392 PHILOSOPHICAL TRANSACTIONS. [aNNO I7O8. 



that it appears from the experiments in April 5th and Sept. 29th, that the 

 stronger winds accelerated the motion of sound; for on the 6th of April, when 

 the motion both of the wind and sound almost conspired, and the same wind 

 was something stronger (as the annexed number 7 shows, in the same manner 

 that denotes a calm, and 1, 2, 3, 4, &c. the different strength of the winds) 

 the sound at that time reached the ear in 1 1 1 half seconds of time; but on 

 April 24th, when the wind blew from the same point, and the air was calm, 

 the sound only moved through the same space in 1 16 half seconds; so likewise 

 on Feb. 7> J706, the wind blowing on the same point, and carrying the sound 

 along with it, but with only half the force, it passed over the same space in 113 

 half seconds; and in fine, on Sept. 29, 1705, the wind being strong and less 

 favourable, the sound moved through the same space in 112 half seconds: from 

 which, and other examples in the table, it plainly appears, that a strong wind 

 accelerates sound, while a weaker wind does not. The same may likewise be 

 said of those winds, or currents of air, which either directly favour or oppose 

 the progressive motion of sound; viz. that they either accelerate or retard it; 

 and that intermediate currents also cause intermediate progressions of sound, or 

 number of vibrations of the pendulum. The greatest difference! have observed 

 in the motion of sound in the space of about 13 miles, was about 9 or 10 half 

 seconds, when a strong wind promotes, and only a gentle wind impedes it; but 

 when only a gentle wind, or almost none at all, opposes or favours the sound, 

 the difference hardly exceeds 2 or 3 half seconds. 



^ 12. Of the Velocity of Winds. — To discover the quantity of space that 

 winds pass over in any given time, I took some light bodies, such as down, &c. 

 and from the several experiments I made with these, when the strength of the 

 wind was different, found that the strongest wind scarcely passed over 60 miles 

 in an hour; for instance, on August 11, 1705, the violence of the wind was 

 such, as almost to beat down a wind-mill, near the place where I made my ob- 

 servations; and estimating by the numeral characters, 0, 1,2, 3, 4, 5, 6, to 

 10, 15, or more degrees, the strength of winds, the strength of this I reckoned 

 at about 12 or 14 of .these degrees; and from repeated experiments I found, 

 that that hurricane passed over about 33 feet in a half second of time, or 45 

 miles in an hour; whence I conclude, that the most violent storms, not ex- 

 cepting that in Nov. 1703, do not move about 50 or 60 miles in an hour. 



Having thus determined the velocity of rapid winds, we may from hence 

 more easily conjecture the velocity of such as are less so ; and I have found 

 from several experiments, that some of them move 15 miles, others 13, some 

 more and some fewer, in an hour ; and that others again have so slow a motion, 

 as scarcely to pass over one mile in an hour: also some are so slow, that a per- 



