ZOOLOGY AND BOTANY, .MICROSCOPY, ETC. 



303 



From 200° to 450° C. quartz or thicker glass covers should be used. 

 Above 450° the requirements of microchemistry and rnicrocrystallography 

 do not usually extend. But in the event of such higher temperatures 

 being required, glass, unless made of a specially high melting-point, is 

 useless, and recourse must be had to quartz slips and covers. A thicker 

 platinum wire (0 * 2 to " 25 mm.) is also desirable. A 6-volt accumulator- 

 battery serves well as the source of energy. For the polarization arrange- 

 ment, the author inserts an analysing Nicol in the connecting-piece 

 between the objective and revolver. The polarizer is placed, as usual, 

 in the diaphragm ring. The cooling of the object, in the case of over- 

 heating, is accomplished by directing an air-current on to the cover- 

 glass. It is remarkable how small a heating effect is produced on the 

 Microscope itself. 



Berek and Jentzsch's Small Intense-light Monochromator.* — 

 This auxiliary has been designed by M. Berek and F. Jentzsch 



Fig- 31. 



with especial reference to the needs of microscopists, although it will 

 also be found useful in several branches of physical research. The 

 external view is shown in fig. 31 and with the ray-path in fig. 32. 

 It has been designed so that it may be used with any type of Micro- 

 scope and with any type of lamp. The apparatus consists of a small 

 box, adjustable in height, containing a Hilger prism, rotation arrange- 

 ment and telescope objective. Two tubes mutually perpendicular 

 contain each an illuminating lens, and a slit. The exit-slit must 

 be directed accurately on the Microscope mirror so that the apparatus 

 can be used as a lamp. Over the entrance-slit a small totally reflecting 

 prism is so arranged that the rays of a light-source can be easily made 

 parallel to the exit-tube. Both the entrance and the exit- slits are 

 bilaterally adjustable, and can be regulated by a micrometer screw and 



* Zeit. f. Iiirftrumenteuk., xxxiv. (1914) pp. 47-51 (2 figs.). 



