34* Things not generally Known. 



reflected or refracted, whether it emanates from a solid or fluid 

 or gaseous body ; it announces even the degree of its intensity. 

 Humboldt's Cosmos, vols. i. and ii. 



MINUTENESS OF LIGHT. 



There is something wonderful, says Arago, in the experi- 

 ments which have led natural philosophers legitimately to talk 

 of the different sides of a ray of light ; and to show that mil- 

 lions and millions of these rays can simultaneously pass through 

 the eye of a needle without interfering with each other ! 



THE IMPORTANCE OF LIGHT. 



Light affects the respiration of animals just as it affects the 

 respiration of plants. This is novel doctrine, but it is demon- 

 strable. In the day-time we expire more carbonic acid than 

 during the night; a fact known to physiologists, who explain 

 it as the effect of sleep : but the difference is mainly owing to 

 the presence or absence of sunlight ; for sleep, as sleep, increases, 

 instead of diminishing, the amount of carbonic acid expired, 

 and a man sleeping will expire more carbonic acid than if he 

 lies quietly awake under the same conditions of light and tem- 

 perature ; so that if less is expired during the night than during 

 the day, the reason cannot be sleep, but the absence of light. 

 Now we understand why men are sickly and stunted who live 

 in narrow streets, alleys, and cellars, compared with those who, 

 under similar conditions of poverty and dirt, live in the sun- 

 light. BlackwoocTs Edinburgh Magazine, 1858. 



The influence of light on the colours of organised creation is well 

 shown in the sea. Near the shores we find seaweeds of the most beau- 

 tiful hues, particularly on the rocks which are left dry by the tides ; and 

 the rich tints of the actiniae which inhabit shallow water must often 

 have been observed. The fishes which swim near the surface are also 

 distinguished by the variety of their colours, whereas those which live at 

 greater depths are gray, brown, or black. It has been found that after 

 a certain depth, where the quantity of light is so reduced that a mere 

 twilight prevails, the inhabitants of the ocean become nearly colourless. 

 Hunt's Poetry of Science. 



ACTION OF LIGHT ON MUSCULAR FIBRES. 



That light is capable of acting on muscular fibres, indepen- 

 dently of the influence of the nerves, was mentioned by several 

 of the old anatomists, but repudiated by later authorities. M. 

 Brown Sequard has, however, proved to the Royal Society that 

 some portions of muscular fibre the iris of the eye, for example 

 are affected by light independently of any reflex action of the 

 nerves, thereby confirming former experiences. The effect is 

 produced by the illuminating rays only, the chemical and heat 

 rays remaining neutral. And not least remarkable is the fact, 



