96 



on the other hand, says, that he has seen the 

 barometer constantly fall at sea, when the hair 

 hygrometer advanced toward extreme humidity. 

 I have had no opportunity of verifying either of 

 these assertions. 



AZURE COLOR OF THE SKY, AND COLOR OF THE 

 SKA AT IT'S SURFACE. 



The cyanoraetrical indications contained in 

 this work are, I believe, the first that have been 

 attempted on the sea, and in the equinoctial re- 

 gions. The instrument I made use of had been 

 compared with that of Mr. de Saussure. I had 

 the satisfaction, in 1795, to consult this illus- 

 trious naturalist on my travelling projects ; and 

 he had engaged me to make, at a distance from 

 Europe, a series of observations similar to those 

 he had collected on the chain of the higher 

 Alps *. 



I shall not here enter into the theory of the 

 cyanometer, and the necessary precautions to 

 avoid errors. Though this imperfect instrument 

 is yet but little known, naturalists are not less 

 acquainted with the ingenious principle, on which 

 the determination of the extreme points of the 

 scale f are founded. In order to assure myself 



* Mr. Leslie has expressed the same desire in his work 

 on the propagation of heat, p. 442. 



t M^moires de Turin, t. iv, p. 409. Journal de Physique, 



