Glacier Work. — Scott. 235 
It should be said that possibly too few recorded experi- 
ments are available upon the properties of ice, and glacier ice 
in particular, for one to be able to reason in a perfectly logical 
manner concerning its behavior under the conditions extant 
in a glacier. It seems well, however, to consider what ex- 
perimental results are given, remembering that conjecture 
alone must account for certain phenomena of a glacier, since 
some portions are quite as inaccessible even as the inner por- 
tion of the earth's crust. Such consideration leads to the as- 
sumption of the zones of fracture, and constant plasticity, 
together with the movements therein. Recorded observations 
appear to verify the reasoning, and to conform to a theory of 
glacier motion, which may include to some extent the causes 
of movements and deformation of the earth's crust. 
The scope of this paper cannot include a presentation of 
such a theory in detail, and only a suggestion of certain prin- 
ciples is here attempted. It is believed by the writer, however, 
that a further study of the properties of glacier ice, including 
tensile and compressive strength, with proper curves to show 
the relation between strength and temperature, together with 
careful examination under the microscope and polariscope of 
the crystalline structure of different parts of a glacier should 
be made. 
Further, the more prevalent use of the camera for the pur- 
pose of illustrating important features of scientific interest 
connected with glaciers, cannot fail to be commendable, and 
possibly may aid greatly in settling disputed questions. That 
photographic work is possible at the present time under al- 
most any circumstances likely to be niet with in glacier study 
is well known, and is most admirably evidenced by the eight 
hundred photographic reproductions in Peary's book on the 
Arctic region. 
Advance and Retreat of Glaciers. 
Early observation upon glaciers appeared to indicate an 
advance or a retreat with reference to the line of lower limit, 
corresponding with variations in precipitation and tem- 
perature of the air. Enlargement apparently took place in 
cold rainy periods of years, and diminution in the warm and 
dry. A report by Prof. Forel (1886) * shows that there ap- 
*Am. Jour, of Science, Vol. 32, 1886. p. 77. 
