A Few BemarJts on Ndberfs Nineteenth Band. 119 



pencil measured to traverse. No, not the same in water as in air 

 necessarily; 100^ of angle is appreciably more than 82', and that 

 difference is the question at issue. 



Lastly, Mr, Wenham says, " His position is an impossible one. 

 In a corrected high-power object-glass, when immersed, the focus 

 does not fall in the centre of the hemisphere, but is considerably 

 beyond it." 



Very well; that does not affect my position. He will not 

 deny that it maij fall in the centre of the hemisphere and give 

 view of the object. 



In the case that I offered in my first communication, also as 

 just related that one given by him in the next following number 

 of this Journal, an objective of 170^ in air, gave only 100^ in water. 

 But that is enough for my " position," and 100° allows of pro- 

 jection " considerably beyond the centre of the hemisphere" for 

 its focal point. The position seems a very possible one, and Mr. 

 Wenham seems to furnish proof of its validity. 



Boston, January \Wi, 1872. 



VI. — A Few Additional Bemarks on " TJie Examination of 

 Noherfs Nineteenth Band." 



By F. A. P. Baenakd, Columbia CoUege, New York. 



The pages of a scientific magazine are too valuable to justify the 

 intrusion upon them of matters of merely personal interest. But 

 when a person is placed before the readers of such a magazine in a 

 light in which he does not appear to advantage, he has no alter- 

 native but to ask for a brief hearing. 



Early in the year 1868 I made a long-continued and laborious 

 examination of Nobert's Nineteen Band Test-plate. I saw lines in 

 the nineteenth band which I supposed to be the real ones. I made 

 counts of these lines with a filar micrometer ; and from these counts 

 deduced by calculation the number of divisions like those counted 

 which would correspond to an English inch. 



It was only with the extremest difficulty that I could obtain 

 what seemed to be the resolution. • To secure the necessary condi- 

 tions of illumination and focussing cost me often much time ; and 

 often I failed, after very protracted trial, to secure them at all. 

 IMoreover, when they were obtained, the image was so feebly 

 illuminated as to require an extremely acute vision (which I think 

 I possess) to see it at all ; and the labour of observation was &o 

 severely trying to the eyes, that I should not be willing to go through 

 such a course again. 



VOL. VII. K 



