350 EPOCHS IN THE HISTORY OP THE CONTEMPLATION OF 



tion of the bottom of the sea and of coast districts, and in 

 the formation of mountains and islands, predominate. The 

 nature of the organic remains of the ancient world even led 

 Hooke to form a conjecture that the Temperate Zone must 

 once have enjoyed the temperature of a tropical climate. 



We have still to speak of the greatest of all geognostical 

 phenomena, the Mathematical Figure of the Earth, in 

 which we recognise as in a mirror the primitive condition of 

 fluidity of the rotating mass, and its solidification into the 

 present form of the terrestrial spheroid. The figure of the 

 earth was sketched theoretically in its general outlines 

 at the end of the seventeenth century, although the 

 numerical ratio of the polar and equatorial diameters was , 

 not assigned with accuracy. Picard's measurement of a 

 degree, executed with measuring instruments which he had 

 himself improved (1670), is the more deserving of regard, 

 because it first induced Newton to resume with renewed zeal 

 the theory of gravitation, which he had already discovered 

 in 1666 and had subsequently neglected : it offered to that 

 profound and successful investigator, the means of demon- 

 strating the manner in which the attraction of the earth 

 maintained in her orbit the moon impelled onward by the 

 centrifugal force. The much earlier recognised fact of the 

 flattening of the poles of Jupiter ( 54 ) had, it is supposed, 

 led Newton to reflect on the cause of such a departure from 

 sphericity. The experiments on the length of the seconds' 

 pendulum made at Cayenne by Richer in 1673, and on the 

 west coast of Africa by Yarin, had been preceded by others 

 less decisive ( 541 ) made in London, Lyons, and Bologna, 

 including a difference of 7 of latitude. The decrease of 

 gravity from the pole to the equator, which had long been 



