms if it did not treat upon their particular branch of business.

In No. 282, A. Stoueraan has published Am "notion to the world respecting millstone balancing, a notion tome quite new, and I believe he will find the universal experience of all practical millers, as well as the laws of centrifugal action or force, to the reverse of his notion, notwithstanding- his own to the contrary. He says *' that a standing and running balance are the same." As he has expressed his willingness to learn, a few hints from one twelvemonths his senior, may be of some service to prove the impracticability of this assumption. It is certainly new to me that millers have been looking to the face of the stones to find out the cause of the dragging. Most millers know perfectly well that the cause Is not in the face, but in the unequal distribution of burr and plaster. The specific gravity of each being as 1 to 2, Borne burrs are a third heavier, consequently, when the stone has obtained its proper velocity, the centrifugal action or force of these two species, causes the apparent waving or, Sb it is termed, "being out of balance." It will exhibit this symptom when at perfect standing balance, and I call such to bo when a pound weight will turn thccenties. It is also quito new to me to find that the level of the bedstone has anything to do with balancing the runner, providing the neck is in good order. We do not shut our eyes to tho fact that the bedstone must be perfectly level, but this has nothing to do with balancing, which is done most effectually by a belt running over pulleys attached to the spindles by bolts, the same being In two halves. As a further illustration of what I have stated above, to save space, J refer him to a diagram (intentionally somewhat exaggerated) by Mr. Smith, on page 588 No. 257, Vol. X. A careful study thereof will, 1 think, throw his " notion " quite out of balance.

Now a word about wire flour-dressing machines. Mr; Sharp** has sent us a description of onelhe once had. which droned tho modest quantity of six sacks (20sl each) per hour. A machine of the same dimensions as his, with revolving cylinder and external brushes, 6in. fall, covered with five sheets of flour wire, the internal brushes runulng 520 revolutions, will ere** 20 sacks per hour—average produce, 75 per cent. I dou't know how many machine* there are in lrei:iud, but I know one in England that does what I have stated above, and the quality of its work will compare favourably with some of that of tho silk machine, which I presume he would recommend Mr. Scott to put down in his mill ; I would also advise him to d<i so in preference to the wire. Its work is finer, and takes better in the market. Thos, Evans.

Sir,—lour correspondent, "A Stoneman," quoting from my letter, asks me to explain how " stones working well out of standing balance only proves that they are in running balance." 1 did not mean to convey that because they are out of standing balauce, that therefore they must be in runuing balance. But "Salisbury Miller" asked how it is that stones work well although being out of Branding balance. I concluded that if they "worked tcett," they must be in running balance; bat I very much doubt that they would be found out of standing b&Unca If properly tested. J. Shaki**;.

"HOMINY."

Sir.—During a long sojourn In the United States, uid while dwelling in the.South, I partook daily, and •ftrgely, of hominy, a very wholesome aud strengthening food, well known to Southern residents. I had never tasted tlai-t fool before, and discarding rice altogether, which is also largely eaten, look to bomlov almost entirely; and since my return to England "I linve done my best to produce a simllir article for my own use, but have not yet obtained the exact tiling; and I now venture to ft*k our American friend* to be kind enough to inform me how the article is prepared. I may mention that the instructions given in the numerous recipe books for the making of it are not reliable, and I tdiould therefore prefer to have the information from a .States man. one who has had practical experience In preparing it. The mill which I use grinds the grain into live qualities of flour, and in the making of hominy I take the coarsest, including the bran, and the next two qualiilos to that, and mix them. A sufficient quantity is then soaked In water for two, or three, or four days In winter, but for one day only in summer, or It might become sour. Boiling it in a certain quantity of water for 15 or 20 minutes, stirring it all the time, it is then allowed to thicken gradually on tho hob, as near to the fire as possible, and it there remain*, sometimes for hours, until it thickens and moat of the wau-r ha* been thrown off by steam. It must be frequently stirred, for it soon burns. Whew cold it becomes somewhat hard, liko pudding, and is most nutritious, since It contains tho very qualities spoken of by Lieblg, and which nre east away by unwise people as dross. I could give much information as to the best way of using it, but it requires beef, pork, or ham fat, and is excellent with rabbit or fowl fricasseed. It can be eaten iu various ways, and in making it palatable people muBt study their own appetites. Its effects on the stomach and bowels are admirable, aud most people like It better if a lew bread-erumbs be mixed with it.

