] 36 STOE-WS AT SEA, 6iC. 



that a gentle breeze passes at the rate of about fifteen miles an 



hour; and that the velocity, if progressively augmented to 



sixty miles an hour, will produce a violent storm, of force suf- 



Qucstion: ficient to overthrow trees and houses. Now the velocity of the 



not caused by ^^^'*^^^ of the sea is so far from being in the least likely to pro- 



the swell, l>at duce any extreme progressive motion in the air, that I really 



the contrary, — , . • • t -i i t^ti 



how happens it think it never exceeds eight or ten miles an hour. Whatever 

 that the suell you may think, Mr. Nicholson, of the importance of this phi- 

 comes before , 11 ,-rr 1 r 1 11 1 1 1 



the storm? losophical duitculty, I hope you will have the goodness to pro- 

 pose it to your numerous correspondents. I have occasionally 

 had the pleasure, in my constant perusal of your Journal, to 

 remark that you have yourself sometimes given answers to 

 questions which have been proposed. May I hope that you 

 will not think mine undeserving your consideration. 

 I am. Sir, 



Your obliged reader, 



M. M. 



Rcpli/. W. N. 

 Description of I do not know that any of our philosophers have expressly 

 It ^is"a sudden* considered the appearances which constitute what is called a 

 and violent squall at sea. A strong wind accompanied with rain comes 

 wind with ram. ^^^^ almost instantaneously, and the impulse of this wind 

 is sufficient to carry away a ship's topmasts, and even to do 

 more material damage, if navigators were not [to hold them- 

 selves in readiness to lower their sails as soon as the first im- 

 pression takes place. The squall is more common in^low lati- 

 tudes than in high latitudes, where its duration is likewise short- 

 er. It usually lasts eight or ten minutes or half an hour, and 

 when it has ceased or passed to leeward, the ordinary wind, 

 with which for the most part it coincides in direction, resumes 

 its course. 

 Theory of Every theory of the winds supposes part of the lower air to 



winds. Much ^gcend, and that its place is supplied by an horizontal current, 



attention has ' . ' ' "^ •' 



been paid to Very few writers have supposed a dcsconding current to operate 



horizontal cur- j^^ jj^^ same wav ; and seldom indeed has any attention been 

 rents of an-, and •' . ,. . , 



hut little to paid to those direct or oblique ascending or descending winds 

 those streans ;^y}jj^.}j mxi^t be produced at the places where the causes of 



which are rlj- '■ * 



rertert upwards motion most powerfully operate. 



or downwards. j apprg- 



