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been described at page 391 of the pre which only requires to be known to be sent volume. To this description, I now duly appreciated. beg to add a few remarks, in order to set I remain, Sir, the importance of Mr. Fenn's invention

Yours respectfully, more fully before your readers.

WM. BADDELEY. All previous coach-wrenches have con 29, Alfred-street, Islington. sisted of a stem, with one fixed and one November 9, 1842. moveable cheek or jaw, capable of being set and held at certain distances, according to the size of the bolt or nut to be acted MOSELEY'S MECHANICAL PRINCIPLES OF upon; the moving power has ever been ENGINEERING AND ARCHITECTURE.* a screw, but applied in a great variety of

The object of the present volume, by the ways. Even when well made, the threads of this screw, after a time, become worn

learned Professor of Philosophy and Astroand strip, while in those of the ordinary nomy in King's College, is to apply the description this effect very rapidly obs principles of mechanics to the investigation tains. Again, with the screw-wrench, and solution of the most important and obwhen nuts, varying greatly in size, are vious of those questions which present them. employed (which is a frequent occurrence) selves in the practice of the engineer and the setting of the wrench to each is a

architect; and it is by far the most original, slow and tedious operation, and the continual working of the screw causes most

ingenious, and useful work which has yet injurious wear of its threads.

appeared on the subjects which it embraces. In Mr. Fenn's new coach-wrench, no The author first treats briefly of those matter how great the discrepancy between portions of Statics on which the “theory of the sizes of the nuts, &c., the adjustment machines” and “theory of construction" is instantaneous, without strain or wear to any part of the instrument. The wedge

depend, namely, the “parallelogram of presbeing free, the jaw A (vide page 391,)

sures "—the “equality of moments "-the is placed against one side of the nut, and * polygon of pressures”—the "parallelothe jaw C slips up against the other ; on pipeds of pressures”_"parallel pressures” grasping the handle and lever to turn the -and the “ centre of gravity." The term nut, the jaw C becomes immediately fixed

pressure Professor Moseley employs in prein its position. When the nut is screwed

ference to the ordinary one of force; but up, the jaw is released by letting go the lever.

the difference between them is not very perThe defects and inconveniences of the ceptible. Granted, that there is no force till ordinary coach-wrench have led, in a num there is pressure; still, the substitution of ber of instances, where the work will ad. the one term for the other is but another mit of it, to the employment of spanners form of expressing that it is pressure which of definite fixed sizes, such as half inch,

constitutes force. Indeed, the Professor inch, and so forth. Mr. Fenn's recent improvement, how

himself afterwards admits as much, when he ever, has so completely turned the tables says, (Note p. 92,) that “pressure and in this matter, that his coach-wrench will moving force are but different modes of the really be found to be the best, and by far operation of the same principle of force.” the most convenient that can be employed:

We are next introduced to Dynamics, or inasmuch as it can be applied to nuts of

that science which “ treats of the laws which every size within its range (about 4 inches) in less time than one of the particular govern the motions of material bodies, and size required could be selected, supposing of their relation to the forces whence those it lay before the workman, instead of motions result.” Various terms have been having, as is often the case, to be sought used to denote the result of the union of a for.

continued pressure or force with a continued I am sure your correspondent "T.B.J." will not take it amiss at my adding this The Mechanical Principles of Engineering and testimony to his own, in behalf of the

By the Rev. Henry Moseley, M.A., merits and advantages of this simple but

F.R.S, Professor of Natural Philosophy and Astro

nomy at King's College. · really beautiful contrivance of Mr. Fenn's, Wood. 8vo., pp. 627. Longman and Co.

Architecture.

With Illustrations on

motion ; such as dynamical effect, efficiency, It will be proper further to bear in mind, quantité d'action, puissance mécanique, &c. that by the pound mentioned in these defini. But, among our French neighbours, all other tions is to be understood the weight of terms have lately given place to the word 22.815 cubic inches of distilled water at travail; and as this has the advantage of 62° Fahr., (with barometer at 30 in.,) which great clearness, distinctness, and simplicity, is equal to 5,760 grains, or 1 lb. troy, and Professor Moseley proposes that we shall 7,000 grains, or 1 lb. avoirdupois. follow their example, and make use of the Newton employed the term vis inertia analogous English term, work. The pro to express the inert or passive force which priety of this recommendation is so obvious, any body opposes to motion; and this term that we make no doubt it will be henceforth has continued in very general use down to universally adopted.

