POLAR ICE-CAPS AND SEA LEVELS. 333 



probable estimate. Now I shall merely ask you to 

 think of a great ice-cap melted off the Antarctic 

 continent, an ice-cap 1,200 feet thick equivalent to 

 1,000 feet depth of water. Imagine this mass of ice 

 melting and flowing into the ocean ; it would just 

 raise the level of the ocean by one-fortieth of a 

 thousand feet, a quarter of a hundred, or 25 feet. 

 Our latest change of sea level here on the Firth of 

 Clyde was only 10 feet. We do not know exactly 

 the date, but it is quite certain that it was not 

 very many thousand years ago. The water-level in 

 the Firth of Clyde was then 10 feet higher than it 

 is now, and that change of level would, on the 

 theory I have stated, involve the melting of only 

 about 400 feet of ice from the southern continent, 

 which would raise the water 10 feet all over the 

 world. When the theory of gravitation is taken 

 into account in the manner I have indicated, the 

 water thus brought to one of the poles and con- 

 verted into an ice-cap, or the water that flows away 

 from the melting ice-cap leaving a deficiency of 

 solid water, does by its own gravitation always 

 exaggerate the effect. Before we go into any 



