TORNADOES. 183 



find a ready answer. Such a current, carrying the 

 warmth of intertropical regions to the temperate zones, 

 produces in the first place, by the mere difference of 

 temperature, important atmospheric disturbances. The 

 difference is so great, that Franklin suggested the use 

 of the thermometer in the North Atlantic Ocean as a 

 ready means of determining the longitude, since the 

 position of the Gulf Stream at any given season is 

 almost constant. 



Bnt the warmth of the stream itself is not the only 

 cause of atmospheric disturbance. Over the warm 

 water vapor is continually rising ; and, as it rises, is 

 continually condensed (like the steam from a loco- 

 motive) 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 vapor is condensed? "We know 

 that to turn water into vapor is a process requiring 

 that is, using up a large amount of heat ; and, con- 

 versely, the return of vapor to the state of water sets 

 free an equivalent quantity of heat. The amount of 

 heat thus set free from 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 Bernini to the Grand Banks, there 



