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At the next sitting of the Academy, ones, on this particular railway, where on the 16th May, M. Perdonnet (who, lighter trains would have to start, at least it will be recollected, was engineer of the on holidays, from each terminus, every line) read a pote, or memoir, which is quarter of an hour; and where any delay chiefly an endeavour to set aside the con would be almost sure to cause the trains clusions of M. Combes, previously stated. to run into each other; and would proHe proposes to consider three questions, duce great danger in the very many bearing upon the causes of the accident, crossings of roads on the level of the viz.-

rails. He contends that two engines are 1st, Are four-wheeled engines really better than one, applied to a heavy train, more dangerous than those of six because by their weight they give the wheels ?

power of rapidly stopping, in case of an 2nd. When a four and a six-wheeled obstacle ahead; and he thinks a train of engine are coupled to one train, is it 30 carriages, drawn by three engines, dangerous to place the four-wheeled one would be safer than three trains of 10 in advance, or should it be behind the carriages, each drawn by one engine, other?

because it is possible that a broken axle 3rd. Would the use of small trains on of an intermediate engine might not, (by the Paris and Versailles (left bank) rail the traction of the others,) be permitted . way be more or less dangerous than large to stop or derange the motion of the train ones, as at present ?

until it would be stopped. On the first question, he comes to the He considers a moderate speed essenconclusion that four-wheeled engines are tial, and that the serious nature of the not more dangerous than six-wheeled, accident was due to a peculiar and rare and are better for going round curves. coincidence of unusual circumstances,

His arguments are chiefly the authori viz., the breakage of a fore-axle, and just ty of certain lines of railway in England, at the passage of a public road over the the non-condemnation of them by the rails. Committee of Parliament on railway ac Lastly, he recommends the adoptioncidents—the fact, that if the fore-axle 1. Of the attachment-hook of M. Bergebreak either in a four-wheeled or six ron, before mentioned. wheeled engine, the foremost end falls for 2. The making the carriages of incomward, and the whole is thrown over--and bustible wood. (He says nothing as to that in the four-wheeled, if the driving the other materials composing them.) axle break it cannot let the engine down, 3. The use of wagons before and after as it is between six bearings--that in Ste the train, loaded with inert matter. phenson's six-wheeled engines, without 4. The establishment of an examination flanges to the driving. wheels, if the fore as to knowledge and ability, &c., of all axle break, the engines must run off the locomotive engine-drivers, plate-layers, line-that on curves, the whole weight &c., and giving them diplomas of the engine is sometimes borne by four Mr. Perdonnet entertains some doubts of the wheels, and hence, the rails are of the possibility, in a fiscal point of view, broken by the enormous weight and the of adopting the third proposal. engine runs off the rails—and, finally, The views contained in this memoir that experience on lines, where both sorts are not to be neglected ; but they are, are used, or either exclusively, there is many of them, flimsy in the extreme, no difference in the amount of acci and throughout there is manifest a spedents.

cial pleading to prove that the arrangeOn the second question he concludes, ments made on the line, at the time of that the four-wheeled engine ought to go the accident, were the best that human first, because less liable to run off the wit could devise, and that no blame is rails; and because a broken fore axle is any where attributable. as bad for one as for the other; and, At the same sitting there was also read lastly, because in gradually gathering up a memoir from a M. Manby, called “A the heavy train, the less powerful engine Defence of four-wheeled Locomotives." should be in advance.

The arguments are almost precisely the On the third question he concludes, same as those preceding, with the addithat heavy trains are more safe and con tion of developing more fuily the causes venient than a greater number of lighter why six-wheelei engines tall forward

THE DISC PHENOMENON-FIRST OBSERV

MANCHES

when the fore axle breaks.

The only

to see, however, in what way some of cause assigned, which has any pretension the difficulties of detail are to be got to novelty, is, that of the reaction of the over; for instance, how the train is to issuing steam, &c., from the blast-pipe be started with all the self-acting brakes and funnel. The author concludes, that on, or how backed. the fracture of a fore axle of any engine, · Seven other communications, not pubof whatever sort, or of a carriage, must lished, were also received, and the whole produce a sudden stoppage, and probably referred to the commission to report an accident; but denies that the number upon. of wheels, &c., had any thing to do with

(To be continued.) the accident of the 8th of May, the real cause of which, however, he does not specify

ED BY MR. ROBERTS, OF Twenty-two other communications

TER, AND NOT BY M. CLEMENT DEwere addressed to the Academy, and are

SORMES. not published, but referred to the commission appointed upon the previous me

Sir,--In your valuable Magazine for

July 9th, 1842, is a communication from moir of M. Perdonnet. The commission

Mr. W. Wynn on what he calls “ the consists of Arago, Poncelet, Coriolis, and

disc problem," to which you have apLeguier. A long letter was also read by M,

pended a note, stating that “ The phe

nomenon alluded to by your correspondDelessert to the Academy, from M. Pre

ent was first noticed by M. Clement vost, who, it appears, is employed upon

Desormes.” This has been often said, the London and Birmingham line, and

but is nevertheless erroneous, as that describes the practice as regards engines,

gentleman first saw it exhibited at the &c., on that line. There is in it nothing

works of Messrs. Sharp, Roberts, and very much to the point, or new to Eng.

