On the theory of compound colours

Helmholtz published a series of observations, some of which were new and ingenious, and from which he comes to the conclusion, that the theory of compound colours, universally admitted since the time of Newton, is erroneous in its most essential points; and that there are properly only two prismatic colours, yellow and indigo, which when mixed give white.  It may consequent|y not be regarded as superfluous to show that the Newtonian theory of compound colours is correct to a certain point, and especially that the opinion that every colour has its complementary colour, with which when mixed gives white, is founded upon mathematically incontestable facts, so that this opinion must be regarded as one of the most tenable in physics.  I will then show that the positive observations of Helmholtz, instead of tending to the subversion of this theory, serve rather to prove and partly to complete it.

Nevertheless, the manner in which Newton distributes the homogeneous colours on the circumference of his discs requires a thorough revision, towards which only the first steps are made by the researches of Helmholtz.  Not until sufficient light has been thrown upon this subject can we attempt the solution of the interesting question with regard to the law by which the vibrations belonging to the various colours combine to produce simple impressions of colour upon the nerves of the sensorium, a question upon the solution of which the idea of the various colours and of colourless light essentially depends.