GULF steea:m, climates, and commerce. G7 



the air, as is manifest in the tendency of the cooled air to "flow- 

 off, and of warmer and lighter to take its place. (2.) Excepting 

 hydrogen and ammonia, there is no gas so light as aqiieons vapour, 

 its weight being to common air in the proportion of nearly 

 5 to 8; consequently, as soon as it is fonned it commences to 

 rise; and, as each vesicle of vapour may be likened, in the 

 movements which it produces in the air, to a balloon as it rises, 

 it will be readily perceived how these vaporous particles, as 

 they ascend, become entangled with those of the air, and so, 

 carrjdng them along, upward currents are produced : thus the 

 wind is called on to rush in below, that the supply for the upward 

 movement may be kept up. (3.) The vapour, being lighter than 

 air, presses it out, and, as it were, takes its place, causing the 

 barometer to fall : thus again an in-rush of wind is called for 

 below. (4.) Arrived in the cloud-region, this vapour, being 

 condensed, liberates the latent heat which it borrowed from the 

 air and water below ; which heat, being now set free and made 

 sensible, raises the temperature of the surrounding air, causing 

 it to expand and ascend still higher ; and so winds are again 

 called for. Ever ready, they come ; thus we have a fourth way. 

 (5.) Innumerable rain-drops now begin to fall, and in their 

 descent, as in a heavy shower, they displace and press the air 

 out below with great force. To this cause Espy ascribes the 

 gusts of wind which are often found to blow outward from the 

 centre, as it were, of sudden and violent thunder-showers. 

 (6.) Probably, and especially in thunder-storms, electricity may 

 assist in creating movements in the atmosphere, and so make 

 claim to be regarded as a wind-producing agent. But the winds 

 are supposed to depend mainly on the power of agents (2), (3), 

 and (4) for their violence. 



178. A cliannel of rarefied air in the atmosphere and over the Gulj 

 Stream. — These agents, singly and together, produce rarefaction, 

 diminish pressure, and call for an inward rush of air from either 

 side. Mr. Espy asserts, and quotes actual observation to sustain 

 the assertion, that the storms of the United States, even those 

 which arise in the Mississippi Valley, travel east, and often 

 march out to sea, where they join the Gulf Stream in its course. 

 That those which have their origin at sea, on the other side of 

 the Gulf Stream, do (§ 174) often make right for it, is a fact well 

 known to seamen. The Gulf Stream from Bemini to the Grand 

 Banks is constantly sending up volumes of steam; this, being 

 lighter than air, produces a channel way of rarefied air through 



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