8 INTRODUCTORY 



and Life would be found in the test tube with it. 

 In fact Life is assumed to be an attribute of Matter. 

 But this view seems to ignore altogether the 

 peculiar character of the energies which it 

 exhibits. Its essential nature is unknown to us, 

 as is also the essential nature of electricity and 

 gravity. And it seems likely to remain unknown, 

 since it lies beyond the scope of our powers of 

 perception. Science is reluctant to admit that 

 the unknown is unknowable ; and the striking 

 success which it has recently gained in the analysis 

 of the constitution of the electric current, and of 

 the emanations of radium, may suggest that no 

 limits should be set to its powers of investigation. 

 But these discoveries, great though they are, 

 only prove that we can increase the acuteness of 

 our senses, and perceive appearances which have 

 hitherto lain beyond our ken. The fact remains 

 that we are dependent upon our sensations for 

 our knowledge ; and our sensations can resemble 

 realities no more nearly than a catalogue resembles 

 the furniture which it advertises. Conscious reason 

 enables us to analyse our sensations, to classify 

 them by their properties, and to deduce from their 

 relations to one another the abstract conceptions 

 that crown the edifice of science. But our sensa- 

 tions are the ground work or this intellectual super- 

 structure, and we can gain no clues to the nature 

 of energies, which are not themselves perceivable 

 by the senses, except by the observation of the 

 perceivable effects that they produce. Gravity is 

 known to us merely by the movements which it 

 causes in material objects. We can form any 

 view of the nature of Life only by scrutinizing 

 and classifying the manifestations of its activity. 

 The appearances upon which we rely are as unlike 

 realities as words are unlike the things that they 

 represent. But they are the only material that 



