510 RESEARCHES IN SOUND. 



tensity of the sound is not in all cases in proijortion to the velocity of 

 the wind. The result of his investigations in regard to the pitch of sound 

 was also similar to those we have given ; and, indeed, all the facts which 

 he has stated are, with a single exception as to the direction of the echo, 

 in strict accordance with what we have repeatedly observed. We regret 

 to say, however, that we cannot subscribe to the conclusions which he 

 draws from his experiments as to the cause of the retardation of sound 

 that it is due to a flocculent condition of the atmosphere, caused by the 

 intermingling with it of invisible aqueous vapor. 



That a flocculent condition of the atmosphere, due to the varying den- 

 sity produced by the mingling of aqueous vapor, is a true cause of ob- 

 struction in the transmission of sound is a fact borne out by deduction 

 from the principles of wave-motion, as well as by the experiments of the 

 distinguished physicist of the Eoj'al Institution of Great Britain ; but 

 trom all the observations we have made on this subject we are far from 

 thinking that this is the efficient cause of the phenomena under consider- 

 ation. A fatal objection, we think, to the truth of the hypothesis Pro- 

 fessor Tyndall has advanced is that the obstruction to the sound, what- 

 ever may be its nature, is not the same in diiferent directions. We think 

 we are warranted in asserting that in the cases of acoustic opacity which, 

 he has described, if he had simultaneously made observations in an op- 

 X)osite direction, he Avould have come to a different conclusion. That a 

 flocculent condition of the atmosphere should slightly obstruct the sound 

 is not difficult to conceive ; but that it should obstruct the ray in one 

 direction and not in an opposite, or in a greater degree in one direction 

 than in another, the stratum of air being the same in both cases, is at 

 variance with any fact in nature with which we are acquainted. We 

 would hesitate to speak so decidedly against the conclusions of Professor 

 Tyndall, for whose clearness of conception of physical principles, skill 

 in manipulation, and i)ower of logical deduction we entertain the highest 

 appreciation, were the facts which were obtained in our investigations 

 of a less explicit character. 



While tlie phenomena in question are incompatible with the assump- 

 tion of a flocculent atmosphere as a cause, they are in strict accordance 

 with the hypothesis of the refraction of the waves of sound due to a 

 difference in velocity in the upper and lower portions of the currents of 

 air. We do not say, however, that the transmission of sound in the 

 atmosphere is fully investigated, or that the abnormal phenomena which 

 are said to have been observed in connection with fog-signal stations 

 have been fully explained. So far from this, we freely admit we are as 

 yet in ignorance as to how the hypothesis we have adopted is applicable 

 to the critical explanation of the obstruction to sound in the abnormal 

 cases mentioned by General Duane. We feel, however, considerable 

 confidence in its power to afford a rational explanation of these pheno- 

 mena when the conditions under which they exist shall have been accu- 

 rately determined. 



