Variation of Motion at different Seasons. 329 



It is on this account, Sir, that I desire that the readers of 

 the scientific journals may be made fully aware of the 

 amount of the evidence by which, in some glaciers at least, 

 the direct connection between the movements of the glacier 

 and the conditions of temperature and moisture have been 

 established ; and it is for this object that I crave a few pages 

 of your Journal, for an extract from a more elaborate and 

 less accessible paper. 



Before quitting the subject, I wish to add, that I concur 

 with M. Collomb in desiring the full publication of M. Doll- 

 fuss's results on the glacier of the Aar, which, latterly at 

 least, I know to have been made with excellent instruments, 

 and it may be hoped with due care. Until such a publica- 

 tion takes place, we must be permitted to withhold our final 

 assent from a conclusion which is in contradiction to obser- 

 vations on at least three other glaciers, and to former obser- 

 vations on the same one. Should it prove correct in the 

 particular case of the glacier of the Aar, I suspect that it 

 can only arise from a curious balance of two opposing in- 

 fluences occasioned by the peculiar circumstances of restraint 

 under which that glacier moves, and probably may apply to 

 only a very limited portion of its surface. 



But I repeat, we must wait for the observations. The 

 public cannot but receive with distrust, reports of conclusions 

 drawn from unpublished observations so repeatedly contra- 

 dicting one another, as those which have been furnished by 

 observers on this same glacier of tbe Aar. Not to go farther 

 back, within four years we have had/owr positive statements 

 of fact said to have been deduced from observation, three of 

 which are irreconcileable. First, we were told that the 

 glacier was absolutely quiescent in winter, and moved on- 

 wards during the summer months only.* It was next ad- 

 mitted, that in winter there is also motion, only the summer 



* Agassiz 1842. — " Ce que je puis annoncer positivement des a present, 

 c'est que le glacier est immobile en hiver." Letter to M. Arago, dated from 

 the glacier of the Aar, Comptes Rendus, 8th August 1842. Compare Edin. 

 Phil. Journal 1842, vol. xxxiii., p. 253, 254. 



