PROCEEDINGS OF THE SOCIETY. 257 



Mr. Stringer's paper, i' On a new method of reading the lines in the 

 Spectroscope,' was read by the Secretary, and an instrument fitted as 

 described was exhibited. 



The Chairman called the attention of the Fellows present to a number 

 of specimens of marine objects mounted by Mr. Waddington, which were 

 exhibited in the room under microscopes by Mr. C. L. Curties, to whom 

 the thanks of the Society were unanimously voted. 



Mr. E. M. Nelson's papers, 'On the Vertical Illuminator,' and 

 ' On the influence of the Antipoint on the Microscopic image shown 

 graphically,' were, in the absence of the author, read by the Secretary. 



Mr. J. "W. Gordon did not suppose he coidd add anything of interest 

 to Mr. Nelson's paper, because it seemed to him to be completely self- 

 explanatory. The only thing which could possibly add to its clearness 

 would be the figures sent in illustration. (He then drew upon the board 

 the hair in question, as seen upon a black and upon a bright ground, and 

 pointed out the difference in the apparent breadth as seen under these 

 two kinds of illumination.) The peculiar interest in the matter was in 

 the fact that the measurements as given in Mr. Nelson's correction table 

 and those made by observation practically agreed. He did not like to 

 suggest that he could draw these figures accurately enough to serve as 

 the basis for the very refined measurements referred to in Mr. Nelson's 

 paper. It should be understood that Mr. Nelson had himself compared 

 the drawings with the object as seen in the Microscope, and had come to 

 the conclusion that they were accurate enough for the purpose. Mr. 

 Gordon pointed out the interesting circumstance, that in the middle of 

 the dark object they had a bright line, due to the overlapping of the 

 antipoints from either side. 



Mr. Eheinberg said he should like to ask Mr. Gordon if he considered 

 that the relative results (i.e. the comparative width of the bright image 

 on the dark ground to that of the dark image on the bright ground) 

 were for practical purposes always the same under different intensities of 

 illumination, and whether this had been experimentally tested. It was 

 well known that a bright edge always appeared to encroach more or less 

 ■on neighbouring dark parts, as exemplified by the experiment of holding 

 a card between the eye and a small bright source of light, when, accord- 

 ing to the brightness of the source, the card appears more or less indented 

 at the portion of it just opposite. Having regard to the important 

 results established by the paper which had been read, it would be of con- 

 siderable interest to know whether the ratio in width between the bright 

 and the dark images held good for every intensity of illumination. 



Mr. Beck presumed that this particular hair was of comparatively 

 small size ; but he should like to know whether the objective was used 

 with its full aperture, or if it was stopped down to increase the size of 

 the antipoint, so as to get an exaggerated effect. 



Mr. Gordon said, with regard to Mr. Rheinberg's point, this was one 

 of extreme interest and of very great importance, and he thought there 

 ■could be no doubt that the apparent size of the antipoint was very 



