ZOOLOGY r 



CHAPTER ONE 



THE PHYSICAL UNIVERSE 



I. IN the vast expanse of the known universe, the The laws of 

 materials composing the stars are essentially the same nature 

 as those found upon the earth, and the forces govern- 

 ing their movements do not differ from those which 

 may be noted and tested in any laboratory. Thus 

 physical nature possesses a unity which is more strik- 

 ing the more we inquire into it, and what we call the 

 "laws of nature," our statements of how things happen, 

 are considered to be valid everywhere. This uni- 

 formity of action extends not only through space but 

 also in time, so that after sufficient experience of 

 natural phenomena, man is able to predict events far 

 in the future, and assert the occurrence of others in 

 the remote past, in spite of the absence of any con- 

 temporary records. To the unscientific it seems 

 miraculous that an astronomer could say to his little 

 son, wondering at the sight of Halley's Comet in the 

 sky: "If you live to be a very old man, you will see 

 that comet again, but I shall never see it" ; and that 

 the boy should have lived, and come to old age, and 

 seen the comet appear in the very year predicted. 

 Such a prophecy is one of the commonplaces of modern 

 astronomy, but it could not be made were not the 



r"laws of nature" valid throughout the ages. 

 2. It must not be supposed, however, that scientific Limitations 



men have discovered all the important facts. The man 



philosopher understands by the term "reality" the 

 totality of what exists, all the phenomena of the 



