232 



tions of Herschel*. I shall not examine whether, as Descartes and his 

 followers imagine, light, consisting of globular molecules, exist of itself, 

 uniformly diffused through space, or as Newton has taught us to believe, 

 it be but an emanation of the sun and fixed stars, which throw off, from 

 their whole surface, a part of their subsistence, without ever exhausting 

 themselves by this continual efflux : It is enough for us to know, 1st, that 

 the rays of this fluid move with such velocity, that light passes, in a 

 second, through a distance of seventy-two thousand leagues, since, ac- 

 cording to the calculation of Roemer and the tables of Cassini, it traver- 

 ses in something less than eight minutes, the thirty-three millions of 

 leagues that separate us from the sun; 2dly, that light is called, direct, 

 when it passes from the luminous body to the eye, without meeting any 

 obstacle ; reflected, when it is thrown back to that organ, by an opake 

 body; refracted, when its direction has been changed, by passing from 

 one transparent medium to another of different density; 3dly, that the 

 rays of light are reflected at an angle equal to that of incidence ; that a 

 ray, passing through a transparent body, is more strongly refracted, as 

 the body is more convex on the surface, denser, or of more combustible 

 elements. It was from this lest observation, mat Newton conjectured 

 the combustibility of the diamond, and the existence of a combustible 

 principle in water, since placed beyond doubt, by the beautiful experi- 

 ments of modern chemistry ; 4thiy, that a ray of light refracted by a 

 glass prism is decomposed into seven rays, red, orange, yellow, green, 

 blue, indigo, and violet. Each of these rays is less refrangible, as it is 

 nearer to the red. This ray is of all, that which strikes the eye with the 

 greatest force, and produces on the retina the liveliest impressions. The 

 eagerness of savages for stuffs of this colour is well known. Among al- 

 most all nations it has dyed the mantle of King? : it is the most brilliant 

 and splendid of all : there are animals whose e^es seem scarcely to sus- 

 tain it: I have seen maniacs whose madness, [after a long suspension, 

 never failed to break out, at the sight of a red cloth, or of one cloathed in 

 that colour. Green is, on the contrary, the softest of colours; the most 

 permanently grateful ; that which least fatigued the eyes; and on which 



they will longest and most willingly repose 

 been profuse of green, in the colouring of all 

 some sort, of this colour, the greater part of th 



When the eyes bear uneasily the glare of too i 



.ccordingly, Nature has 

 lants; she has dyed, in 

 ; surface of the globe. 



this colour are used to soften the impression, which slightly tinge, with 



their own hue, all the objects seen through then 

 last in the scale, of which the middle place isfi 



trong a light, glasses of 



Lastly, the violet ray, 

 ed by the green, is of all 



the weakest, the most refrangible. Of all colouts, violet has the least lus- 

 tre; forms show to less advantage under it; their prominences are lost; 

 painters accordingly make but little use of it. "V^hen an enlightened body 



* This celebrated Astronomer has published, in the Philosophical Transactions of the 

 Royal Society for 1800, a series of experiments, which show, that the different coloured 

 rays, heat, in different degrees, the bodies on which they tall, and tJuit the red my, 

 which is the least refrangible, gives also the greatest heat. 



The thermometer placed out of the spectrum and towards the red ray, so that it 

 would receive any rays yet less refrangible, rises higher than when it is placed in that 

 colour, From waich Herschel concludes that rays are given out by the sun, too little 

 refrangible to produce the sensation of light, and of colours, but which produce the 

 Sensation of heat Author's J\f"otr. 



