NOTES. 



Ixxi 



falling drops of rain. This ingenious discussion also shews how, under certain 

 conditions, an accurately observed optical phenomenon may throw light on 

 difiicuit meteorological phsenomena. 



( M ) p. 208. Boii'singault's researches appear to me to leave no douht on 

 the fact, that within tlie tropics the temperature of the ground, at a very small 

 depth below the surface, corresponds with the mean atmospheric temperature. 

 I subjoin a few examples : 



The doubt respecting the temperature of the earth within the tropics, to 

 which T may myself have given occasion by my observations in the caves of 

 Guaripe Cueva del Guacharo (Rel. hist. T. in. p. 191 196), is removed by 

 considering that I compared the presumed mean temperature of the air at the 

 convent of Caripe (18'5 C., 65'3 Fah.), not with the temperature of the air 

 in the cavern (which was 18'7 C., or 65'6 Fah.) but with that of the sub- 

 terranean rivulet (16'8 C., or 62'2 Fah.), although I had before remarked 

 (Vol. iii. p. 164 and 194) that the waters of the cavern might very probably 

 be affected by waters coming from greater heights. [See addition to note 139. 

 EDITOR.] 



C 205 ) p. 209. Boussingault, in the Annales de Chimie, T. Iii. p. 181. The 

 temperature of the spring of Chaudes-Aigues, in Auvergne, is not more than 

 80 C. (176 Fah.) It may also be remarked, that while the aguas calientes 

 de las Trin cheras, south of Porto Cabello (in Venezuela), issuing from granite 

 divided in beds, show a temperature of 97 (206'6 F.), all the springs on the 

 still active volcanoes of Pasto, Cotopaxi, and Tunguragua, have temperatures 

 of only 36 to 54 C. (96'8 to 129'2 Fah.) 



t 206 ) p. 210. See the descriptions of the Kassotis (the fountain of St. 

 Nicholas), and of the Castalian spring at the foot of the Phedriades, in 

 Pausanias, x. 24 5, and x. 8 9 ; of the Pirenean spring (Acrocorinthus), 

 in Strabo, p. 379 ; of that of Erasinos (on the Chaon, south of Argcs), in 



