ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



241 



Wollaston's Goniometer.* — This instrument (fig. 52), the circle of 

 which is 140 millimetres in diameter, is provided with regulating screw 

 apparatus for centring crystals, and vernier reading to 30 seconds. 



""WliiiiiaiiiiiiiiH 



F.g. 52. 



Fig. 53. 



The same instrument, as improved by Mallard (fig. 53), has, in addition, 

 a collimator with slit of various forms and an adjustable support for the 

 black mirror. 



* List Pkys. and Mech. Instr. Soc. Genevoise (1907) pp. 4S-9. 