This is, however, not the hominy as prepared in the South of the United State?, although perhaps n near approach to It; and I should therefore be glad to hear from a States man on the i-ubjeet, who can give me reliable information as to the Wuhih* operandi, and who Is as fond of buckwheat cakes, hominy, and fre*h corn cobs as Tautau

CHINA GRASS.

Sir,—As there have been several discussions about China grass lately In your paper, I think that the fol lowing extract from a notification by the Governor General of India in Council will bo interesting to many of your readers:— Minnehaha.

"The Government of India, after communication with various agricultural and horticultural Bocietiesin India, and with persons interested in (he subject, has arrived at the conclusion that the only real obstacle to the development of as extensive trade in the fibre of rheea or China grass is the want of suitable machinery for separating the fibre nnd bark from the stem, and the fibre from the bark, the cost of effecting such separation by manual labour being great. The demnnd for the fibre is now large, and no doubt might bo extended with red need prices, and there Is a practicably unlimited extent of country in India where the plant could be grown. The requirements of the ca.se appear to be some machinery or process capable of producing, with the aid of animal, water, or steam power, a ton of fibre of a quality which shall average in value rot less than €50 per ton In the English market, at a total cost, all processes of manufacture nnd allowance for wear and tear included, of uot more than £15 per ton. The said processes are to be understood to inelude all the operations performed after the cutting and transport of the plant to the place of manufacture, to the completion of the manufacture of fibre of the quality above described. Tho machinery must bo simple, Btrong, durable, and cheap, and should be suited for election at or near the plantations, as the refuse is very useful as manure for continued cultivation. To stimulate the invention or adaptation ol such machinery or process, the Government of India hereby offers a prize of £5(.-00 for the machine and procesn that best fulfils all the requirements named above. Rewards of moderate amount will bo given for really meritorious inventions, even though failing to meet entirely all tho conditions named."

THE "PHANTOM" WnEF.L,

Sir,—In the last impression of "our Mechanic" I observe an advertisement by "The 'Phantom' Voloce nnd Carriage Wheel Co., Limited (Reynolds aud May's Patent)," wherein is set forth as a new invention a wheel of a precisely similar kind to the one I published in your journal four years ago, and which you will find on page 335, No. *MS of Vol. III., illustrated under the bending "The Spider Wheel." It was constructed for ine by my brother—of Bedford— in It*«4, who also afterwards made a velocipede upon the name principle, the first, 1 believo, that was ever constructed with pattens fixed directly on tlu cranks.

The form of wheel under discussion—i.e., on the suspensory principle, was finally ubautoned by us on account of several defects that appear to be inseparable from it,

1st. It was found to have a tendency to fiattcn at the spokes after a short time using.

2nd. The wires being necessarily drawn up "taut," the slightest blow was certain to break them—ample evidence of which was afforded by a countryman, in examining the machine, putting hiss foot through several of the spokes.

3rd. The passing of the wires, or hooks, through the felloes or rim of the wheel was found greatly to weaken it, and to lead to the first-named defect, however carefully mnde; and

4th. What altogether condemned it for uso as a crank wheel or moving power was that lacking tho rigidity of the ordinary wheel, there was a upriugiuess in moving it by the cranks when loaded that caused a considerable loss of power in driving it. Otherwise It is very elegant iu appearance, and a wheel that will bear an Immense weight, and I should say—barring the 2nd defect mentioned above—would bo lound very

suitable for carriages, <tc. but certainly is by no means admissible as a driving wheel.

As a singular coincidence I also notice, illustrated on page 01 of the gam" number, a device of mine, whilt at Cardiff In 1861, but one which does not. auswor in practice, by reason of the impossibility oi keeping one's balance, and also on account of the strain biHh on tho ancles and on the wheels through the weight falling on one side, Instead of directly over tho wheel. Neither do I believe these single wheel skates have over been used as shown In your illustration.

Kdmund M. T. Tvdkman, 9, MIg hell-street,
Brighton.

AMATEUR FARMING, &C.

Sin,—Now there Is such an Improvement in our Mecu A Nic, I think it would not be a bad idea to place a column (as a trial) to questions and answers respecting the breeding, keeping, and rearing of horses, cattle, pigs, agricultural implements, Ac, as I am sure a go->d many of our readers have hobbies of that kind, as well as lathes, organs, &c ; but before I Bay any more, 1 should liko tj hear other opinions on it, as f am sure it would uike well In the country, and even in tho towns. It. W. P.

