96 



count of it's less inclined position, as of the 

 greater transparency of the air *. It would ap- 

 pear singular, that long before Childrey and 

 Dominic Cassini, the navigators who frequented 

 the seas of the two Indies had not directed the 

 attention of the philosophers of Europe toward 

 this light, of a regular form and progress, if we 

 did not know how little, till the middle of the 

 eighteenth century, mariners were interested by 

 any thing, that had not an immediate relation 

 to the course of the ship, and the demands of 

 navigation. 



However brilliant the zodiacal light in the 

 dry valley of Tuy, I have observed it more 

 beautiful still at the back of the Cordilleras of 

 Mexico, on the banks of the lake of Tezcuco, 

 eleven hundred and sixty toises above the sur- 

 face of the ocean. On this table-land, the hy- 

 grometer of Deluc goes back as far as 15° ~f ; 

 and under 21 inches eight lines of barometrical 

 pressure the extinction of light is ~- 0 weaker 

 than on the plains. In the month of January, 

 1804, the light rose sometimes to more than 60° 

 above the horizon. The Milky Way appeared 



* It was the great serenity of the air, that caused this 

 phenomenon to be remarked, in 1668, in the arid plains of 

 Persia. 



t To 42-8°, Sauss,, at the temperature of 23'4° cent, 

 therm. 



