ON GEOLOGICAL TIME. 31 



the frictional resistance would be something 

 between the amount estimated, and one-fifth of 

 it, if the angle HOM were anything between 45 

 and 84. But if, as is most probably the case, 

 the average lateness of the spring tides behind the 

 full and change, amounts at least to twelve hours, 

 the angle MOS cannot be less than 6, this being 

 the angle through which the moon moves in her 

 orbit in twelve hours ; and HOS is certainly 

 something short of 90. Hence it is almost 

 certain that HOM has some value between 45 

 and 84. I conclude that either the average 

 spheroidal tide must be less than ij ft. or the 

 amount of resistance to the earth's rotation must 

 exceed one-fifth of the amount which I had esti- 

 mated as a superior limit ; the only doubtful 

 assumption being, that the lateness of the spring 

 tides behind the times of full and change, is not 

 less on the average than twelve hours. 



1 3. The general tendency of that action, then, 

 is to diminish the velocity of the earth's rotation 



from lowest to highest, for the whole surface of the earth, ig feet, 

 if the tides were everywhere, those of the luni-tidal spheroid covering 

 the whole earth. 



