76 CROONIAN LECTURES 



by stimulants, or be kept up by whips, whether 

 ponderable as alcohol, aether, ammonia; or 

 imponderable as heat, light, electricity, friction; 

 or that it can be made less active, or let down 

 or untoned by excessive use or by withdrawal 

 of the stimulants. 



When any excess of motion takes place, we 

 must have an answer where the equivalent of 

 that motion comes from, and whither it will 

 go. Our ponderable and imponderable whips 

 and stimulants are bound up with the matter, 

 and produce more active motion according to 

 the latent energy which the matter itself 

 possesses. 



When any want of motion occurs, we must 

 ask whence the deficiency of motion comes. Is 

 there a want of matter possessing latent energy ? 

 or is there increased resistance to the conversion 

 of latent energy into active motion ? 



It may be said that this is only a verbal 

 alteration ; but it is, in truth, an alteration in 

 the foundation on which all our knowledge is 

 based. 



It is an alteration which represents the 

 direction in which science is advancing ; and 

 it is an alteration which not only marks the 



