Capt. W. de W. Abney. Colours of Sky Light, [June 



June 1, 1893. 

 The LORD KELVIN, D.C.L., LL.D., President, in the Chair. 



Professor Alexander Pedler (elected 1892) was admitted into the 

 Society. 



A List of the Presents received was laid on the table, and thanks 

 ordered for them. 



The President gave notice that at the next meeting of the Society 

 he would propose the Duke of York for election as a Fellow of the 

 Society by immediate ballot, to which, as a Prince of the Blood 

 Royal, His Royal Highness was entitled. 



The following Papers were read : 



I. "On the Colours of Sky Light, Sun Light, Cloud Light, 

 and Candle Light." By Captain W. DE W. ABNEY, C.B., 

 D.C.L., F.R.S., P.R.A.S. Received May 9, 1893. 



The author has made several comparisons of the above lights 

 throughout the different parts of their spectra, and has been able to 

 verify their correctness by means of templates rotating in the 

 spectrum of electric light, as described in Part II, " Colour Photo- 

 metry," ' Phil. Trans.,' 1889. It seemed, however, that it would be 

 useful if the colours of these lights could be expressed in single 

 wave-lengths, together with the amount of added standard white 

 light, the latter being expressed in terms of the luminosity of the 

 dominant colour, in accordance with the method brought before the 

 Royal Society in ' Proc. Roy. Soc.,' 1891. 



When measuring light from the sky, a beam from the zenith or other 

 desired part was reflected through a blackened tube into a darkened 

 room in which the colour patch apparatus (" Colour Photometry," 

 Abney and Festing, 1886) was placed, and the image of the end of 

 the tube was focussed on to the front surface of a cube, the front 

 surface of which was coated with zinc white, its background being 

 black velvet. The patch of colour from the apparatus was also 

 thrown on the cube. A rod placed in the paths of the two beams 

 enabled the sky light and the spectrum colour to be examined side by 

 side. The slit in the spectrum was an adjustable one, so that any 

 intensity of colour within limits would fall on the cube. A beam of 



