68 
GILBERT. 
from isostatic adjustment. Its small amount gives confi¬ 
dence not only in the high precision of the observations, 
but in the postulate that the interior plain is approximately 
in isostatic equilibrium. 
Table II. 
Gravity at Eleven Stations of the Interior Plain . 
1. 
Station. 
Altitude above 
tide. 
Reduction to mean M 
plain. 
Gravity after re¬ 
duction to mean + 
plain. 
Departure from 
mean of quanti- ^ 
ties in column 4. 
Feet. 
Dynes. 
Dynes. 
Dynes. 
Ithaca. . 
810 
+.006 
980.151 
.000 
Cleveland. 
689 
.000 
.158 
+.007 
Cincinnati. 
804 
.000 
.141 
—.010 
Terre Haute. 
495 
.000 
.149 
—.002 
Chicago... 
597 
.000 
.161 
+ .010 
St. Louis. 
505 
.000 
.153 
+.002 
Kansas City. 
912 
.000 
.141 
—.010 
Ellsworth... 
1,538 
+.002 
.169 
+.018 
Wallace.... 
3,296 
.000 
.145 
—.006 
Colorado Springs. 
6,038 
+.009 
.155 
+.004 
Denver.... 
5,373 
+.008 
.136 
—.015 
Mean. 
980.151 
.008 
The mean value of gravity for the interior plain, 980.151 
dynes, having been thus assumed as a standard for the dis¬ 
cussion of the results at the stations of the chain, it was sub¬ 
tracted from the values obtained at the several stations, after 
they had been corrected for latitude, altitude, and local 
topography. The residuals appear in column 4 of Table 
III. A correction for mean plain (column 5) was then ap¬ 
plied, giving a new set of residuals (column 6). In the 
computation of this correction a circular district with 30 
miles radius was used, as before, except at Pikes Peak, where 
the part falling within the interior plain was neglected, and 
