THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



AUGUST 1884. 



IX. On a new Apparatus for Colour- Combinations. By 

 H. H. Hoffert, B.Sc, A.R.S.M., Assistant in the Physical 

 Laboratory, South Kensington*. 



[Plate V.] 



VARIOUS arrangements for the mixture of colours have 

 already been devised by Maxwell, Rayleigh, Helmholtz, 

 and others, by means of which the laws of colour-combinations 

 have, in their main features, been firmly established. 



Wishing to observe for myself the principal phenomena 

 connected with this subject, I have repeated, during the past 

 winter, many of the experiments thus described, both with the 

 colour-top and with overlapping spectra. Being desirous of ob- 

 taining some convenient arrangement whereby any two or three 

 colours of the spectrum could be combined in any required 

 proportion, and compared with the colours either of natural 

 objects or of other spectral combinations, I tried various ex- 

 periments, using the method first adopted by Maxwell, of 

 observing, by means of a slit-eyepiece, the spectra produced 

 by light proceeding from illuminated slits, and passing through 

 a train of glass prisms; this method being equivalent to look- 

 ing through a hole in a screen on to which are cast two or 

 three superposed spectra, so that the colour perceived is that 

 due to the mixture of those parts of the several spectra which 

 fall on the hole. 



In these experiments I have been assisted by my colleague 



* Communicated by the Physical Society. Read June 14, 1884. 

 Phil. Mag. S. 5. Vol. 18. No. 111. Aug. 1884. G 



