588 Transactions of the American Institute. 



been found in the Woon district, containing from fifty-three to sixty- 

 eight per cent of iron. 



The President remarked that probably the coal found was 

 bituminous. 



II. Interesting Experiments on Color. 



Dr. Clerk Maxwell recently made some striking experiments on 

 light and color at the Koyal Institution, London. A mixture of blue 

 and yellow pigments produced a green color. When discs of blue 

 and yellow light were projected on a screen and made to over-lap, 

 the combined lights produced not a green color, but pure white. In 

 the same manner, by throwing red and green rays upon the screen, the 

 area of the junction gave the impression of a brilliant yellow. Simi- 

 lar colors have been thus combined by American experiments, but 

 with very different results from those obtained by Mr. Maxwell. 



Mr. J. K. Fisher — I think Dr. Maxwell is very much mistaken. I 

 do not believe he has a good perception of color. That blue and 

 yellow rays will produce white, is contrary to all the theories and 

 experiments of philosophy ; for they produce green. Blue, yellow 

 and red rays will produce white. • 



Dr. P. H. Yan der "Weyde — It is very curious ; but, although it is 

 utterly impossible in the chromoscope to make blue and yellow pro- 

 duce white, or to blend a red and green disc to produce yellow, yet it 

 is true that blue and yellow light produces white. We must distin- 

 guish between the prismatic colors and the common pigments. If 

 you throw upon a screen, by means of a 'prism, the seven colors, and 

 intercept all but the green rays, you may look at that green disc 

 through another prism, and you will see no color but green. But 

 look through the prism at a disc painted green, and you will see blue 

 and yellow. The blue and yellow mixed in the pigment produce a 

 color corresponding to the mean undulation velocity. The number 

 of undulations per second of the yellow light is about 500 millions of 

 millions, of blue light about 700, making an average of about 600, 

 which corresponds to green light. But the prismatic green rays all 

 have 600 millions of millions of undulations per second, none moving 

 faster and none more slowly ; so that the prism cannot separate them. 



In the same lecture, Dr. Maxwell speaks of a yellow spot in the 

 eye. I have not much belief in that. There is a spot in the retina 

 where the optic nerve passes through it ; the fibers separating and 

 feeling the image from the front like so many transparent fingers; 

 but that spot is insensible. 



