xiv.] FORTIES' SCIENTIFIC WORK. 465 



l)i i that blue and yellow do not make green, but a pinkish 

 tint, when neither prevails in the combination. It was 

 plain that no addition of red to this could produce a 

 neutral tint. The fact that green cannot be formed by a 

 mixture of blue and yellow was pointed out by E. C. 

 Wiincli 1 and by Young, 2 but the contrary was still be- 

 lieved by the highest optical authorities, The reason why 

 mixtures of blue and yellow pigments are often green 

 soon after explained by Helmholtz ; and Clerk- 

 Maxwell, who was one of Forbes' pupils and witnessed 

 his experiments, was led by them to make experiments 

 on the mixtures of the colours of the solar spectrum, 

 which showed that a yellow, equal to that of the spec- 

 trum, can be produced by the mixture of green and red 

 light. 



Of some other physical investigations by Forbes, such 

 as those upon the Trevelyan experiment, and upon Am- 

 xperiment which exhibits the repulsion between 

 ;ients of the same straight current, with various other 

 questions connected with heat and electricity, we need 

 not say much. There can be little doubt that Forbes 

 did not so clearly apprehend the nature of the questions 

 at issue as to be enabled to bring his unquestioned ex- 

 perimental skill properly to bear upon them. Con- 

 s' ''jiiently he was led to oversights, and, in one case at 

 least, to serious mistakes. Some of this may be traced 

 to a singularly erroneous idea, as to the nature of the 

 n -lation between heat and electricity, which seems to 

 ha\ <: haunted him all his life, and occasionally to have led 

 him to waste a great deal of time on experiments which 

 jili\ i'-nce enables us to say could not possibly lead 



to anything in the direction in which he was seeking to 

 go. He possessed, indeed, untiring energy coupled with 

 nd experimental skill, and everything he 

 published may b,- fully relied on as a faithful description 

 of what he observed. But it must be recollected that he 



und Bcobachtungen iibcr die Farben dus Lichts 



' 



ro XXXVII. 



II II 



