106 THE POPULAR SCIENCE MONTHLY. 



made up ; hence Huygens concluded that Saturn could have but one 

 satellite. 



When chemistry emerged as a distinct branch of science from the 

 superstitions and conceits which had so long overshadowed her, the 

 line of demarkation between chemical and mechanical action was made 

 clear and unmistakable. On this side were ranged all phenomena purely 

 mechanical ; on that, all phenomena purely chemical. Nature's laws 

 must be simple. One great fact was predicated of each class of phe- 

 nomena the distinction was a simple distinction. But as Nature's 

 facts were more thoroughly searched into, phenomena were remarked 

 which tended to discredit the extreme simplicity of the division into 

 chemical and mechanical actions ; those phenomena were passed by as 

 too trivial for serious notice. But the residual phenomena at last forced 

 themselves upon the attention of chemists ; and one great result of the 

 examination of these phenomena has been the discovery that the simple 

 classification into chemical phenomena on that side and mechanical on 

 this was too simple was, in fact, an artificial classification ; that there 

 is no sharp line of demarkation in Nature, but that a series of facts ex- 

 ists which bridges over the gulf formerly supposed to be fixed between 

 the two sets of phenomena. 



The earlier study of biological science tended to show a great sim- 

 plicity in the vital processes occurring among all living things ; but the 

 more advanced study of the same science has altogether overthrown 

 the simplicity of the earlier scheme. Certain animals, and classes of 

 animals, seem deliberately to adopt strange expedients for reproducing 

 their kind, as if to warn us against such hasty generalizations. How 

 should we have imagined the possibility of fertilization for successive 

 generations, of hermaphroditism, or of reproduction by fissure, etc., 

 being found among the methods Avhich Nature adopts for replenishing 

 the earth, had we contented ourselves with an examination of the com- 

 paratively simple methods of ordinary sexual reproduction ? 



The importance of residual phenomena is undoubtedly great ; the 

 difficulties which attend the study of these phenomena are likewise 

 great. 



A phenomenon, supposed to be residual, may be found on closer ex- 

 amination to be fully explained by some known law, acting either under 

 ordinary or under modified conditions. Before, therefore, attempting 

 to find a new hypothesis which shall explain the residual phenomenon, 

 it is necessary to determine the fact of the phenomenon being truly 

 residual. Of course, if an explanation be found for the seemingly in- 

 explicable phenomenon without the necessity of introducing a new hy- 

 pothesis, a distinct step has been made in scientific advance. If, how- 

 ever, the phenomenon refuse to be explained by any known law, a new 

 hypothesis must be found, or the old must be modified so as to admit of 

 an explanation being given for the hitherto inexplicable fact. 



Of the new hypotheses which present themselves to the mind, which 



