E21 152

GRAND adi tant adt et mi towards the wheels, and embrace like two arms the boiler between them. E one of the connecting-rods which give motion to the wheels; a, the slide of the piston of the cylinder seen in the engraving; and o, one of two escape-pipes. Mis the part of the tender appropriated to the carriage of fuel; N the water-cask.

The performances of this engine indicate a very abundant and wellsustained production of steam; but the extent of surface which it has been found necessary to expose to the heat, in order to obtain that effect, the great size of all the parts, and the quantity of fuel required-are faults which even a still more copious generation of steam would scarcely com pensate. It is not by means of its heavy weight alone thatsuch an engine would operate injuriously on the rails. The chimney from its great heighta height necessary to obtain that draught which in "The Novelty" is produced by means of the air-forcing apparatus gives a swaying motion to the engine from side to side; and the rails have thus a lateral as well as a longitudinal force applied to jerk them out of their places.

We observed in our first notice of this engine, (No. 322, p. 115) that it exhibited but a very partial fulfilment of the condition that it should "effectually consume its own smoke." As far as regards its performances on the first day of the competition, this statement was perfectly correct. It is only fair however to state, that in its more recent exhibitions there was scarcely any emission of smoke perceptible. We have heard that on the first day there was an accidental intermixture of coal with the coke; a circumstance which, if true, would sufficiently account for the appearance of smoke on that occasion.

3

(To be continued in our next.)

RAIL-ROADS.

Sir,-Permit me, through the medium of your excellent publication, to suggest to your numerous readers the following alteration in the construction of railways, which are at this period so much in vogue.

2

The difference in the construction→ here proposed is to have the railwaynd inverted (if I may be allowed the sexe pression), that is, the wheels upon the i ground and the rails upon the carriages The wheels or rollers should be of small diameters, and of a proper breadth, mov at certain distances in parallel lines siing upon axles of cast iron, and placed milar to the present rails; the distance between each in a longitudinal direction to correspond with the length of the waggon, so that the carriage-rails may rest upon four or six of the wheels or rollers at one and the same time. If this mode be attended with less expense: than the present roads, and as conver nient, why not adopt it? Less iron will be required than for rails made upon the present system. It may be urged that the mode here suggested would only an swer upon straight roads, but

may be obviated by a very simple piece of machinery, so that the carriages may travel along any curved or other cir cuitous rail-road whatever.v

Merely giving this hint, which some upon, as the proposed alteration has not of your scientific friends may improve to my knowledge been thought of before, I am, Sir, yours, &c.

Oct. 18, 1829.

W. B.

mela

choly effects, which have resulted from the ravages of the mers

buildings supported by

in

of wood. At the lamentable fire which occurred last May in the Lon

don-road, six persons met an untimely

end from this circumstance; the fire broke out on the ground-floor with great fury, and almost immediately burned the brestsummers through: the consequence was, that the front of the house came down, within a few minutes after the discovery of the fire, before the inmates could escape, or those without could possibly render them assistance.

It is sincerely to be hoped that iron will in future be every where em ployed for this essential part of buildings; the increased stability will of itself more than make up for any trifling difference in expense.

Yours respectfully,

seat to nu WM. BADDELEY, Jun. Oct. 9, 1829.

MROCHAPMAN'S SPECIMENS OF THE DIVISION OF THE ELLIPSIS. การ ปาน

Sir, I see in a note you have appended to my communication respecting the division of the ellipsis, you state that my accompanying specimen is not correct. I agree that it is not so, and it would have been very odd if it had, considering the hasty and imperfect manner in which was got up. For in

the apparatus the two principal wheels

stance, one

JA

was an old one I had by me, which I gave to my moulder to cast a duplicate by, teeth and all. After he tried to mould it, the teeth being too parallel, would not strip the sand. I therefore gave him leave to file them sufficiently bevel, and they were no otherwise adjusted than by the file at chance. It could not, of course, be reasonably expected that the effects of the apparatus would be very correct. But that I think little about; it is the principle of the thing I contend for: not doubting that when time and inclination suit, I shall be able to produce the figure as correctly divided as any you have yet seen, or, needs be.

