1847.] OBSERVATIONS ON THE GLACIER OF THE AAR. 209 



siderably above the annual average.* Now (1846) we are de- 

 sired to consider these opinions and deductions to be erroneous, 

 as well as the measured distances ascertained by M. Wild, who 

 has hitherto been believed to be a competent surveyor, and who 

 had found the advance of the points of his triangulation on the 

 glacier to be more than one-half more rapid during summer than 

 in the remainder of the year.f The opinion of MM. Dolfuss, 

 Martins, and Collomb, is, that seasons and weather make no 

 difference whatever on the motions of the glacier of the Aar ! 



From these conflicting results, it is plain that there have 

 been reckless assertions made, and also observations unworthy 

 of confidence. It is very much to be desired, for the credit of 

 all the parties who have had a share in the experiments on the 

 glacier of the Aar, that the source of these discordances should 



be investigated. I remain, etc. 



* 



EDINBURGH, 12th March 1847. 



[The observations on the motion of the Mer de Glace, re- 

 ferred to in the preceding letter, and which were printed at its 

 close in the Edinburgh Philosophical Journal, being textually 

 taken from the paper in the Philosophical Transactions for 1846, 

 and already printed at page 125, etc. of the present volume, are 

 of course omitted.] 



* Comptes JRendus, 9th Dec. 1844, p. 1301. " L'avancement [journalierj etait 

 loin ,d'etre uniforme, il variait considerablement suivant les conditions atmosphe- 

 riques." Compare Ninth Letter [p. 73 above]. 



f Bull, de la Soc. de Neufchatel, No. 1. From the results there mentioned, I 

 give the comparative motion of seven points of the glacier during fifty-seven days of 

 summer, and for the same length of time taken from the average of the remainder 



of the year. 



Summer. Other Seasons. 



Feet. Feet. 



50-2 33'4 



54-8 34-9 



47'9 27'9 



47-1 29-6 



35-0 26-3 



25-5 16-5 



18-3 11-4 



