110 



water*"; for the open sea is often green, where: 

 it is more than eight hundred fathoms deep. 

 Perhaps, at certain hours of the day, the red 

 or yellow light of the Sun contributes to the 

 colouring it green ^. The waves, like moveable 

 and inclined mirrors, progressively reflect the 

 shades and tints of the atmosphere from the 

 zenith to the horizon. The motion of the sur- 

 face of the water modifies the quantity of lights 

 that penetrates toward the inferior strata ; and 

 it may be conceived, that those rapid changes 

 of transmission, which act as it were like changes 

 of opakeness, may, when they are united to other 

 causes unknown to us, change the tint of the 

 ocean, 



DIP OF THE MAGNETIC NEEDLE. INTENSITY OP 

 THE MAGNETIC FORCES. 



The variations of terrestrial magnetism belong 

 to a kind of phenomena, on which I have em- 

 ployed myself with singular predilection, during 

 the course of my travels, and in the subsequent 

 years. The objects to which I directed my re- 

 searches were, first, the dip of the magnetic 

 needle ; secondly, the variation, or angle which 



* Decade Egyptienne, vol. i, p. 161, 



+ The beautiful greenish blue color of ice, when we see it 

 in a great mass, is a phenomenon well worthy of investiga- 

 tion, and known by every naturalist, who has visited the gla- 

 ciers of the Alps. 



