EESEAECHES IN SOUND. 521 



In tills and the subsequent experiments of the same day but one 

 steamer — the Mistletoe — was employed. It started at 10:30 A. m. from 

 the point C, Fig. 4, at the foot of the clifl', and steamed W. S. W. along 

 C B for about 12 minutes, or a distance of two miles, blowing the whistle 

 every half- minute. To note the duration of the sound, Dr. Welling was 

 stationed at the foot of the cliflf, at the level of the sea, while the chair- 

 man of the Light-House Board, with an assistant who acted as clerk, 

 was on the upper gaUery of the tower, the ears of the latter being almost 

 precisely 200 feet above those of the observer at the foot of the cliff. 



The watches having been i)reviously set to the same time, on compar- 

 ing results it was found that the whistle was heard at the top of the 

 tower for twelve minutes and at the bottom of the cliif for five and one- 

 half minutes, making the difference in favor of audition on the tower six 

 and one-half minutes. In this experiment the sound came to the ob- 

 servers nearly against the wind. 



The fourth experiment consisted in directing the Mistletoe to proceed 

 in the opposite direction from the same point, along the line C D. It 

 started at 11:5 A. m. the breeze being light at the time, and proceeded 

 about two and one-half miles before the sound was lost to the observers. 

 On comparing notes it was found that the sound was heard at the top 

 of the tower during fifteen minutes, and at the level of the sea for eleven 

 minutes, giving a difference in favor of the hearing on the top of the 

 tower of four minutes. 



In the Jifth experiments the Mistletoe steamed again in the direction 

 ■udth the wind, the sound from its whistle coming to the ears of the ob- 

 servers against the wind. Starting about 11:45 A. m. and steaming about 

 two miles, the sound was heard on the tower during twelve minutes 

 and at the foot of the clLS' during five and one-half minutes, making a 

 difference of six and a half minutes in favor of audition on the tower. 

 Previous to this experiment the wind had veered one point to the west, 

 bringing the direction of the sound to the observers in less direct oppo- 

 sition to the wind than in the last experiment. 



The sixth experiment. — In this case the steamer was directed to proceed 

 in the opftosite direction, or against the wind, so that the sound of the 

 whistle would reach the ear of the observers in the same direction as 

 that of the wind. It started at 12:19 p. M. and proceeded two and one- 

 sixth miles ; the whistle was heard during thirteen minutes on the top of 

 the tower, and at the bottom of the cliff during precisely the same time, 

 the difference between the top of the tower and the bottom of the cliff 

 in this case being nothing. 



The vessel having again been called off on other duty the seventh ex- 

 periment was made the 1st of September. On this day the wind was 

 northeast ; the velocity at the top of tlte tower was thirteen and a^ half 

 miles per hour, and at the bottom of the tower eleven miles per hour. 

 The barometer indicated 30.20 inches pressure, the dry bulb 72^, and the 

 wet bulb G7io 



