12 POPULAR LECTURES AND ADDRESSES. 



more than one ton. It is possible that it is 

 enormously more than one ton, to make up the 

 ascertained amount of work of four and a half 

 centimetre-grammes performed in a space of fifty 

 micro-millimetres. 



But now let us vary the circumstances a little. 

 I take the two pieces of rigidified water, and bring 

 them to touch at a pair of corresponding points 

 in the borders of the two surfaces A and B, keep- 

 ing the rest of these surfaces wide asunder (see 

 Fig. i). The work done on my hands in this 

 proceeding is infinitesimal. Now, without at all 

 altering the law of attractive force, let a minute 

 film of the rigidified water become fluid all over 

 each of the surfaces A and B : you see exactly 

 what takes place. The pieces of matter I hold 

 in my hands are not the supposed pieces of 

 rigidified water. They are glass, with the surfaces 

 A and B thoroughly cleaned and wetted all over 

 each with a thin film of water. What you now 

 see taking place is the same as what would take 

 place if things were exactly according to our ideal 

 supposition. Imagine, therefore, that these are 



