288 Proceedings of the Royal Irish Academy. 



The latest accurate estimate of tlie difPerence is that made by 

 Mr.'Croll, viz., 4^ feet. 



This head of water, if it could produce an oceanic flow at all, 

 would be one at the rate of one mile in 42*567 days ; or a flow that 

 would occupy 700 years to pass from the equator to the poles. 



