Memoirs of Eiasmus Darwin , M.Di 305 



3nd such machines, or that they act simultaneously or not : 

 this 77iomentum of activity is always equal to the produce of 

 a certain force, bv a velocity, and by a time, or the sum of 

 several products of this nature; and this sum should always 

 be the same, in whatever way we take it ; the agents there- 

 fore will gain nothing on the one hand, which they do not 

 lose on the other. 



To conclude, let us suppose that in general we have any 

 system of animated bodies, of anv motrix forces, and that 

 several external agents, such as men or animals, are em- 

 ployed to move this system in various and different ways, 

 either by themselves or by machines : — This being granted, 



I'Vhatever be the change occasioned in the system, the mo- 

 mentum of activity consumed during any time by the ex- 

 ternal powers, iviil be always equal to the half of the quan- 

 tity by which the sum of the active forces will haveajigynent- 

 ed during this time, in the system of bodies to which they are 

 applied: minus the half of the quantity by which this same 

 su?n q/' active forces would have augmented, if each of the 

 bodies were freely moved upon the curve it has described, sup 

 posing that it had then undergone at each point of this curve 

 the same motrix force as that which it really undergoes : 

 providing always that the motion changes by insensible de- 

 grees, and that if we employ machines with springs, we 

 leave these springs in the same state of tension in which we 



found them, [To b3 continued.] 



LiV. Memoiri of the late 'E.RASMVs Darwin, M.D^ 



[Continufd from vol. xxx. p. 115.] 

 DARW'INIANA. 



XjLaving laboured under a severe illness, the author of this 

 memoir must apologize for so long delaying the continuation 

 of the remarkable medical opinions of the great Dr. Darwin, 

 whose powers of mind, fully bent upon one important sub- 

 ject, namely hciUh, and the causes of disease, a^id the re* 

 niedies to be applied, with the rationale of -ifach, cannot fail 

 lo interest the philosophic world. 



Vol.il. No. 124. 5£p^ 1S08. U Dr 



