’ 
TRANSACTIONS OF THE SECTIONS. 39 
distance, that has not been deprived of its vapour, flows in and ascends. 
Then cloud will again begin to form, and the violence and rapidity of 
the outflowing of the air above will be increased by the evolution of 
the caloric of elasticity—the barometer will rise rapidly in the annulus, 
and fall in the central part of the ascending column; and these alterna- 
tions may continue while the volcano is in activity, more particularly 
if the violence of the volcano itself should be increased periodically. 
“ As air cannot move upwards without coming under diminished press- 
ure, and as it must thus expand and grow cooler, and consequently 
form cloud, any cause which produces an up-moving column of air, 
whether that cause be natural or artificial, will produce rain, when the 
complement of the dew-point is small, and the air calm below and 
above, and the upper part of the atmosphere of its ordinary temperature, 
“ Volcanoes, therefore, under favourable circumstances, will produce 
rain; sea-breezes, which blow inwards every day towards the centre 
of islands, especially if these islands have in them high mountains, 
which will prevent any upper current of air from bending the up- 
moving current of air out of the perpendicular, before it rises high 
enough to form cloud, such as Jamaica, will produce rain every day; 
great cities where very much fuel is burnt, in countries where the com- 
plement of the dew-point is small, such as Manchester and Liverpool, 
will frequently produce rain; even battles, and accidental fires, if they 
occur under favourable circumstances, may sometimes be followed by 
rain. Let all these favourable circumstances be watched for in time 
of drought (and they can only occur then), and let the experiment be 
tried; if it should be successful, the result would be highly beneficial 
to mankind. It might probably prevent the occurrence of those de- 
structive tornadoes which produce such devastation in the United 
States ; for if rain should be produced at regular intervals, of no great 
duration, the steam power in the air might thus be prevented from 
rising high enough to produce any storm of destructive character.” 
Independently of its utility in this manner, Mr. Espy pointed out in 
what way a knowledge of this theory would be highly useful to the 
mariner, to enable him to direct his vessel so, when one of these great 
storms comes near him, as to use as much wind in the borders of the 
storm as will suit the purposes of navigation; to know in what direc- 
tion a great storm is raging when it is yet several hundred miles from 
him; and if the storm should be of such great length, moving side 
foremost, as to preclude the possibility of avoiding it, to know in what 
direction to steer his ship, so as to get out of the storm as soon as pos- 
sible. The sailor also will be able to know when he is out of danger, 
and by observing storm clouds on their approach to ascertain the di- 
rection in which storms move. 
On this important subject the author added other remarks and 
illustrations, which would lose their value by the abridgement rendered 
necessary by the rules of the Association. 
