228 THE LESSON OF EVOLUTION 



these positive and negative ions, we may understand 

 why the atoms appear to be elastic. 



The vortex-ring hypothesis explains the elasticity 

 of matter, but not its inertia. And the idea of motion 

 in a continuous fluid is inadmissible, because there 

 cannot be movement without something to be 

 moved. 



Matter is invisible, unless it is aggregated into 

 large masses, with the atoms so closely approximated 

 as to reflect light. But, however closely approxima- 

 ted the atoms may be, they are never in actual con- 

 tact with each other. They are supposed to maintain 

 a constant oscillatory movement, passing rapidly 

 backwards and forwards through a small space, the 

 extent of the oscillation depending on the tempera- 

 ture of the atoms. But on the atomic hypothesis 

 matter is unchangeable. There are a fixed, but at 

 present unknown, number of different kinds of 

 atoms, which may combine with each other in dif- 

 ferent ways, but which cannot be changed the one 

 into the other. 



Energy we can divide into five different kinds. 

 1. Vibrations of the aether, or radiant energy. 

 This includes light, radiant heat, and radiant elec- 

 tricity. 



2. Vibrations of molecules. Sound, heat, and 

 current electricity. 



3. Mechanical, or molar, motion. A progressive 

 movement of molecules, generally united into a 

 mass. 



4. Chemical affinity and static electricity. 



5. Gravitation, which is instantaneous in its 



