LIVING THINGS AND MACHINES 207 



of the question that it should be thoroughly 

 understood. We have excellent parallels and 

 precedents for entertaining our belief. No_one 

 doubts the reality of gravitation, since all can Gravitation 

 perceive its operations, yet no one has ever seen 

 his force nor has any person yet propounded 

 an explanation of its nature which has met with 

 anything like general approval in the scientific 

 world. 



Or again take the question of the ether, of The ether 

 the existence of which at least the greater num- 

 ber of scientific men seem to have no doubts. 

 Yet Professor Duncan * says that " any dis- 

 cussion of ether leads out upon the high road 

 to incredulity. A thing," he proceeds, " must 

 be defined by its properties and the properties 

 of the ether are for the most part negative ; so 

 negative, indeed, are they, that when one says 

 boldly that we cannot see ether, hear it, taste 

 it, smell it, exhaust it, weigh it, or measure it, 

 one feels timid that sane-minded people will 

 meet these negative qualities of our ether by 

 a decided negation of belief in its existence. 

 But the fact of the matter is that if this thing 

 ' ether ' is not visible to the eye of sense it is 

 visible to the eye of the mind which is much less 

 liable to err." And he proceeds to show the 

 grounds on which the ether is believed in, purely 



* The New Knowledge, 1907, p. 3. 



