ZOOLOGY AND BOTANY^ MICROSCOPY, ETC. 



291 



Fig. 39. 



Tlie chief object which this instrument seeks to attain is the rapid 

 change of certain parts ; the heating apparatus, the magnesium-light, the 

 camera, the cooling apparatus, and the polarizer, are all so constructed 

 that they may be introduced and withdrawn without loss of time, since the 

 operations have to be conducted with great rapidity during the growth of 

 the crystals. The author suggests other additions and improvements 

 which might be made ; for instance, 

 a water cooling-apparatus for fusion 

 experiments ; a roll of sensitive 

 paper to be used for a continuous 

 series of photographs in place of a 

 set of dry plates, &c., and promises 

 an account of observations which he 

 has recently made with the Micro- 

 scope upon bodies under high pres- 

 sures, in small capillaries, and in 

 vacuum. 



The Crystallization Microscope 

 for projection is shown in fig. 39. 

 A is the objective which is adjusted 

 by a parallelogram movement B by 

 means of the screw P. The stage 

 C is movable along a vertical slot 

 in the upright V, and is clamped 

 by the screw D. The object lies 

 upon the two edges a, which allow 

 a free passage of the air, and h h 

 are as before the two tubes by 

 which the object is cooled ; (Z is a 

 glass burner which receives its 

 supply of gas and air through the 

 two screw-taps e and/; the current 

 of air in h being regulated by the 

 screw-tap g. 



The light from an electric lamp 

 enters the apparatus at M through 

 two parallel plates of glass through 

 which circulates a current of water 

 free from lime, such as rain-water ; 

 ordinary water soon leaves a deposit 

 of carbonate of lime upon the glass, 

 and cannot be used for the purpose. 

 N is a water-tight chamber filled 

 with concentrated solution of alum 

 containing also a few loose crystals of alum, which are dissolved when the 

 temperature rises ; the hypothenuse of this triangular chamber is occupied 

 by the plane mirror Q, which reflects the light upwards through the 

 plano-convex condensing lens E of short focal length, which illuminates 

 the object with a convergent beam of light from the electric lamp. 

 After the rays have traversed the objective they enter a rectangular 

 prism S, by which they are reflected in a horizontal direction and throw 

 an image upon the screen; the prism 8 being adjusted by means of a 

 screw and hinge. 



This instrument may conveniently be used not only for demonstration, 

 but also for photographing, by allowing the rays to enter an ordinary 



