508 
PHILOSOPHICAL SOCIETY OF WASHINGTON. 
edge of the level shore-ice produced at one point, half a mile west of the 
International Polar Station, a permanent arch of ice. This arch was a 
regular anticlinal uplift, with the ridge of the anticlinal at right angles to 
the direction of the pressure, and, as was to he expected, was steeper on 
the side toward the pressure and arched along the ridge. The span of 
the arch was about 45 feet and its height in the clear 6 feet. The strip of 
ice was 20 feet wide and 4 feet thick. The temperature at the time was 
about 0° F. 
Such arches must frequently be formed during heavy ice-pressure, but 
it is apparently very rare for the pressure to stop in time to leave the arch 
intact. A similar arch is mentioned by Dr. Kane (“ First Grinnell Expe¬ 
dition,” p. 286), which was probably formed in the same way and not, as 
he believed, by the bending over of an erect cake of ice. 
Mr. H. G. Ogden read a paper on Distortion in Plane Table 
Sheets. 
[Abstract.] 
A brief reference was made to the difficulties experienced in all classes 
of precise work arising from the hygrometric properties of paper, and the 
method employed by draughtsmen of shrinking paper on a board was 
cited as the most ready means of overcoming them. The same devices 
have been resorted to by topographers using the plane table, where they 
had not the check afforded by the points of a triangulation previously 
plotted. A general knowledge of the change in the form of the sheet, it 
was asserted, however, permits a determination of the change that takes 
place in the relations of all the fixed points marked upon it. The per¬ 
centage of expansion, it was stated, is less in the direction of the grain 
of the paper than at right angles to that direction, or across the grain, 
and the difference between these percentages is practically the “ distor¬ 
tion.” If the per cent, of increase should be the same in both direc¬ 
tions there would result only a change of scale. The change that takes 
place was said to be uniform in each direction throughout the sheet, pro¬ 
vided the paper had been carefully made apd subjected to equal exposure, 
and it was this fact that permitted an analysis of the disturbance in the 
relations of the fixed points previously marked upon it, and the determi¬ 
nation of rules to guide the operator in the selection of points, or to elimi¬ 
nate the error of points not well conditioned. 
The general result of changes that take place is a permanent contraction 
that varies little except on exposure to excessive moisture. All sheets do 
not change alike. In some no change is apparent, and in others the per¬ 
centage is so nearly the same in both directions that the “ distortion ” is 
not appreciable. Experiments conducted at the Coast Survey office some 
years ago, with strips of hand-made antiquarian paper backed on muslin, 
were then cited, showing a “ permanent distortion ” in the strips that 
was quite appreciable in a foot of paper, with a maximum distortion 
about twice as large, but Mr. Ogden stated that he had frequently found a 
