Chemical fistruments and Operations. " 993 
those immense masses of ice from the polar regions; no 
city. No other cause that we are acquainted with, is suffi- 
ciently powerful to separate those frost bound masses and 
set them afloat. It is a well known fact, that those floating 
continents of ice are much larger, at some periods, than at 
others; and that they have greatly increased within the pe- 
riod that the northern lights have been observed to increase, 
is certainly true; but to decide whether the former have fol- 
lowed so soon as to be coupled as cause and effect, requires a 
knowledge of facts beyond my observation and_ research. 
Many facts in confirmation of these views, might indeed be 
added, but they would introduce other subjects vastly more 
important, which I am not prepared now to discuss: and 
perhaps enough has been offered to determine whether the 
discussion is worth pursuing. Ss. 
Whitesborough, Oneida county, N. Y. Feb. 16, 1829. 
Ant. XV.—Chemical Instruments and Operations ; by Ros- 
ert Hare, M. D. Professor of Chemistry in the University 
of Pennsylvania. 
A modification of the process for ascertaining the specific 
gravity of the gases. 
The principal difficulty in weighing the gases accurately, 
arises from the small proportion which the weight of any 
