710 Bevieivs. [Oct., 



further, yellow rays appear beside the orange, after the yellow, green 

 rays are emitted, and after the green come in succession blue, indigo, 

 and violet rays. To display all these colours at the same time the 

 platinum wire must be white hot, the impression of whiteness being in 

 fact produced by the simultaneous action of all these colours on the 

 optic nerve."* 



It has already been stated, and is no doubt well known to our 

 readers, that these variously-coloured rays i>ossess different properties, 

 thus, the undulations which reach the eye, as orange or red rays, 

 possess specially a heating property, the yellow, an illuminating 

 power, and the blue or violet an actinic or chemical influence, and 

 in the white or colourless light of the sun we have these three 

 properties perfectly combined, for the complete fulfilment of the ends 

 of nature. If, then, we glance hastily over the whole series of 

 phenomena of radiation, we find that physically they take their origin 

 in the motion of matter. Whilst the nature of the substances, or 

 form of matter acted upon, is diversified in the extreme, the force in 

 operation, or the mode of motion seems to be uniform ; at least it 

 appears to vary only in the speed with which the atoms or molecules 

 are agitated. But the results, as conveyed through the organs of 

 sense to the brain, are incalculably diversified ; sounds which charm 

 the ear or soothe the soul ; others that fill the mind with terror ; 

 various degrees of heat, from the gentle warmth of the morning sun, 

 to the glowing metal from the furnace ; and light of all hues and 

 tints, direct and colourless, or partially resolved into its original 

 elements, by reflection from the pansy or the rose, or from the 

 verdant carpet of the pastures ; each affects with its power to minister 

 to life or modify the character of nature's forms or forces. 



The ascription of these phenomena to so simple a cause as the 

 motion of matter, known as radiation, is not the result of speculation 

 only ; for much is already known concerning the rapidity with which 

 the atmosphere and the presumed luminiferous aether (or whatever may 

 be the medium through which light is transmitted) are set in motion. 

 It is well established that a sonorous wave moves at the rate of 

 1,100 feet per second, or rather that the impression of sound is 

 conveyed to the ear at that rate ; also, that a ray of colourless light is 

 projected through the ether, at the speed of 192,000 miles in a 

 second ; that if such a ray be resolved into its constituent elements 

 as exhibited by the prism, red light travels more slowly than 

 orange, orange than yellow, and so on to the violet, whilst at either 

 end of the spectrum there are " non-luminous rays " which move 

 either too slowly or too rapidly to produce any effect upon the human 

 retina. 



These non-luminous rays although invisible to us have still very 

 marked properties ; those beyond the red end of the spectrum 

 possessing great heating power, whilst those at the other extreme are 

 endowed with considerable actinic properties; indeed Dr. Tyndall 

 has shown that as far as the electric light is concerned by far its 



* ' Loc. Cit.\ p. 3 (Dr. Draper's experiment). 



