301 



Young, and figured in his Lectures on Natural Philosophy. The 

 original conception, however, seems to be due to Newton, who gives 

 the complete theory, with an indication of a construction in his 

 Optics. 



The success of this method depends entirely on the truth of the 

 supposition that there are three elements of colour as seen by the 

 eye, every ray of the spectrum being capable of exciting all three 

 sensations, though in different proportions. It is at present impos- 

 sible to define the colours appropriate to these sensations, as they 

 cannot be excited separately. But it appears probable that the 

 phenomena of colour-blindness are due to the absence of one of 

 these elementary sensations, and, if so, a comparison of colour-blind 

 with ordinary vision will show the relation of the absent sensation to 

 those with which we are familiar. 



A method was then described, by which one observation by a 

 colour-blind eye was made to determine a certain point representing 

 the absent sensation, which thus appears to be a red approaching to 

 crimson. The results of this hypothesis were calculated in the form 

 of " equations of colour-blindness" between colours which seem to 

 defective eyes identical. These equations were compared with those 

 previously determined from the testimony of two colour-blind but 

 accurate observers, and found to agree with remarkable precision, 

 rarely differing by more than 0-02 in any colour. The effect of red 

 and green glasses on the colour-blind was then described, and a pair 

 of spectacles having one eye red and the other green was proposed 

 as an assistance to them in detecting doubtful colours. 



2. Notice of the Occurrence of British newer Pliocene Shells 

 in the Arctic Seas, and of Tertiary Plants in Greenland. 

 In a letter from Dr Scoular of Dublin. Communicated by 

 James Smith, Esq., of Jordanhill. 



Dr Scoular writes : — 



" I have lately had the opportunity of examining a series of fossils 

 from high arctic latitudes, brought home by Captain M'Lintock, 

 R.N. The series in one sense is extensive, as there are Silurian 

 and oolitic shells, and also other fossils of the tertiary times. Among 

 these last there are some things which, I am sure, will be of interest 

 to you. Among the specimens are some recent and living shells 



