Velocity of Sound. 4,99 



cinity of so many carriages as were incessantly passing, I could 

 not here avail myself of the benefit of comparing the above in 

 tervals with those in which the direction of the transmission 

 should be reversed. I venture, therefore, to add the velocity 

 of the wind to that of the sound, as obtained by the experi- 

 ment, and thus obtain 1085-8 + 30=1116 feet nearly, for the 

 velocity of sound, the therm, standing at 64°. 



Monday, August 18. On this day, the same six-pounder 

 gun was placed upon the wharf by the side of the Thames in 

 the Royal Arsenal, and I took a station at the opposite 

 extremity of the Gallion's Reach, not far from the mouth 

 of Barking Creek ; the distance from the gun was 9874 feet, 

 the time of high water there, on that day, was about 11 

 o clock A.M. 



At half past 11 A.M., barom. 29'84 inches; therm. 66°; 

 air dry, sky rather cloudy : very gentle wind nearly perpen- 

 dicular to the hue of transmission of the sound. Six rounds 

 were fired with the muzzle of the gun towards me: the inter- 

 vals were 8"-8, 8"'84, 8"-86, 8"-86, 8"«83, 8"'85; their mean 

 8 *84. 



At three quarters past 1 1 A.M., barom. &c. as before ; six 

 more rounds were fired, the gun muzzle being directed from 

 us (up the river) in a horizontal angle of about 140 decrees- 

 the intervals were 8"'86, 8"-84, 8"'82, 8"'82, 8"-85, 8"-86; 

 their mean 8""841. 



-g^-= 1117 feet, velocity of sound; therm. 66°, over a 

 surface of water. 



Although there was no perceptible difference in the mean 

 intervals occupied by the transmission of sound, in the two 

 different directions of the gun, yet there was a considerable 

 modification of the intensity; the sound being much weaker 

 when the gun muzzle was directed westerly, up the river, 

 than when it was pointed down Gallion's Reach, towards the 

 place where I stood. In the former case, too, besides the 

 first report, which was marked and distinct, though compa- 

 ratively feeble, there was a series of audible re-percussions, at 

 intervals of about a tenth of a second, and gradually dying 

 away: these, I conjecture, were reflected sounds from the 

 faces of storehouses and other buildings standing on or near 

 the side of the river at Woolwich. 



Same day, August 18, one o'clock P.M., barom. 29*82 

 inches, Fahr. therm. C6°; fair, but cloudy; scarcely any wind: 

 I took a station on the* Essex bank of the Thames perpendi- 

 cularly opposite the large storehouse on Rolf's Wharf at 

 Woolwich, in order to ascertain the interval occupied by both 



Vol. 63. No. 314. June 1824. 3 F the 



