VOL. XXVI.] PHILOSOPHICAL TRANSACTIONS. 381 



should do. Or if the distance be a sufficient length, yet an error may arise, 

 if 3. There be not a regard had to the winds. 



All these are certain, inevitable, and perpetual inconveniences, that attend 

 the mensuration of the progressive motion of sound, which at small distances 

 as mentioned above, especially if the instruments are bad, may occasion great 

 errors; and doubtless, these were the chief cause of the difference among the 

 authors. But it may be observed, how nearly the spaces in the table, assigned 

 by the last three observers, agree, which undoubtedly is owing to their using 

 good movements, while the ear is only employed in receiving the vibrations of 

 the pendulum, and the eye observes the flash, or some other signal of the 

 emission of the sound: and these observations were made at pretty large dis- 

 tances, so that a small error is but of little consequence. Mr. Flamsteed and 

 Dr. Halley made their observations on Shooter's-hill, about 3 miles distant from 

 the Royal Observatory at Greenwich, and the sound reached them in 13-1- 

 seconds of time. The Academy del Cimento made their experiments nearly at 

 an equal distance, and some again they made at only a mile distance. And 

 lastly, M. Cassini, Picard, and Roemer, made theirs at the distance of 1280 

 French toises, which is upwards of an English mile and a half. 



In order to find out the truth amidst such a variety of observations, I have 

 made several experiments at different distances, viz. from 1 to 12 miles and 

 upwards: and for measuring the time, employed a very accurate portable move- 

 ment, with a pendulum vibrating half seconds. And, to proceed with the 

 greater certainty, I proposed to myself to resolve the following queries: 1. How 

 much space sound passes through in a second, or any other interval of time? 

 2. Whether a gun discharged towards the observer, transmit the report in the 

 same space of time, as when discharged the contrary way } 3. Whether, in any 

 state of the atmosphere, when the mercury either ascends or descends in the 

 barometer, sound pass over the same space in the same interval of time? 4. 

 Whether sound move with greater velocity in the day-time than in the night? 

 5. Whether a favourable wind accelerate sound, and a contrary wind retard it; 

 and how winds affect sound ? 6. Whether sound move with a greater velocity 

 in a calm day, than when the winds blows? 7- Whether a violent wind blowing 

 transversely accelerate or retard the motion of sound? 8. Whether sound have 

 the same degree of motion in summer and winter, by day and by night? 9. 

 And whether also in snowy and fair weather ? 10. Whether a great and small 

 sound have the same degree of motion ? 11. Whether in all elevations of a gun, 

 viz. from point blank to 10, 20, &c. to QO degrees, sound reach the observer's 

 ear in the same space of time ? 12. Whether all sorts of sounds, as those of 

 guns, bells, hammers, &c. have the same degree of motion? 13. Whether 



