ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



181 



Water-heated Stage.* — This apparatus (fig. 18) is for the study of 

 preparations at temperatures between 0° and 100° C. As may be seen 

 from the illustration, it consists of a central chamber mounted in a metal 

 plate, and communicating immediately with two thermometer chambers, 

 through which the water from any convenient circulating apparatus 

 enters and leaves. The thermometer chambers are so arranged that 

 they can be lagged, and all metal surfaces are nickel-plated to check 

 loss of heat. The central chamber is closed above and below by stout 

 1-in. cover-glasses, its lower side being ^ in. away from the surface of 

 the Microscope-stage on which the apparatus rests. Metal plates with 

 any special form of cell, and of any depth up to | in., can be readily 

 fitted and are interchangeable. The three joints are made water-tight 

 by rubber washers. 



The special advantages of the apparatus are : — 1. The interchange- 



Fig. 18. 



ability of washers and cover-glasses in case of breakage. 2. The 

 adaptabibty at small cost to any form of cell desired. 3. The small 

 distance between the chamber and the stage of the Microscope, per- 

 mitting the use of a condenser. The apparatus is specially adapted to 

 the study of extinction angles and other properties in crystal sections, 

 but small-scaled preparations of any nature can be examined with equal 

 facility. 



(5) Microscopical Optics and Manipulation. 



Optical Character of the Faint Interference-figure observed in 

 High-power Objectives between Crossed Nicols.f — F. E. Wright 

 points out that to the petrologist the appearance under crossed nicols 

 of a faint, apparently uniaxial interference-figure in an objective of 

 short focal length is a matter of common observation. It was at first 

 considered to be the result of strain in the objective lenses, but Rinne, 



* James Swift and Son's Catalogue, 1914, p. 25. 



+ Journ. Washington Acad. Sci., iv. No. 12 (June 19, 1914) 9 pp. (2 figs.). 



