346 Prof. Barton and Miss Browning on a Syntonic 



will in like manner be referred to under the names of other 

 colours. 



Colour Mixtures. 



Red and Green make Yellow. — Photo 1 shows the response 

 to a yellow driver. Photo 2 shows a response to two drivers, 

 red and green, acting simultaneously. It is seen that the 

 responses in .1 and 2 are precisely alike in character as 

 might be expected from the resonance curves of figure 1. 

 Thus, on our hypothesis, it is shown that red and green 

 make yellow. That is to say, this set of only three responders, 

 red, green, and violet, cannot differentiate between (i.) the 

 simultaneous stimuli of red and green drivers, and (ii.) the 

 single stimulus of a yellow driver, whose frequenc} T is inter- 

 mediate between those of red and green. Photo 3 shows the 

 response to drivers representing red and bluish green. 



Blue and Yellow fail to make Green. — It might be supposed 

 that on our hypothesis any two colours of the spectrum being 

 used as simultaneous stimuli, the system would give the same 

 response as if under a single stimulus of intermediate 

 frequency. If so, blue and yellow would make green, 

 whereas, with the eye it is not so. On the contrary, the 

 true addition of blue and yellow give the sensation of white 

 or a faint pink. It is therefore a crucial test of the present 

 hypothesis to ascertain the response of the three vibrators 

 when under the action of blue and yellow drivers. This is 

 shown in photo 4. It is seen that all the responders move, 

 the middle or green responder least of all, and the red one 

 most. Thus, so far as the colour departs from white, it is 

 certainly not green but pinkish. It therefore accords with 

 the known facts of colour vision as exhibited by colour tops 

 and converging beams. It is easily seen why with this set 

 of three responders, blue and yellow drivers do not give the 

 effect of a single intermediate frequency as the red and 

 .green did. The latter have each a special responder, neither 

 of the former has a special responder in tuue with it. 



Blue and Red give a Colour not found in the Spectrum. — 

 Photo 5 shows the effect of blue and red drivers acting 

 simultaneously. As might be expected, we have here a 

 response that could not be due to any single spectral colour, 

 i. e. to the vibrations of any single driving pendulum of 

 length anywhere in the range of the responders. This result 

 accords with the known fact that the true addition of red 

 and blue gives a purple which does not occur in the 

 spectrum. 



