210' Proceedings of the British Association for [Sept. 



Roche and others, may very probably be brought into 

 accordance, since they were perhaps, not always speaking 

 of the same thing, when they spoke of radiant heat. 



Another question of importance which has occurred to 

 the author is this : whether, in the polarization apparatus, 

 supposing one glass, or pile of mica, heated, it will radiate 

 the same quantity of heat to the other in the two rectangular 

 positions 1 The question is purely a mathematical one, and 

 has been in some degree considered at the author's sugges- 

 tion by Mr. Murphy of Cambridge ; the integration has not 

 been completed, but Mr. Murphy thinks it clear that there 

 will be a difference. 



4. Dr. H. Hudson read a paper on the phenomena usually 

 classed under the denomination of radiation of heat. 



He exhibited experiments with the reflecting and differen- 

 tial thermometer, to illustrate the radiating powers of 

 surfaces, interposing occasionally screens with plain and 

 coated surfaces. He tried the diathermancy of rock salt, 

 and shewed several experiments with Melloni's thermo- 

 multiplier, in which the effects were much smaller than 

 those of Melloni. 



5. Captain Sir John Ross detailed a new theory of the 

 aurora borealis, founded on seventeen years observation. 

 He observed, that the aurora was always found near the 

 earth, and he explained its appearance, by the reflection of 

 the sun's rays on a mass of polar ice, and from thence on 

 the clouds. He stated, that he had succeeded in finding 

 rules for correcting the local attraction of the ship on the 

 needle. 



6. Mr. Robert Mallet on an economic application of electro- 

 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 ren- 

 dered magnetic by electro induc^on, and deprived of it by 

 breaking the connexion. 



Tuesday, Wth August. — A communication was read from 

 Colonel Colby, respecting the Ordnance Survey, accom- 

 panied with a specimen. 



7. Mr. Whewell continued his report ; he noticed the law 

 of cooling, the geometrical progression, which is only correct 



