PROCEEDINGS OF THE SOCIETY. 257 



Mr. J. W. Gordon read a paper entitled " An Early Criticism of the 

 Abbe Theory," written in answer to a paper by Mr. Conrady with the 

 same title, read before the Society on October 17, l'J(»6, and printed in 

 the Journal of December, 1906, pp. 645 to 647. At the conclusion of 

 his paper Mr. Gordon exhibited some photographs of the spectrum 

 produced by the fine ruling of an Abbe Diffractionsplatte, and showed 

 thereby that as the radius of curvature of the incident wave-fronts was 

 reduced from (»M)11 in. to 0M)()8 in. and ()'()04 in. successively, the 

 spectrum became more and more compressed as if the grating interval 

 were becoming larger. When the radius of curvature was reduced to 

 • 002 in. the spectrum of the grating disappeared, giving place to the 

 spectrum due to a single opening of the grating, and when the source 

 of light was focused in the same plane as the grating, the spectrum 

 disappeared altogether. Only one or two lines of the grating were at 

 all illuminated by the direct light, but a finely resolved image of the 

 grating was shown lighted up by the diffused liglit irregularly reflected 

 from the lens and other internal surfaces of the instrument. 



Mr. Conrady, in reply, said : Mr. Gordon suggests that he should 

 have been made aware of the fact that my note was being sent in. 

 Seeing that, owing to its nature, Mr. Gordon could not possibly have 

 replied to it without having first carefully studied Dr. Altmann's paper, 

 and that I wrote the note only the evening before it was read, I do not 

 see much force in his argument. On the contrary, he should be grateful 

 that I have thus given him a full month in which to prepare a reply, 

 with the added advantage that he will have the last word on the subject 

 to-night.* 



The issue concerning Mr, Gordon which I raised in my note is 

 clearly stated in the last paragraph but one, in the words : 



" For this Society there is a further interest in Altmann's paper, 

 inasmuch as it obviously represents a singularly complete anticipation of 

 a paper read before it more than twenty years later by Mr. J. W. 

 Gordon. Altmann's modified diffusion disks are completely identical 

 with Mr. Gordon's antipoints, and it will be noted that even the argu- 

 ments employed are very similar in many cases." 



One would think that if Mr. Gordon intended to dispute this state- 

 ment, he would first have carefully studied the paper by Dr. Altmann, 

 and, supposing the result to be encouraging, would have stated, with all 

 the clearness of which he is so capable, in what respect his antipoints 

 differ from Altmann's diffusion disks, and what essentially new points he 

 — Mr. Gordon — had brought forward in his paper of 1901. 



Now the supposed reply just read clearly states the remarkable fact 

 that Mr. Gordon has not read Dr. Altmann's paper ; it cannot therefore 

 show in what respect Mr. Gordon's paper marked an advance on 

 Dr. Altmann's, and it does not, as a matter of fact, deal with a single 

 one of the clear points of similarity which I mentioned, Mr, Gordon 

 prefers to discuss side issues which really do not affect the case under 

 discussion. He clings to the fact that Dr. Altmann knew and referred 



^&"- 



* Mr. Conrady has omitted to allude to the advantage he obtained from an 

 advance copy of the paper, forwarded to him, with Mr. Gordon's accustomed 

 courtesy, a full week before the February Meeting. — Ed. 



April 17th, 1907 S 



