Changes in tlte Muir Glacier. — Baldwin. 369 
the highest rate of velocity ever observed in a glacier, namely, 
100 feet in 24 hours, or over 4 feet an hour. A measurement at 
about the same point gave only 34 feet per day in April. " 
In another place* we find that Prof. Steenstrup writes to Prof. 
Joseph Prestwich: "Mr. Care R3'der has measured a progress or a 
flow of the great glaciers, ninetj'-nine feet per diem or in twenty- 
four hours in summer, and thirty to thirtj'-five feet in twenty-four 
hours during winter months." 
The great size of the Muir glacier maj' well lead one to ex- 
pect a high rate of motion, while its form, and the small outlet 
through which its several hundred square miles of ice must be 
forced, would point to even a higher rate. The measurements of 
1886t were taken with a sextant, reading by vernier to ten seconds, 
from a base line, which was ver}' carefully measured several 
times. The}^ were taken every four days, and everj^ reading was 
made independently by Prof. Wright and the writer, and in case 
of disagreement each read the angle again. In no case did the 
two readings differ by more than twenty seconds, and seldom more 
than ten seconds, a variance which would not cause more probable 
error, in the greater motions, than a few inches or a foot. The 
central portions of the glacier were so broken that it was impos- 
sible to cross or to set flags near the center, so measurements were 
taken to certain well defined pinnacles of ice. 
From the fact that Prof. Reid's party were unable to recognize 
from day to da}' any definite ice pinnacles from their base line, 
it has been suggested that Prof. Wright ma}' have mistaken one 
point for another. Professor Wright's base line was at the same 
level as the ice surface, and the faster moving points were white 
seracs of unusual form, seen against the dark background of the 
mountain beyond, while several of the nearer points were black 
with moraine matter and were seen against the white ice be- 
yond. 
Prof. Reid's base line was several hundred feet above the level 
of the ice, and he, of course, saw each point projected against its 
own color. I well remember that we could not recognize our 
points when we were above their level. The identification was 
complete, for to this day I remember the points well enough to 
*Nature, Dec. 29, 1887. 
fFor full account see Am.Jour.Sci., Jan., 1887, p. 8, and The Ice Age in 
North America, p. 50. 
