176 DR. J. D. MACDONALD, I.H.R.N., F.R.S.^ ON 



division of tlie string is found in this diagram, and the number is 

 determined exactly by the string of the monochord — for instance 

 if the whole string sounds C, you get off |^th, and ^ths go on D, 

 and you divide their parts according to the ratio given in this first 

 series, f , ~, f, and so on, and divided into three parts you get three 

 G's, one part G, and two parts G, and the whole three sounded 

 together give you the note of the string itself. The same law 

 applies to these colours. If you have a certain number of 

 pigments here you would have double the number of vibrations 

 \_explaining the diagram.^ 



Professor Orchard. — One of the most important parts of the 

 paper is at the commencement, viz., that colour is, in fact, not 

 merely subjective but also objective. 



The phenomenon of colour-blindness, to which allusion has been 

 so interestingly made, and also those other phenomena, coloui' 

 sensations, when the eyes are closed to external objects, abund- 

 antly prove that there is a subjective aspect of colour, and we 

 should, indeed, on other grounds, be led to that conclusion. It is 

 very important, to ray mind, to remember the two sides of the 

 shield — that it is not merely objective on this colour (though it is 

 objective), but that it is also subjective ; but it is only when those 

 two are on this colour that you call it unison and we get the 

 sensation of colour. 



It is rather surprising that Dr. Rutherford, on page 3 of the 

 paper, should have reasoned in the fashion he did in regard to the 

 cones and rods : "The cones alone occur in the yellow centre, where 

 the visual sensitiveness is most perfect. Here, then, we perceive 

 that the colour sense is not impaired by the absence of the rods." 

 That is, indeed, a very curious conclusion to adduce from that 

 premiss. I think it is cleai^ly shown that the rods also play their 

 part in connection with colour sensations. 



We have to thank Dr. Macdonald for a most concise presenta- 

 tion of a most fascinating subject, and as one reads the concluding 

 sentence one may endorse the hope and expectation that the art 

 may become a science and be taught at the Royal Academy in the 

 future. 



Dr. BiDULE. — One does not like appearing as a critic of such an 

 admirable paper as this, but I feel that exception ought to be 

 taken to one or two passages at the beginning of it. The author 

 objects to our affirming that *' colour is in fact an internal 



