NOTE TO BOOK XIII. 117 



It appears that M. le Bailli had shown, in 1829, that 

 both bismuth and antimony and bismuth repelled the mag- 

 netic needle ; and as Dr. Faraday remarks, it is astonish- 

 ing that such an experiment should have remained so long 

 without further results. M. Becquerel in 1827 observed, 

 and quoted Coulomb as having also observed, that a needle 

 of wood under certain conditions pointed across the mag- 

 netic curves ; and also stated that he had found a needle 

 of wood place itself parallel to the wires of a galvanometer. 

 This he referred to a magnetism transverse to the length. 

 But he does not refer the phenomena to elementary repul- 

 sive action, nor show that they are common to an immense 

 class of bodies, nor distinguish this diamagnetic from the 

 magnetic class, as Faraday has taught us to do. 



I do not dwell upon the peculiar phenomena of copper 

 which, in the same series of researches, are traced by Dr. 

 Faraday to the combined effect of its diamagnetic charac- 

 ter, and the electric currents excited in it by the electro- 

 magnet ; nor to the optical phenomena manifested by 

 certain transparent diamagnetic substances under electric 

 action ; as already stated in the Notes to Book ix. See 

 the Twentieth Series of Experimental Researches in Elec- 

 tricity, read to the Royal Society, Dec. 18, 1845. 



When a voltaic apparatus is in action, there may be 

 conceived to be a current of electricity running through its 

 various elements, as stated in the text. The force of this 

 current in various parts of the circuit has been made the 

 subject of mathematical investigation by M. Ohm, (Die 

 Gahanische Kette MatJiematisch bearbeitet von Dr. G. 8. 

 Ohm. Berlin, 1827.) The problem is in every respect 

 similar to that of the flow of heat through a body, and 

 taken generally, leads to complex calculations of the same 

 kind. But Dr. Ohm, by limiting the problem in the first 



