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314

EXPERIMENTS WITH THE NOVELTY STEAM-CARRIAGE.

variation of curvature in the nodated lines (some of which I think are superior in beauty to the cuspidated), which gradually decrease from the vertex to the node, I cannot for an instant (putting all demonstrations quite out of the question) think such can be the fact.

Again, if a cycloid be continued at the cusp by a straight line which is a tangent to the cusp, these two together should form a fuir line on Mr. J.'s supposition, that the radii there are infinitely great. To me it appears that there would be something of an elbow; but of this that gentleman may easily satisfy himself. It would be interesting to me to know whether, if the inflected curves were united, similarly, to a straight line at the point of contrary flexure, it would have the appearance of being (as in truth it is) a fair line.

I am, Sir, yours, &c.

Nov. 2, 1829.

R. C. Jun.

P.S.-I will take this opportunity of correcting an error of my own, at p. 30 of this volume. I have there stated that the evolute of the parabola is the common parabola, whereas it is the semicubical parabola, of which the radius of curvature at the cusp is infinitely small or nothing: of course the difficulty there mentioned no longer exists.

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FARTHER EXPERIMENTS WITH THE NOVELTY" STEAM-CARRIAGE Extract from a Letter from a Correspondent, dated Liverpool, Dec. 17, 1829.

"The anxiety universally entertained by the people here to see their favourite, The Novelty,' again at work, has been at length partially gratified. Having undergone a thorough repair at Messrs. Fawcett and Co.'s factory, and been privately proved there in various ways, she made her re-appearance this morning on the Railway under the charge of Mr. Ericsson, and has been going the whole day with the greatest success: no accident or interruption of any kind (as far as regards the engine) occurred. She travelled sometimes with-sometimes without passengers, and at various speeds, generally from 25 to 32 miles per hour. In several turns her rate of going averaged full 40 miles per

hour! The bearings most liable to be effected by this rapid speed-namely, the crank-couplings, the eccentrics, and the axle-tree brasses-were not once oiled, from the time the carriage began working till the conclusion of the day's operations. Nothing can be conceived more beautifully smooth than the entire action of this carriage; all its parts worked in admirable harmony with each other. The steam appeared to be got up and kept up at the requisite pressure, with the greatest ease, and at a wonderfully small expense of fuel. The spectators, who were at one time very numerous, were much delighted, and repeatedly testified their admiration by loud cheers. But that the Railway shares have already reached so high a premium, (about 80 per cent!) as scarcely to admit of any farther advance, I should not be surprised to see them take another start to-morrow. The Rocket' has been also doing wonders in the way of speed; but the superior compactness, steadiness, and elegance of

·

The Novelty,' combined with even the same speed as The Rocket,' would be sure to procure for it a decided preference. In order to prove the power as well as speed of the engine, a number of loaded waggons were attached to it; but by this time it was becoming dark, and the distance performed was not sufficient to furnish any satisfactory result. The experiments will be probably resumed tomorrow, or in a day or two after, when I shall again write you all about them."

Extract from another Letter from the same Correspondent, dated Liverpool, Dec. 21.

66

"I am just returned from Rainhill, and have but time, before the departure of the post, to acquaint you briefly with the results of another long day's experiments with The Novelty.' It drew for several hours a gross weight of thirty-five tons, that is at least ten times its own weight, at the rate of twelve miles per hour!!! Can it now be doubted that this is as an efficient engine for weight as for speed? The superiority of the blast principle may be now considered as established beyond all doubt."

EXPERIMENTS ON THE FRICTION OF WHEEL-CARRIAGES.

315

IMPORTANT EXPERIMENTS ON THE
FRICTION OF WHEEL-CARRIAGES.

A number of experiments were made lately on the Liverpool and Manchester Railway, under the directions of Mr. Hartley and Mr. Rastrick, engineers, with a view of determining, 1st, what are the comparative merits of various patent wheels and axles for railway waggons; and, 2nd, what is the actual degree of friction of each; or, in other words, what proportion the force requisite to move or propel such waggons upon a railway bears to their load.

As the report of the engineers has not been yet made public, we cannot inform our readers which of the different patent wheels has been found to answer best, but we learn with great satisfaction that the following results have been deduced from the experiments:

1. That a reduction of the proportion of the bearing of the axles of railway-waggons to the circumference of the wheels, causes a proportionate reduction in the friction.

2. That with loaded waggons, the bearing part of the axles of which is only 1 inch diameter, the diameter of the wheels being 3 feet or thereabouts, the friction is less than 6lbs. to the ton, that is, only 1 in 400.

3. That though friction-rollers at the axles of waggons are in some respects advantageous, the great modern improvement consists in reducing the diameter of the axles.

