220 Mr. T. E. Doubt on the Measurement of Colour 



Table I. 



Scale. 



Wave-length. 



Scale. 



Ware-length. 



11 



8470x10-8 cm. 



7999 



7579 



7199 



6856 



6545 



6260 



5999 



5760 



5538 



5333 



5142 



4965 



4799 



4644 



58 



4499x10-8 cm. 



4363 



4235 



4113 



3999 



3891 



3788 



3692 



3599 



3512 



3428 



3346 



3064 



14 



62 



66 



16 



19 



70 



22 



75 



79 



84 



89 



94 



99.. 



104 



24 



275 



31 



335 



37 



40 



43-5 



47 



110 



130 



51 



54 







One of the standard sources is placed in front of the 

 Donder's double slit. The observer sits between the two 

 arms of the instrument and looks at the optical mirror through 

 the diaphragm. In the lower field the original light appears 

 that has passed through the entire optical system. In the 

 upper part of the field the mixture of the colours that escapes 

 being cut off by the shutters appears. There is no dark line 

 between the parts of the field if it is properly diaphragmed. 



To obtain a match to the colour of the original light with 

 two colours, one is chosen in position, and the other is sought 

 by adjusting the shutters until the right colour is found. The 

 upper part of the Donder's slit which gives the original light 

 is narrowed so that the two fields may be of the same intensity. 

 For making a match with three or four or any number of 

 colours the procedure is about the same. Two colours are 

 chosen and other components selected by experiment, so that 

 a match may be obtained in this manner. The number in 

 parenthesis represents position on the scale, the wave-length 

 corresponding to these positions may be found from the 

 preceding table. 



9. 

 10. 



Table II. May 1-8, 1896. 



22(27) 

 24(29) 

 20(16) 

 62(11) 

 38(17) 



+25(55)=W. 



+17(60)=W. 



+19(41) + 20(67)= 1/7 W. 



+23(46) + 25(61)=7/33W. 



+52(44) + 46(62) =9-2/33 W. 

 25(19-5)+46(44-5)+ 66(64)=7'3/33 W. 

 21(21-5)+37(45) + 67(64) = 65/33 W. 

 35(22-5)+61(44-5)+ 71(66 5)= 11-5/33 W. 

 41(23-5) +77(48) +100(65-5)= 10-5/33 W. 

 30(24-5)+51(48-5)+ 59(70-5) =7-9/33 W, 



