POWER OF DISTINGUISHING COLOURS. 187 
mitting colour. Taking the wave-length of the ex- 
treme visible red as 760 and that of the extreme 
violet as 397, we have 
760 to 647 give red. 
647 ,, 585 4, orange. 
585 ,, 575 4, yellow. 
575 ,, 497 ,, green. 
497 ,, 455 ,, blue. 
445 ,, 397 ,, violet. 
The result of his examination of my glasses and 
solutions was as follows :— 
The light-yellow glass cut off the high end down 
to wave-length 442. 
The dark-yellow glass cut off the high end down 
to wave-length 493. 
The green glass cut off the high end down to wave- 
length 465, and also the red to 616. 
The red glass cut off the high end down to wave- 
length 582. 
The violet glass cut off the orange and yellow from 
wave-length 684 to 583, and a band between 
wave-lengths 543 and 516. 
The purple glass cut off the high end down to 
wave-length 528. 
The solution of chromate of potash cut off the 
high end to 507. 
The saffron cut off the high end to about 473. 
The blue fluid cut off the low end to 516. 
The red fluid cut off the high end to 596. 
