368 W. J. McGee—Local Subsidence produced by an Ice-sheet. 
difference of behavior noticed by the latter physicist in the 
case of different specimens of platinum. 
The brief discussion of the above mentioned results suffices 
we think to show, that: 
1st. The formule in question are based for the most part 
upon unwarrantable suppositions, such as the constancy of the 
specific heat of copper and of platinum; the constancy of the 
coefficient of expansion of the latter metal, and upon the accu- 
racy of certain very doubtful values for the boiling points of 
zinc, cadmium, ete. 
2d. That, aside from the inaccuracy of those data, the vary- 
ing resistance of different specimens of platinum renders any 
formula for the calculation of temperature of that metal from 
its electric resistance applicable only to the identical wire for 
which the law of change of resistance with the temperature has 
been determined. 
3d. That from the data at command we are not in position 
to calculate the temperature of an incandescent platinum wire 
from its change of resistance, nor from its length, nor indeed in 
any other manner, further than to express the temperature in 
terms of the length or the resistance of the wire. 
4th. That, owing to the great variations shown by different 
specimens of platinum as regards its resistance, the determina- 
tion of the expansion of the wire is to be preferred, whenever 
practicable, to the measurement of its conductivity. 
Art. XLIX.—On Local Subsidence produced by an Ice-sheet ; 
by W McGEE.* 
THE influence of a polar ice-cap on the earth’s center of 
gravity has been computed by Croll and others on the supposi- 
tion of an inflexible crust. But geological investigation has 
demonstrated that the terrestrial crust is flexible, and hence 
subject to local deformation. Now the problem requiring the 
influence of an ice-cap on the earth’s center of gravity, on the 
supposition of a flexible crust, is so complex as to be capable 
of solution in the present state of knowledge; but the local 
deformation may be considered. 
be subsidence of areas of deposition is a well-known phe- 
the High Plateaus of Utah,” p. 13), of the subsidence of the ter- 
restrial crust in Utah during the Cretaceous-Hocene time to the 
extent of 6,000 to 15,000 feet, may be here referred to. From 
* Supplementary note to p. 267 (line 33) of the last number of this Journal. 
Loy Sea ee 
