66 



Royal Society ; — Prof. Reynolds on 



which did not appear to me to make the least difference to the 

 direction in which I could hear small sounds most distinctly, should 

 yet be sufficient to cover one's approach to partridges, and more 

 particularly to rabbits, even until one was within a few feet of them 

 * — a fact which shows how much more effectively the wind obstructs 

 sound near the ground than even a few feet above it. 



Elevation, however, clearly offered a crucial test whether such an 

 action as that I have described was the cause of the effect of wind 

 upon sound. Having once entertained the idea, it was clearly 

 possible to put it to the test in this way. Also, if the principles 

 hold in sound, something analogous must hold in the case of waves 

 on the surface of a running stream of water — for instance, waves 

 made near the bank of a river. 



I had just reached the point of making such tests when I dis- 

 covered that the same views had been propounded by Professor 

 Stokes so long ago -as 1857*. Of course, after such a discovery, 

 it seemed almost unnecessary for me to pursue the matter further ; 

 but as there were one or two points about which I was not then 

 quite certain, and as Prof. Stokes's paper does not appear to be 

 so well known as it might be (I do not know of one writer on 

 sound who has adopted this explanation), it still seemed that it 

 might be well, if possible, to put the subject on an experimental 

 basis. I therefore made the experiments I am about to describe ; 

 and I am glad that I did not rest content without them, for they 

 led me to what I believe to be the discovery of refraction of sound 

 by the atmosphere. 



Kg- 1. 



The results of my iirst observation are shown in fig. 1. This 

 represents the shape of the waves as they proceeded outwards 

 from a point near the bank of a stream about 12 feet wide. Had 

 the water been at rest there would have been semicircular rings ; 

 as it was, the front of the waves up the stream made an obtuse 

 angle with the wall, which they gradually left. The ends of the 

 waves, it will be observed, gradually died out, showing the effect of 

 divergence. The waves proceeding down the stream were, on the 

 other hand, inclined to the wall, which they approached. 



I was able to make a somewhat better observation in the Med- 

 lock, near the Oxford Road Bridge, Manchester. A pipe sent a 

 succession of drops into the water at a few inches from the wall, 

 * Brit. Assoc. Report, 1857, Trans, of Sect. p. 22. 



