1S47.] 



THE CIVIL ENGINEER AND ARCMITECrS JOURNAL. 



173 



fall = 144 feet, only triples the velocity ; sisteen times tlie fall, or 25U feel, 

 produces only a four-fold velocity, &c. 



As to otiier moving bodies, Smeatou's experiments upon (lies, prove he- 

 youd all doubt, that they Hre subject to the sauie laws — viz. : that to iiouhk 

 the speed of a i;iveu Qy, requires the expenditure of/our times the jnv.ftr-> 

 which produced the original speed ; while to triple the original speed, re- 

 quires tile expenditure of nine tinu-s the original power, he. 



Subsequent experinieuis have shown that a Hy, running round at a given 

 speed, produced four times the eli'ect (in rolling long strips of lead) v^hich 

 it woulil produce at half the speed; nine times the eli'ect it nouki produce 

 ut a third of the speed, &c. lu short, if we take units of time, and suijject 

 a body to the action of an invariable impressed force during one, two, Ihree^ 

 four, &;c. of such portion of time^ we shall find that the spaces travtr-.ed by 

 such body in these times will be as the squares of the numbers denoting 

 such times. While, if we take units oi space ^ and su!)ject a body lo the ac- 

 tion of an invariable impressed force, while it moves through one, two 

 three, four, &c. of such portion o( Sjiace, we shall find that the times occu- 

 pied by such boily in traversing such spaces will be as the square roots of 

 the numbers deuoting sucii spaces. 



In relation to mechanics, I think that the correct mode of measuring 

 force is that last named — viz. : to take the sjxiee through which a given 

 pressure acts, as the measure of the force expended ; because all power 

 which is under our control, is naturally so measured. 



To wind up a given weiglit, 16 feet, requires a given power ;<, whether 

 animal or mill power, and whether the weight be wound up slowly or with 

 moderate rapidity. Release the weight and it falls in one second of lime, 

 obiainiug an acceleration of 32 feet per second, which call a. 



To wind up a like weight 04 feet requires 4;;; release it and it falls in 

 two seconds, obtaining an acceleration of 2« ouly. 



A like weight wound up 144 feet requires 9p, and will full in 3 seconds 

 obtaining 3u only of acceleration. 



The time occupied in the fall of ihe weights being respectively 1, 2, and 

 3, and the amjuut of acceleration bt*ing also respectively 1, 2, and 3, while 

 the power expended in raising the weights is respectively as 1 , 4, and 9, 

 it is clear that neitiier the time nor the acceleration alfords a measure con' 

 venient for mechanical purposes ; but the spaces traversed, viz. : 10 feel, 

 G4 feel, and 144 feet, are in ilie same proportions of 1, 4, and 9, as the re- 

 spective qualities of power expended ; therefore, the lenglli of the space tra. 

 versed by a body while acted upon by a given power is tlie true me;isiire 

 of the power expended by the mover ; and with a freely moving body it is 

 also the true measure of the force which is absorbed by such body, and 

 which that body will discharge upon any obstacle which shall slop its pro- 

 gress. A falling body, for instance, must discharge upon the earth just 

 the power expended in winding it up; audit is obvious that thij c/iarg-c 

 and discharge (if I may so term il), can be repeated at pleasure, and that 

 the power first communicated and then discharged is precisely measured 

 by ibe vertical space through which the weight is first raised and then 

 allowed to fall. 



A hammer of a given weight being wielded with double speed will 

 strike four times as hard a blow. 



A bullet being shot ofTwilh triple velocity will penetrate with nine times 

 the force. 



An engineer wishing to quadruple the power of his fly may either pro- 

 cure a wheel four times as heavy, retaining the present speed, or he may 

 double the speed of his present lly without adding to its weight ; in either 

 case, his object will be equally allained. 



Upon a future occasion, I propose to adduce instances in which the want 

 of attention to these principles has occasioned lamentable waste of valuable 

 lime, exertion, and of money. 



I am. Sir, your obedient servant, 



K. Hill. 

 [We have much pleasure in acknowledging the receipt of the above 

 letter, from Mr. E. Hill, in which, as will be seen, the writer animadverts 

 tui certain statements and definitions given by us in a paper *'On the Laws 

 of Motion," that appeared in a late number of the .luurnal. In reply to 

 the objections urged by Hr. Hill, we beg again to state that momentum is 

 » term used to denoie the product of the mass and velocity of a body ; 

 a;id, moreover, that there is no doctrine iuvohed in it. It is an arbitrary 

 t- clinical expression, and to object to ils signification is to dispute about 

 words— not about principles. Mr. Hill evidently confounds momentum 

 with what is called by engineers " power expended," or sometimes " work 

 done" — which no doubl varies as the tquara of the velocity, as we will 

 iuiuiediately show : 



Let m lie the mass of a boily caused to mive from rest by a pressure 

 which is X, at the dislance .r : then if i) be the velocity acquired at the 

 distance .r, we shall have inedv = Xd.v, by the equations of motion. 



