ZOOLOGY; AND BOTANY, MICROSCOPY, ETC. 



509 



Polariscope.* — E. Holmes writes that a good polariscope for some 

 purposes may be made by black varnishing two sheets of glass, and so 

 placing them that the light reflected from one lying flat on the table is 

 again reflected to the eye by the second plate. Objects to be examined 

 are placed in the beam of light. There is no gain whatever in using 

 a pile of plates for a reflecting instrument in this way. A dozen micro- 

 scopical cover glasses put in a paper tube at an angle of about 57° make 

 a good analyser. Whatever the number of plates the angle remains the 

 same for maximum effect. 



The Micro-pantograph as a Drawing Apparatus.! — G-. C. van 

 Walsem has re-designed this instrument (fig. 105), which was originally 

 contrived in 1872 by J. Roberts. It is described by von Apathy in his 



Fig. 105. 



" Mikrotechnik der tierischen Morphologic"! Rooerts' instrument, how- 

 ever, had the disadvantage of reproducing the microscopic image reversed. 

 The essential feature of WaJsem's improved form is a special double 

 ring-link which embraces the " object-point," i.e. the Microscope tube. 

 The diameter of this ring is 37 mm., so that the ring is large enough 

 not only to encircle the tube and to be moved freely about within cer- 

 tain limits without jarring it, but its centre in the case of a weak ocular 

 and a correspondingly large ocular diaphragm can be made to explore 

 the, whole field. It is obviously important to reduce friction as much as 



* English Mechanic, lxxxi. (1905) p. 383. 



t Zeitschr. wiss. Mikrosk., xxi. (1904) pp. 166-72 (2 tigs.).' 



X Zweite A bteilung. p. 361. 



