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 



