ig 
the Theory of Light and Colours. 
{t of several bignesses, that is, the rays of several colours, which 
« are blended together in light, must be parted from one an-- 
tc other by refraction, and so cause the phenomena of prisms, 
e£ and other refracting substances ; and that it depends on the 
“ thickness of a thin transparent plate or bubble, whether a 
“ vibration shall be reflected at its further superficies, or trans- 
“ mitted ; so that, according to the number of vibrations, inter- 
“ ceding the two superficies, they may be reflected or transmitted 
“ for many successive thicknesses. And, since the vibrations 
“ which make blue and violet, are supposed shorter than those 
“ which make red and yellow, they must be reflected at a less 
“ thickness of the plate : which is sufficient to explicate all the 
“ ordinary phenomena of those plates or bubbles, and also of 
“ all natural bodies, whose parts are like so many fragments of 
£C such plates. These seem to be the most plain, genuine, and 
“ necessary conditions of this hypothesis. And they agree so 
“ justly with my theory, that if the animadversor think fit to 
“ apply them, he need not, on that account, apprehend a divorce 
“ from it. But yet, how he will defend it from other difficulties, 
“ I know not/' (Phil. Trans. Vol. VII. p. 5088. Abr. Vol. I. 
p. 145. Nov. 1672.) 
“ To explain colours, I suppose, that as bodies of various 
“ sizes, densities, or sensations, do by percussion or other 
“ action excite sounds of various tones, and consequently vi- 
te brations in the air of different bigness ; so the rays of light, 
“ by impinging on the stiff refracting superficies, excite vibra- 
“ tions in the ether, — of various bigness ; the' biggest, strongest, 
“ or most potent rays, the largest vibrations ; and others shorter, 
“ according to their bigness, strength, or power: and therefore 
“ the ends of the capillamenta of the optic nerve, which pave 
D 2 
