THE FINITE UNIVERSE 



difficult suppositions about the atoms necessary, 

 so that for many the atomic theory is something 

 of a double cross. The question of valency that 

 is, the ability of some atoms to hook on to two 

 or more of other kinds, is an especial stumbling- 

 block. 



In the mind of the writer the evidence for the 

 objective existence of the atom has recently gained 

 a very solid support. Thin solutions of glue or 

 jelly, which do not ordinarily solidify, may be pre- 

 cipitated by adding small quantities of various 

 substances. Barus took note that the precipitants 

 are always the substances which, dissolved in water, 

 are able to convey electricity. Sixty years' puz- 

 zling over these electric solutions has finally obliged 

 the puzzlers to assume that the substances dis- 

 solved in the water are torn apart by the tremen- 

 dous molecular forces at work therein. Thus, if 

 ordinary salt is so dissolved, it is supposed to be 

 separated into its elements, sodium and chlorine, 

 and that these exist in a free state in the water. If 

 the water is evaporated, they are said to recombine 

 gradually, so that when all the water is gone there 

 is dry salt again. The particles of sodium and 

 chlorine are supposed to bear electric charges very 

 great in comparison with their mass. If a ball of 

 pith could be so highly charged as these particles, 

 it would act with an explosive energy like dyna- 



