Velocity of Sound. 133 
all the preceding results, is simple enough to be easily recollected 
by practical men; and may, perhaps, be employed in our own 
climate. It is this:— 
At the temperature of freezing, 33°, the velocity of sound is 
1100 feet per second. 
For lower temperatures deduct 
For higher temperatures add 
From the 1100 
to the 1100 
Fahr. therm. ; the result will show the velocity of sound, very nearly, 
‘at all such temperatures. 
Thus, at the temperature of 50°, the velocity of sound is, 
half a foot. 
t for every degree of difference from 33° on 
1100 x $(50 — 33) =11083 feet. 
At temperature 60°, it is 1100+3(60—33) =11133 feet; agreeing 
with the experimental result quite within the limits of a practical 
rule. ; 
The theorem 333.44 met. ,/1+00375 t, before cited, gives nearly 
1094 feet for the velocity at the freezing point ; and 1114 feet for the 
temperature 10° centigrade, or 50° Fahrenheit: thus occasioning 
a greater augmentation to the velocity in the higher temperatures, 
than my experiments seem to indicate. 
The above practical rule, so far as it may be entitled te con- 
fidence, may be useful, Ist, to the military man in determining the 
distance of an enemy’s camp, of a fortress, a battery, &c. 2d, to 
the sailor, in determining the distance of another ship, &c. 3d, to 
the land surveyor in ascertaining the length of base lines, &c. in 
conducting the survey of a lordship or county; 4th, to the philo- 
sophic observer, in appreciating the distances of thunder-clouds 
during a storm. Yet, in either of these applications, the rule must 
be regarded as approximative only ; because, few practical men 
