420 The Origin of the Great Cyclones. (October, 
relates to the agency of aqueous vapour, is entirely in- 
ductive—it would be inferred that great cyclones, hurricanes, 
and typhoons ought to occur in regions of great evaporation, 
where the intro-moving winds would take up large quantities 
of moisture for the central area of the storm, and keep its 
furnace well supplied with appropriate fuel. I need hardly 
say that such an influence is sustained by actual observation 
all over the globe. The tropical hurricanes of the West 
Indies are violent indeed. But they do not attain the 
violence of the East Indian typhoons; in the former the 
barometer does not fall so low, and for a very obvious 
reason. The water of the equatorial current in the Atlantic, 
which leaves the Antilles, has been but a short time beneath 
the tropical sun in its passage from the coast of Africa. 
The waters of the Bay of Bengal, the China Seas, the 
South Indian Ocean, have been more than three hundred 
days under a vertical sun, and are all aglow with its heat, 
and the evaporation from their superheated billows exceeds 
that of all other waters on the globe. The moment a storm: 
centre is formed in the Indian Ocean, and the intro-moving 
air currents reach it, the quicksilver suddenly drops in the 
barometric tube, and before the mariner can reef his sails, 
they are often torn into a thousand ribbons, and his vessel 
thrown on her beam ends. 
It is a remarkable fact that the hurricane season in the 
West Indies closes with heavy rains in the early or middle 
part of November, when the sun has been nearly two 
months below the line, when solar evaporation in the 
Caribbean Sea has been partially arrested, and the reservoirs 
of the air exhausted of their vapour or storm-fuel by the 
drenching rains of which we speak. 
From what has been said of the immense amount of con- 
densation due to an ascensional movement of air in the 
storm centre, it must not be supposed that the chilling 
arises solely from the elevation of the air to colder regions 
of the atmosphere. As the air ascends into the upper regions 
the pressure of superincumbent atmosphere is taken off 
from it on all sides, and it expands and loses heat, the force 
required for the expansion being withdrawn from the store 
of heat. The glass receiver of an air-pump full of humid 
air, when exhausted partially, shows a frost of vapour and 
clouds within, proying that the process of rarefaction has 
chilled the contents of the receiver. Air was compressed 
by Professor Tyndall, by means of a column of water 
260 feet high, to an eighth of its original volume, and then 
allowed to escape by a stop-cock. As it rushed out it 
