4 Colours of Sky Light, Sun Light, Cloud Light, Sfc. [June 1, 



From, these measures it may be concluded that the dominant colour 

 of a blue sky is X 4800. 



Amongst artists it is not uncommon to employ cobalt to render 

 this colour, and in many instances this is mixed with Chinese 

 white. 



The dominant colour of cobalt was found to be at scale No. 29, or 

 X4812, when illuminated by ordinary day light, whence it seems 

 that, as far as colour is concerned, it is singularly fit for the purpose. 



Sun light was compared in the same manner, but the beam was 

 reflected from the surface of a prism into a dark room, and again 

 diminished in intensity by placing in its path rotating sectors with 

 very narrow apertures. 



Near mid-day on July 8 the sun was very clear, the sky being free 

 from clouds, and a strongish wind blowing from the west. Two 

 separate sets of measures were made with an interval of an hour 

 between each. It was found that the dominant colour was X4885 in 

 both cases, and in the first set it was diluted with 5 '45 of white, and 

 iu the other with 5'14 of white. This indicates that sun light 

 contains slightly more green-blue rays than the light emitted from 

 the crater of the positive pole of the electric light. This agrees with 

 the spectrum measures made in " Colour Photometry." 



Cloud light was next matched on days in which the sky was over- 

 cast. A comparison of the general light of the zenith was all that 

 was attempted, and near mid-day. 



It was found that it required 1 part of X4864 diluted with 5*5 

 parts of white to make a match. It will be seen that the dominant 

 colour of cloud light lies between that of the sky and of the Sun, as 

 might be expected, and is decidedly whiter than the sky, as might 

 also be anticipated. 



Various comparisons of sunset colours have been made, and found 

 to range from X 6300 up to X 4800 ; in some cases it was necessary to 

 match by means of complementary colours. 



The light from a paraffin candle it was found could be very closely 

 matched with D sodium light. The equation may be expressed as 

 follows : 



Candle light = X5880 + 0'4W. 



The amount of added white varied from O'l to 0*5, and it is in this 

 part of the spectrum that a large number of separate observations are 

 required in order to get a good and fairly trustworthy mean. 



