105 
for ascertaining the velocity of sound. 
the atmosphere and weather that according to the first table, 
sound at one time has been as long as 27 ,6 seconds in travel- 
ling from the Mount to the Observatory station ; and at 
another time only 24,8 seconds ; the distance being 29547 
feet. In the first case, therefore, the velocity of sound was 
only about 1078 feet in a second; while in the other, its 
velocity was nearly 1191-i- feet. The extremes in Table VI., 
show a still greater difference. This proves the necessity for 
making experiments during a long interval, in order to ob- 
tain an accurate general result. 
In Tables II. and VII. we find, as the thermometer rose, 
the atmosphere at the same time decreasing in density and 
increasing in its elasticity, that the sound moved with greater 
rapidity. 
That with the wind in the SE. quarter the velocity was 
considerably increased, both from the Mount and Fort ; more, 
however, in proportion, as might be expected, from the for- 
mer than the latter. 
That with the wind at NE. the sound from the Fort gun 
travelled with a greater, and from the Mount gun with a 
less velocity, than when the wind was in any other direction; 
that wind being favourable for increasing the velocity from 
the Fort, and unfavourable from the Mount : the full effect 
of the wind, however, is not to be ascertained by this table 
alone, as the thermometer during the time the NE. wind 
prevails is comparatively low, and the barometer high ; both 
which, as will have been seen by inspection of the tables, 
occasion the sound to travel slower than ordinary. 
The wind SW. W. and NW. the velocity from the Mount 
was accelerated, and that from the Fort retarded ; but not in 
P 
MDCCCXXIII. 
