ON GEOLOGICAL TIME. 



Along the Atlantic Coast of Europe the interval 

 seems to be between eighteen hours, which may 

 be about its amount at the Cape of Good Hope, 

 and thirty-six hours its value on the West Coast 

 of Ireland ; and it is probable that in all seas 

 the spring tides are late by an interval of, in 

 general, something more than twelve hours and 

 less than three days after the time of new moon 

 and full moon. Hence, the crests of the luni- 

 tidal and soli-tidal spheroids are not coincident 

 when the earth, moon, and sun are in one line, 

 but are coincident at some time, probably ex- 

 ceeding twelve hours, after the moon has crossed 

 the line joining the earth and sun. This then 

 is decisive in showing a sensible effect of resist- 

 ance to the tidal motions, as was first, I believe, 

 remarked by Airy. 1 That there must be such 

 resistance is quite certain to us, from our know- 

 ledge of the properties of matter ; but it is very 

 interesting, and it is very important with refer- 

 ence to the subject of my present statement, 

 to find a sensible effect on the average tides 

 1 "Tides and Waves," 544 Encyclopedia Metropolitans 