153

On the improved side are laid downt double lines of decimal numbers, disp vided as on the other side, which are marked decimal, because they are divided into tens. Underneath this line are figures 1, 2, 3, 4, and 5, &ood to 1; then 2, 3, 4, 5, &c. to 10 at the end; and under this line of figures is T a line of divisions called duodecimal, & because it is divided into twelves or b

parts of twelve. Under this line of divisions is a line of figures from 2 to 20, which are for the number of shillings in one pound. This line is 1 marked shillings. Under this line is{ another line of figures, from 3 to 245 marked pence, for the number of pence in two shillings, corresponding to the line above, but decreased in value in a tenfold proportion; under this line of is another line of pence

farthings and pence, in a still further decreased proportion to the others, At the right hand of these last three lines of figures are marked the value of the line descending from one r ground the integer to one farthing. The upper stock of the rule contains the exact counter part of the figures and

J

In the plate of the Improved Sliding-Rule in No. 322, the subdivisiona lines denoting pence between the shillings on the duodecimal line on the slide, and which lines should have been laid down in a corresponding manner to the lines on the upper part or stock of the rule are omitted: but as I shall in a short time submit to the readers of the "Mechanics' Magazine" a plan for laying down the lines of a sliding-rule of the same dimensions, it will be a ready means for enabling any person to correct the error. En vol ages audiom

154

divisions as laid down on the slide, but the order of them is reversed. On the lower stock is a line of num hers corresponding to the line on the slide and upper stock. There are also lines of inches divided into eight, ten, and twelve parts to an inch, for any purpose they may be wanted.

In proceeding with the description of this side of the rule, it will not be necessary to notice the line of numbers, that being already done in the description of the other side. The line of divisions called duodecimal belong to either the line of numbers, 1, 2, 3, &c. to 10, or to the line of shillings 2, 3, 4, &c. to 20. The spaces between each figure on the duodecimal line are divided into parts of a shilling, from 2 to 6 are six divisions, each being valued at twopence, from 6 to 10 at four-pence each, and from 10 to 20 at six-pence each. The long strokes will be 11, 13, 15, 17, and 19 shillings; this line must be always made use of when the subject of calculation relates to money in pounds and parts of a pound sterling; but when the subject of calculation relates to superficial or cubical measure in feet and inches, then the line of numbers must be made use of, and the divison on the duodecimal line will be inches for the parts of a foot measure; of which more will be explained in the examples of measuring surfaces. The other two lines of pence, and farthings and pence, are figues denoting their respective value. When, the decimal line of numbers is used for pounds, and parts of a pound sterling, the long and short divisions must be carefully attended to in forming the estimated value in any question or answer. The space from 1 to 2 is divided into ten long strokes or divisions, and ten subdivisions, making together twenty; so that if I is called one pound, then each of the long divisions will be two siillings, and the subdivisions will be one shilling. From 2 to 5 is divided into ten strokes, so that if 2 is two pounds, each stroke will be two shillings. From 5 to 10 is divided into five strokes, so that if 5 is five pounds, then each stroke will be four shillings, and 6 will be six pounas, and so on to 10 for ten pounds. Again, if I is

called ten pounds, each stroke between 1 and 2 will be one pound, and the subdivisions or short strokes ten shillings; 2 will be twenty pounds, 5 will be fifty, and 1 at the end will be one hundred; in the same manner as has been explained as to the other side of the rule.

