416 



oscillation of temperature which he assumes, to the action of water, 

 as in the following passage : " Glaciers are, on an increased scale, 

 sheets of ice placed upon the slopes of mountains, and subjected to 

 atmospheric variations of temperature throughout their masses by 

 variations in the quantity and the temperature of the water, which 

 flowing from the surface everywhere percolates them" (p. 339). 

 This action therefore clearly brings the temperature of the ice up 

 to 32 during the day. But how is the cold of the night to operate 

 in reducing the temperature of a mass of ice certainly from 300 to 

 600* or more feet in thickness through the enormous average depres- 

 sion of 9 degrees ? The water so efficient by its percolation in 

 raising the temperature (if necessary) to 32, being frozen, is now 

 powerless. Cold can be conveyed downwards, or to speak more 

 correctly, Heat can be transmitted upwards through the ice only by 

 the slow process of conduction, and this on the supposition that the 

 depression of superficial temperature is all that the theory might 

 require. But how stands the fact ? Mr. Moseley quotes from De 

 Saussure the following daily ranges of the temperature of the air in 

 the month of July at the Col du Geant and at Chamouni, between 

 which points the glacier lies. 



At the Col du Geant 4'257 Reaumur. 



At Chamouni 10'092 Reaumur. 



And he assumes " the same mean daily variation of temperature to 

 obtain throughout the length" [and depth?] "of the Glacier du 

 Geant which De Saussure observed in July at the Col du Geant." 

 But between what limits does the temperature of the air oscillate ? 

 We find, by referring to the third volume of De Saussure's Travels, 

 that the mean temperature of the coldest hour* (4 A.M.) during his 

 stay at the Col du Geant was 0-457 Reaumur, or 33 0- 03 Fahrenheit, 

 and of the warmest (2 P.M.) 4'714 Reaumur, or 42 0- 61 Fahrenheitf. 

 So that even upon that exposed ridge, between 2000 and 3000 feet 

 above where the glacier can be properly said to commence, the 

 air does not, on an average of the month of July, reach the freezing- 

 point at any hour of the night. Consequently the range of tempera- 

 ture attributed to the glacier is between limits absolutely incapable of 



* The observations were made every two hours day and night. 



t The corresponding extremes at Chamouni are 53 0< 25 and 75-96 Fahr. 



