12 FIRST LETTER ON GLACIERS. [1842. 



absolute uniformity, at least without any considerable anomaly. 

 On the 28-29th June the motion 



from 6 P.M. to 6 A.M. was 8.0 inches, 

 .. 6 A.M. to 6 P.M. ... 9.5 ... 

 29th-30th, ... 6 P.M. to 6 A.M. ... 8.5 ... 

 ... 6 A.M. to 6 P.M. ... 8.9 .. 



seeming to show a greater motion during the day. 



4th. Tn the particular case of the Mer de Glace, the higher 

 part (the Glacier de Lechaud) moves slower than the lower 

 part near the Montanvert in the proportion of 3 to 5. 



5th. The central part of the glacier moves faster than the 

 edges in a very considerable proportion ; quite contrary to the 

 opinion generally entertained. 



There cannot be a doubt of the accuracy of these results 

 within the limits in which the experiment has been made. 

 They prove how completely problems of a purely physical cha- 

 racter admit of accurate investigation ; and when a larger 

 induction shall have freed the results from local errors, it is 

 evident that we shall have the solid foundations of a theory. 

 My wish to see the total eclipse of the sun on the 8th, has 

 brought me to the south side of the Alps sooner than I could 

 have wished ; but I have now fixed so many points on the Mer 

 de Glace, that, on my return thither, I shall be able to obtain 

 more comprehensive results. But what is most important in 

 the whole matter is this that an observer furnished with the 

 proper instruments and methods may, by spending a few days 

 on a glacier, determine at any particular season the amount of 

 its motion at all the essential points, within the limits which 

 any glacier theory can require. 