I

The following rules are necessary to be observed for estimating the amount or value of any question or answer, in pounds, shillings, and pence. The figures on the three lowest lines on the slide, are expressive of their value. If any nomination is wanted between the figures, it must be carefully estimated. Suppose sixpence half-penny is required, look for 6 on the line of pence, and estimate the half towards seven-pence, and that will represent the point wanted. Suppose nineteen-pence halfpenny is wanted, look for 18 and one division on the same line, and estimate half towards the next division, and that will represent the required point. Again, if two-pence half-penny is wanted, look for 2 on the line of farthings and pence, and estimate half towards 3 on the line of pence, and a supposed line drawn across that point will be the answer required, namely, over the figure of one farthing which is a tenfold decreased proportion from two-pence half-penny. Or take the example ascending, and twopence half-penny will be a tenfold increase of one farthing. Suppose 2s. 6d. is wanted, look for 2 on the line of shillings, and three of the divisions towards 3 will be equal to two shillings and six-pence. Again, required 2s. 9d.; continue one and a half more divisions towards 3, and that point will be the answer. Again, required 13s. 3d; look for the figures 12 on the line of shillings, and one long stroke will be 13; then estimate half between that point, and the next short stroke towards 14 will be the required point. Suppose 18s. 4d, is wanted, look for 18 shillings, and the next short stroke will be six-pence, from which point the 4 for pence must be estimated. Suppose 21. 4s. 9d. is wanted, look for the figure 2 on the decimal line for two pounds, and the second division will be four shillings, and nearly half another division

for nine-pence will be the proper point.

Again, 41. 15s, is wanted, look for 4 on the decimal line, which will be four pounds, and count seven strokes for fourteen shillings, and half the space to the next stroke will give the required point.

Suppose 127. 4s. is wanted, call 1 in the middle for 10, and two of the 1 long strokes will represent 12 as in inteIgral numbers, and estimate nearly half towards the short stroke for the re *quired point.

Again, 361. 8s. is required, call the figure 3 for thirty, and six strokes for six pounds, which will give thirty-six pounds, and nearly half towards the next division for eight shillings.

Note.-In all operations every inIncrease or decrease is in a tenfold proportion.

Example decreasing.

1

Estimate 21. 1s. 8d. on the decimal line, and under it on the duodecimal line, you have 4 on the line of shillings, and one division which gives four shillings and two-pence; under this point on the line of pence you have 5 for five-pence, and under this last division on the line of farthings and pence, you have one half-penny.

Example increasing,

Look for 1 on the line of farthings and pence, which is one penny, and over it on the line of pence, is 10 for ten-pence; over this on the duodecimal line is 8, and one division for eight shillings and four-pence; and over it on the decimal line is 4 for four pounds, and nearly two divisions for four pounds, three shillings, and four pence. Again, this point being increased tenfold, would represent nearly forty-two pounds, which will be more J fully explained and better understood 2 by the following examples, which I 2 have selected for the purpose, from Walkingham's Arithmetic, the twentyeighth edition; in making which selection, I have used such of them as *refer to transactions of practical utility in real business.

VARIATION OF THE COMPASS.

Sir-In your Magazine (No. 301 an enquiry is made relative to the variation of the compass. In answer to which, the following are assigned as reasons why the method proposed by Mr. Copcake has not been adopted

When the sun is not very high at noon he appears stationary, during which period the alteration in his being nearly parallel to the horizon. azimuth is rapid, the apparent motion

When he is very high at noon, though his descent is more readily discovered, the change in the azimuth is exceedingly rapid: hence, suppose only a few seconds to elapse before it is ascertained that the sun is on the meridian, there could be no dependance placed on such an observed azimuth.

Besides, there is great difficulty in taking the azimuth of an object that is much elevated.

Farther, the advantage of taking a mean of several observations would by this method be lost.

To save calculation, it is usual to take the altitude when the sun's centre is about his own diameter

above the horizon, to allow for re

fraction.

But if it be desirable to know the variation accurately, let several observations be taken in the morning and in the evening, not only when the sun is very near the horizon, but also when he is between five and ten degrees above the horizon; and, if the ship be sailing to windward, observations should be taken when on each tack; by which the error, arising from the iron in different parts of the vessel would be corrected.

The medium of these several observations-ather, of the azimuths found thereby would be extremely near the truth.

I am, Sir, Yours, respectfully,

J. N.

(A private teacher.)

Devizes, Oct. 1, 1829.