REVIEWS. 
77 
A chapter on Colour-blindness is rather alien to the present notice. 
Helmholtz and Young’s colour theory is reached in the eleventh chapter, 
and Maxwell’s colour discs are explained. Overlapping spectra in Helmholtz’s 
hands proved the singular fact that union of pure blue with pure yellow 
light, produces, not green, but white, thus overthrowing the hypothesis of 
Brewster. A section follows on the Mixture of Colours, founded mainly on 
Maxwell’s Kotating Colour-discs and Dove’s Dichroscope, the results of 
which are compared with mixtures on the artist’s palette. Binocular Vision 
is afterwards called in aid, and many valuable practical results are recorded. 
The book, indeed, from this point, becomes less physical, but none the less 
useful, from the predominance of aesthetic detail. It would be impossible in 
limited space to analyze minutely the last chapters ; but their general scope 
may be gathered from their successive headings : — Systems of Colours ; 
Contrast ; Combinations in Pairs and Triads ; and the Use of Colour in 
Painting and Decoration. 
It will be easily seen from what has been hastily sketched above, that 
this book is of exceptional value and originality ; chiefly because it succeeds 
in blending harmoniously the latest researches in Physical Optics with the 
rules and dicta which are the hereditary property and the traditional founda- 
tion of Pictorial and Decorative Art. 
W. H. Stone. 
