174 DK. J. D. MACDONALDj I.F.R.N., P.E.S., ON 



So in matching colours I will say, " What are those three colours ? " 

 (red, violet, and green). Perhaps ninety-nine out of one hundred 

 wil't distinguish them, and the hundredth will go up and see the 

 red and violet, and will go up to the green and not know what to 

 make of it. Then I will give him my skeins of silk, and say, 

 *' Match those," and probably he will put the red on the green. 



Dr. Macdonald. — I remember in the case of my brother, when, 

 as boys, we used to make paper soldiers and paint them, he would 

 paint a soldier's coat with emerald green with the same 

 satisfaction that he would vermilion. 



Mr. HuLME. — What is the percentage of coloui'-bliud boys or 



men ? 



Dr. Macdonald. — It is seriously stated, but it is remarkable, 

 that ladies are more highly gifted than men in this respect. 

 There is a matter of great importance connected with this, and 

 that is the subject of signals. As to violet, if you extend it to 

 blue, the blue is more constantly present than green — consequently, 

 if signals were red and blue instead of red and green, there Avould 

 be much less likelihood of confounding them. 



[Dr. Macdonald here further explained his diagrams.] 

 Mr. Walter H. Thelwall, M.Inst.C.E. — I think it may be as 

 well to mention, though no doubt it is known to many, that 

 these vibrations are, of course, only theoretical. The actual 

 vibrations of the sounds we hear are not these vibrations, because 

 all music is planned on what is called a tempered scale, and it is 

 these sounds we hear in listening to music. The notes of the 

 diatonic scale, C, D, E, F, ai-e almost always used by mathematicians 

 in dealing: with matters of music, and they form, to a great extent, 

 the basis of the theoretical laws of harmony; but those inter- 

 mediate notes, D sharp and F sharp, and so on, have po existence 

 at all. They are neither tempered sounds, nor are they the 

 sounds required by theoretical harmony. I do not know whether 

 this has relation to the question of sound and colour, but that 

 really is the case, and the ratio of one musical note does not 

 continue below — it is always a twelfth, or 1-05946. I am not quite 

 certain of the figure, and I do not know whether that fact has a 

 bearing at all upon it ; but if this table is going out as a table of 

 sound used in music, I think it well that the correction should be 

 made, i)articnlarly as the author speaks of the improper tuning 

 of the organ. That is just one of the points that theoretical, 