As the waggons used on this occasion were the same which were employed at the Railway Competition, in October last, it follows that the power of the competing engines was then underrated one-half, inasmuch as the friction at the time was computed at 12lbs. to the ton, or rather less than 1 in 200. But the most important deduction we are disposed to draw from these experiments is, that steam-carriages can never be expected to run successfully except on rail-roads. The resistance to the rubbing surface of the wheels on a railway is as nothing, and the friction only 1 in 400: and admitting the power of an engine to carry a load up an ascent of 1 in 30 to be only one-eighth part of its power on a level, still the force of the

engine working on a railway must be ever pre-eminently superior to one working on our common roads, on the very best of which the resistance and friction together are as much as 1 in 20 in summer-time, and 1 in 10, 1 in 12, and never less than 1 in 15, during the winter half of the year. For heavy goods, at a slow rate of travelling, and on comparatively level roads, steam-drags may be used as substi tutes for waggons and vans; but the rapid pace now required by modern impatience can only be expected to be attained along railways, which, to obviate danger, should be as completely isolated by fencing and bridging as canals now are.

FORMATION OF ORES.

Vauquelin informs, that, on examining the fragment of a statue which had been long buried, he found the exterior of red copper, and the interior of copper in its metallic state. It is evident that these changes in the copper, in the specimens just enumerated, had been produced by the action of the atmos phere and of percolating water. It is equally well known that similar changes have been produced on copper when fused under particular circumstances. Examples of this kind were met with in masses of copper inclosed in the lava which, in the year 1794, flowed over a considerable space of the district of Torre del Greco. Common copper coins were converted into red copper, and in some specimens the surface was crystallized, while the interior had a radiated structure. In some of the specimens of brass candlesticks from Torre del Greco, preserved in the museum of the University of Edinburgh, the zinc has separated from the copper. On some of them there are small brownish crystals of translucent blende, numerous octahedrons of red copper, and very beautiful copper-red cubes of pure cop

per.

In other specimens from Vesuvius, mentioned by authors, the zinc and copper have separated, and each appears crystallized in their due forms. Masses of iron, partly crystallized in octahedrons, and also in the state of iron-glance and sparry iron, have been found in the lava of Vesuvius. Silver in beautiful octahedrons, lead in the state of litharge, and galena, or leadglance, in the cubo-octahedral form, have also been collected from the lava of Torre del Greco. Schweigger's Journal.

316 HARRISON'S ESCAPEMENTS.-HULL AND BOSTON CLOCKS.

HARRISON'S ESCAPEMENTS. Sir, I now proceed, agreeably to the pledge in my last communication, to show, in opposition to the assertion of Mr. Wynn, that my escapements have both merit and novelty to recommend them. Amongst all escapements for clocks which have hitherto been published, will Mr. Wynn have the goodness to point out any detached ones that roll in and out, as those we commonly use do-or any that maintain the motion of the pendulum by an impulse given only every second swing, as my other escapement, which I esteem the most complete, does ;' and which with the detached palletwheel, (the construction of which detachment is such as perhaps has not occurred to any person besides myself,) I consider to be the ne plus ultra of escapements for pendulum-clocks; for I do not see any possibility of either any greater simplification or any farther improvement being admitted. Besides completely cutting off every irregularity in the impulse given to the pendulum, this escapement is also susceptible of being adjusted to compensate the different densities of the medium, so that the isochronism of the pendulum may not be affected by any variation therein; I may therefore perhaps be permitted to doubt whether there really be any escapement equal to it.

With respect to Boston clock escapement, I must give Mr. Wynn credit for the whole of his statement respecting it, as I know well that such pallets must needs act just as he has described; and yet I could give him two sufficient reasons why that clock would really keep a better rate with common recoiling-pallets than with those pallets.

Having prevailed on the gentleman whom I mentioned in a former paper as having an excellent transit instrument and a regulator with a compensation-pendulum, to take the trouble of observing the rate of the new clock made by my son for Christ Church, Hull-I have the pleasure of giving Mr. Wynn the opportunity of comparing it with the "unequalled accuracy of rate" of Boston clock. The time-keeper by which the clock was compared was 26" slow of true

time, and the clock was forward of the time-keeper as in the following register, in which also the times at which sidereal observations were ob tained, are distinguished by the abbreviation obs. placed against those particular days:

March 12 obs.

16 obs.

17

18

19

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21 obs.

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23

24 obs.
25
26

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1 5

Daily vari ation in the rate.

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17 obs.
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From this register it appears that the rate of the clock is 1 second per day slow, it having lost just 44" in ‍44.

HARRISON'S ESCAPEMENTS.-HULL AND BOSTON CLOCKS.

days; and during this period the greatest deviation in its daily rate has been only 2 seconds. It is to be observed that this is a regular daily register, very different from that Mr. Wynn has given of Boston clock in No. 189, p. 214, consisting of a period of 18 days, during which, according to his method, it did not vary quite 14" per day. It seems the time was found by observations on the days he mentions; and to get the daily variation, that found by these observations seems to have been divided amongst

Clock fast.

min. sec.

