1.16 Prof. A. M. Mayer on the History of Young's 



the manner that vibrations in the air cause a sensation of 

 sound, by beating against the organs of hearing. Now the 

 most free and natural application of this hypothesis to the solu- 

 tion of phenomena I take to be this : that the agitated parts 

 of bodies, according to their several sizes, figures, and motions, 

 do excite vibrations in the ether of various depths or bignesses, 

 which being promiscuously propagated through that medium 

 to our eyes, effect in us a sensation of light of a white colour ; 

 but if by any means those of unequal bigness be separated 

 from one another, the largest beget a sensation of a red colour, 

 the least or shortest of a deep violet, and the intermediate ones 

 of intermediate colours ; much after the manner that bodies, 

 according to their several sizes, shapes, and motions, excite 

 vibrations in the air, of various bignesses, which, according to 

 those bignesses, make several tones in a sound ; that the largest 

 vibrations are best able to overcome the resistance of a refract- 

 ing superficies, and so break through it with least refraction ; 

 whence the vibrations of several bignesses (that is, the rays of 

 several colours which are blended together in light) must be 

 parted from one another by refraction, and so cause the phe- 

 nomena of prisms and other refracting substances ; and that 

 it depends upon the thickness of a thin transparent plate or 

 bubble whether a vibration shall be reflected at its further 

 superficies or transmitted ; so that, according to the number of 

 vibrations interceding the two superficies, they may be reflected 

 or transmitted for many thicknesses. And since the vibra- 

 tions 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 

 such plates. These seem to be most plain, genuine, and neces- 

 sary 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. I. 145, 

 November 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 vibrations on 

 the air of different bigness, so the rays of light, by impinging 

 on the stiff refracting superficies, excite vibrations 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 



