SQO PHILOSOPHICAL TRANSACTIONS. [aNNO 1708. 



is likewise uncertain as to fair and cloudy weather: for I often observed, that 

 in a rainy wet season the sound was impaired, and after heavy showers of rain, 

 as Kircher found at Rome, it acquired a great deal of strength; yet the case is 

 often quite otherwise. At Upminster, May 3J, 1705, the air was clearer and 

 freer of vapours, than ever I observed it before, so that I could easily and 

 distinctly see objects at a considerable distance; yet I could not hear at that 

 time the report of the great guns on Blackheath (excepting one, which was 

 quite languid, when it reached my ears) though I plainly saw all the flashes, 

 and at the same time the motion of the clouds and wind conspired with the 

 sound, there being a very gentle gale abroad; and in line, though every thing 

 seemed to contribute both to the force and motion of the sound. But on the 

 contrary, when the atmosphere was quite changed, and full of vapours, and all 

 seemed louring, I often heard the sound shrill, and again as often languid, 

 and remiss. 



The causes of these variations I leave to others to determine, as also to assign 

 the proper medium or vehicle of sound: whether it be the asthereal and more 

 subtile part of the atmosphere, or the vapours and grosser parts thereof, or both 

 together? But as to thick clouds, it is certain they very much weaken sound 

 which for the most part seems to be then languid and dull ; and this doubtless 

 proceeds from the interposition of vapours, and the gross particles which form 

 the cloud. I likewise observed the same thing in snowy weather: for when 

 snow is newly fallen, sounds are presently weakened; but as soon as its surface 

 is frozen, they suddenly become more acute; and I have heard the ringing of 

 bells and firing of cannon, as distinctly as if there had fallen no snow at all. 

 Mr. Townley affirmed he had once observed, as I had also done, that riding 

 through a certain town, the sound of the bells that were ringing but a little 

 way of, could hardly reach his ears, if a house covered with snow happened to 

 interpose; so that when he entered the town, he was exceedingly surprised to 

 find, whilst he passed by the first houses that interposed, the bells became silent 

 of a sudden ; but as soon as he came to the next vacant space, presently they 

 were heard again. And this Mr. Townley observed all the way through that 

 town; viz. that the sound of the bells either did, or did not reach his ears, 

 according as the houses covered with snow happened to interpose or not. 



§ 11. Of the Influence of the Winds on the Motion of Sounds. — The academy 

 del Cimento found by experiments, that the motion of sound was neither re 

 tarded by contrary winds, nor accelerated by favourable ones, but that from 

 whatever quarter the wind blew, sound passed over the same space in the same 

 time. Gassend^s, and almost all the other philosophers, were of the same 

 opinion, though the contrary appears from experience; and they seem to have 



