But the warmth of the stream itself is not the only cause of atmospheric disturbance. Over the warm water vapour is continually rising; and, as it rises, is continually condensed (like the steam from a locomotive) by the colder air round. ‘An observer on the moon,’ says Captain Maury, ‘would, on a winter’s day, be able to trace out by the mist in the air the path of the Gulf Stream through the sea.’ But what must happen when vapour is condensed? We know that to turn water into vapour is a process requiring—that is, _using up_—a large amount of heat; and, conversely, the return of vapour to the state of water _sets free_ an equivalent quantity of heat. The amount of heat thus set free over the Gulf Stream is thousands of times greater than that which would be generated by the whole coal supply annually raised in Great Britain. Here, then, we have an efficient cause for the wildest hurricanes. For, along the whole of the Gulf Stream, from Bemini to the Grand Banks, there is a channel of heated—that is, _rarefied air_. Into this channel, the denser atmosphere on both sides is continually pouring, with greater or less strength. When a storm begins in the Atlantic, it always makes for this channel, ‘and, reaching it, turns and follows it in its course, sometimes entirely across the Atlantic.’ ‘The southern points of America and Africa have won for themselves,’ says Maury, ‘the name of “the stormy capes,” but there is not a storm-find in the wide ocean can out-top that which rages along the Atlantic coasts of North America. The China seas and the North Pacific may vie in the fury of their gales with this part of the Atlantic, but Cape Horn and the Cape of Good Hope cannot equal them, certainly in frequency, nor do I believe, in fury.’ We read of a West Indian storm so violent, that ‘it forced the Gulf Stream back to its sources, and piled up the water to a height of thirty feet in the Gulf of Mexico. The ship “Ledbury Snow” attempted to ride out the storm. When it abated she found herself high up on the dry land, and discovered that she had let go her anchor among the tree-tops on Elliot’s Key.‘