EDITORIAL. 965 
by the mode of manipulation as by the nature of the substance 
manipulated. The experiments of Mr. Case, therefore, only 
whet our interest to a keener edge. Is it the viscidity of the 
wax and the mode of thrust that gives the similitude to the 
phenomena of the Greenland glaciers ? le. 
* 
Tue beautiful investigations of Dr. O. Migge, which have 
come to hand since the above was put in type, go straight to 
the heart of one phase of the subject, viz., the method of inter- 
nal movement of ice crystals when deformed by an external 
force.‘ Prisms were cut from carefully formed ice in various 
directions to the principal crystallographic axis, z. ¢., the optic 
axis of the crystal, particularly in directions parallel and trans- 
verse to it. These were tested by placing their ends on supports 
and weighting them in the center. In testing the transverse 
prisms the optic axis was first placed in a vertical position. The 
prisms sagged and their ends were drawn inward. Optical 
examination showed that the optic axis remained normal to the 
bent surface. Subsequent observations on surfaces fractured for 
the purpose showed striation and other indications that plates of 
the crystal parallel to the basal plane had sheared upon one 
another. 
When similar prisms were placed so that these gliding planes 
stood on edge, xo appreciable result followed, even though greater 
weights and longer times were employed. 
When prisms cut parallel to the principal axis were tested, 
the gliding planes being transverse to the prism, the weight 
sunk sharply into the upper face of the prism, and a correspond- 
ing protrusion appeared below. As the process continued, the 
protrusion below kept closely parallel to the indentation above, 
both widening somewhat, until a section of the prism had been 
pushed entirely out. Optical examination showed that the optic 
axis remained parallel to itself throughout. The block remained 
transparent and free from fracture. The weight appeared to 
*Uber die Plasticitat der Eiskrystalle. Separat-Abdruck aus dem Neuen Jahrbuch 
fur Mineralogie, etc., 1895. Bd. II. 
