EXPLORING THE ATOM 



would be described by Reynolds as "normal piling," 

 and in such a case the "bag containing the shot or 

 grains can not be changed without at the same time 

 changing its bulk or volume, because if you shift the 

 mutual relations of the shot, they roll into such 

 positions as to increase the interstices between them. 



Interesting experiments are shown by Professor 

 Mackenzie, in which a bag filled with sand and water 

 has inserted into it a brass tube connecting with a 

 mercury pressure guage and on the other side of 

 the bag a connection with a rubber tube leading to a 

 glass tube rilled with colored water. When a pres- 

 sure of 200 pounds is applied to the sides of the bag, 

 the mercury guage shows that notwithstanding the 

 great pressure on the outside of the bag, the pressure 

 inside the bag is reduced. The same thing is proved 

 in another way by closing the pressure guage and 

 opening the valve in a rubber tube which connects 

 the bag with the glass tube filled with colored water. 

 When pressure is applied to the bag as before, the 

 colored water falls in the glass tube and passes into 

 the bag until nearly a pint has been drawn in. "One 

 would think/' says Professor Mackenzie, "that the 

 pressure on the outside of the bag would squeeze 

 anything that was in the bag out of it, but these 

 experiments show that the reverse is actually the 

 case, due to the dilation of the granular medium/' 



Practical experiments such as this put Reynolds 

 on the track of his explanation of the cause of gravi- 

 tation. He argued that if the ether, consisting of 

 infinitesimal granules in normal piling, extends in- 

 definitely in the universe, there can be no mean motion 