Co. of Manchester, in company with the lish professional readers. M. Prevost is

late Dr. Henry, of the same place. altogether in favour of four-wheeled en

I herewith send you a copy of a paper gines, which alone are used on his line ;

read to the Literary and Philosophical and attributes the accident solely to ex

Society of Manchester, many of the cessive speed: he would prohibit any members of which were cognizant of the speed upon inclines beyond 30 miles per hour.

facts respecting my first observation of On the 23rd of May, M. Franchot

the phenomenon,--the visit of M. Cle

ment Desormes, to whom it was shown, brought before the Academy his contriv

--and his subsequent statement respectance for preventing a shock to the train, whenever the locomotive preceding is

ing it. That statement did not, however,

distinctly affirm that it was first noticed stopped by any cause. The contrivance consists in connecting the engine to the

by him, but merely gave the fact that train by a series of jointed parallelograms,

such phenomenon had been observed,

leaving it to be inferred by the reader, like a " Lazy tongs,” which are stretched

that it was then observed for the first at length while all goes on right; but on

time. The paper which I send was pubthe stoppage of the locomotive, the pa lished the Memoirs of the Manchester rallelograms are forced together, and each

Literary and Philosophical Society, with is reacted on by a spring. It is, in fact,

the note explaining that M. Clement a plan of uniting, in succession, a great Desormes first saw the phenomenon in number of separate buffers, and is not

Manchester; and I believe that that gendevoid of ingenuity.

tleman has never denied the correctness Another plan was also brought forward

of the explanation given in the note. by M. Jouffroy, for effecting the same

The cause of truth and fair dealing object, by means of brakes, acting con

induces me to request that you will insert stantly upon each individual carriage,

this in your Magazine and should it apand only relieved by the traction of the

pear to you advisable, also some extracts engine upon the draw-bar in front of the

from the

paper. carriage. As soon as the traction ceases,

I am, Sir, your obedient servant, froin any cause, the brake of each car.

RICHARD ROPERTS. riae instantly begins to act. No details Manchester, August 11th, 1842. are given, but a plan is said to have accompanied the communication. It is hard The printed paper which Mr. Roberts

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has been so good as to send us along with raised the valve to 1-12th of an inch above the preceding communication establishes the seat. Twenty-six ounces raised it to incontrovertibly, that the merit of having 1-8th of an inch, and thirty-two ounces first observed the remarkable phenomenon

raised it to 1-4th of an inch, but any weight in question rests entirely with him. It is a beyond this last caused the valve to fly pity that a philosopher of M. Desormes'

abruptly off. eminence should not have had candour

“ It thus appeared, that when the valve

raised from its seat a quarter of an inch, enough to spare Mr. Roberts the trou.

there was the greatest difference between the ble of thus reclaiming his own. The paper

force of the issuing current of air pressing is entitled “Experiments and Observa

against the under side of the valve, and of tions on Diverging Streams of Com

atmospheric pressure on the upper side of pressed Air,” and was read before the

the valve. The pressure of the atmosphere Literary and Philosophical Society of was greater than the force of the issuing Manchester, March 9, 1827. The author stream of previously compressed air, a is Mr. T. Hopkins, but the experiments weight of thirty-two ounces being requisite related, as will be seen by the following to establish an equilibrium. extracts, were made by Mr. Roberts, with “ That we might ascertain what was the the assistance (latterly) of the writer of

state of the stream of air under the valve, in the paper :

different parts of it, four double syphon

tubes were procured, and proper quantities " On the eleventh of October, in the year

of mercury being put into them, they were 1824, Mr. Roberts affixed a valve to the

inserted in holes made through the valve at aperture of a pipe, used as a waste-pipe, for

certain distances from each other. The the purpose of regulating or equalizing the

inserted limbs of these tubes being thus left force of a blast of air which was blowing a

exposed to the action of the stream of air, furnace. To his surprise, however, he found

the compressed air was again admitted into that the valve, instead of being readily blown

the pipe, and the valve rose as before, 1-32nd off by a strong blast, remained at a small

of an inch. distance from the aperture of the pipe, and

* * * was removed to a greater distance only by a

From a general view of the results thus considerable exertion of the power of the

obtained, it appeared that while the valve hand. This singular phenomenon was wit

adhered to the seat, and remained but a nessed by many gentlemen, members of this

small distance from it, a circular stripe or society, in the same week, and appeared to

flat ring of attenuated air was found between be viewed by them all, as equally new and

the valve and its seat, and near to the aperextraordinary.* “Mr. Roberts made some experiments on

ture, the air at the same time in the parts

further from the aperture becoming more his air-valve at the time, and various theo-,

dense, until close to the periphery it became ries were then suggested to account for the adherence of the valve to the pipe. It was

nearly of common atmospheric density ; but

as the valve was raised, the ring of attenuated not, however, until the month of September

air approached the outer part or periphery in the present year 1826, that I agreed to

of the valve. join him in making further experiments, a

* To find the form and nature of this part of which I now proceed to give.

