ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



939 



and crosses in crystals. An analyzer and a Klein's quartz-plate are 

 mounted in sliding boxes in the lower end of the body, each admitting 

 of removal when their respective openings may be closed by sliding 

 shutters provided for the purpose. An extra analyzer is mounted to 

 slip over the eye-piece, and is furnished with a graduated disk with 

 index. 



For stauroscopic measurements a double calcsjpar plate is arranged 

 to rotate between the analyzer and eye-lens. 



The eye-piece is also provided with cross lines ruled on glass. 



The instrument can, of course, be readily converted into an 

 ordinary monocular when not required to be used for its special 

 purpose. 



Browning's Platyscopic Lenses. — An addition has been made to 

 this series of achromatic pocket lenses by a new one of lower power — 

 magnifying 10 diameters — and larger field than has previously been 

 made. The series now consists of lenses magnifying respectively 10, 

 15, 20, and 30 diameters. 



Nachet's Porte-loupe. — This (Fig. 211) is substantially a modi- 

 fication of Strauss-Durckheim's lens-holder, the movements of the 



Fig. 211. 



arms (which are articulated by balls held between claws) allowing the 

 lens to be readily placed in every position. By the screw A, a fine 

 adjustment is obtained. 



Lacaze-Duthiers' Porte-loupe. — This (Fig. 212), also made by 

 MM. Nachet, consists of three articulated arms attached to a horizontal 

 support, and the latter to a standard, as shown in the figui-e, the whole 

 of the arms together being movable vertically or horizontally. Two 

 of the arms are fixed to a piece of tubing sliding on the horizontal 



