266 THEORY OF LIGHT. 



largest were two lines in diameter, the smallest only one, and the others 

 were about one and a half. They were on the south side of the house, 

 and made an angle of twenty or thirty degrees with the horizon. They 

 were stretched and kept tight by wheels for the purpose. Every time 

 the weather changed, these wires made so much noise that it was 

 impossible to continue concerts in the parlour, and the sound sometimes 

 resembled that of a tea-urn when boiling, sometimes that of an harmonica, 

 a distant bell, or an organ. In the opinion of the celebrated chemist M. 

 Dobereiner, as slated in the Bulletin Technologique, this is an electro- 

 magnetical phenomenon. 



THEORY OF LIGHT. 



THE nature of light has ever been a subject of controversy. It was 

 Newton's explanation, that luminous objects give out particles of incon- 

 ceivable minuteness, and move with extreme velocity. " What mere 

 assertion, "says Sir John Herschel," will make any man believe, that in one 

 second of time, in one beat of the pendulum of the clock, a ray of light 

 travels over 192,000 miles; and would therefore perform the tour of the 

 world in less time than a swift runner would make one stride?" In 

 short, there is nothing like it but the influence of attraction ; which is so 

 instantaneous as to admit of no calculation of time at all. A different 

 theory from that of Newton was suggested by Huyghens, who supposed 

 a highly elastic fluid to fill all the space, and which, when moved, pro- 

 duced the effects ascribed to light. Instead of minute particles diverging 

 from the luminous body, he substituted waves of vibrations, propagated 

 through this elastic ether. The late Dr. Young, and some Continental 

 philosophers, more recently, took up this hypothesis and supported it by 

 ingenious experiments. But notwithstanding that it is the favourite 

 theory of the day, difficulties appear still to encumber it. The theory 

 of undulations implies the advance and recoil of the elastic medium, and 

 that gives the idea of retardation. The supposition of light being the 

 effect of the motion of an ether, does notfall in with our conceptions of the 

 manner in which it enters into the composition of bodies, or influences 

 chemical combinations, or effects the living power of animals and vege- 

 tables. The merits of the two theories, however, need not be discussed 

 here. It will be sufficient for our purpose to enter on the explanation of 

 a few of the laws which influence a ray of light in passing through 

 transparent media. 



When the ray of light passes perpendicularly from a rarer into a denser 



