2 ZOOLOGY 



universe, many of which can never be examined by 

 our human senses. The limitations of our percep- 

 tions are well shown when we realize that the vibra- 

 tions or waves which give us the sensations of light, 

 sound, or electric shock are only a few of those which 

 must exist. The ultra-violet light, which we cannot 

 see, we can determine by its chemical effects, and no 

 physicist doubts that there are innumerable vibrations 

 which we cannot detect at all. 

 The nature -? Yet the known and unknown facts are so related 



of truth , * , . r . ... 



that the known part 01 nature is in a sense a tair 

 sample of the whole. The unknown does not con- 

 tinually disturb the known -in unexpected ways, and 

 when it does so, it is usually brought into the region 

 of the known. Its nature is calculated from the 

 character of the disturbance. The scientific man has 

 to deal with "truth," and by truth he means not the 

 absolute reality of the philosopher, but such reality 

 as he has been able to test and examine. He does 

 not absolutely know that the "laws" deduced from 

 the experience of mankind will always be found valid, 

 but the mass of accumulated experience is such that 

 he finds he can rely upon them. This is especially 

 true in the realm of physics. 



LIFE 



The unique- 4. Modern science tends to emphasize the unique- 

 ness of life, in spite of the fact that vital phenomena 

 are said to be "explained" by laws of chemistry and 

 physics. The ancients imagined life, in some form 

 or other, to be as widely diffused as heat or light, 

 and saw in the starry heavens a region peopled by 

 innumerable sentient human beings. Today, while 



