38 W. B. Taylor— Recent Researches in Sound. 



seven and three-quarter miles. Toward the close of the day 

 the signals were heard at twelve and three-quarter miles. 

 (p. 196, 197.) 



[7.] On the same day at one o'clock, the echoes from the direc- , 

 tion of the open sea were very distinct at the signal station. 

 " The instruments hidden from view, were on the summit of a 

 cliff 235 feet above us, the sea was smooth and clear of ships, 

 the atmosphere was without a cloud, and there was no object 

 in sight which could possibly produce the observed eft'ect 

 From the perfectly transparent air, the echoes came, at first 

 with a strength apparently but little less than that of the direct 

 sound, and then dying gradually and continuously away." 

 (p. 198.) These remarkable echoes are supposed by Professor 

 Tyndall to be returned from the invisible surfaces of the 

 vaporous strise, whi«3h thus render the air opaque to the sono- 

 rous waves. Subsequently, on the 8th of October, the Ameri- 

 can siren being just received and set up, its loud echoes were 

 observed to be " far more powerful than those of the horn," 

 and to last eleven seconds, while those of the horn had eight 

 seconds duration, (p. 199.) On the 15th of October, the 

 direction of the echoes was found to correspond with the prin- 

 cipal axis of the direct or primitive sound ; the direction of 

 the return sound changing with the rotation of the horn. 

 (p. 200.) 



[8.] On October 8th rain and hail were found not to obstruct 

 sound. While in the morning (after a thunder storm) from 

 Dover and the South Foreland across the English channel " for 

 a time the optical clearness of the atmosphere was extraordi- 

 nary, the coast of France, the Grisnez lighthouse, and the 

 Monument and Cathedral of Boulogne being clearly visible in 

 positions from which they were generally quite hidden ; the 

 atmosphere at the same time was acousticallv opaque ;" and 

 the horn was feebly heard at six miles, (p. 205.) But in the 

 afternoon a storm arose, and although the rain was falling 

 heavily all the way between the signal station at Foreland and 

 the point of observation on the steamer, " the sound instead of 

 being deadened, rose perceptibly in power. Hail was now 

 added to the rain, and the shower reached a tropical violence.' 

 "In the midst of this furious sciuall both the horns and the 

 siren were distinctly heard," and as the shower lightened, 

 diminishing the local pattering on the deck, they were heard 

 "at a distance of seven and "a half miles distinctly louder 

 than they had been heard through the rainless atmosphere at 

 five miles." (p. 206.) On the 23d of October, a similar expe- 

 rience was noticed on land, and, contrary to the usual im- 

 pression, snow was also observed to offer no serious obstacle 

 to sound, (p. 207.) 