317

the number of days that had inter-
vened: so that although it might
have varied considerably in the inte-
rim, such variation could not appear,
provided it had gained as much at
one time as it had lost at another.
But notwithstanding the vagueness of
this method, we are constrained to
have recourse to it in order to com-
pare the rates of the two clocks, be-
cause the same method must needs
be taken for the one that has been
adopted for the other.
observation were-

The days of

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Thus, according to Mr. Wynn's indefinite method of keeping a register, the greatest variation of this clock has been only "+and+"— = 4" during 44 days; which (though it is only one-sixth part of its real variation) is not half as much as Boston clock varied in 18 days. And were we to take the time from March 30 to April 18, which includes 19 days, the variation during that time is only", which is not quite one-eighth part of the variation of Boston clock during 18 days. But this is not all. Boston clock has no external dials, nor any thing to disturb its rate; whereas Christ Church clock has four external dials, each having both hour and minute pointers; and it is to be noticed also that very boisterous weather happened during the time these observations were making on its rate.

But though we profess to make clocks of a very superior kind to the one at Christ Church, we make none of an inferior sort, it having only a common wooden-rod pendulum. And although it may be considered superior to most clocks on account of hav

44"

ing roller-pinions, yet its chief superiority is in the escapement, which is the inferior one of my invention on the detached principle, which rolls in and out; and by means hereof the pendulum can scarcely receive any perturbation, the greater part of the irregularities being hereby cut off.

Mr. Wynn gives a curious reason for the durability of "horological machines," viz. that they must be made durable in order to keep good rates. Were I to give a reason for their durability, it would be the slowness of their motions, whereby they do not wear so much in a hundred years as some machinery does in a month. For instance, the best speed of a millstone of 4 feet in diameter and perhaps near a ton weight, is about 100 revolutions in a minute, and it continues to run at this rate for length of days: and the machinery for dressing flour makes a much greater number of revolutions, to say nothing of various other machines which are kept constantly going, and the motions of which are far more rapid than those of a flour-mill. Whereas, the first

318

DR. LARUNER'S LECTURES ON MECHANICS.

movements of clocks frequently do by its own gravity, would be AC;

not make more than 3 or 4 revolutions in 24 hours; and as the motions in the train become quicker, the pressure becomes less, and the works are made lighter of course. What comparison then can there be between the wear of a clock and the wear of most other machines?

As to the dead-beat, which Mr. Wynn recommends the republication of, it is easy to demonstrate its principle to be inferior to that of the recoiling-pallets. I know there is a general predilection for the dead-beat; and I am well aware of its being an easy matter to give very specious reasons why it is the best-such reasons indeed as must needs be considered altogether conclusive, until their preponderance is overweighed by a superior reason being given why the recoil is preferable. This reason I may probably give in some future Number. JAMES HARRISON.

Barton-upon-Humber.

NOTES OF DR. LARDNER'S LECTURES ON MECHANICS, AT THE LONDON

UNIVERSITY.

(Continued from p. 271.)

The next thing to be considered is a very important one, viz. the centre of gravity. If there be several points separately attracted by the force of gravity, the different forces may be supported by one fixed point; and if these several forces act on different parts of a body, this certain point is one which has the same effect as those forces, and this point is called the centre of gravity. In considering the mechanical effect of a solid body, the whole of it, except that one point, may be supposed to be quite deprived of weight, whilst the whole weight or gravity is concentrated in that one point.

One of the properties of this point is, that it always descends, or endeavours to descend, in the straight line perpendicular to the surface of the earth, or as near that line as possible. Let A represent a body, fastened by a rod or string to the fixed point B. Now the line in which this body would fall, were it at liberty to do so

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but this force may be resolved into the two other forces AD and AE, being the sides of a parallelogram, of which AC is the diagonal. But the force AD only stretches the rod, therefore AE is the only force which tends to produce motion, and the body will consequently fall in the curve AFG. If the direction of the rod AB be supposed to be more perpendicular than before, it is evident that the side AE will be much less, therefore the body will move with a much less velocity than before; and the velocity can be proved, in like manner, to be less and less, until at last, when the rod is exactly perpendicular, there will be no motion, the only effect being that of tension.

Consequently, if the centre of gravity be not directly under the point of suspension, the body will descend, or endeavour to descend, until it is exactly under that point; and this position is one of equilibrium.

But there is another state of equilibrium; viz. when the centre of gravity is directly over the point of suspension.

If the body be supposed to be in the former position, it is evident that any motion given to it must cause the centre of gravity to ascend; but one property of gravity being, as before stated, that it will always descend (or endeavour to descend), the body will return to its former position. Now it is different in the latter state of equilibrium for there, the least motion given to it will throw it on one side,

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