REVIEWS. 



353 



out much success. We infer, from what we perused, that 

 the few Hnes to be found at page 200 of his first volume, 

 give us a great deal better explanation than the ten preceding 

 pages. 



He says that the question of glaciers involves more than 

 a simple consideration either of temperature or any other 

 single cause, but the annual falls of snow may be considered 

 as an important agent, inasmuch as the extension of glaciers 

 is derived from this source. There is, he continues, an inti- 

 mate relation between temperature and snow-storms; and 

 when the one is variable the other follows in the same rule, 

 and this argument he applies with considerable effect to the 

 increase of the glaciers in more elevated districts, and the 

 recession of those situated lower, and after deliberating upon, 

 each of these several causes, he informs us that there is a 

 contrast between the advancement of the glaciers of the ele- 

 vated regions, and the retrogradation of those situated in 

 lower districts, proving that there are real and permanent 

 modifications both of temperature, and the hygrometric state 

 of the air, distinct from each other, in both these situa- 

 tions. 



In order to substantiate this assertion, he enters minutely 

 into the consideration of the subject, in which we have nei- 

 ther the inclination nor the means of following him; for 

 however applicable certain reasonings deduced from physical 

 science may be under circumstances of a like nature, we 

 have often found that philosophers have been puzzled by the 

 intervention of unforeseen agents, and an elaborate theory 

 has been overturned by an apparently simple circumstance. 

 M. Necker's reasonings involve much of this species of re- 

 search, and when we find such an able man as Sir John 

 Herschel hesitating to assign reasons for natural phenomena 

 evinced in localities which he has never visited, we naturally 



