200 MANAGEMENT OF THE MICROSCOPE. 



repeated ten times along the rule, gave 6 inches and 2J tenths, 

 the value of each division vpould be "625 of an inch, and the 

 magnifying ,power 625. The superficial magnifying power is ot 

 course estimated by squaring the linear ; but this is a mode of 

 statement never adopted by scientific observers, although often 

 employed to excite popular admiration, or to attract customers, 

 by those vphose interest is concei'ned in doing so.' 



' An ingenious method has been devised by Prof. Harting, of Utrecht, for determining 

 " the utmoBt limits of penetrating and separating power possessed by a Microscope,'' 

 by using as test-objects the very reduced images of various bodies formed by air-bubbles 

 in gum-mucilage. The mode of obtaining and employing these images for the above 

 purpose, will be found in the " Quarterly Journal of Microscopical Science," vol. i, p. 29a, 



