ARTICLES 599 



force, however, at once discovers a difference of action. The 

 cleavages of the diamagnetic specimens stand equatorial ; of the 

 magnetic, axial. 



Again, " a cube cut from a prism of scapolite, the axis of 

 the prism being perpendicular to two of the parallel faces of 

 the cube, suspended in the magnetic field, sets itself with the 

 axis of the prism from pole to pole. 



" A cube of beryl, of the same dimensions, with the axis 

 of the prism from which it was taken also perpendicular to 

 two of the faces, suspended as in the former case, sets itself 

 with the axis equatorial. Both these crystals are magnetic. 



" The former experiments showed a dissimilarity of action 

 between magnetic and diamagnetic crystals. In the present 

 instances both are magnetic, but still there is a difference ; 

 the axis of the one prism stands axial, the axis of the other 

 equatorial. With regard to the explanation of this, the follow- 

 ing fact is significant. Scapolite cleaves parallel to its axis, 

 while beryl cleaves perpendicular to its axis ; the cleavages in 

 both cases, therefore, stand axial, thus agreeing with sulphate 

 of nickel." 



The above quotation clearly shows how closely allied are 

 the forces of cohesion in different directions, with the magnetic 

 behaviour of the crystalline medium, and lead us to suspect 

 that the forces of crystallisation are probably of a magnetic 

 nature. The fine points are so completely explained by the 

 magnetic deportment that it is difficult to dissociate the co- 

 hesive forces from a magnetic origin. If the cohesive forces 

 had an electrostatic origin, an electrostatic field would only 

 disclose the above information regarding the orientation of 

 the planes of cleavage providing the magnetic and electro- 

 static axes of the molecules coincided. This we know is not 

 the case. Again, A. W. Porter and D. K. Morris (Proc. Roy. 

 Soc, A, vol. lvii, p. 469, 1895) have shown that in paraffin, 

 dielectric hysteresis (as distinct from viscosity), under the 

 influence of a powerful electrostatic field, does not exist to 

 within one part in fifty thousand. If the molecules of the 

 dielectric were held together by electrostatic forces, we should 

 expect that here, if in any substance, the molecular groups 

 would be reorganised by the applied field, the process being 

 accompanied by hysteresis. In the corresponding cases of 

 ferro-magnetic substances, under the influence of a magnetic 

 field, considerable hysteresis effects are observed. In dia- 

 magnetic media, we could hardly hope to observe any appre- 

 ciable effect, since the molecule has initially a zero magnetic 

 moment and only orientates an account of its dissymmetry, 

 after the small diamagnetic moment has been induced, thus 

 giving rise to a minute magnetic double refraction. (Langevin, 



