THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



SEPTEMBER 1851. 



XXVII. On Diamagnetism and Magnecrystallic Action, 

 Bij John Tyndall, PLD."^ 



§ 1. On Diamagnetism. 



FIVE years ago Faraday established the existence of the force 

 called diamagnetisnij and from that time to the present some 

 of the first minds in Germany, France and England have been de- 

 voted to the investigation of this subject. One of the most import- 

 ant aspects of the inquiry is the relation which subsists between 

 magnetism and diamagnetism. Are the laws which govern both 

 forces identical ? Will the mathematical expression of the attrac- 

 tion in the one case be converted into the expression of the re- 

 pulsion in the other by a change of sign from positive to negative ? 



The conclusions arrived at by Pliicker in this field of inquiry 

 are exceedingly remarkable and deserving of attention. His 

 first paper, " On the relation of Magnetism and Diamagnetism/' 

 is dated from Bonn, September 8, 1847, and will be found in 

 Poggendorff^s Annalen and in Taylor's Scientific Memoirs. He 

 sets out with the question, '' Is it possible, by mixing a mag- 

 netic substance with a diamagnetic, so to balance the opposing 

 forces that an indifferent body will be the result ?'' This ques- 

 tion he answers in the negative. " The experiments,' ' he writes, 

 ^^ which I am about to describe, render it necessary that eveiy 

 thought of the kind should be abandoned.'^ 



One of these experiments will serve as a type of the whole, 

 and will show the foundation on which the negative reply of 

 M. Pliicker rests. A piece of cherry-tree bark, 15 millims. long 

 and 7 millims. wide, was suspended freely between the two move- 

 able poles of an electro-magnet ; on bringing the points of the 



* Communicated by the Author, having been read before tlie Physical 

 Section at the Meeting of the British Association at Ipswich, July 2, 1851, 



Phil Mag. S, 4. Vol. 2. No. 10. Sept. 1851. N 



