454 Prof. Plucker and Dr. Beer on the Magnetic Axes of Crystals, 



the peculiarity of crystallization does not rest alone in the clea- 

 vages, but in the entire relations of cohesion ; for were the former 

 admitted, we must expect cleavages where they do not appear. 

 And these are the causes which, acting together, determine the 

 position and relative magnitude of the three axes of elasticity of 

 Fresnel, which produce the modification suffered by the light in 

 its passage, and also, I am convinced, the modification of mag- 

 netic induction. 



17. Here, however, we are met by the important question, 

 whether evei-y ultimate particle as mass is magnetic, as stated by 

 the above-named physicists, or whether the same aether whose 

 oscillations produce light can produce magnetism and electricity 

 when otherwise excited. By the latter assumption the all-pene- 

 trating aether would transmit the action of both in the same 

 manner as it transmits light. This second notion was the spur 

 by which I was particularly driven to try my strength in this 

 field. 



18. The beautiful experiments of M. Wiedemann, which have 

 been corroborated by the later experiments of Senarmont, prove, 

 as regards the spreading over the surface, that the electric con- 

 duction is different in different directions, and seem to establish 

 a relation between it and the axes of elasticity. The conductive 

 power may in this way be determined ; likewise tlie mean con- 

 ductive power in a circular stream, which, as it would be inde- 

 pendent of its dimension, might be immediately apphed to the 

 molecular currents of Ampere, that is to say, to magnetism. In 

 this way the position of the magnetic axes, as well as of the optic 

 axes, might be mathematically determined. 



19. 1 am not, however, ignorant of the uncertainty which attends 

 the carrying out of such theories, for which the necessary expe- 

 rimental data are wanting. In the memoir appcarmg in Crelle's 

 jom-nal, I have therefore confined myself to crystals with a single 

 magnetic axis, and for tlie present added only one independent 

 paper, which is to serve as foundation for further mathematical 

 development. On the other hand, in connexion with Dr. Beer, I 

 have turned my attention to experimental investigations, the 

 principal object of which is to determine the nature of the mag- 

 netic axes, and their position as regards the crystalline form. 

 The first series of experiments which here follows embraces 

 ci-ystals belonging to all systems. We have placed together the 

 results which for the present we regard as closed. The latest 

 memoir of Messrs. Tyndall and Knoblauch, in the Philosophical 

 Magazine, reached us too late to permit of its being noticed in 

 the present paper. — Plucker. 



The authors then pi-oceed to examine crystals of various 



