452 Prof. Plucker a7idJ)i'. Beer on the Magnetic Axes of dystals, 



rently the same deportment as the tourmaUne. The mechanical 

 question in this case was soon brought to a decision ; it was a 

 conflict between two opposite forces, between the diamagnetic 

 I'epulsion and magnetic attraction of the mass, the one or the 

 other of which triumphed according to the distance. 



11. The explanation of the magnetic action upon the axes 

 concentrated itself for nie more and more upon the qiiestion 

 expressed in (5): — "The crystal is attracted, but its centre 

 of gravity recedes :" generallj^ understood, this is in open con- 

 tradiction with the laws of mechanics. There is no force, what- 

 ever form it may assume, which can afford an explanation here. 

 And if, notwithstanding this, om* expei'imeuts seemed to exhibit 

 the above action, ive have merely to do with a mechajiical paradox. 

 In the case before us, a full explanation is furnished by the fact 

 that the crystal was not completely free, but compelled to rotate 

 round a fixed vertical axis. A bar swinging horizontally, with 

 a magnetic needle laid perpendicularly across its middle, sets 

 itself in relation to the poles of the earth exactly as a prism of 

 tourmaline between the poles of the magnet. The following out 

 of the above view, including its experimental proof, ])articularly 

 the imitation of the phsenomena which are obsei'vcd in crystals 

 of one and of two optic axes, will be found in the appendix to the 

 memoir of December 1849 above alluded to; not long after, a 

 memoir containing further mathematical developments, under the 

 title of Theorie Mathematique de I' Action des Aimants sur les 

 Crystaux non appurtenant au Systeme Tesseral, was sent to 

 M. Crelle, and will find a place in his journal. I must here 

 limit myself to this citation and to the few remarks which follow. 



12. Under the inductive action of a magnetic pole, each of the 

 ultimate particles of the ciystal will be either polar magnetic or 

 polar diamagnetic. The polarity, however, as in the case of 

 common induction, does not manifest itself in a variable direction 

 determined merely by the position with regard to the poles, but 

 in one or more than one fixed direction according to the form of 

 the crystal. Such directions as ai'e thus given by the foi-m, 1 

 have named the magnetic axes of the crystal. An ultimate par- 

 ticle which assumes polarity in a certain direction, and is free 

 to rotate round a fixed axis, either recedes from the pole or ap- 

 proaches it according as its distance fiom the pole is more or 

 less. We stand here on a mathematical foundation ; and all 

 phfenomena heretofore observed can be completely explained by 

 calculation. 



13. An immediate consequence of the action here supposed 

 is, that in the same crystallization, by which are meant the same 

 cohesion and a similar position of the optic axes, the magnetic 

 axes also coiTespond. When the substance of the ciystal at one 



