Mathetnatkdl and Physical Science. 35T 



make an extended series of observations at various levels among 

 the Pyrenees and Swiss Alps. Accordingly, having last summer 

 provided himself with a sufficient number of magnetic needles fit 

 for making proper observations upon magnetic intensity, and their 

 times of vibration at Paris having been accurately ascertained, he 

 commenced his tour for this purpose in the neighbourhood of 

 Barege and Bagnieres ; and, from a multitude of observations which 

 he had made and recorded, he now wished to select a series of forty- 

 five observations made at thirteen different stations, the elevation 

 of which above the level of the sea varied from 6000 to 1 0,000 feet. 

 Before he detailed these observations and their results, he described 

 the principle upon which they were conducted, and which appeared 

 ingenious, and well calculated to lead to satisfactory results. Ip 

 each instance, the observations were made at three distinct stations 

 — one on the summit of the mountain peak, or most elevated spot ; 

 and two at a lower, but equal level on each side of the hill, so 

 chosen, that a vertical plane would pass through the three stations, 

 and be perpendicular to the axis or length of the hill. It is ob- 

 vious then, that, speaking generally, any disturbing effect exercised 

 upon the needle by the materials of the hill at one of the lower sta- 

 tions, would be opposite in kind to thatexercised at the other of 

 the two lower stations ; and, therefore, the mean between these ob- 

 servations, made at the two lower stations, would give the magnetic 

 intensity at a point immediately beneath the upper station. By a 

 comparison of this mean intensity, therefore, with the intensity at 

 the upper station, it could be readily proved whether or not the in- 

 tensity diminished as you ascended to a greater elevation. The 

 result of the entire of this laborious course of experiments was, 

 that, with the exception of one solitary instance, the station be- 

 ing in the Pyrenees and in the neighbourhood of iron mines, 

 there was no diminution of the magnetic intensity at the higher 

 stations, at least beyond the limits of the necessary errors of instru- 

 ments and observations : even at the station where some diminution 

 did manifest itself, the quantity of that diminution was very much 

 smaller than that which resulted from the views of M. Kuppfer. 



Professor Powell read a paper " Respecting the impermeability 

 of water to radiant heat." 



A paper by Sir David Brewster, " On the action of crystallized 

 substances upon Light," was then read by the Secretary, Mr Snow 

 Harris. 



Dr Williams gave an account of an improved Ear Trumpet. 



