PEO0EEDING3 OF SOCIETIES. 235 



of this very subtle process of regulating the thickness of the waves 

 of light as applied to the binocular. He thought Mr. Stephenson had 

 very perspicuously explained the action of the coloured fields which 

 he employed. He (Dr, Pigott) had not tried any experiments of the 

 kind, but the ideas set forth by Mr. Stephenson were very suggestive. 



After referring to the effect produced when one is looking through 

 a pair of spectacles, and the two rims are noticed or not, Dr. Pigott 

 continued : Suppose that the two glasses were of different colours, 

 what would be the effect upon the eye and brain? He imagined 

 that if they were complementary colours, they would be united by the 

 brain, and that if we were looking at snow we ought to see it tole- 

 rably white. He thought that Mr. Stephenson had touched upon a 

 new point in optical science, which might be developed with very great 

 utility. The ingenuity of the whole thing struck him with admira- 

 tion. Looking at the very complicated manner in which rays of light 

 are refracted and reflected by internal reflexion, and according to the 

 position of the prism, it was wonderful that such good effects were 

 obtained. 



Mr. Slack said there was one point in Mr. Stephenson's paper which 

 seemed to require explanation. He referred to the portion of it which 

 treated the effects described as having a character distinct from stereo- 

 scopic binocular vision, which it really resembled very closely. Mr. 

 Stephenson explained that the remark alluded to was not his own, but 

 a quotation. Mr. Slack proceeded to point out the resemblance between 

 the combination of two perspective views, and two complementary 

 colours. In both cases it seemed that the perceptive portions of the 

 brain acted upon the combined images. 



The Chairman said the interesting point in Mr. Stephenson's paper 

 was that in which he referred to the fact that in each retina there was 

 a different colour, and yet it was seen combined into one colour. He 

 did not remember in any work the subject being treated in the same 

 way as Mr. Stephenson had treated it. 



Mr. Slack said he should like to suggest an experiment, viz. to try 

 with all sorts of persons. It was known that there were very few 

 people who had two eyes exactly focussing alike, and probably it would 

 be rare to find a pair of eyes in which the chromatic corrections were 

 the same. It would be very interesting to notice what would be the 

 different effects the same images produced upon persons whose eyes 

 had different corrections. 



Dr. Pigott said he had met with the case of a gentleman who, 

 looking through his microscope, said he could never distinguish a red 

 colour in the instrument. It always appeared to him more like black 

 and white. He never saw anything red, but objects that appeared red 

 to other persons were black to him. 



Mr. Ingpen referred to an experiment tried with the stereoscope, in 

 which tinted glasses were used, having complementary coloiu'S. The 

 result was sometimes combination of colours, and not unfrequently 

 alternation of colours. The alternation might be attributed to the 

 fact that the eyes got alternately fatigued by each colour. 



Mr. Slack read a paper " On the Supposed Fungus on Coleus 

 leaves," and " Notes on Podiaoma fuscum and P. juniperi." 



