118 Nohert's Nineteenth Band 



remains the same in eacli, and of course if Canada balsam is run 

 under the cover to mount the object, the aperture will be equally 

 reduced thereon in both cases. This has been shown years ago. 

 That the mere fusing by a refractive medium of the thinner or im- 

 mersion lens and cover into one, whose combined thickness barely 

 exceeds that of the dry lens and cover together, wdl be the means 

 of collecting a greater angle of rays from the object, is a fallacy 

 that must be obvious, even though my friend in Egypt, the great 

 Ptolemy, is now brought up as evidence against me ; and whether 

 the object is mounted in balsam or not — I challenge Dr. Pigott, or 

 anyone, to get, through the object-glass with the immersion front, 

 a greater angle, or any portion of the extraneous rays that would 

 in the other case be totally reflected, as no object-glass can collect 

 image-forming rays beyond this limit. 



I now leave it to impartial observers to consider my objections. 

 I have nothing more to say concerning the immersion lens, and in 

 this particular the controversy with Dr. Pigott must end — if only 

 for the tone last assumed — that of mutilated quotations, imputed 

 " personahties " ? want of " refinement," &c. I might rebut these 

 insinuations by referring to the November number of this Journal 

 for some expressions, first emanating from himself. 



I trust that I have not hitherto tried the patience of the kind 

 readers of this Journal. It is not my forte to write on any but 

 practical subjects, and in my last I gave the marginal rays traced 

 through an entire object-glass. Little or nothing of this kind has 

 been previously published. I expect shortly to be able to carry out 

 some experiments that I have in view, and to give another illustra- 

 tion, I hope to better purpose. 



VII. — Ndbert's Nineteenth Band and its Observers. 



By Chakles Stoddee. 



J. J. Woodward, Assistant-Surgeon and Brevet Lieut.-Colonel 

 U. S. Army, having, in a letter published in this Journal in the 

 August issue, afiirmed his disbelief in the fact claimed by myself 

 and Mr. E. C. Greenleaf, of the resolution of the lines of the 19th 

 band of the Nobert test-plate, and his disbelief that I ever saw the 

 hues with the instruments named, I wish to make a rejoinder which 

 shall close the discussion on my part in regard to that matter. 



Dr. Woodward writes, that " if Messrs. Stodder and Greenleaf 's 

 original claims were really well founded, they certainly ante-dated 

 mine." I have aheady stated (this Journal, May, 1870) that our 

 original claim rests on our behef, no one else having seen the reso- 

 lution with the instrument then used. But in my letter I then 



