340 Froi^esaor Forhes' Account of his recenf 



day to day, but from hour to hour ; so that I can tell nearly 

 what o'^clock it is by the glacier index. That you may have 

 an idea of the coincidence which these experiments present, 

 I give you tlie longitudinal motion of a point on the Mer de 

 Glace during four consecutive days. 



15.2 inches. 16.3 inches. 17.5 inches. 17.4 inches. 



2(/, This motion, evidently incompatible with sudden starts, 

 takes place in the glacier as a whole, undisturbed by the most 

 enormous dislocations of its surface, for these measures were 

 ta];en where the glacier was excessively crevassed. 



3'/, This motion goes on day and nighty and if not with ab- 

 solute uniformity, at least without any considerable anomaly. 

 On the 28th-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 shew a greater motion during the day. 



4//f, In the particular case of the Mer de Glace, the higher 

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

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



5//;, 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 

 character 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 im- 

 portant in (he whole matter is this, — that an observer fur- 

 nished with the proper instruments and methods may, by 



