214 POPULAR LECTURES AND ADDRESSES. 



glass balls, 1 scattered at random through a space 

 equal to 1,000 times the sum of their volumes. 



o 



. t 







V 



FIG. 



43- Diagram illustrating the number of molecules in a space of i-io,oooth 

 of a centimetre square and i-ioo,ooo,oooth of a centimetre thick. 



Such a crowd may be condensed (just as air may 

 be condensed) to i/ioooth of its volume, but this 



1 The piece of apparatus now exhibited, illustrated the collisions 

 taking place between the molecules of gaseous matter, and the 

 diffusion of one gas into another. It consisted of a board of about 



