8 



A YEAR IN SCIENCE 



are of equal size, but they are of different sizes in 

 different substances. The same is true of the inter- 

 molecular spaces. All molecules of water are of equal 

 size, but they differ in size from those of mercury. 

 Molecules are so small that they cannot be seen even 

 through the most powerful microscope. The smallest 

 particles that can be detected with our best micro- 

 scopes have a diameter of 1/100,000 of an inch. The 



average diameter of mole- 

 cules has been computed 

 by some authorities to be 

 about 1/62,500,000 of an 

 inch. 



Another statement has 

 been made to the effect 

 that if a cubic inch of 

 molecules of air tightly 

 packed together could be so 

 controlled that 100,000,000 

 of them could escape each 

 second, it would take over 

 100,000 years for all to 

 escape. 

 Molecules in solids. For 



Fig. 4. Metal ball and ring. proof that Solids are COm- 



posed of molecules we need only to recall the experi- 

 ment of the ball and the ring. With both the ball and 

 the ring at the same temperature, the ring just slips 



