130 Dr. GreGory on 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 perpendicular to the 
line of transmission of the sound: Sita rounds were fired with the 
muzzle of the gun towards me: the intervals were 8’.8, 8”.84, 
8’.86, 8.86, 8’.83, 8.85; their mean, 8”.84. 
At three quarters past 11, 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 degrees: the intervals were 
8.86, 8.84, 8”.82, 8”.82, 8’.85, 8”.86; their mean 8”.841, 
9874 
aT 17 feet, vel. of sound ; therm. 66° over a surface of water. 
Although there was no perceptible difference in the mean in- 
tervals 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 comparatively 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 stone houses 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. 66°, fair, but cloudy; scarcely any wind: I took 
a station on the Essex bank of the Thames perpendicularly opposite 
the large storehouse on Roff’s Wharf at Woolwich, in order to 
ascertain the interval occupied by both the direct and the reflected 
transmission of the sound from a musquet fired by my side, and 
