465 
When the two sets of observations were reduced and laid 
down in curves, it was found that they presented no simila~ 
rity; in other words, that there was no correspondence whate+ 
ver between the smaller changes of the declination at Dublin 
and at Philadelphia. The determination of differences of 
longitude, by means of the magnet, is, therefore, impracti- 
cable at such distances; but the attempt has revealed the 
important fact, that the irregular changes of declination, 
which have exhibited so marked a correspondence at the 
most distant stations at which simultaneous observations 
have been heretofore made, do not correspond on the Ame- 
rican and European Continents. Prof, Lloyd observed that 
much light would, erelong, be thrown upon this curious sub- 
ject, by a comparison of the observations made at the Mag- 
netical Observatory of Toronto, in Upper Canada, with 
those of Europe. 
A Paper ‘‘on the Cooling Power of Gases,” by Thomas 
Andrews, M.D.,M.R.I.A., was read by Dr. Apjohn. 
Leslie observed, long ago, that a heated body cools 
more rapidly in hydrogen gas than in atmospheric air; but 
Dalton and Davy were the first who attempted to estimate 
the cooling powers of the gases, by observing the times 
which a thermometer, heated to the same point, took to 
cool through the same number of degrees in different gases. 
So difficult of execution, however, is this method, that their 
results differ, in every respect, most widely from each 
other: thus, for example, Davy found that a thermometer 
cooled twice as fast in olefiant gas as in nitrous oxide, while 
Dalton found the rate of cooling in both these gases to be 
the same. $ 
The subject appeared to be deserving of further inyesti- 
gation, and the author has endeavoured to pursue it by a 
novel method, which may, perhaps, be susceptible of other 
applications in inquiries connected with the science of heat. 
