122 Philosophy of Storms. 
the height of 4800 feet before it begins to form cloud, the whole 
column would then be 100 feet of air lighter than surrounding 
columns ; and if the column should be very narrow, its velocity 
of upward motion would follow the laws of spouting fluids, which 
would be 8 times the square root of 100 feet a second, that is 80 
feet a second, and the barometer in the centre of the columm at 
its base, would fall about the ninth of an inch. 
As soon as cloud begins to form, the caloric of elasticity of the 
vapor or steam is given out into the air in contact with the little 
particles of water formed by the condensation of the vapor. This 
will prevent the air in its further progress upwards from cooling 
so fast as it did up to that point, and from experiments on the 
Nephelescope, it is found to cool only about one half as much 
above the base of the cloud as below—that is, about five eighths 
of a degree for one hundred yards of ascent, when the dew point 
is about 70°. If the dew point is higher it cools a little less, and 
if the dew point is lower, it cools a little more than five eighths- 
of a degree in ascending one hundred yards. 
Now it has been ascertained by aéronauts and travellers on 
mountains, that the atmosphere itself is about one degree colder 
for every hundred yards in height above the surface of the sea; 
therefore, as the air in the cloud, above its base, is only five 
eighths of a degree colder for every hundred yards in height, it 
follows, that when the cloud is of great perpendicular height 
above its base, its top must be much warmer than the atmosphere 
at that height, and consequently much lighter. 
Indeed the specific gravity of a cloud of any height compared 
to that of the surrounding air at the same elevation, may be 
culated when the dew point is given. For its temperature a 
known by experiments with the Nephelescope, and the quantity 
of vapor condensed by the cold of diminished pressure at every 
point in its upward motion, and of course the quantity of calorie 
of elasticity given out by this condensation is known, and also 
the effect this caloric has in expanding the air receiving it, be- 
yond the volume it would have, if no caloric of elasticity was 
evolved in the condensation of the vapor. 
For example, according to the experiments of Prof. Walter R. 
Johnson, of Philadelphia, a pound of steam at the temperature of 
212° contains 1030° of caloric of elasticity, and as the sum of 
the latent and sensible calorie of steam is the same at all tempe- 
