^^ INFLUENCE OF LIGHT ON THE PROPAGATION OF SOUND. 



which was the object of my inquiry: but T also knew, from 



the experiments made in 1738 by Maraldi, De la Caille, 



and Cassini, and from those of Bianconi in 1740, that the 



thickest fog had been found to have scarcely any effect on 



the velocity of sound. To proceed more satisfactorily 



therefore, 1 determined first to examine by means of my 



apparatus and meteorological observations, the effect of 



changes in the atmosphere on the velocity and propagation 



of sound. 



Trials of the These trials I made on the 9th, 12th, and 15th of Sep- 



ciiaiu'es in the tember, the same year, each time about noon, and with 



atmos|)here. striking differences in the state of the sky and atmosphere. 



The following table exhibits the results of these. 



Sept. 

 1803 



Therm. 

 Fahr. 



Barom 

 eter. 



Hygro- 

 meter. 



Phono- 

 meter. 



Observations. 



9 



62-96° 



30-37 



58° 



99-9 



Half an hour after noon. Sky 

 clear. 



12 



53-6 



30-32 



51-5 



99-7 



45^ after noon. Sky covered 

 with thick clouds, t 



15 



59-72 



30-12 



51 



99-8 



40'after1. Cloijdy and threaf- 

 cning rain. 



Trifling, if 

 any. 



Experiments 

 in the dark. 



The small differences in the results of these experiments, 

 the greatest of which does not exceed three thousandth parts, 

 appeared to me not ascribableto changes in the atmosphere. 

 In my opinion they are the consequence of the imperfectioii 

 of my method, which is incapable of mathematical precision! 

 Not being able at the moment to procure more certain data 

 for this discussion, I was inclined to think, that the com- 

 rhon changes of the atmosphere could not effect such a 

 change in the nature and arrangement of the particles of the 

 elastic fluid, as to restrain or accelerate the agitation occa- 

 sioned by sonorous bodies. 



Nothing remained but to ascertain by strict trials the de- 

 crease of the propagation of sound in tHe dark, which should 

 give the solution of my problem, J. began my experiments 

 the 20th of September following, and I chose a night and 



