1866.] Extract of Letter from Mr. Chambers, Bombay, 111 



upon the neighbouring walls. When viewed from that distance, the rays 

 proceeding from the reflector have all the rich effulgence of sunshine. 



A piece of the ordinary sensitized paper, such as is used for photographic 

 printing, when exposed to the action of the light for twenty seconds, at a 

 distance of 2 feet from the reflector, was darkened to the same degree as 

 was a piece of the same sheet of paper when exposed for a period of one 

 minute to the direct rays of the sun, at noon, on a very clear day in the 

 month of March. 



The extraordinary calorific and illuminating powers of the 10-inch 

 machine are all the more remarkable from the fact that they have their 

 origin in six small permanent magnets, weighing only 1 lb. each, and only 

 capable, at most, of sustaining collectively a weight of 60 lbs, ; while the 

 electricity from the magneto-electric machine employed in exciting the 

 electro-magnet was of itself incapable of heating to redness the shortest 

 length of iron wire of the smallest size manufactured. 



The production of so large an amount of electricity was only obtained 

 (as might have been anticipated by the physicist) by a correspondingly 

 large amount of mechanical force ; for it was found that the large electro- 

 magnet could be excited to such a degree that the strong leather belt was 

 scarcely able to drive the machine. 



When the electro-magnet of the 10-inch machine was excited by means 

 of the 2|-inch magneto-electric machine alone, about two-thirds of the 

 maximum amount of power from the 10-inch machine was obtained. 



From a consideration of the combined action of the magneto-electric 

 and electro-magnetic machines, the author points out a remarkable analogy, 

 subsisting between the operation of the static forces of magnetism and 

 of cohesion in modifying dynamical phenomena, which throws additional 

 light upon the nature of the magnetic force. 



On reviewing and comparing the whole of the analogous phenomena 

 manifested in the operation of the magnetic and cohesive forces under the 

 varied conditions to which the author invites attention, it appears to him 

 that magnetism is a mode of the force of cohesion, or is, if the term be 

 allowed, polar cohesion acting at sensible distances, the equivalent of 

 magnetic force being obtained at the expense of an equivalent of ordinary 

 cohesive force (in an axial direction) so long as the iron continues to be 

 magnetized. 



III. "Extract of a Letter from Charles Chambers, Esq., Acting 

 Superintendent of the Bombay Magnetic Observatory, to the 

 President. Dated March 28, 1866." Communicated by the 

 President. Received April 26, 1866. 



You will probably have heard from Mr. Stewart that the opportunity 

 of applying usefully the experience which I acquired at Kew has been tem- 



VOL. XV. L 



