522 EESEARCHES IN SOUND. 



The theoretical conditions for exhibiting the effect of height on audi- 

 tion in this exi)eriment were much more favorable than any of the pre- 

 ceding. First, the velocity of the wind was greater; second, the differ- 

 ence between the velocities at top and bottom of the tower was well 

 marked, and the direction of the wind was more favorable for direct 

 opposition to the sound as it came to the ear of the observer. In this 

 case General Woodruff was the observer at the bottom of the cliff, while 

 the chairman of the Light-House Board and his assistant, with several 

 visitors, were at the top of the tower. 



The steamer started at 10:58 A. m. and proceeded during eight minutes, 

 or a mile and one-third, when the sound was lost at the top of the tower. 

 In this case, though the sound was heard for eight minutes from the top 

 of the tower, and the first five blasts marked on the notes as quite loud, 

 it was not heard at all at the bottom of the cliff at least a hundred yards 

 nearer the source of the sound. 



This result, which interested and surprised a number of intelligent 

 Aasitors, who were in the tower at the time, strikingly illustrates the 

 effect of elevation on the audibiUty of sound moving against the wind. 

 The result was so important that it was thought advisable to imme- 

 diately repeat the experiment under the same conditions. 



In the eighth experiment^ the Mistletoe was again directed to proceed 

 in the direction of the wind, along the line it had previously traversed. 

 It started at 11:25 A. M.^ and proceeded during six minutes, or one mile, 

 when the sound was lost at the top of the tower. In this case, the first 

 blast of the whistle was feebly heard at the base of the cliff, but no 

 other, while thirteen blasts were heard at the top of the tower, of which 

 the first six were marked as loud. 



That this remarkable effect was not produced by an acoustic cloud or 

 a flocculent atmosphere is evident from the exijeriment which imme- 

 diately succeeded. 



The ninth experiment. — In this trial, the Mistletoe was directed to pro- 

 ceed against the wind, so that the sound of its whistle should come to 

 the ears of the observers with the wind. It started at 11:48 A. ]\t., and 

 proceeded during sixteen minutes, or two and two-thkds miles, when 

 the sound of its whistle was lost to the observers on the toj) of the tower. 

 In this case the sound of the whistle became audible at the bottom of 

 the cliff as soon as the position of the vessel became such as to bring the 

 sound to the observers approximately with the wind, and continued to 

 be audible during fifteen minutes, or within one minute as long as the 

 sound was heard at the top of the tower. 



It may be mentioned as an interesting fact, that an assistant who was 

 observing the sound with General Woodruff at the foot of the cliff, when 

 the sound could not be heard at the level of the sea, in the sixth experi- 

 ment perceived it distinctly by ascending the side of the cliff to a height 

 of twenty-five or thirty feet. 



All the conditions and results of these experiments are strikingly in 



