126 



SmOIABT OF CUKEEST EESEAKCHES RELATING TO 



Prof. Elein thus describes Ms observations on some crystals of 

 leTicit.e whicb -vrill illustrate the application of the Microscope : — 

 Sections parallel to the faces of the cube, octahedron, dodecahedron, 

 and icositetrahedron (reffardinor the crystals as cubic for the sake of 

 simplicity), all behaved in the same way when heated. Darkness 

 spread over them, the characteristic twin lamellae disappeared, and 

 the sections remained dark between crossed Nicols untQ the flame 

 was withdrawn, when they transmitted light as before (beginning with 

 the coolest side), acd the lamellae returned. The same section could 

 be repeatedly heated with the same results. It follows from these 

 experiments that leucite becomes isotropic when heated, and Prof. 

 Elein draws the conclusion that it originally crystallized at a high 

 temperature as a cubic mineral, and became rhombic (as he shows 

 elsewhere) on cooling. 



Frencli Dissecting Microscope. — This instrument (fig. 9), though 

 called a "dissecting" Microscope, is in the ordinary form of a 

 small student's compound Microscope. Its special feature is not so 

 much the stand itself as the case in which it is packed, which has a 



Fig. 9. 



