180 Messrs. J. Tyndall and H. Knoblauch on the Deportment 



equatorial position : they do not attain it, however ; the bar 

 stands almost axial. 



The question, " Is the substance magnetic ordiamagnetic?'* 

 necessarily lay at the threshold of all attempts to explain these 

 phaenomena. To answer this question by experimenting with 

 the full crystal was impossible, as a diamagnetic crystal, it is 

 well known, can set itself axially. This being evidently owing 

 to some hidden property of the crystalline structure, we 

 thought it might be destroyed by reducing the mass to powder. 

 Portions of crystals of each class were finely pounded in an 

 agate mortar; by the addition of a little distilled water the 

 powder was made into a paste, from which small bars were 

 constructed and carefully dried. On being hung between the 

 excited poles, those whose optical axes were repelled stood 

 equatorial, the others axial. 



Adopting the plan already followed by Faraday, we next 

 brought the two classes of crystals to the test of a single pole. 

 At first, little bits of crystal were attached to the cocoon 

 thread by means of a soft sticky kind of wax ; the presence of 

 this, however, was found to interfere with the purity of the 

 experiment, and it was therefore abandoned ; fine silver wire 

 was next tried and also found ineligible ; we next hung a straw 

 horizontally, into each end of which a bit of crystal was thrust; 

 but the straw was diamagnetic, and permitted no safe conclu- 

 sion. Common white taper- wax was at length found exactly 

 suited to our purpose; it must, however, be handled with 

 clean fingers, and even thus very little ; after two or three 

 suspensions it invariably showed signs of magnetism. We 

 chose long thin bars of crystal and hung them vertically, thus 

 bringing the wax so far above the poles, that, on examination, 

 it showed not the slightest trace of magnetism or diamag- 

 netism. A former remark explains why this vertical hanging 

 is to be preferred to horizontal; in the latter case, a rotation 

 towards the pole, easily mistaken for an attraction, and diffi- 

 cult to distinguish from it, might occur with a diamagnetic 

 body; hung vertically, however, it could be distinctly seen 

 whether the mass of the crystal was attracted or repelled. 

 The results here delivered were in harmony with those already 

 mentioned : those whose optical axes were attracted, were 

 attracted J those whose optical axes were repelled, were re- 

 pelled. 



Anxious to investigate this difference of action to the bot- 

 tom, we chose two perfectly pure and transparent crystals 

 from each class, and submitted them to chemical analysis. 

 An experienced mineralogist was unable to detect the slightest 

 visible difference between these crystals; the analysis, how- 



