W. B. Taylor -Recent Researches in Sound. 37 



Later experiments in October showed that the pitch of the 

 sound had variable penetration on different days and even at 

 different times on the same day. The siren (an American in- 

 strument lent by the United States Lighthouse Board, and put 

 in use Octobers, 1873) was generally decidedly triumphant, 

 " ut not always so. {Trans., pp. 220, 221.) 



[2.] The defect of sound in the acoustic shadow of an inter- 

 . ening obstacle (a chalk cliff) was very strikingly manifested. 

 In June the same sharpness of shadow line was observed ; and 

 1 with the instruments in view, at the distance of a mile, 

 f souiLd entirely failed near the shadow line at one side. 

 {Trans., p 190.) 



[3.] Although " the wind exerts an acknowledged power over 

 sound" yet, on the 25th of June, " when the range was only 

 ix and a half miles, the wind was favorable ; on the 26th 

 ^rhen the range exceeded nine and a quarter miles, it was 

 opposed to the sound." (p. 194.) On October 11, the sound 

 was observed to be much affected by an adverse wind. It was 

 al?() noticed on this as well as on subsequent occasions, that 

 ''an ()j)posing wind affects the gun-sound far more seriously 

 than tliat of the siren." With a favoring wind, sounds were 

 heard twice as far as with an adverse wind, even at a point 

 "more deeply immersed in the sound-shadow." (p. 224.) 



fl.J July 1, at a distance of five and a quarter miles from a 

 rotating horn it was observed that the sound was sensibly 

 stronger in front than at the rear of the trumpet, the reduction 

 being" estimated as seven to ten. (p. 192.) 



[5. J July 1, " In a thick haze, the sound reached a distance of 

 twelve and three-quarter miles, while on May 20, in a calm 

 and hazeless atmosphere, the maximum range was only from 

 five to six miles." (p. 193.) And subsequent observations 

 made in London, December 10 and 11, showed that a thick 

 fog offered no sensible obstruction to the passage of sound, 

 (p. 209, 210.) 



[6.] On July 3, at 2. 15 P. M. " with a calm clear air and smooth 

 sea," at three miles from the signal station " neither horn nor 

 whistle was heard. The guns were again signaled for ; five of 

 them were fired in succession, but not one of them was heard." 

 (p. 194, 195.) As a hot sun was pouring its beams on the sea, 

 Professor Tyndall supposed that the copious evaporation re- 

 sulting, would most probably act very irregularly, producing 

 streams or wreaths of vapor, and thus render the air ^ccw/ewi; 

 \x\\\\ these invisible cloudlets, whose surfaces would occasion a 

 iar-v amount of repeated reflection and dispersion of the sound 

 waves. As the sun afterward became clouded at 3.15 v. M., 

 thy sounds of the signal were heard at three miles, and very 

 faintly at four and a quarter miles ; and later at six miles, and 