ring, it now appeared desirable that the dif.

ferent heights of mercury in the same tube, “ The valve was attached to one end of a

indicating degrees of vacuum should be as. scale beam by a string, and balanced by

certained at small and equal distances, beweights placed in a scale, attached to the

ginning at the edge of the aperture, and opposite end of the beam. The valve being

proceeding along a radial line to the perithus placed on the seat, without any weight

phery of the valve. of its own to press downward, the stream of compressed air was admitted into the pipe,

“ These experiments showed, that until when the valve rose from the flange or seat,

the valve was raised to a certain height above 1-32nd of an inch, and there remained sta.

its seat, the under side of that part of the tionary. Thirteen ounces, avoirdupoise

valve which was over the aperture, was exweight, were now put into the scale, which

posed to a pressure of 1} inches of mercury

more than atmospheric pressure ; and the • Monr. Clement, of Paris, was, I understand, in

under side of all the rest of the valve, form. Manchester at this period, and saw the air-valve ing an outer stripe or ring, was exposed to a adhere to the pipe, yet he afterwards, it appears, represented the discovery to have been made in

pressure less than atmospheric, or had a France long subsequent to the time he saw it at

partial vacuum varying from one and 8-10ths Mr. Roberts' works.

of an inch of mercury up to atmospheric

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pressure. The superior pressure against that the substance projected should be elas. the under side of the centre of the valve, tic, for if the ring were made of lead, the must then have been counterbalanced by effect would be the same; or if grains of the inferior pressure against the under side sand, or small lead shot, could, in like manof that part of the valve which is nearer to ner, be thrown from a centre, in all directhe periphery,—and more than counter tions around, it is clear that as they were balanced, for atmospheric pressure on the removed farther from the centre, the grains top of the valve was still so superior as to or shot would be more distant from each admit of a weight of 32 ounces being other, or the stream of them would be more applied, before that pressure could be over attenuated. come and the valve raised.

“ It has been suggested, that the formation

of the vacuum may be accounted for from In endeavouring to account for these the known tendency of a compressed spring, phenomena, it appeared, that the air in the when liberated, to fly beyond the point at aperture was projected or driven from the which it will finally settle. But this action aperture as from a centre, in radiant lines of a spring is only one instance of the operain every direction through enlarging circles, tion of a general law of nature which is apand thus became attenuated as it was thrown plicable to all bodies. When any body elas. off from the centre, in the way that light is tic or non-elastic is put in motion, its inertia diminished according to its distance from its causes it to continue in motion in the direcradiating point.

tion in which it has been impelled until its

force is expended. The force of a liberated “ When the circular valve is placed on metallic spring is expended in the effort to the seat, there is stagnant atmospheric air overcome the tenacity of the substance of within the aperture. On the condensed air which it is composed, while the force of a being admitted into the pipe, the stagnant cannon ball, fired into an earthen bank, is air is put into motion, and before it can over expended on the resistance presented by the come the inertia of the valve, is forced be. earth ; but it is projectile force that is extween the outer parts of the valve and its pended in both instances. seat. The air, while being thus forced is, however, compelled to diverge from a circle,

Addenda. whose diameter is 2fths to one of a larger diameter, and is consequently dilated and

“In a short time after the phenomenon of attenuated. The impulse given by the com

the adherence of the air-valve was observed pressed air on its first admission to the by Mr. Roberts, he ascertained, by experistagnant air in the pipe, causes the stagnant ment, without knowing that it had been air to commence the process, but the com

done before, that water, when forced through pressed air follows instantaneously, and

a conical pipe, with considerable velocity, through the force with which it is impelled

will draw out other water, placed below in by the original moving power, is projected an open vessel, if one end of a small tube is under the valve, and there forced to diverge

inserted in the conical pipe, and the other with a velocity proportioned to the amount

end is immersed in the water, in the vessel of the projectile force.

below: thus showing that water, an inelastic The projectile force acting through the fluid, produced the same effect that air did, stream of compressed air, and the peculiarly

when rushing out in a stream, confined in a shaped and confined space through which the

peculiar manner. And at the time this paper air is driven, are then the causes of its dila

was going to press, water was, by pressure tation, until its degree of rarity is beyond

from a column of considerable height, made that of the atmosphere, when atmospheric

to issue from a pipe with a valve placed over pressure on the upper side of the valve pre

it, when the valve, instead of being forced ponderates.

