THE AMERICAN 



MONTHLY 



MICROSCOPICAL JOURNAL 



Vol. IV. 



Boston, June, 1883. 



No. 6. 



The Podura Sccile. 



BY THE EDITOR. 



An article on this subject, published 

 in the December number of this Jour- 

 nal, called attention to the podura 

 scale as a valuable test-object, al- 

 though the structure 

 of the scale is still to 

 many minds, a mat- 

 ter of uncertainty. 

 There are still a few- 

 persons who cannot 

 grasp the idea which 

 has been set forth 

 time and time again 

 in these columns, 

 that the appearance 

 of an object in the 

 microscope is not 

 necessarily a truth- 

 ful- representation of 

 its structure. But 

 those who, from in- 

 experience, or want 

 of accurate informa- 

 ation concerning the 

 present theory of mi- 

 croscopical vision, 

 do not understand 

 how this can be, 

 should not be too 

 hasty about ques- 

 tioning facts so uni- 

 versally admitted by the best informed 

 and experienced microscopists. 



In the February number of this 

 Journal, on page 30, it was briefly 

 explained that objectives cannot be 

 properly corrected by the use of un- 

 known objects — that is, by objects of 

 which the correct appearance is not 

 known. If the podura scale is to be 



used as a test-object, it is important 

 that its correct appearance should be 

 known. In the first article two differ- 

 ent appearances of the spines were 

 described. Which is the correct ap- 

 pearance is still uncertain, but Mr. 

 Stodder, in a recent article,* even 



questions the existence of true spines 

 on the scale. 



A long time ago our attention was 

 drawn to some photographs by Dr. J. 

 W. S. Arnold, of this city, which have 

 been on exhibition in Mr. Woolman's 

 store. The photographs were made 



* Vol. IV. p. 4. 



