464 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



The uew apparatus works perfectly. Instead of two prisms, apposed 

 by their edges, as in Inostranzeff s instrument, there are two prisms of 

 large size, a, c, figs. 104 and 105, but of slight width and in apposi- 



FiG. 105. 



tion by one of their triangular faces. The two images are brought together 

 in the direction of their length : the piece carrying the two prisms is 

 movable, can turn on its axis, and be fixed in any position whatever. By 

 slightly turning it, the line of separation of the two prisms altogether 

 disappears, and so thoroughly, that a perfect valve can be made up of two 

 halves of a valve, each belonging to one of the fields, and the photograph 

 must be examined very attentively to find the place where the valves join. 



Thus the comparisons are as complete as possible, and the images so 

 clear that high powers may be used. In each part of the tube the 

 diaphragms D cut off any interfering light coming from the opposite side. 



Vignal's Hot Stage with Direct Regulator.* — M. W. Vignal's hot 

 stage (fig. 106) consists of a rectangular brass box open on one side and con- 



FiG. 106 



Longitudinal transverse median section of the hot stage. A, D'Arsonval's regula- 

 tor ; a, entrance tube for gas ; b, exit tube for gas ; g, glass tube fixed with caoutcliouc 

 band ; h, tube for introduction of water ; c, hot chamber proper, with slide P and ther- 

 mometer T ; L, door closing chamber ; /, aperture for objective ; e, glass disc in copper 

 ring for closing the illuminating aperture ; D, heating cylinder. 



taining a second small rectangular box. These two boxes are perforated by 

 an aperture which allows the light to be reflected upwards from the mirror. 



* Arch, de Physiol., vi. (1885) pp. 1-10 (2 figs.). 



