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 

 Dal ton 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 investi- 

 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. 



