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



sound-wave moving against the wind is tilted upward." (Rep. 

 Brit. Assoc, 1857, pp. 22, 23, of Abstracts.) An opposing 

 wind exercises no sensible influence on either the velocity or 

 the range of sound, nor (if uniform) on the direction of sound. 

 Ordinarily indeed, a wind (which may be likened to an aerial 

 river) is retarded at the earth precisely as the current of a stream 

 is, over its bed.* When, however, the mouth of the aerial 

 chimney of ascent is low, it may very well happen that the 

 lower current of air (excepting immediately at the surface of 

 the earth) is considerably swifter than the successive layers of 

 wind above it ; and in such a case the effect of the opposing 

 wind will be not to tilt upward the sound-beam, but to tilt it 

 downward. In like manner a "favoring" wind, if more slug- 

 gish above, will tilt the sound-beam upward, and thus prove 

 unfavorable to its audibility. In short, the postulate required 

 for acoustic refraction is simply that there shall be a difference 

 of amount between the upper and the lower currents of wind. 

 And as this condition is certainly not an unusual one, we have 

 here apparently a true and satisfactory account of the seeming 

 anomalies of sound with reference to the influence of the wind. 

 But if the natural tendency of a mere dimmution of velocity 

 in the upper strata of an adverse wind is thus to bend an ad- 

 vancing sound downward, " a precisely similar effect " as Pro- 

 fessor Henry has well remarked, "will be the result but per- 

 haps in a considerably greater degree, in case an upper current 

 is moving in an opposite direction to the lower, when the latter 

 is adverse to the sound." (Rep., p. 107.) In September, 1874, 

 when a signal near Sandy Hook, N. J., was observed to be audi- 

 ble at a greater distance against the afternoon sea-breeze than 

 with it, Professor Henry ascertained by the employment of 

 small toy balloons, that the upper current was opposed to the 

 lower one, and in the direction of the maximum sound i 



Obs [11.] He was enabled thus to demonstrate experimentally 

 the reality of the "ideal wind " which had been so con: 

 jepted before, from other conspiring i 



3 confidently 



The critical commentary above cited, which postulates for 

 this doctrine of acoustic refraction the super-position of "an 

 ideal wind blowing in a direction opposite to the real one," as 

 a condition " which more than neutralizes its action," quite fails 

 to apprehend its true import. No action analogous to "neu- 

 tralization " is assumed by the doctrine. There is no solution 



* Professor Henry detei 



irmined by experiment in : 

 six miles per hour, that th( 