the present day. But as it would be ob. The “work” of overcoming a pressure of viously inconsistent with the preceding defione pound through a space of one foot has, nitions, to recognize the existence of force in this country, been considered as the dy. (vis) where there is no motion-no pressure namical unit, or term in which any other -no work done (dynamically considered)amount of work may be estimated ; and in Mr. Moseley abandons the use of that term France, the "travail" of overcoming a pres altogether; and endeavours to make up for sure of one kilogramme through a space of it by the following new enunciation of the one metre has, on the suggestion of M. principle of the vis viva, or moving force. Dupin, been called a dyname. Professor “ The difference between the aggregate Moseley thinks " unit of work" a better

work done upon the machine, during any

time, by those forces which tend to accele. term than dyname; and here, again, we

rate the motion, and the aggregate work, think the universal scientific world will go during the same time, of those which tend to along with him.

retard the motion, is equal to the aggregate For dynamical effect and dynamical unit,

number of units of work accumulated in the therefore, let the terms work and unit of time, if the former aggregate exceed the lat.

moving parts of the machine during that work be henceforth and for ever substituted; ter, and lost from them, during that time, if and let the engineering student, who desires the former aggregate fall short of the latter." to start with clear notions of the elements he - Page 9. has practically to deal with, commit to me

We submit that this is but avoiding one mory the following definitions.

inconsistency, to fall into a greater. The

learned Professor has taught us, before, that " Work is the union of a continued pres. “a man who merely supports a load upon sure with a continued motion. A mechanical

his shoulders, without moving it, no more agent is thus said to work when a pressure is continually overcome, and a point (to

works, in the sense in which that term is which that pressure is applied) continually

here used, than does a column which sus. moved by it. Neither pressure nor motion tains a heavy weight upon its summit;" and alone is sufficient to constitute work; so

yet, he here speaks of the “ that a man who merely supports a load upon

aggregate work" his shoulders, without moving it, no more

done by certain "forces," which are of just works, in the sense in which the term is here as passive a character as either the man or used, than does a column which sustains a the column. It cannot be said that any heavy weight upon its summit.”-Page 53.

thing is gained, either in exactness or clearThe unit of work is the work necessary to overcome a pressure of one pound through

ness, by calling the motion obstructive proa distance of one foot, in a direction oppo perty, which bodies in a state of rest possess, site to that in which the pressure acts. a force which “ tends to retard motion," inThus, for instance, if a pound weight be

stead of vis inertia. The thing itself re. raised through a vertical height of one foot, one unit of work is done; for a pressure of mains, though the old definition be shelved. one pound is overcome through a distance Neither can it be considered correct to of one foot, in a direction opposite to that say, that the active forces are those which in which the pressure acts.”- Page 54. merely " tend to accelerate motion," for

the "

they cause it as well. And this is consistent sequent period of the motion ; so that, not with the definition given elsewhere by Mr. only is the exertion of a certain force necesMoseley himself (Part I., p. 1) of the term

sary to cause the one body to pass at first

from a state of rest, to a state of motion "force," namely, that “force is that which

upon the surface of the other, but that a tends to cause or to destroy motion, or certain force is further requisite to keep up which actually causes or destroys it."

this state of motion. The resistance thus The word inertia, (an obvious abbrevia

opposed to the motion of one body on the

surface of another, when the two are pressed tion of vis inertiæ,) has come into such com

together, is called friction; that which opmon use amongst us, that it may almost be poses itself to the transition, from a state of considered as adopted into our vernacular

continued rest to a state of motion is called tongue; and it conveys so intelligibly to

the friction of quiescence ; that which con

tinually accompanies the state of motion is every one the thing meant by it, that we

called the friction of motion.”—p. 137. think it a waste of labour and ingenuity to

To this definition, there is this insuperable go farther a-field in search of a better.

objection, that it rests on an assumption which The “work of pressures applied in dif

in point of fact is not true. Au friction is ferent directions to a body movable about a

not all resistance to motion ; for without fricfixed axis; moment of inertia ;

tion there would in many cases be no motion. the " acceleration of motion by given moving

On railways, for example, and in such hydrauforces"—the “ descent of a body upon a

lic machines as the “Danaide," or Whitelaw curve''-thesimple pendulum'

"_" im

and Stirrat's mill, if we were to take away Mr. pulsive force "_" the parallelogram of mo

