S66 Proceedings of the British Association, 



Evening Meeting at the Theatre. 



The Secretaries having read abridged reports of the proceedings 

 of the Sections, a very interesting letter was read from Sir John 

 Herschel to Sir William Hamilton. 



Thursday, August 25. 



Section A — Mathematical and Physical Science. 



Mr Peacock read a communication from Mr Talbot, " On the 

 Integral Calculus." 



Dr Apjohn made a communication " On the use of the Wet- 

 bulb Thermometer, in determining the specific Heat of Air." 



Professor Sir W. R. Hamilton then made a communication " On 

 the Calculus of Principal Relations." 



The Rev, Mr Scoresby gave an account of two very delicate 

 Magnetic Instruments. 



Professor Forbes read a paper " On Terrestrial Magnetic Inten- 

 sity at great Elevations from the Earth." The author began by 

 giving a rapid review of Saussure's observations connected with 

 this subject. It was well known (he said) to men conver^nt with 

 these researches, that this enterprising philosopher and naturalist 

 ascended Mont Blanc, nearly at the summit of which he resided 

 for many days, making and recording numerous meteorological ex- 

 periments, at an elevation of about 11,000 feet above the level of 

 the sea ; but when his observations upon the magnetic needle were 

 properly corrected, for the depression of temperature well known 

 to exist at these great elevations, the result of them was, that at 

 this great elevation there was no alteration of magnetic intensity 

 which could be safely pronounced to be beyond the limits of the 

 errors of observation. Subsequently, Gay-Lussac ascended in a 

 balloon to the altitude of about, or perhaps beyond, 23,000 feet, 

 yet his observations also, when due allowance was made for altera- 

 tion of temperature, gave no alteration of the magnetic intensity. 

 But the researches of M. Kuppfer seeming to conduct to a quite 

 opposite conclusion, and the result, as stated by him, being such as, 

 if the observations were correctly made, would give a diminution 

 of the magnetic intensity for stations whose elevation above the 

 earth was considerable, which could by no means be accounted for 

 by ordinary errors of observation, Professor Forbes deemed this a 

 matter of so much importance to science, that he determined to 



