On Peals of' Thunder. 101 



Killarney, in a spot which the guides pointed out to him, Mr 

 Scoresby heard the noise of a pistol-shot for half a minute* We 

 require for our present object three-quarters of a minute at least ; 

 but we may be allowed to suppose, that had the resounding noise 

 of a cannon been substituted for that of a pistol, the thirty 

 seconds would have increased to forty-five seconds, or even 

 more. The intensity, I conceive, merits better to be taken in- 

 to consideration in this case, than in a locality in the neighbour- 

 hood of Paris, which, so far as I know, has never been cited as 

 any thing remarkable on the score of echo, viz., that one at the 

 foot of the tower of Montlhery, where the experiments upon 

 the velocity of sound were conducted, in the month of June 

 182^, by Messrs de Humboldt^ Bouvurd^ Gay-Lussac, audEmile 

 de Laplace. On this occasion they heard the echo from the dis- 

 charge of a cannon quite near them for from twenty to twenty- 

 five seconds. We may thus then hope to arrive at something 

 decisive concerning the exact part which echoes produce in 

 thunder peals. 



Mariners assure us, that in the wide ocean, thunder is ac- 

 companied with prolonged peals as on land, although there the 

 sound cannot be reflected either by long walls or by rocks, or 

 by woods, hills, or mountains. Those who adduce this enu- 

 meration, seem to forget, or rather they would appear not 

 to admit, that the clouds possess the power of reflecting 

 sounds. Muschenbroek, notwithstanding, has remarked, that 

 in the same locality in which, when the heaven is serene, the 

 discharge of cannon is attended with a single and distinct re- 

 port, the sound is often repeated when the weather is cloudy. 

 Does this observation of the Dutch philosopher appear not suffi- 

 ciently circumstantial to be admitted ? I shall extract from 

 a note which I published in 1822, some remarks relating to 

 experiments on the velocity of sound. " It has happened, that 

 at Ville-Juif we have four times heard, at an interval of two 

 seconds, two distinct reports of the cannon discharged at Mont- 

 lhery. On two other occasions the report of the cannon was 

 accompanied by a prolonged peal. These phenomena never 

 happened except at the time when clouds were visible ; when 

 the sky was perfectly serene the report was single, and did not 

 continue longer than a moment.*" 



