ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



117 



Fig. 2. 



(as shown in the figure) by sliding it down the inclined fitting without 

 altering the position of the substage. The front lens is removable for 

 work with low powers, and for dark-ground illumination is replaced 

 by a truncated lens. Below the condenser is placed a revolving 

 polarizing prism which can 

 be thrown out, as shown in 

 fig. 2, when not in use. Be- 

 tween the polarizing prism 

 and condenser are two re- 

 volving diaphragm plates ; 

 one containing a series of 

 apertures for varying the 

 angle of the condenser, the 

 other containing two selenites 

 and a blue glass disk for 

 moderating the light. It will 

 thus be seen that with this 

 compound substage apparatus 



the polariscope may be used *^'' 



by itself, or in combination 



with the achromatic condenser, or with dark-ground illumination ; 

 and all the different modes of illumination requisite for general 

 work may be obtained with it. 



Lehmann's Crystallization Microscope.* — 0. Lehmann describes 

 the arrangement which he has devised for examining microscopically 

 small crystals, amorphous deposits, gas bubbles, &c., under different 

 conditions of temperature or pressure and with powers up to 100. 

 The Microscope proper is shown in fig. 3, the work-table to which it 

 is attached in fig. 4. 



The body-tube of the Microscope is supported on a stout bar of 

 iron, which is bent at right angles and is fastened at its base to the 

 plate a a (fig. 3), which fits into the place marked aaaah in fig. 4. 

 The stage-plate o is attached to a revolving plate p, rotated by the 

 handle y, and showing the extent of rotation by the graduations on 

 the lower plate z, seen through an aperture closed with glass at w. 

 A lamp and mirror are fixed at r and s respectively, with a bull's-eye 

 interposed at t. A polarizing prism u is attached to a movable arm 

 m, and an analyser at n, the latter supported on a hinge so as to be 

 slipped in and out of the body-tube. For heating the objects a gas- 

 burner d ex is introduced into the central aperture of the stage, the 

 heated air passing off between o and p. The pipe is double, for 

 conveying gas and air. The jet can be removed by the handle at e, 

 and the two taps I and II regulate the admission of the gas and air. 

 For cooling the object a pipe is provided at / in connection with the 

 tap III, by which a stream of air is admitted. A board for camera 

 lucida drawing is placed at g, and a photographic arrangement can 

 be used as with an ordinary Microscope. 



The work-table is symmetrical on both sides of the Microscope, 



* Zeitsclir. f. Instrumentenk., iv. (1884) pp. 369-76 (4 figs.). 



