ZOOLOGY AND BOTANY, MICI.'OKCOPY, ETC. 



769 



the ordinary plane-parallel mineral slab in a cork mount. A wooden 

 handle h closes the slit. Two small holes are provided for the passage of 

 thermo-elements intended for recording the temperature. The slit is also 

 used for pouring through a special funnel the liquid air into the lower 

 i ri mgh. Graduations of temperature were arranged by partly filling 

 the lower trough. The upper trough is covered with a lid d, of 

 nickel or of boxwood. The illuminating apparatus is placed in the 

 lower central glass tube, and consists of a push-out collar with a plano- 

 convex lens, and eventually with the condenser for convergent light. 

 The observation tube is placed below, and is shut off by a vacuous 

 double window/, this arrangement excluding trouble arising from ice or 

 water condensation. Ordinary objectives do not suffice, because they are 

 too short ; a lengthening tube-piece is therefore required. Moreover, 



v ',v/-" "~T r , 



Fig. 120. 



the microscope-stand is, iu general, not sufficiently high to receive on 

 the object-stage the cooling apparatus of some 10 cm. in height. A 

 metal connecting-piece must therefore be fitted to the stand. The 

 author tested his apparatus on gypsum, and used carbonic acid and ether 

 as the first cooling agent. The interference colours of the gypsum plate 

 instantly changed from red of the first order to the vivid blue of the 

 second order. The effects with liquid air were still more marked. The 

 author considers that his apparatus will also be of great use in examining 

 the fluid deposits sometimes found in minerals. 



Highly Reflecting Lantern Screens for Autochrome and other 

 Projections. — A translation of a paper by H. Lehmann on the above 

 subject has appeared in the Monthly Supplement to the British Journal 

 of Photography.* Lehmann's paper was originally contributed to a 

 German learned society, and appears in amplified form in recent issues 



* Vol. iii. No. 30. June 1909, pp. 41-7 (4 figs.). 



