Murray's Researches in Natural History, 155 



it retains the light of the sun for several hours after being 

 exposed to it; but Mr. Murray takes no notice of this pro- 

 perty, only that it becomes luminous, like many other sub- 

 stances, on being heated, independent of light. He also points 

 out the potato, decayed wood, several fish, as mackerel, whiting, 

 &c., as emitting light ; and of plants, the Tremella meteorica^ 

 the Indian cress, and the subterranean Rhizamorpha {rhiza^ 

 root, morphe, form ; resemblance) also evolve light in certain 

 temperatures. 



Percussion and friction are common sources of light, and 

 many instances of luminous exhibitions occur in chemical 

 practice, as well as in nature, which lead to the conclusion, 

 that " ,the light in luminous animals is a consequence of, and 

 has its being in, a peculiar organisation," 



The luminous spherulae of the glow-worm is a transparent 

 sac or capsule, through which, as through a window, the light 

 shines : it is quite distinct from chemical combustion and solar 

 light. Of the latter the author gives a concise description, 

 which may be best detailed in his own words. 



" When a beam of solar light is intercepted by a prism, it 

 unfolds a very beautiful and interesting spectacle. Seven 

 colours are presented; and the * bow of promise in the storm' 

 affords a magnificent illustration of its phenomena. The colours 

 thus unveiled are violet, indigo, blue, green, yellow, orange, 

 and red; and they are refrangible in this order, the violet 

 being the most easily refracted or bent, and the red with diffi- 

 culty refracted. Agreeably to the doctrine of chromatics, 

 taught us by Sir Isaac Newton, when all the colours are ab- 

 sorbed the object is black. Black, therefore, is the absence 

 of all colour. On the other hand, when all the colours are 

 returned or reflected, the object is white ; when a particular 

 colour is reflected, while the others are absorbed, the body 

 appears of that particular tint." It is added, " that colour is 

 the gift of light, numerous phenomena concur to assure us;" 

 but he also avers that " there remain many circumstances ex- 

 tremely difficult to be accounted for; so that colours are to 

 be considered accidental rather than essential properties of 

 bodies." This part of his observations on light would, per- 

 haps, have been clearer had he said that colours are the gift 

 of form and position. 



After some further disquisition on light and colours, in 

 which a considerable share of sound philosophical knowledge 

 is elicited, he comes to the examination of the light of the 

 glow-worm. 



Of luminous insects in this country, the Zampyris {lampo, 

 to shine, pyr, fire) noctiluca {noctiluca^ a candle) (j%. 58.), 



