18 Popular summary of Experiments, fyc. 



duced, their order, as thus obtained, being as follows, viz. 

 copper, zinc, tin, lead, antimony, and bismuth, which latter 

 is very feeble in its action, compared with the first two. A 

 second method was also employed, viz. by finding the times 

 of rotation of a neutralized system of magnets suspended 

 over them. The two methods gave always the same results, 

 except in the cases of zinc and copper ; the former according 

 to three experiments, and the copper in the former, occupied 

 respectively the first place. 



Our authors next investigated the fact which M. Arago 

 had stated, viz. that if the disc of copper, or other revolving 

 metal, be cut from the circumference towards the centre like 

 radii, but without taking away the metal, it will produce, 

 upon the needle, a very diminished action. This was verified 

 bv Messrs Herschel and Babbage, and the farther curious 

 fact ascertained, namely, that re-establishing the metallic 

 contact with other metals, restores, either wholly or very near- 

 ly, the original powers, and that, too, even when the metal used 

 for soldering has in itself a very feeble magnetic power. The 

 law of increase of force, with a decrease of distance, was 

 next examined, but it was not found to follow any constant 

 ratio; it appeared to vary between the square and the 

 cube. 



The remaining part of the paper is employed in general- 

 izing and explaining the facts detailed. The explanation 

 given by Messrs Babbage and Herschel, is nearly the same 

 as that given above relative to the rotation of iron. The 

 different metals, for example, are conceived to contain a cer- 

 tain portion of latent magnetism, which is induced or called 

 into action by the power of the magnets employed ; but, in 

 consequence of the coercive power of these metals, (although 

 very small,) this developement is not instantaneous, nor is it 

 lost instantaneously when the magnets are removed ; the 

 needle is therefore constantly urged forward by the mag- 

 netism which it has itself exerted, till it at length acquires the 

 rotation above stated. 



The preceding paper by Messrs Babbage and Herschel, is 

 followed by a letter from Mr Christie, stating that he had re- 

 peated and verified all the foregoing results, and adding some 



