34 MR. J. SMITH ON THE ORIGIN OF COLOUR 



being again reflected from the black. Nor could any one 

 suppose for a moment that the white contained a blue of 

 some order, and reflected more of that than of any other 

 colour. Of course I am aware that this argument may 

 be turned round in a circle, and I shall be told over again 

 that the black reflects blue, or is an obscure blue of some 

 order ! In order to explain phenomena such as this, in 

 accordance with sound logic, we must suppose that the 

 efi'ect is produced by beats or vibrations of light, and that 

 these beats or vibrations of light are connected with dark- 

 ness or shadow — a proposition which, as I shall presently 

 show, may also be proved experimentally. 



^2. Colour then, I conceive, cannot be changed "by 

 reflecting it on the confines of shadow,^^ which would not 

 indeed in the least degree reduce its momentum; but if 

 we do reduce the momentum of a ray of light without 

 decomposing it, and by reflecting it at regular intervals 

 with black, that is, giving it by motion, as it were, two 

 different planes — a positive and a negative basis — pro- 

 duce two sensations, alternate indeed, but so rapid as to 

 be considered coordinate ; and if we by this means can 

 change one colour into another, then are we warranted 

 in arriving at the conclusion, that the efi'ect of colour is 

 produced by intervals of light and darkness. 



^3. Although I find it difi&cult to define the negative 

 term which I am labouring to introduce, but which does 

 nevertheless denote something having a real existence, 

 still it is not more difficult to understand the necessity 

 of it than to understand the necessity of intervals of silence 

 in the science of acoustics. There is one advantage, how- 

 ever, in our experiments ; what we cannot define or make 

 intelligible in the present state of scientific language, we 

 can show to exist and to have an appreciable value. By 

 and by, when once the experiments have become familiar, 

 the effects of intervals of light and shade will be as easily 



