PROCEEDINGS OF THE SOCIETY. 97 



nonienon of the enlarged circle might also be seen very plainly in 

 looking at distant objects through a "pair of spectacles held away from 

 the eyes. 



Mr. Rheinberg said that Mr. Cheshire had referred to his (the 

 speaker's) remarks in regard to stereoscopic effects, and had said that by 

 having the oculars nearer or farther apart different images could be 

 obtained with the result that pseudoscopic or orthoscopic effects came 

 about. From this he feared he had not made it sufficiently clear that 

 he had been referring solely to high power microscopy. When the 

 Ramsden disks were large, then it was possible of course to allow different 

 parts of these to enter the two eyes ; but this, as had been pointed out in 

 the paper by Dr. Jentzsch himself, w ? as not feasible when they were 

 small as they w r ere with high powers, to which he was more particularly 

 referring. 



Mr. Blood said that there was one point about Dr. Jentzsch's paper 

 w T hich had specially appealed to him personally, and that was what had 

 been said in regard to the use of binocular Microscopes being of benefit 

 where there was any idiosyncrasy in colour vision. He himself had 

 noticed that his left eye was more sensitive to the blue end of the 

 spectrum and his right to the red end — whether this were owing to his 

 using the left eye a good deal with a green screen he could not say ; but 

 he had had a curious example of this idiosyncrasy recently when looking 

 at some organism which he had had quite a difficulty in distinguishing 

 with his right eye, after having seen it clearly as a bluish-green object 

 among a number of green ones with his left. 



He thought Mr. Beck's form of binocular more convenient to use 

 than Leitz's, though it was quite possible that after working a Leitz for 

 a long time one could get used to it. There were one or two disadvan- 

 tages, however, which seemed to be offered by Mr. Beck's instrument, 

 one being the varying length of the tube, which w^ould clearly make it 

 unsuitable for high power objectives, unless fitted with a correction 

 collar. 



Another small objection, in his opinion, to the Beck Microscope was 

 that in the alteration of the tube-length correction was interfered with 

 from the fact that the light of the side tube came through a considerable 

 length of glass. In the same way a spherical correction was interfered 

 with by the use of thicker covering glasses. 



Another point, when speaking of the Abbe binocular, Mr. Beck had 

 said that the only disadvantage in the D -shaped diaphragm was that 

 one lost half the amount of light, but it must not be forgotten that half 

 the aperture was lost also, whether it was cut off at the upper focal plane 

 of objective or at the Ramsden circle. Personally, when using a 

 Wenham binocular he had found it a good plan not to slide the prism 

 quite home, but to let it merely cover about one-third of the diameter 

 of the object-glass only, leaving two-thirds of the area of the object- 

 glass, or even more, in the direct tube. He had found that with one 

 good image, a very imperfect image with the other eye was sufficient to 

 give a sense of stereoscopic relief as well as relief to physical strain, and 

 as, like most other microscopists, he had found that the eye not generally 

 used was the one most sensitive to light, curtailing the amount of light 



Feb. 18th, 19H ii 



