384 PHILOSOPHICAL TRANSACTIONS. [anNO 1708. 



reports of great guns, especially in a calm and clear air, I often observed that 

 a murmuring noise, high in the air, preceded them ; and in a thin cloud, I 

 often heard the firing of guns run for several miles high over head in the air, 

 so that the murmuring noise continued for 15 seconds of time ; the continuance 

 of this murmuring noise I suppose proceeded from vaporous particles suspended 

 in the atmosphere, which oppose the course of the undulations of sound, and 

 reverberate them to the ears of the observer, like indefinite echos, which we 

 call the murmuring noise in the air. On thoroughly considering these things, 

 it will appear, that an echo, made at a distance, may be heard ; and that the 

 said reduplication of the report of the guns on Blackheath, undoubtedly pro- 

 ceeded from Blackheath itself, as was said above. 



^ 4. Of the Report of Guns Jired in all Directions. — What was before suggested 

 of the report of the guns on Blackheath, I found the same to hold in all others, 

 viz. that the motion of sound is neither swifter nor slower, whether the gun be 

 discharged with its muzzle towards the observer, or from him ; as also, that 

 there is no variation of the sound in any position of the gun, whether hori- 

 zontal or vertical, nor in any elevations, as 10, 20, &c. degrees, as the Aca- 

 demy del Cimento truly observed : gunpowder, whether strong or weak, and a 

 greater or less quantity of it be used, though it may increase or diminish the 

 sound, yet it neither accelerates nor retards its motion. 



^ 5. Of the Motion of Sound in any Weather , and at any Time of the Year. — 

 Kircher affirms that he always found the velocity of sound, different, at differ- 

 ent times in the morning, at noon, in the evening, and at night : but I, having 

 a better chronometer, and being at a more convenient distance, never found 

 the velocity of sound different at these times : for in all weathers, whether fair 

 and clear, or cloudy and lowering ; and whether it snow or rain (both which 

 weaken very much the audibility of sound) and whether it thunder or lighten ; 

 in hot or cold weather ; by day or by night ; in summer or in winter ; or whe- 

 ther the mercury ascend or descend in the barometer ; in short, in all the 

 various states of the atmosphere (excepting only the winds) the motion of sound 

 is neither swifter nor slower ; only it is more or less clear by that variation of 

 the medium, which perhaps, might have deceived the sagacious Kircher. Hence 

 it follows that the conclusions drawn by Dr. Walker, from his own ingenious 

 observations, and from those of Dr. Plot and Kircher, are erroneous. 



^ 6. Of the Motion of an intense and languid Sounds and of various sonorous 

 Bodies. — Though Kircher be of a different opinion, yet I doubt not, but that 

 the sounds of all bodies, as guns, bells, hammers, &c. have the same degree of 

 velocity ; and for this end I compared the strokes of a hammer, and the report 

 of a gun, at the distance of a mile (being the greatest at which I could hear 



