188 On Zeiss ^^th Immersion. By W. J. Hichie. 



the statemeat has been made in good faith, and the contrariety is 

 more seeming than reaL Magnification is the product of objective, 

 length of tube, and focal length of eye-piece. Now, Zeiss' figures 

 are based on a length of tube of only G inches (while the length in 

 England is about 10 inches), and on a focal length of eye-piece 

 somewhat more than 2 inches, while our A eye-piece is, I believe, 

 about 1^ inch focal length. 



One quality in this glass (designated as C) which attracted my 

 notice very strongly is its extraordinary resolving power. Its 

 *' grip " of an object is something enormous. And, as regards its 

 definition, I may here briefly say, that I am perfectly contented 

 with it ; which is saying a good deal ; as few are so hard to 

 satisfy in this respect. This I infer from having observed the (in 

 my opinion) very moderate performance which has satisfied my 

 microscopical friends. Indeed, I have often been called upon to 

 admire what (in my own work) I should call a failure. In this 

 connection, a very singular remark is put forward by Otto Miiller : * 

 " The resolving power of Zeiss' objectives is nothing specially 

 great. On the other hand, their definition is surpassed by none 

 of the objectives I have examined, and only equalled by few : the 

 clearness and repose of the picture is a perfect pattern." 



While accepting Miiller's happily-chosen words " Klarheit " 

 and " Euhe," as exactly conveying my impression of the per- 

 formance of my own glass (C), under which the object appears, as 

 I have heard it described, like a sunlit landscape, with all the 

 details vividly delineated, and the edge of the stride, to the outer- 

 most margin, as sharp as a knife, I consider the former sentence so 

 singularly in conflict with fact, that I must confess my inability to 

 understand it as having been written by him, unless I am at liberty 

 to suppose that he wanted to see how facts look when turned topsy- 

 turvy. Here in this country, if anyone were asked to mention the 

 most noticeable feature in Zeiss' objectives, he would unhesitatingly 

 single out precisely this resolving power, as the one that struck him 

 most. Or may Miiller's remark find its explanation in the fact, 

 that he knew only Zeiss' older issues ? He himself adds in his 

 Preface : " I ought to mention further, that Zeiss' objectives have 

 in these latest times [i. e. subsequently to the year 1870] been 

 considerably improved, in consequence of which the results I have 

 recorded no longer correspond to the present standard of perform- 

 ance of Zeiss' objectives." I notice also that his list mentions no 

 higher power of Zeiss' than his tV ii^ch (dry). Some, indeed, 

 among ourselves profess to have detected in Zeiss' objectives a 

 lower scale of definition when compared with those of Hartnack ; 

 but, as they omit to mention what lenses of each maker were com- 

 pared, the remark need not detain us. On one occasion I spent 



* ' MoJeru Objectives Compared,' p. 4. 



