Geological Society. 409 



its specific gravity, according to Reich, =5*44. If, for the 

 sake of simplicity, we assume the density of the earth to be 

 uniform throughout its mass, we obtain from the above pre- 

 mises, and the known velocity of rotation, 25,840 quadrillions 

 of kilogrammetres as the rotatory effect of the earth. If, during 

 every second in 2500 years, 464,000 millions of Km of this 

 effect were consumed by the ebb and flow of the tidal wave, it 

 would suffer a diminution of 36,600 trillions of Km, or about 

 ?Wooo th of its quantity. 



The velocities of rotation of a sphere stand to each other in 

 the same ratio as the square roots of the rotatory effects, when 

 the volume of the sphere remains constant. From this it 

 follows that, in the assumed time of 2500 years, the length of a 

 day has increased * 00() th ; or if a day be taken equal to 86,400 

 seconds, it has lengthened T Vth of a second, if the volume of the 

 earth has not changed. Whether this supposition be correct or 

 not, depends on the temperature of our planet, and will be 

 discussed in the next chapter. 



The tides also react on the motion of the moon. The stronger 

 attraction of the elevation nearest; to, and to the east of the 

 moon, increases with the tangential velocity of our satellite ; 

 the mean distance of the earth and the moon, and the time of 

 revolution of the latter, are consequently augmented. The 

 effect of this action, however, is insignificant, and, according to 

 calculation, does not amount to more than a fraction of a second 

 in the course of centuries. 



[To be continued.] 



LI V. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



[Continued from p. 238.] 



February 18, 1863. — Prof. A. C. Ramsay, President, in the Chair. 



THE following communication was read : — 

 " On the Middle and Upper Lias of the Dorsetshire Coast." 

 By E. C. H. Day.. Esq. 



The subdivisions of the Lias instituted by Sir Henry De la Eeche 

 and Dr. Buckland from stratigraphical considerations, and the sub- 

 sequent modifications and further subdivision established by recent 

 careful comparisons of the fossils, having been briefly noticed, the 

 author proceeded to define the two portions of the Lias which were 

 treated of in this paper. The Middle Lias was stated to comprise 

 all the beds between the zone of Ammonites communis above and 

 that of A. raricoslatus below, and the Upper Lias to include the 

 beds commencing with the zone of A. communis and ending with 



