50 
PUTNAM. 
While it is somewhat unsafe to draw general conclusions 
from a single series of observations, yet the favorable and 
systematic situation of these stations with respect to an un¬ 
usual variety of continental conditions perhaps warrants the 
pointing out of a few possible inferences. With Bouguer’s 
reduction there is apparently a considerable defect of gravity 
on the western mountains and plateaus, increasing with the 
average elevation of the country. This cannot be accounted 
for to any great extent by a supposed abnormal condition in 
the mass above sea level, as it would require that that mass 
should have a density of zero to offset this defect. The pre¬ 
sumption is, therefore, that there is a deficiency of density 
below sea level, which in general compensates the elevated 
masses. Contrary to a recent assertion, the residuals do not 
appear to have any relation to distance from the sea or to 
the elevation of the particular point of observation, as is 
shown by the fairly horizontal line under that part of the 
central plain (Cincinnati to Ellsworth) where the altitude is 
nearly the same, and the nearly equal deficiencies found at 
stations which, like Gunnison, Pikes Peak, Colorado Springs, 
and Denver, vary enormously in elevation. It is interesting 
to note that the defect is largest at Gunnison, which is nearest 
the main mass of the Rocky mountains, and not at Pikes 
Peak, the most elevated station. With the reduction for ele¬ 
vation the apparent defect of gravity largely disappears, as 
shown by the nearly horizontal line of residuals under the 
great central plains, where the altitude varies from 495 to 
6,041 feet (151 to 1,841 meters), and by the average result in 
the mountain regions. In the latter, however, the line shows 
considerable departures from the normal, both positive and 
negative, the residuals showing a striking relation to the 
elevations of the stations as compared with the elevation of 
the surrounding country. Mount Hamilton, Pikes Peak, 
Pleasant Valley, and the Yellowstone Park stations are above 
the average level and show an excess of gravity, while the 
remaining Rocky Mountain stations are below the general 
level and all show a defect of gravity. This condition is 
especially marked in the case of Green River and Grand 