Moseley's “ certain resistance" to motion, tion”—“ the polygon of motion "_" the

there would be no motion at all! Innumeprinciple of d'Alembert,” (that in any sys

rable would be the similar paradoxes in tem of bodies mechanically connected in any

which such a definition would involve us. way, so that their motions may mutually Something better in the way of definition influence one another, if forces equal to the

undoubtedly remains yet to be worked out. effective forces were applied in directions

But till all the facts about friction have opposite to their actual directions, there

been incontrovertibly ascertained, it would would be an equilibrium with the impressed

be idle to hope for any complete definition, forces)--the “motion of translation "_"the

and this assuredly has not yet been done. motion of rotation about a fixed axis

The following summary by Mr. Moseley " the centre of percussion "_" the centre of

of the “principal facts” which have resulted oscillation "_" projectiles” centrifugal

from the experiments made on friction, all force"-the “principle of virtual velocities"

of them, be it observed, of a very recent date, _" the principle of vis viva," (before ad

is excellent in its way ; but when the profesverted to,)—are all successively treated of

sor adds that they constitute the laws of as branches of dynamics, and with great friction," he evidently goes further than he ability, though in a more scholastic style,

is warranted by his premises. He says him(of which more hereafter,) than seems to us

self afterwards, (p. 144,)“it is to be regretted absolutely necessary.

that with the means so munificently placed We come now to what has been so long

at his disposal by the French Government, sort of opprobrium mechanicum, the

M. Morin did not extend his experiments to subject of friction, and shall first present

higher pressures,” &c. Why regretted, if to our readers Mr. Moseley's definition of

the laws of friction" have been already it.

established : " It is a matter of constant experience, "The principal experiments on friction have that a certain resistance is opposed to the been made by Caulomb, Vince, G. Rennie, motion of one body on the surface of an N. Wood, and recently (at the expense of other under any pressure, however smooth the French Government) by Morin. They may be the surfaces of contact, not only at have reference, first, to the relation of the the first commencement, but at every sub friction of quiescence to the friction of mo.

VOL. XXXVII.

KK

tion ; secondly, to the variation of the fric to the insistent pressure, a continuous stratum tion of the same surfaces of contact under of unguent remains continually interposed different pressures; thirdly, to the relation between the moving surfaces, and the friction of the friction to the extent of the surface of is thereby diminished, as far as it is capable contact; fourthly, to the relation of the of being diminished, by the interposition of amount of the friction of motion to the velo the particular unguent used. In this state city of the motion; fifthly, to the influence of the amount of friction is found (as might be unguents on the laws of friction, and on its expected) to be dependent rather upon the amount under the same circumstances of nature of the unguent than upon that of the pressure and contact. The following are surfaces of contact ; accordingly M. Morin, the principal facts which have resulted from from the comparison of a great number of these experiments ; they constitute the laws results, has arrived at the following remarkof friction.

able conclusion, easily fixing itself in the * 1st. That the friction of motion is sub.

memory, and of great practical value; 'that ject to the same laws with the friction of with unguents, hogs' lard, and olive oil, quiescence, (about to be stated,) but agrees interposed in a continuous stratum between with them more accurately. That, under them, surfaces of wood on metal, metal on the same circumstances of pressure and con wood, and metal on metal, (when in motion,) tact, it is nevertheless different in amount. have all of them very nearly the same co

* 2ndly. That when no unguent is inter efficient of friction, the value of that coposed, the friction of any two surfaces (whe efficient being, in all cases, included between ther of quiescence or of motion) is directly 0:7 and 0.8.' proportional to the force with which they “. For the unguent tallow, the co-efficients are pressed perpendicularly together, (up to are the same as for the other unguents in a certain limit of that pressure per square every case, except in that of metals upon inch); so that, for any two given surfaces metals. This unguent appears, from the of contact, there is a constant ratio of the experiments of Morin, to be less suited to friction to the perpendicular pressure of the metallic substances than the others, and one surface upon the other. Whilst this gives for the mean value of its co-efficient, ratio is thus the same for the same surfaces under the same circumstances, 10.'” of contact, it is different for different surfaces of contact. The particulər value of it in

The points which most want clearing up are respect to any two given surfaces of contact these : is called the co-efficient of friction in respect 1. What the “ certain limit,” or pressure to those surfaces. The co-efficients of friction in respect to those surfaces of contact,

per square inch is, at which the friction of which for the most part form the moving sur

any two surfaces ceases to be in a constant faces in machinery, are collected in a Table.* ratio to the force with which they are pressed

