90 The Microscope. 



to be placed between the objective and the body tube with a 

 thumb screw to fasten a movable stop in an}^ desired position. 

 When the focus has been obtained, all the microscopist need do 

 t© prevent the objective front from coming in contact with the 

 slide or the cover glass, even in the most awkward and careless 

 hands, is to fasten the movable stop in the proper position ; 

 then Samson himself could not bring the lens and cover in con- 

 tact, unless he should destroy the instrument. Especially in 

 schools where a number of pupils have to look through the 

 same microscope, or for microscopical soirees, Mr. Griffith's in- 

 dicator should be a welcome assistant. To a novice with his 

 first stand it vvould be a great help and would relieve him from 

 much anxiety as to the safety of his objectives and covers. 



NEV/S FRp/A 

 THE Vv'ORKERS 



The Zeiss apochromatic, 1.60 N. A.* — It is possible to push 

 one phase of optical construction so far as to accomplish the 

 object, but to leave doubtful the usefulness of the object gained. 

 We have all heard of the new objective produced by the firm of 

 Zeiss, of Jena. It has a numerical aperture of 1.60. This from 

 one point of view is a great advantage. None would have 

 greater reason to hail it than I, in the special work with which 

 my life has largeh^ been occupied. 



Now, I have spent five consecutive days in the close and 

 critical examination of one of these objectives which, so far as I 

 know, has been in no other hands but my own and those to 

 whom I have shown it. I desire to take the sole responsibility 

 of estimating its ^'alue. In my hands it is an extremely beauti- 

 ful lens ; it is well centred, well corrected, and shows plainly 

 the advantage of its enormous aperture. It is a triumph of the 

 optical firm which produced it. But I would hasten to say that 



*Dr. W. H. Dalliuger's piesideutial address to the Qaekett Club. Journ. 

 Q. M. C. 