off by the issuing stream of water, was found “ This view will, perhaps, be illustrated,

to adhere to the seat, at a small distance from by supposing the compressed air at the edge

it. And when the apparatus was inverted, of the aperture to be an elastic ring of and the valve consequently placed below the 24ths diameter, and that every part of this seat, upon the water being permitted to flow, ring shall be struck with equal force from the valve, instead of obeying the law of the centre, in a radiating direction to the gravity and falling by its own weight, or of circumference. By the time that the ring is being driven off by the force of the stream of projected to a sufficient distance to be a water, adhered, with considerable firmness, diameter of, say 4 inches, it will be stretched to the seat." from a smaller to a larger circumference, and every part of the ring will be equally stretched or attenuated. It is not however necessary

APPENDICES TO MR. WEALE'S NEW EDITION OF TREDGOLD ON THE STEAM

ENGINE AND STEAM NAVIGATION. Mr. Weale has recently published two exactly as we were at the beginning.' very useful Appendices to his excellent “ In every description of steain-engine, edition of Tredgold on the St am-engine and in all machinery whatsoever, there is and Steam Navigation.

some fault; no class of work is perfect, The first, (called Appendix C) is by

and it would be unreasonable to expect that industrious and promising young

the absence of every defect in the Gorgon engineer, Mr. Samuel Clegg, jun., whose engine.” All this, and much more to “ Practical Treatise on Coal Gas " we the same effect, we feel bound in friendly had occasion some time ago to commend sincerity to tell Mr. Clegg, is sad twaddle. to the favour of our readers; and is oc Words—nothing but words. We should cupied entirely with the well-known be sorry to think that he is unequal to the Gorgon engines, as fitted to H. M. S. task of such a “ thorough investigation;" Cyclops. “For a correct delineation of but we must at the same time confess, our subject we are indebted,” says Mr. that we never met with reasons for not Clegg, *

to the liberality of the Messrs. grappling with a subject, which savoured Seaward; the late Mr. Samuel Seaward, more of inability to do so. Where, after whose premature death we have to de all, exists the necessity for “the thorough plore, having expressed his anxiety for a investigation” talked of ?

We cannot thorough investigation of the Gorgon en help thinking that Mr. Clegg must have gines, and which it now hoped will be greatly misunderstood “the anxiety” duly appreciated and valued by the pro

which the late lamented Mr. S. Seaward fession. It will naturally be infer "expressed” on this point. Mr. Samuel red from this, that " a thorough inves Seaward was not ignorant, of course, of tigation ” is what is contained, or at least the excellent explanatory pamphlet on attempted, in this Appendix. Strange to the Gorgon engines, written by his brosay, it contains nothing of the kind ! On ther, Mr. John Seaward; and the utthe contrary, Mr. Clegg is at pains to

most he could have meant to convey to assure his readers, beforehand, that " Mr. Clegg must have been, a wish to attempt will be made to solve questions have the argụments of that pamphlet which admit of discussion, or have been weighed, sifted, and tested, in every poscontradicted, or differently answered by different authors-no theories will be The plates illustrative of the construcgiven-no examinations of merit will be tion of the Gorgon engines are ten in entered into; but merely simple expla- number, and produced in a style which nations given of the engines as they are does unexceptionable credit both to the -the work they actually perform--noi

author and publisher. Some valuable what they might be made to do." (Page assistance in this department, from Mr. 3.) “ Thorough investigation,” therefore, E.J. Biven, late draughtsman to Messrs. there is absolutely none-nothing of the Seaward and Co., is very gratefully and sort, to be " duly appreciated and valued properly acknowledged. They are all by the profession." The utility-by no “ given to a working scale, or with means small-of Mr. Clegg's Appendix- figured dimensions." consists solely in its giving an exact and From the letter-press explanation we minute account of “the engines as they

must find room for a few extracts:are," and “the work they actually per

The Slides. form.”

We are disposed, however, to blame Mr. Clegg less for not trying his

“ The slides, which admit the steam above hand at the “ thorough investigation,"

and below the piston, and open passages than for sundry not very wise reasons

therefrom to the condenser, are those pawhich he gives for refraining from the

tented by Mr. S. Seaward in 1835, and are

peculiar in their construction, quite indeattempt. “It is not opinions which are wanted now, for they are already va

pendent of one another, and therefore caprious.”

able of separate adjustment. Any degree of “ Much has been said about the

expansion can be given to the steam by Gorgon engines-much both for and

altering the throw of the steam slide by the against-ingenious arguments have been grooved lever and horizontal rod : the slides used on both sides, but the end finds us themselves are of cast iron, 3 inches thick,

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sible way.

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