Changes in the Muir Glacier. — Bald ir in. 367 
Prof. Wright's observations were confessedh' made with less care 
than Prof. Pteid's his results were discredited. For that reason 
it seems necessary', before explaining the causes of difference, to 
turn attention for a few moments to the measurements themselves. 
This is made more necessar}' by the strange position taken by a 
recent writer, who, assuming that a glacier alwa3's moves at the 
same rate, and assuming that the measurements were taken in the 
same place, and in similar manner, has overlooked the statement 
made by Mr. Cushing, that "undoubtedl}' the ice was in more rapid 
motion at the time of Prof. Wright's visit, "* and overlooked the 
other literature of the subject, to attribute the entire discrepancy 
to inaccuracj' of Prof. Wright's observations, f 
When Forbes began his observations on the Mer de Glace, in 
1842, he made the following table of the results given by pre- 
vious observers, and after perusal of the table he declared that no 
confidence whatever could be placed in their records. 
Bakewell 540 feet per year. 
De la Beche 600 " " " 
Shirwell 300 " " " 
Rendu 365 " " 
Saussure's ladder 375 '' " " 
But Kendu pointed out to him the reason for the differences, 
and in 1845 Forbes seems to have accepted Rendu's point of 
view. Prof. Tyndall says in his "Glaciers of the Alps:"! "The 
numbers in the above table differ widely, and it is perhaps natural 
to conclude that such discordant results are of no value, but the 
fact reall}' is that every one of them may he perfectly correct. " This 
old lesson is perhaps not yet quite out of date. 
The reasons for the discrepanc}' may well be divided into three 
classes: first, the probable error; second, difference in manner or 
locality of measurement; and third, actual difference of motion of 
the glacier. 
1. Probable Error. 
A. When Prof. Wright's results were announced six years ago, 
comparatively little was known of the motion of the glaciers in 
Greenland, or of other large glaciers, and the contrast of the Muir 
♦American Geologist, Oct., 1891, p.216. 
fW J McGee, Am. Anthropologist, Jan., 1803, p. 89, and Scienoo, Dec. 
2, 1892, p. 317. 
JPage 305. 
