LORD RAYLEIGH ON THE COLOURS OF THIN PLATES. 



161 



Table I. 



Scale. 



Wave-length. 



Colour. 



(24) 



(44) 



(68) 



16 



2580 



red 



+440 







20 



2450 



red 



•420 



+ •009 



+ ■063 



24 



2328 



scarlet 



1000 







28 



2240 



orange 



1-155 



•360 



-•006 



32 



2154 



yellow 



•846 



•877 



•005 



36 



2078 



yellow-green 



484 



1-246 



•032 



40 



2013 



green 



+ •127 



1-206 



-•008 



44 



1951 



green 





1-000 





48 



1879 



bluish-green 



-•063 



•759 



+ •085 



52 



1846 



blue-green 



•055 



•506 



•282 



56 



1797 



greenish-blue 



•050 



•340 



•495 



60 



1755 



blue 



•047 



■190 



•753 



64 



1721 



blue 



-033 



•033 



•905 



68 



1688 



blue 







1-000 



72 



1660 



indigo 



+ 019 



•006 



•944 



76 



1630 



indigo 



•025 



+ •016 



•693 



80 



1604 



indigo 



•005 



-028 



•479 



84 



1580 









•333 



88 



1560 







* • • 



•208 



92 



1540 





. . . 





•146 



96 



1520 



. . . 







•083 



100 



1500 



... 







•042 









+ 3973 



+ 6-520 



+ 6460 



The colour produced by combining all the light which passed the prisms 

 from (16) to (100) is the white of the apparatus. Its equivalent in terms of 

 the standards is given by 



W' = 3-973(24) + 6-520(44) + 6-460(68). 



It differs a little from the standard white of the original matches, i.e., 



W = 18-6(24) + 31-4(44) + 30'5(68) , 



not only in consequence of omission of some extreme red and violet, but 

 probably also on account of absorption by the prisms. 



The colours of the spectrum were exhibited by Maxwell in Newton's 

 manner, and are reproduced on our diagram (Plate X.), in which each colour 

 is represented by the centre of gravity of three weights at the corners of an 

 equilateral triangle, the magnitudes of the weights being taken proportional to 

 the quantities of (24), (44), and (68) required to compound the colour, so that 

 the corners themselves represent the standard colours. 



The wave-lengths are given in Frauenhofer's measure (in terms of the Paris 

 inch).* The scale is such that for D, X = 2175, and for F, X = 1794. 



* 1 Paris inch = 2-7070 cm. 



