VOL. XXVI.] 



PHILOSOPHICAL TRANSACTIONS. 



3gi 



fallen into this error, from the experiments being made at too short distances; 

 as at i or 2, or at most 3 miles; whereas, had they made their observations 

 with accurate instruments, at 10 or 12 miles distance, they would easily have 

 found out the mistake. I had (from the authority of those philosophers) given 

 in for some time to this common error, till by the frequent observation of the 

 firing of guns on Blackheath for three years and upwards, I was happily unde- 

 ceived: at first when I observed the report reach my ears, sometimes sooner, 

 and sometimes later, I began to suspect my accuracy, either in reckoning the 

 vibrations of the movement, or in exactly observing the flash of the gun, or 

 that I had, through inadvertency, fallen into some such other mistake; but 

 after I caused guns to be fired every half hour, from 6 in the evening till mid- 

 night, and found the report always reach the ear, without any remarkable 

 variation, in 120 or 122 half seconds of time, though the wind was directly 

 against it; but at other times, when the wind was favourable, and blew either 

 direct transversely, or obliquely; observing the report of the same guns reach 

 in 1 1 1, 1 12, 1 13, 114, 115, 1 1 6, or at most in 117 half seconds of time; I 

 was at length assured, that some real difference caused this variety in the ob- 

 servations. And not only do winds with or against the sound accelerate or re- 

 tard its motion, but likewise according to the various degrees of their strength 

 and weakness, is the sound more or less promoted or impeded; of which I 

 made particular observations, as in the following table; where it is to be ob- 

 served, that the guns were about 6o degrees from the south, that is, pointed 

 something better than S.W. and by W. 



A Table of the Sounds of Cannon on Blackheath, according to the variety of the 

 Winds J and the Foi'ces with which they blow. 



Dates. 



1704. 

 Feb. 13 



21 



1705. 



Mar. 30 



April 2 



3 



5 



13 



24 



Barometer. 



29.99 

 29.99 

 30.22 



29.30 



29.80 

 29-70 

 29.26 

 29.59 



Dates. 



1705. 



Sept. 1 1 



II 



29 



Oct. 6 



Nov. 30 



1706 



Feb. 15 



Nov. 29 



1707. 

 Feb. 7 



Barometer. 



Saker. 



Mortar. 



2.9.38 



29.34 



29.10 



29.60 

 3006 

 30.06 



29.83 



Winds. 



W.2 



W. b. N. 2 

 S. S.W. 6 

 E. S.E l\ 

 S. 8. W. 4 



S. b. W. 1 



S. W.O 



S. W. b. S. 1 



S. W.b.W4 



Vibra- 

 tions. 



115 



\\5\ 



112 



117 



115 



116 

 116 

 118 



113 



I have selected these observations from a great many others, which were all 

 carefully made, each of them being repeated twice or thrice, or oftener; so 



