356 Proceedings of the British Association. 



borealis, founded on seventeen years' observation. He stated 

 that his attention was directed to the phenomenon by the late 

 Dr Wollaston, who considered that it was beyond the terrestrial 

 atmosphere ; but having observed in his first expedition, that 

 sometimes the aurora appeared between the two ships, and also 

 between the ships and the icebergs, he considered it unquestion- 

 ably proved, that it could not be at that beyond the atmosphere 

 of the earth. Both at his observatory in Scotland, and during 

 his late and long protracted residence in the Arctic Regions, his 

 attention, had been particularly directed to this subject, and his 

 conclusions are, that the splendid phenomenon called the aurora 

 is entirely occasioned by the action of the sun's rays upon the 

 vast body of ice, and snowy plains and mountains which sur- 

 round the poles. 



6. Mr Robert Mallet on an Economic Application of Electric 

 . Magnetic Force to manufacturing purposes. The object in this 

 proposal is, to accomplish the separation of iron filings from other 

 materials, such as brass and copper, in engine-manufactories, 

 iron-foundries, &c. by means of bars rendered magnetic by elec- 

 tro-induction, and deprived of it by breaking the connexion. 



Tuesday, 11th August. — A communication was read from 

 Colonel Colby, respecting the Ordnance Survey, accompanied 

 with a specimen of the grand national work now in progress. 



7. In the Physical Section, Professor Whewell read an import- 

 ant report on Heat. He reduced his subject to four heads — ■ 

 1st, The experimental evidence of the principles of the doctrine 

 of heat. 2d, An examination of certain difficulties which affect 

 the fundamental equations. 3d, The mathematical principles 

 upon which their equations have been discussed ; and, 4tth, The 

 application of these mathematical results to several subjects of 

 practice and speculation. Under the first head, he began with 

 Newton, as the earliest experimental investigator, and gave the 

 history of the law determined by him, viz. that when the tem- 

 perature of a body exceeds that of the surrounding medium, if 

 the times of cooling be taken in arithmetical progression, the re- 

 ductions of temperature proceed by a geometrical series. It was 

 soon found that this law was not exact, as it failed to give exact 

 results when the temperature was very high, the rate of cooling 



