Oti Light. 391 



iht fine tints, which in an infinite variety adorn the uni- 

 verse around us. This, at least, has been the current of 

 my own apprehensions. But from the facts, which have 

 been recited, it is certain, that the splendour, and the 

 colours, which we attribute to light, are the result of 

 mere pressure. But there are neither colours, nor splen- 

 dour, in pressure ; nor in the iinger, fiom which it pro- 

 ceeds. These extraordinary, and delightful, phenomena 

 have their seat in the optic nerve ; and exist in all their 

 diversities, only as effects of the variations of pressure. 

 Light itself has no more brilliancy than the iinger. Its 

 whole power is merely that oi gentle, and imperceptible, 

 pressure, or impact, upon the optic nerve: and this pres- 

 sure, like that of the disease, and like that of the finger, 

 awakens in the nerve the sensation of luminousness. 



2dly. lAght is matter, and not a Qiiality of matter. 

 No degree, or kind, of impulse, whether such as we call 

 pressure, or any other, can possibly be the effect of anv 

 mere quality. Both weight, and motion, are indispensa- 

 ble to its existence. Motion and weight, therefore, are 

 certainly attributes of light. 



3dly, The Colours of light are the result of nothings 

 but different degrees of pressure, and impulse. The col- 

 ours, mentioned as seen in the case, specified above, 

 were exactly the same with those of the prismatic image; 

 equally bright ; and, of course, sensibly brighter than 

 those of the rainbow. In this case they were certainly 

 derived from different degrees of pressure. There is not 

 the least reason for attributing the effect to any thing 

 else, when these colours are seen in the prism, or the 

 rainbow. As the three strongest colours are less easy, 

 and, when viewed for some time, more painful, than the 

 other four ; it is probable, that they are produced by a 

 stronger impulse, or greater pressure. 



4thly. This difference of impulse can he derived from 

 nothing, but the weij-ht, or in other words the mass of 

 matter, and the velocity, or both, of the particles of light. 

 As they come to us from the sun, perfectly, or almost 

 perfectly, blended ; (there being, for some reason or oth- 

 er, a small predominance of the yellow;) it seems proba- 

 ble, that their velocity is the same. Otherwise, it will 



