109 
for ascertaining the velocity of sound. 
the gun and station were even at a moderate distance ;* we 
must therefore be led to conclude, that these differences have 
chiefly arisen from the experiments having been made during 
a limited period only, and at unfavourable times for obtaining 
a mean result, instead of the interval which appears by these 
experiments to be necessary. 
A particular examination of the Tables and results, will 
show the difficulty of ascertaining what proportion of the 
differences should be allowed to each of the instruments used 
for finding the state of atmosphere, exclusive of the effects of 
the wind. 
During the calms, we might expect that the proportional 
parts to be allowed for the difference in the thermometer, 
barometer, and hygrometer, might be found with some de- 
gree of accuracy ; the discrepances, however, are very con- 
siderable. Comparing the results of Tables II. and VII. we 
find the barometer 0,121 lower, the thermometer 4 °,6 higher, 
and the air about 8^- more dry by the former Table than by 
the latter, while the velocity in a second is only 17,7 feet 
greater by one Table than the other. 
We give however in addition the following results taken 
from the Tables of calms, and arranged according to the 
different heights of the thermometer and barometer. These 
results may assist us in coming to some conclusion upon this 
part of the subject. 
* For example, a difference of about twenty-six feet in the distance, between 
the Observatory station and the Mount gun, would make only about a foot dif- 
ference in the velocity in a second. 