[Perhaps our correspondent would bo good enough to net the ball rolling. We will place some Bpaco at his disposal.—Ed. E.M.J

QUANTITATIVE ANALYSIS, &C.

Sir,—Mr Somorville and others, who have addressed queries to in\ may think perhaps f have forgotten them ; such, however, is not the case. 1 have been exceedingly busy, aud nownarrng a little spare time, I send the answers to their queries.

Estimation of Ferrocyanogeu in Tea.—A good general sample of the tea should be taken, and of cour-e, examined qualitatively. K PrtauUM blue be present, take one ounce or so of the tea, add warm water In a flask, and shako well for a few minutes, strain oil the leaves, and let the rest settle, pour off a great deal of the water, add a solution of caustic potash, and then acidify with hydrochloric acid. Make a solution of potassium permanganate by dissolving ■i-lt\i grains in lOOO grains of water; this is to be added to the above acidified solution until n faint, pink coloratiju is produced. Now, the amount of Pntssian blue cannot be determined from the amount of solution used, as the organic matter present consumes a certain quantity. A second determination must be made of the amount of ferrlcyanogen which exists in the solution ; this may be effected by adding Iodide of potassium, allowing the liquid to stand for some time, and then neutralising the solution with sodium carbonate. The amount of iodine which Is liberated is then determined by dissolving 124 grains of sodium hyposulphite in 1000 grains of water; each 10 grain division of the burette will equal 0422 grains of ferrocyaulde of potassium, from which the amount of feirocyanogeu or Prussian blue can easily be calculated. Starch solution must be used as an ludicator. Tho determination of the ferrocyanogeu-should never be made by burniug the tea, and estimating the amount of Iron fouud in the ash. Sulphate of Iron is often used for blackening spent leaves; in such a case, the iron which naturally would occur as sulphate, would erroneously be set down as existing iu Prussian blue. The sulphate may be detected by Its reaction with barium chloride.

Estimation of Organic. Nitrogen, Carbon, Ac, in water.—1 shall not give all the mtuuthe, but only those details which will lead to a good general result.

Take two pints (32 oz.) of tho water, add to It In a glass tUsk half an ounce of a solution of sulphurous acid, boil for live minutes, and transfer to an evaporating basin, evaporate steadily, and finish off in a drying oven to prevent loss by Bpirting. Mix the dry residue with oxide of copper and chromate of lead, and transfer it to a warm combustion tube, fill up with warm oxide of copper, and cud by placing some clean copper filings iu the anterior portion of the tube. This part of the tube is now connected with a Sprengel pump and the air drawn out ; the end of Jthe pump is then placed under the end of a graduated tube (this may either be graduated into cb. inches or cb. centimetres, the Utter is much to be preferred), 50c. centimetres graduated into 250 parts. Heat Is then applied to the copper, aud gradually carried back until all the tube U nt a full red heat; when no more gas is given off, work the pump again to abstract any gas which may remain iu the tubes, and let the receiver cool down to the temperature of the laboratory. Its volume is observed, and the temperature and pressure also noted. The height of the column of mercury having been taken In millimetres (or inches) above the level in the trough, the amount must be subtracted from the height of the barometer; this will give the pressure to which the gas is subjected, which must be calculated toO«C. and 700mm. A moistened ball of potash (or a concentrated solution), must then be introduced into the gas to absorb the carbon dioxide, the amount of absorption being read off as this latter gas, making the necessary correction for the tension of tho aqueous vapour with which the gas is saturated. A bubble or two of oxygen is then added to detect the presence of nitric oxide, and pyrogallic acid solution is added to absorb the excess. The pressure aud temperature being noted, the volume of carbon dioxide is known, from which tho amount of organic carbon by weight can easily be obtained.

The amount of ammonia present in the water must now be estimated by comparison with a standard solution coloured by Nessler's re-agent.

The amount of gas left in the tube is calculated to 0-' C and ?iWmm., aud the weight found. The weight of nitrogen iu the ammonia is subtracted from the weight of the gas, and set down as organic nitrogen. The amounts of carbon nu'-l of nitroiren, if multiplied by five, give the organic carbon and organic nitrogen per gallon. This is Frank land's process, but as practised by him the receiving apparatus is much more exact, though, as here stated, the process will give good results. The cut on next page shows the apparatus iu full work.

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