376 schemes for Pi-rpctiial Tifct'icr.. 



the thing propofed to be tlone ? Is it to caufe a body, or fydem of bodies, to aft in fucli a 

 manner that the rc-aiflion fliall be greater than the atlion itfclf, and by that means generate 

 force by the accumulation of the furplus ? Or, can the motion communicated be greater 

 than that loil by the agent ? Since thefe pofitions are evidently contrary to the pliyfical 

 axioms called the Laws of Nature, and fricflions and refidances would fpeedily deftroy «1I 

 motions of fimple uniformity, it may be prefumcd that s'Gravefande, wlio thought that all 

 the demonftrations of the abfurdity of fchemes for perpetual motion contained paralogifm, 

 would have dated the propofition under different terms. But without entering into this ap- 

 parently unprofitable difquifition, it may be ufeful, as well as entertaining, to make 3 few 

 obfervations on the mechanical contrivances which depend on a miftakcn dedu<£lion from the 

 general theorem refpe£ling the balance, among which that of Dr. Shiviers mud be clafTed. 

 There is no doubt but numerous arrangements have been made, and dill are Laboured at 

 by various individuals, to produce a machine wiiich (liall poflefs the power of moving itfelf 

 perpetually, notwithftanding the inevitable lofs of force by fridtion and refidance of the air. 

 Little, however, of thefe abortive e.vcrtions^as been entered upon record. The plans of 

 Bidiop Wilkins, the Marquis of Worccder, and M. Orfyreus, are all which at this time oc- 

 cur to my recolle£lion. 



There is no doubt but the celebrated Wilkins was a man of learning and ability. His 

 EITay towards a real character and a pliilofophical language is fufficient to render his name 

 immortal. Twenty years before the appearance of that work he publidied his Mathema- 

 tical Magic, namely in the year 1649, containing 295 pages fmall o6lavo, which, from the 

 number of copies dill in being, I fuppofe to have been a very popular treatife- It is In this 

 work that I find, among other contrivances for the fame purpofe, a wheel carrying fixtecn 

 loaded arms, limilar to that delineated in fig. 4, plate xv. in which, however, for the fake of 

 fimplicity, I have drawn but fix. Each lever A B C D E F is moveable through an angle of 

 45°, by a joint near the circumference of the wheel, and the inner end or tail of each is 

 confined by two duds or pins, fo that it mud either lie in the direiTtion of a radius, or elfc 

 in the required pofition of obliquity. If the wheel be now fuppofed to move in the diredioa 

 EF, it is evident that the levers ABC D,by hanging in the oblique pofition againd the an- 

 tecedent pins, will defcribe a lefs circle in their afcent, than when on the other fide they 

 come to defcend in the pofitions EF. Hence it was expedled that the defcending weights, 

 having the advantage of a longer lever, would always predominate. Dr. Wilkins, by re- 

 ferring the weights to an horizontal diameter, has fliewn that in his machine they will not. 

 A popular notion of this refult may alfo be gathered from the figure, where there are three 

 weights on the afcending, and only two on the defcending fide ; the obliquity of pofition 

 giving an advantage in point of nutnber, equal to what the other fide may poflefs in inten- 

 fity. Or if this contrivance were to be driflly examined, on the fuppofition that the 

 levers and weights were-indefinitely numerous, the quedion would be determined by fliew- 

 ing that the circular arcs AK, HI, are in equilibrio with the arcs AG, GL. 



The fimplcft method of examining any fchemc of this kind with weights, confids in en- 

 quiring whether the perpendicular afcents and defcents would be performed with equal 

 malTes in equal times. If fo, there will be no preponderance, and confcquently no motion. 

 This is clearly the cafe with the contrivance before us. 



5 The 



