INFLUENCE OF LIGHT ON THE PROPAGATION ©F SOUND. 2Q 



The magic power this emanation from the lieaveus exerts It affects other 

 on our eyes, in exhibiting to <;s the spectacle of the "ni- thafof tS«S 

 verse, camot be sufficiently admired : but its power is not 

 confined to the organs of sight ; all our senses are subjected 

 to the action of light, a d it is from this mode of conceiv- 

 ing its action, that I lidertook the experiments., of which I 

 intend to give an account to the academy. The part that I Its connection 

 shall treat of at present relates to the effects resulting from ^"'' ^°"" * 

 the relations that subsist between the rays of light, and the 

 vibrations of sonorous bodiesf. The following observations 

 first began to fix my thoughts on this subject. 



In 1803 1 lived at Paris. Being accustomed to rise be- How first snj- 

 fore day, to finish a work on which I had been long em- ^'^*^j^^^i.^°^*^® 

 ployed, 1 found myself frequently disturbed by the sound 

 of carriages, as my windows looked into one of the most 

 frequented streets in that city. This circumstance, which 

 disturbed me in my studies every morning, led me to re- 

 mark, that the appearance of daybreak peculiarly affected 

 the propagation of the sound : from dull and deep, which it 

 was before day, it seemed to me to acquire a more sonorous 

 sharpness in the period that succeeded the dissipation of the 

 darkness. The rolling of the wheels seemed to announce 

 the friction of two substances grown more elastic ; and my 

 ear on attending to it perceived this difference diminish, in 

 proportion as the sound of wheels was confounded with 

 those excited by the tumult of objects quitting their noc- 

 turnal silence. 



Struck with this observation, I attempted to discover, Confirmed in 

 •whether any particular causes had deceived my ears. T rose that'light'as^ 

 several times before day for this purpose alone, and was sisted in pro- 

 every time confirmed in my suspicion, that light must have P*S*^i°"' 

 a peculiar influence on the propagation of sound. This 

 variation however in the manner in which the air gave sounds 

 might be the effect of the agitation of the atmosphere, pro- 



^ I have traced out for myself a series of inquiries, that I conceive Object of the 

 roust lead to some important discovery. My object is to ascertain the author. 

 action of light in the various phenomena, that take placa in the elastic 

 fluids around us. This object, which on the one hand is connected with 

 the mechanism of our sensations, on the other embraces the results of 

 lh«se first combinsitioas, that escape our apprehension. 



duced 



