254 Prof. Faraday's Magnetic Remarks. 



be induced to put forth such explanations, acknowledgements, 

 or conclusions, as the state of the subject may then seem to 

 reader necessary or useful. 



In the mean time, the more we can enlarge the number of 

 anomalous facts and consequences the better it will be for the 

 subject ; for they can only remain anomalous to us whilst we 

 continue in error. I may say, however, that the idea you sug- 

 gest presents no difficulty to me ; for having on former occasions 

 (Exp. Res. 2501.) had to consider the magnecrystallic pheno- 

 mena presented by the same body in different media, and having 

 found the magnecrystallic difference unchanged in the media, I 

 have no difficulty in conceiving that a body (as bismuth), which 

 in the amorphous state is of the same magnetic character as the 

 medium around it, shall, when employed as a crystal, be para- 

 magnetic in one direction and diainagnetic in another (3157.). 

 "What happens in a medium may, according to my knowledge of 

 the facts, happen in space ; and is in full accordance with 

 Thomson's clear paper on the theory of magnetic induction in 

 crystalline bodies*. 



In respect of the effects of pressure, to which you refer in 

 your letter, we cannot easily draw conclusions on either side 

 until we know better what pressure does. I am not aware 

 whether you consider that pressure on bismuth, whilst it makes 

 the metal more diamagnetic in one direction than another, also 

 makes it more diamagnetic as a whole than before ; or whether 

 you suppose it less diamagnetic in the transverse direction of the 

 pressure than at first. Gmelin says, on the authority of Mar- 

 chand and Scheerer (vol. iv. p. 428), that the density of bismuth is 

 diminished as pressure upon it is increased, and extraordinary as 

 the fact seems, gives densities of the following degree for increasing 

 pressures, 9783, 9 - 779, 9-655, 9-556; a change in texture at 

 the same time occurring. If the statement be true, then the 

 line of pressure in your beautiful experiments may be the line 

 of least density or of least approximation, though I hardly know 

 how to think so ; still it becomes difficult for us to draw reasons 

 from the constitution of a compressed body, until we know what 

 happens during the compression, although no difficulty arises in 

 considering it, after compression in one direction, like to a mag- 

 necrystallic substance. 



You are aware (and I hope others will remember) that I give 

 the lines of force f only as representations of the magnetic power, 

 and do not profess to say to what physical idea they may 

 hereafter point, or into what they will resolve themselves. Ad- 



* Phil. Mag. 1851, vol. i. p. 177- 



t It is nearly twenty-four years since I first called attention to these 

 lines; Exp. Res. 114, note. 