,, , mr- /•■^-•'' ->.-_, 



I onscquentiv, = / Xa.r; 



/•') — .1 

 bill / Xi/.r is the ''work done" — which, therefore, varies as Ihe 



square of Ihe velocity. There is considerable confusion manifested by 

 Mr. Hill in the use of the word " force" : he talks of a bullet penetrating 

 with nine times the force, instead of nine times as far ;— in ibis instance, 

 Mr. Hill uses " force" to mean what he misconceives by the term " mo- 



mentum" 



-viz., /\(l 



X, or " power expended." M'e are sorrowfully wil- 



ling to concede, that much time and money have been wasted in engineer- 

 ing matters — not, however, as Mr. Hill would insinuate, from a too rigid 

 regard for the laws of motion and measures of force, but from gross 

 ignorance of bolh. Unfortunately, the confused ideas of men unacquainted 

 with mechanical principles, by jiinibling together force and its eflects, and 

 giving birth to vague and useless leriiis, such as *' living force" — and 

 "power expended" — and " power absorbed," and the like — have done 

 considerable mischief to the science of engineering, by divesting it of its 

 simplicity, and basing it upon anything rather than what it ou^ht to be 

 based upon— namely, tlie six equations of statical equilibrium, and the six 

 dynamical equations of mo'iou.] 



ARMY AND NAVY CLUB. 



We do not think it needful to make any lengthened remarks on the com- 

 petilion of designs for the Aimy and Navy Club, or lo enter inio any detail 

 with regard to them, as the designs were, according to our views, far below 

 the proper standard, and we are glad to perceive that the Committee have 

 I ad the good se.ise not lo carry out those which received the prizes. So 

 far as the competitors were concerui'd, the whole affair must be considered 

 highly derogatory from them, for they came before an irresponsible tribunal, 

 they subjected themselves to the consequences of a ballot, and they resorted 

 to canvassing — some of them, we believe, sending round bills and lesti- 

 inonials, like the Morrison's pills or Holloway's ointment sellers. It 

 is in perfect keeping witli these proceedings, that some competitors resorted 

 to false perspective views and other tricks to catch the unitiated. Thus 

 ended the lottery at the Army and Navy, or Derby, Club, with the loss of 

 time and money to between sixty and seventy architects. 



Prudent men among Ihe architectural profession of course refrained from 

 engaging in a competition which depended upon the voles of a number of 

 members of a miscellaneous club, passed through the dark ordeal of the 

 ballotling box. The Committee Club, we presume, indulged the members 

 iu this mock election, as the cheapest way of getting rid of the clamour of 

 those ultra members, who are sticklers in principle for competition and 

 vole by ballot, because of course it could have only one resull — the utter 

 impossibility of getting a good and feasible design. A first rate competi- 

 tion is not to be got by such haphazard proceedings, for neither old men of 

 talent, or young men of talent, like to expose themselves to the chances of 

 defeat before an iucompelent tribunal, while they are really lo afford at their 

 own expense the materials of their own overthrow. A painlino- executed 

 in competition for a prize, if unsuccessful in gaining the prize, may be ex- 

 hibileil and sold elsewhere; bill a design for a club, which has cost week* 

 of labour and entailed much expense, cannot be rechauffe for an almshouse 

 a theatre, or a church— Ihough iu the paucity of ideas the same Ionic porti- 

 co, or Italian campanile are made to figure as Ihe stock of all and sundry 

 the compositions of some of our inspired artists. 



Southampton Docks. — The Dock Company have, we understand cou- 

 Iracted for and coiniiienied the construction of a second dry dock 'to b« 

 completed iu November next. Messrs. William Cubilt and Co. we're the 

 successful competitors, the amount of their tender being a little above 

 £17,000. whilst that of Messrs. G. 15aker and Son, the contractors for th« 

 new custom-house now so near completion, was we believe near £18 000 

 The dock is to be 250 feet in length upon Ihe blocks, and hold two 500 luu 

 ships at once, or one of all but the largest of the gigantic steam-ship* m 

 luuiiliar to our waters, aud one sailing ship of 500 tons burlhen. 



2S 



