91 



As the formula already given applied to any ray, it should be 

 possible to photograph on a plate what cannot be seen with the 

 eye. The 100,000 lines to the inch could only be seen most 

 faintly with the "95 objective, but inasmuch as the wave-length 

 oi photografJiiG light was about g^ig-Q of an inch, twice that x '95 

 gave a photographic limit of a little ov^er 100,000 lines to the 

 inch His son. Dr. Harold Spitta, and himself had tried to 

 do this. As they could not focus the lines on the ground glass 

 screen of the camera, they had to make trial and error exposures, 

 and failed several times, but at last succeeded in just showing the 

 lines in the print exhibited. Dr. Spitta illustrated his remarks 

 by diagrams, etc., drawn upon the board as he proceeded. 



Mr. E. M. Nelson was sure that those present had listened to 

 Mr. Merlin's interesting paper and to Dr. Spitta's remarks upon 

 it, which had been placed so ably and concisely before them, with 

 great pleasure. Mr. Merlin had spoken to him about the subject- 

 matter of this paper before the holidays, which led him to make 

 a few experiments of his own. Unfortunately his eyesight was 

 not so good as it used to be, and he no longer possessed the same 

 facility for picking up undiscovered new details ; but Mr. Merlin's 

 eyesight was exceptionally keen, and Mr. Merlin had, too, con- 

 siderable experience with the telescope, which was probably as 

 good if not better training for the eye than the microscope. The 

 fact of his being unable to see any particular structure which 

 Mr. Merlin had described in his paper would not, therefore, be 

 evidence that Mr. Merlin was likely to have been mistaken in what 

 he had seen. Before the vacation he had tried a |^ths cone with 

 the dry 4 mm. apochromat of "95 N.A. with the g-inch wick of 

 a paraffin lamp and an acetate of copper filter, but he was not 

 able to effect any resolutions to anything like the extent Mr, 

 Merlin had done. He next tried sunlight with a heliostat, but the 

 heliostat proved untrustworthy and the sunlight fickle, so he was 

 not able to push his experiments as far as he would have liked. 

 He found, however, that with sunlight he could use a filter of 

 much greater thickness, and then he was able to see some of the 

 structures Mr. Merhn had mentioned. He hoped to be able to 

 pursue this subject still further next summer. 



There was another point — viz., that the Abbe diffraction 

 theory did not fit in with all the observed phenomena bearing 

 upon that branch of microscopy. It was highly probable that 



