KINETIC OR MECHANICAL VIEW OF NATUKE. 29 



branches of research, it will be useful to define them 

 more clearly. 



Ever since Newton laid down the general laws of 

 motion, it has been seen with increasing clearness to be 

 the object of mathematical physics to describe the exist- 

 ing observable or supposed forms of motion in nature by 

 having recourse to the fundamental laws of motion 

 coupled with the smallest possible number of assumptions 

 as to the ultimate constitution of matter or of the 

 moving substance. As soon as any definite assumption 

 was made, it became necessary to follow it into all 

 possible consequences, and not to make any new assump- 

 tions so long as the capabilities of the old ones were un- 

 exhausted, or so long as it was not shown either that the 

 new assumption was based upon observable facts, or 

 did not involve latent contradictions with those already 

 admitted. Newton had led the way by making one 

 great assumption in addition to laying down the laws of 

 motion. This was the property of gravitation. Heed- 

 less of Newton's warning that this assumption, though 

 proved by experiment, did involve certain seeming 

 absurdities which called for further examination, philo- 

 sophers like Boscovich, and mathematicians like Laplace, 

 busied themselves with drawing all the consequences of 

 the assumption, and they saw the most hopeful way of 

 further progress in an extension of it into the realm 

 of molecular physics. Young was probably one of the 

 first to see the futility or the mere semblance of truth 

 in the astronomical view of nature. He approached 

 both by experiment and mathematically the great class 

 of phenomena of small, extremely rapid, periodic move- 



