540 Prof. O. Reynolds on the 



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 having 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 llth 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 opportunity 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 ; and 

 the intensifying of the sounds to windward by the raising of the bell was 

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





