Man's Place in Nature 229 



of matter, and forms theories of the constitution 

 of matter, e. g., that it consists of molecules which 

 consist of atoms, which consist of corpuscles sur- 

 rounded by positive electricity, which are them- 

 selves units of negative electricity. We know that 

 we cannot add to or take from the sum-total of 

 matter in the world. As far as we are concerned 

 it is quite indestructible. What matter ultimately 

 is, science does not pretend to tell us, unless it ex- 

 plains it away altogether in terms of electricity. 

 The "Ding an sich" is not a subject of scientific 

 inquiry. 



It has apparently become necessary to postulate 

 besides matter and energy a third something 

 the ether. This is a hypothetical "medium of 

 extreme tenuity and elasticity diffused throughout 

 all space, the medium for the transmission of 

 radiant energy." What it is, whether matter or 

 non-matter, we do not know; nor, in the strict 

 sense, do we know that it is at all. It is a necessary 

 fiction in the scientific redescription of occurrences, 

 and corresponds to something real. 



Riddles of History. To understand things as 

 they are, we must throw upon them the light of 

 past history. This is a familar dictum, and it is, 

 of course, in a measure true. But we must not 

 forget how far from complete this genetic knowl- 

 edge is. How far we are from any security as to 

 the history of the solar system, of the earth, of its 



