272 MAJOR A. E. OXLEY ON THE INFLUENCE OF MOLECULAR 



'' 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 following 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 

 cleavages hence appear to take up a determinate position regardless of outward form, 

 and they seem to exercise a ruling power over the deportment of the crystal. 



" A cube of saltpetre, suspended with the crystallographic axis horizontal, sets 

 itself between the poles with this axis equatorial. 



" A cube of topaz, suspended with the crystallographic axis horizontal, sets itself 

 with this axis from pole to pole. 



''We have here a kind of complementary case to the former. Both these crystals 

 are diamagnetic. Saltpetre cleaves parallel to its axis ; topaz perpendicular to its 

 axis. The planes of cleavage, therefore, stand in both cases equatorial, thus agreeing 

 with sulphate of zinc and sulphate of magnesia. 



' Where do these facts point ? A moment's speculation will perhaps be allowed us 

 here. May we not suppose these crystals to be composed of layers indefinitely thin, 

 laid side by side, within the range of cohesion, which holds them together, but yet not 

 in absolute contact ? This seems to be no strained idea ; for expansion and 

 contraction by heat and cold compel us to assume that the particles of matter in 

 general do not touch each other ; that there are unfilled spaces between them. In 

 such crystals as we have described these spaces may be considered as alternating with 

 the plates which compose the crystal. From this point of view it seems very natural 

 that the magnetic lamina? should set themselves axial, and the diamagnetic equatorial. 



" Our fundamental idea is, that crystals of one cleavage are made up of plates 

 indefinitely thin, separated by spaces indefinitely narrow. If, however, we suppose 

 two cleavages existing at right angles to each other, then we must relinquish the 

 notion of plates and substitute that of little parallel bars ; for the plates are divided 

 into such by the second cleavage. If we further suppose these bars to be intersected 

 by a cleavage at right angles to their length, then the component crystals will be 

 little cubes, as in the case of rock-salt and others. By thus increasing the cleavages, 

 the original plates may be subdivided indefinitely, the shape of the little component 

 crystal bearing special relation to the position of the planes. It is an inference which 

 follows immediately from our way of viewing the subject, that if the crystal have 

 several planes of cleavage, but all parallel to the same straight line, this line, in the 

 case of magnetic crystals, will stand axial ; in the case of diamagnetic, equatorial. It 

 also follows that in the so-called regular crystals, in rock-salt, for instance, the 

 cleavages annul each other, and consequently, no directive power will be exhibited, 

 which is actually the case." 



The above quotation from TYNDALL'S work clearly shows how closely allied are the 



