346 POPULAR LECTURES AND ADDRESSES. 



minutes only with years instead of minutes. It 

 would have taken months, I believe, instead of 

 minutes, for an ordinary ball of shoemaker's wax 

 to flatten in this way, if it had not been hurried by 

 heat. I have made a calculation of this, but I 

 will not trouble you with the somewhat intricate 

 dynamics of the matter. 



Turn again to this model showing the flattened 

 ball : you may imagine this semi-fluid wax pulled 

 in all round, held in as it might be by the sides of 

 a containing box. Well it would then just take its 

 level as water would. Now imagine the box placed 

 in water and the sides taken away : the effect would 

 be the same as if the wax were drawn out all round. 

 There is no limit to the extent to which it would 

 flatten itself, provided you did not keep adding 

 material. But if you keep adding material, you 

 arrive at a certain definite thickness. Suppose 

 there to be a quantity of ice covering a large area, 

 and all of uniform thickness. 1 low is this uniformity 

 to be preserved ? A great island covered with ice, 

 .5 ft. thick and 10 miles across, with snow falling on 

 it : at what rate must the snow fall upon it to keep 



