70 Royal Society : — Prof. Reynolds on 



could hear only the ring, and at others the beats. The ring seemed 

 to preserve itself the longest ; whereas near the ground at short 

 distances the ring was lost first. This is explained by the fact that 

 the rate at which sound-waves diverge depends upon their note : 

 the lower the note the more will they diverge. Thus the beats 

 diverge more rapidly than the ring, and consequently die out 

 sooner ; whereas when the head is on the ground near the bell it 

 is only the diverging waves that are heard, and here the beats 

 have the best chance. The intensity of the sound invariably seemed 

 to waver ; and as one approached the bell from the windward side, 

 the sound did not intensify uniformly or gradually, but by fits or 

 jerks ; this was the result of crossing the rays' interference, such 

 as those shown in fig. 2. 



During the observations the velocity of the wind was observed 

 from time to time at points 1 foot and 8 feet above the surface. 



On the 9th, that is over grass, it varied from 4 feet per second 

 at 1 foot and 8 feet per second at 8 feet, to 10 feet at 1 foot and 

 20 feet at 8 feet, always haviug about twice the velocity at 8 feet 

 that it had at 1 foot above the ground. 



Over the snow there was not quite so much variation above and 

 below. On the 10th the wind varied from 3 feet at 1 foot to 4 feet 

 at 8. feet *. On the 11th the variation was from 12 at 1 foot and 

 19 at 8 feet to 6 at 1 foot and 10 at 8 feet. Thus over snow the 

 variation in the velocity was only about one third instead of half. 



Since the foregoing account was written, I have had an oppor- 

 tunity of experimenting on a strong west wind (on the 14th of 

 March) ; and the results of these experiments are, if any thing, 

 more definite than those of the previous ones. The wind on this 

 occasion had a velocity of 37 feet per second at an elevation of 12 

 feet and of 33 at 8 feet and 17 at 1 foot. The experiments were 

 made in the same meadows as before, the snow having melted, so 

 that the grass was bare. 



With the wind I could hear the bell at 120 yards, either with 

 the bell on the ground or raised 4 feet above it. At right angles 

 to the direction of the wind it ranged about 60 yards with the 

 bell on the ground, and 80 yards when the bell was elevated. 



To windward, with the bell standing on the ground (which, it 

 must be remembered, means that the bell was actually 1 foot above 

 the surface), the sound was heard as follows : — 



Full. Lost. 



With the head close to the ground At 10 yards. At 20 yards. 



Standing „ 30 „ „ 40 „ 



At an elevation of 25 feet Not heard at 90 yards. 



With the bell at an elevation of 4 feet 6 inches : — 



Full. Lost. 



Head to the ground At 18 yards. At 30 yards. 



Standing up „ 40 „ „ 60 „ 



At an elevation of 12 feet „ 90 „ 



At an elevation of 18 feet „ 90 „ 



These results entirely confirm those of the previous experiments ; 



* The wind fell rapidly towards the close of the observations on this day. 



