POLAR ICE-CAPS AND SEA LEVELS. 347 



its thickness uniform ? Taking the calculation of 

 viscosity of ice from Main's experiment, I find that 

 ice 10 metres thick would require 33 centimetres 

 per annum to fall upon it, to keep it of equal thick- 

 ness. A metre is 39'3/o8 inches, or say 40 inches. 

 The rate at which snow must fall upon ice 10 

 metres thick so as to keep its thickness uniform, 

 would be the equivalent to 33 centimetres of rain 

 per annum. Double the thickness, or treble it, and 

 you would require an increased snowfall to pre- 

 serve it uniform double thickness requiring a 

 quadruple fall, and so on. Thus if you assume 

 a snowfall four times the amount stated, you would 

 only get double thickness. So that if the thick- 

 ness of the ice depended solely on its viscosity, you 

 may say that, between reasonable limits as to 

 amount of snowfall, the floating ice on the Arctic 

 Sea could not be thicker than from 10 to 20 

 metres; that is to say, 10 to 20 yards = 30 to 60 

 feet. This is about the thickness that it can have, 

 if there is nothing whatever carrying it away. 



In a wholly enclosed Arctic Ocean such an ice 

 sheet would go on extending till it came to the 



