508 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



the polarizer in any way, as illustrated (fig. 58). It is probably the 

 simplest and most effective arrangement yet devised. The substage is 

 fitted with centring screws, and the whole of the substage apparatus can 



Fig. 58. 



be used for ordinary microscopical purposes. It can also be turned out 

 of the optical axis with the apparatus in it. 



Nachet — Microscope pour determiner les taches de sang, visibles ou invisibles, 

 reeentes ou anciennes, sur un corps opaque. 



C.R. Assoc. Anat., lOme reunion, Marseilles, 1908, pp. 201-3. 



(2) Eye-pieces and Objectives. 



F. E. Wright's New Petrographic Ocular.* — P. E. Wright has 

 designed this ocular for use with the petrographic Microscope, and its 

 purpose is to obtain actual numerical measurement of cleavage angles, ex- 



t- 



Pig. 59. 



tinction angles, optical axial angles, refractive indices, and bi-refringence. 

 In ordinary circumstances these properties are frequently observed, 

 owing to cumbersome methods, in only a very approximate manner. The 



* Amer. Journ. Sci., xxix. (1910) pp. 415-20,(12 figs.). 



