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, vre have 



760 to 647 give red. 



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. 



