ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



645 



scratched, came immediately under the objective, the scratch bisecting 

 the field. With strong magnification the scratch appears as a band. Its 

 breadth can be accurately measured with an ocular micrometer and its 



Fig. 109. 



depth with a micrometer-screw, to a limit of 2 or 3 \x. In order to get a 

 serviceable result as regards the comparison of various crystals, the 

 diamond scratching-point must remain completely unaffected, a con- 

 dition which can be examined by the Microscope. The author, however, 



Oct. 20th, 1909 2 x 