"3rdly. That when no unguent is inter perpendicularly together. posed, the amount of the friction is, in every case, wholly independent of the extent of

M. Morin's experiments (from which the surfaces of contact, so that the force chiefly the preceding “ laws” are deduced) with which two surfaces are pressed together were made with insistent pressures of only being the same, and not exceeding a certain from 14.3 to 28.6 lbs. per square inch; but limit (per square inch) their friction is the same whatever may be the extent of their

the experiments of Mr. George Rennie, surfaces of contact.

which were carried in some instances to us " 4thly. That the friction of motion is high as 5 and 7 cwt. per square inch, show wholly independent of the velocity of the that the co-efficient of the friction of quiesmotion. “5thly. That where unguents are inter

cence increases rapidly as the pressure adposed, the co-efficient of friction depends vances to the point at which the substances upon the nature of the unguent, and upon begin to abrade or destroy one another, the greater or less abundance of the supply.

though at what particular stage that increase In respect to the supply of the unguent, there are two extreme cases, that in which

begins, and in what ratio it proceeds, has the surfaces of contact are but slightly rub

yet to be ascertained. Professor Moseley bed with the unctuous matter, and that in thinks it probable that the coefficient of the which, by reason of the abundant supply of friction of motion remains constant under a the unguent, its viscous consistency, and the extent of the surfaces of contact in relation

wider range of pressure than that of quies.

cence; but this also is a point which future • This Table we shall give at length at some future opportunity.-Ed. M. M.

experiment only can determine.

2. How far the approach to the point of the particular moduli of all the ordinary abrasion or destruction is accelerated by the elements of machinery, as the wheel and velocity of the moving surface (that it is 'axle, cord and pulley, rack and pinion, &c. ; accelerated to some unknown extent appears

so that when we wish to ascertain the modulus certain), and what the amount of destruc of any machine, we have but to combine the tion of surface, or wear of material is, which moduli of all the elements of which it is corresponds to the same space traversed compounded. under different pressures, and at different Of these elements, the most frequent in velocities.

occurrence, as well as the most useful in The “ limiting angle of resistance" is a application, are those which rotate about cyvery appropriate name first given by Mr. lindrical axes; and in treating of these the Moseley to that particular degree of inclina author is particularly happy. We may select, tion from the perpendicular at which one for example, two passages relating to that body, moving on another fixed body, will often and still much debated question, the cease to be sustained by it; and its proper comparative merits of the beam and direct ties were also first investigated by him in a action steam-engines, which ought, in our paper read before the Cambridge Philoso. humble judgment, to set that question at phical Society, in December, 1833, and pub.

rest for ever. lished in the Transactions of the following Article 168. " A machine to which are year. The results of that enquiry are here applied any two pressures P1 and P2, and

which is moveable about a cylindrical axis, given in a condensed, but sufficiently intel

is worked with the greatest economy of ligible form ; besides which the author has

power, when the directions of the pressures been at the pains to calculate the value of

are parallel, and when they are applie:l on that angle in respect of every one of the the same side of the axis, if the weight of numerous surfaces contained in the Table

the machine itself be so small that its influ.

ence in increasing the friction may be of Friction before alluded to, as intended to

neylected. be presented to our readers in extenso at

· For, representing the weight of su h a some future opportunity.

machine by W, it appears by equation (166) The “ Theory of Machines,” which comes

that the modulus is next, occupies by far the largest portion of U1 U2

pL 1 +

sin.

al a? the volume, and is beyond all doubt the most valuable, and important.

when it follows that the work Ui hich In a memoir by Mr. Moseley, “On the

must be done at the moving point to yield Theory of Machines,” which was published

a given amount U2 at the working point is

less as L less. in the Philosophical Transactions for 1841, he showed that the moving power in every

Fig. 1.

Fig. 2. machine divides itself into, First, that which overcomes the prejudicial resistances (the vis inertiæ); Second, that which causes the progression of the machine, or accumulates power in it; and Third, that which operates at the working point or points, and is represented by the work done by it. Mr. Moseley showed also, that between these three elements there obtains in every machine a mathematical relation which he called its modulus. Now what the learned Professor has done in the part to which we are now

“Now L represents the distance A' A?

between the feet of the perpendiculars CA' come of the present volume, is to determine and CA”, which distance is evidently least,

;

P2

K

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