92 POPULAR LECTURES AND ADDRESSES. 



" assumed uniformity of tidal retardation, that ten 

 " thousand million years ago the earth must have 

 " been rotating more than twice as fast as at present, 

 " and, therefore, that we geologists are ' in direct 

 " ' opposition to the principles of natural philos- 

 " 'ophy' if we spread geological history over that 

 "time?" I answer that tidal retardation cannot 

 be permanently overthrown by temporary con- 

 ditions ; that its true amount may be considerably 

 greater than that which we have estimated from 

 the theory of the moon's motion ; and that from 

 million of years to million of years it must always 

 be a positive retardation : whereas the integral 

 effect of the others in millions of years must be 

 zero. Professor Huxley's remarks, instead of mak- 

 ing my assertion less worthy of confidence, give 

 us a probability that we may repeat it with equal 

 confidence, for a smaller limit than ten tliousand 

 million years, when in the course of a few years the 

 committee of the British Association on tides 

 gives us, for all seas, more knowledge of the times 

 of spring tides relatively to the changes of the 

 moon ; of the times of daily high water relatively 



