POWER OF DISTINGUISHING COLOURS. 187 



nitting colour. Taking the wave-length of the ex 

 areme visible red as 760 and that of the extreme 

 riolet as 397, we have 



760 to 647 give red. 

 647 585 orange. 

 585 575 yellow. 

 575 497 green. 

 497 455 blue. 

 445 397 violet 



The result of his examination of my glasses and 

 jolutions 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. 



