Bodies are repelled from the Poles of a Magnet. 155 



Shortly after the publication of M. Pliicker's first memoir, Mr. 

 Faraday observed the remarkable magnetic properties of crystal- 

 lized bismuth ; and his researches upon this, and other kindred 

 points, formed the subject of the Bakerian Lecture before the 

 Royal Society for the year 1849. 



Through the admirable lectures of Professor Bunsen on Electro- 

 chemistry in 1848, 1 was first made acquainted with the existence 

 of the diamaguetic force; and in the month of November 1849 

 my friend Professor Knoblauch, then of Marburg, now of the 

 University of Halle, suggested to me the idea of repeating the 

 experiments of M. Pliicker and Mr. Faraday. He had procured 

 the necessary apparatus with the view of prosecuting the subject 

 himself, but the pressure of other duties prevented him from 

 carrying out his intention. I adopted the suggestion and 

 entered upon the inquiiy in M. Knoblauch's cabinet. Our 

 frequent conversations upon the subject led to the idea of our 

 making a joint publication of the results : this we accordingly 

 did in two papers, the first of which, containing a brief account 

 of some of the earliest experiments, appeared in the Philosophical 

 Magazine for March 1850, and some time afterwards in Pog> 

 gendorfF's Annalen; while the second and principal memoir 

 appeared in the Philosophical Magazine for July 1850, and in 

 Poggendorff's Annalen about January 1851*. I afterwards 

 continued my researches in the private laboratory of Professor 

 Magnus of Berlin, who, with prompt kindness and a lively 

 interest in the furtherance of the inquiry, placed all necessary 

 apparatus at my disposal. The results of this investigation are 

 described in a paper published in the Philosophical Magazine for 

 September 1851, and in Poggendorff's Annalen, vol. Ixxxiii. 



In these memoirs it was shown that the law according to 

 which the axes of positive crystals are attracted and those of 

 negative crystals repelled, was contradicted by the deportment 

 of numerous crystals both positive and negative. It was also 

 proved that the force which determined the position of the optic 

 axes in the magnetic field was not independent of the magnetism 

 or diamagnetism of the mass of the crystal ; inasmuch as two 

 crystals, of the same form and structure, exhibited altogether 

 different effects, when one of them was magnetic and the other 

 diamagnetic. It was shown, for example, that pure carbonate 

 of lime was diamagnetic, and always set its optic axis equatorial ; 

 but that when a portion of the calcium was replaced by an iso- 



those possessed by the substance itself, or which at least are altogether 

 independent of it." — Treatise on Electricity, vol. i. p. 359. 



* The memoirs in the Philosophical Magazine were written by me, and 

 the second one has, I believe, been translated into German by Dr. Kronig ; 

 the papers in Poggendortf's Annalen were edited by my colleague. — J. T. 



M 2 



