66 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



Ocean, but storms travel with nearly double velocity. This anomaly may be partly explained if 

 we admit that the progress of storms is determined, not by the wind which prevails in close contact 

 with the earth's surface, bnt by that which prevails at an elevation of several hundred feet, where 

 the velocity is probably much greater than at the' earth's surface. The same anomaly, however, is 

 found when we compare the storms of the United States with those of Europe. In Northern 

 Europe the surface winds have a velocity greater than those of the United States, and we may 

 infer that the same is true for elevations of 1,000 or 2,000 feet above the surface, yet storms in 

 Europe advance with but little more than half the velocity of those in the United States. There 

 must then be a powerful cause which accelerates the movement of storm areas in the United 

 States, and which does not operate in Europe or over the Atlantic Ocean ; and apparently the same 

 cause does not operate in Southern Asia or in the West Indies, at least in an equal degree. This 

 cause (or one of these causes) is probably the precipitation in the form of rain or snow which usually 

 takes place on the east side of a storm area, greatly in excess of that on the west side, by which 

 means the progress of the storm center is greatly accelerated. This is a question which will be 

 carefully examined hereafter. 



