260 



Essay on Motion and Force. 



racy of definition, force of argument, ingenuity in experi- 

 ment, and close analysis, are exhibited to a degree, unsur- 

 passed in the literature of science. Heimholtz says : it is 

 " a peculiar shivering motion of the ultimate particles of 

 bodies." The arguments sustaining this view of heat are to 

 be found in the •writings of the great investigators I have 

 named, and I will not here review them, but considering it 

 as admitted that heat is motion of the ultimate particles of 

 masses, consider briefly other modes of molecular motion. 



The same reasoning that has led to the doctrine that 

 heat is motion, has established the doctrine that all the 

 radiant forces, so called, are modes of molecular motion. 

 Youmans says : " these forces have passed through their 

 material stage, and are now to be regarded as kindred 

 and convertible modes of motion." We now have all 

 the changes which matter undergoes reduced to motions 

 of the particles which compose it, or the mass as a whole, 

 or of portions of it in different directions ; and if the 

 arguments which sustain this doctrine are sound, the 

 general proposition, that all motion is change and all 

 change is motion, follows, I think, as a logical sequence. 

 The desire not to extend this paper has induced me to 

 omit a synopsis of these arguments which are well,known 

 to students of physical science. They are advocated by 

 the first thinkers of the present time, and the opinions 

 they sustain were also although not fully, entertained by 

 Locke, Newton, Bacon, and other great lights of the 

 past. To me they are satisfactory, and will, I think, 

 endure the test of future experiment and discovery. 



But agreeing as I do with the theories to which I 

 have referred, I am forced to differ in some important 

 particulars, from those who originated, and who advocate 

 them. Nearly all of the physicists of the present day, 

 while admitting that what have been considered as forces 

 in former times are now to be considered as motions, 

 refer them to some occult or hidden force as their cause, 

 inherent in matter and inseparable from it, immaterial and 



