PNEUMATICS. 17. j 



If one of these whirlwinds happen at sea, the 

 pressure of the atmosphere being taken off that 

 part of the surface over which the vacuum is 

 formed, the water, on the principle of the Torri- 

 cellian tube, will rise to the height of thirty-two or 

 thirty-three feet, before it will be in equilibrio with 

 the external pressure. The ascending warm air, 

 being most probably charged with vapours, will suffer 

 them to be condensed as it arrives at a colder 

 region, and thus, the course of the current will be 

 marked by a dense and opaque vapour, and by the 

 continual ascent a cloud will be formed above. 

 This forms the phenomena of waters-spouts. At 

 first a violent circular motion of the sea is ob- 

 served, sometimes for the space of twenty feet 

 diameter: this rises afterwards by degrees into a 

 tapering column of about thirty feet in height, at 

 the same time that a cloud appears, from which a 

 dark line or column descends. This column is 

 met by another, which ascends somewhat like 

 smoke in a chimney, from the lower or solid part 

 of the spout. After this junction the cloud con- 

 tinually increases until the whirl ceases, and the 

 appearance terminates. 



