PHENOMENA AT SEA. J 1 



direction by the wind, whether the sea be smooth, or 

 high; and in general do not appear to be more than from 

 twelve to twenty hours, in changing their direction. 



In No. 57 of your Journal, in a reply to M. M. your The author 

 correspondent, the squall is thought to be occasioned by a ^^^ ^hat the 

 descending wind, produced by the imi)ulse of falling rain, squall is a des- 

 This suggestion secins to agree with your observation, cenduigwind. 

 for I have several times, in calm weather, seen a cloud 

 generate and diffuse a breeze on the surface of the sea, 

 which spread in different directions from the ])lace of de- 

 scent. A remarkable instance of this occurred in Malacca 

 Strait during a calm day, when a fleet was in company: a Remarkable 

 breeze commenced suddenly from a dense cloud, its cen- I^q^^^ *" 

 tre ofaction seemed to be in the middle of the fleet, which 

 was much scattered. This breeze spread in every direc- 

 tion from a centre, and produced a singular appearance 

 in the fleet, for every .ship hauled close to thcAvind as the 

 breeze reached her, and when It became general, exhibit- 

 ed to view the different ships sailing completely round a 

 circle, although all hauled close to the wind. 



With this descending wind there was no rain fell on the 

 ^hips at the extremities of the fleet, but a partial shower 

 was observed to have falllen on the ships in the centre. .• 



Notwithstanding what has been just observed, squalls or 

 brisk winds Avhich commence suddenly after calms^ are 

 generally experienced to have their m.otion in a horizon- 

 tal direction, when the impulse is perceived on the sails 

 of a ship ; but it appears probable, that the current of 

 M'ind may descend until near the surface of the sea, when 

 calm over the surface ; and then be deflected in a hori- .^r 



zontal direction on approaching it. ' *-*" 



Your correspondent, M. M. thinks the velocity of the The velocity of 



swell of the sea not greater than eight or ten miles an ^^^'\ *^ 



" ^ greater than 



hour. It IS much greater in general, but mutable accord- supposed by 

 ing to circumstances. ^'^- M. 



The velocity of the swell ("or waves) in a strong breeze 

 or trade wind, probably is about twenty, miles an hour ; 

 for they pass a ship fast when she has a velocity of ten 

 or eleven miles an hour in the same direction as the 

 wayes. At such times the velocity of the waves is easily 

 measured with the common log, by noticing with a pro- 

 € 2 per 



Hnvc to mea- 

 sure, &c. ■' * 



