DISCOURSE OF W. B. TAYLOR. 347 



In October, 1867, a series of observations was made at Sandy 

 Hook (New Jersey) with various instruments. A sound reflector 

 being employed, the distance at which the sand on the phonometer 

 drum carried in front, ceased to move was 51 yards, as compared 

 with a distance of 40 yards, without the reflector. At a greater 

 distance, with a more sensitive instrument, the ratio was very much 

 diminished. Experiments were also made on the relative distances 

 at which the trumpet affected sensibly the drum of the phonometer 

 in different directions, giving as their result a limiting spheroid 

 whose reach in the forward axis of the trumpet was about double 

 that in the rear axis, and at right angles to the axis, was about a 

 mean proportional between the two. With greater distances, these 

 differences were evidently very much reduced, the radii becoming 

 more equalized. In the summer of 1871, Henry made investiga- 

 tions at different Light-stations, on our western coast of California. 



The very important observation that a sound could best be heard 

 at an elevation when the wind is adverse (that is when it blows 

 from the observer towards the acoustic signal,) and that after it had 

 even been entirely lost to the ear in such case, it might be regained 

 in full force by simply ascending to a suitable elevation, admitted 

 apparently but one explanation, namely that the line of successive 

 impulse constituting a sound-beam was deflected or bent upwards 

 by the action of the opposing wind. If as had already been 

 .shown to be the case sometimes, and as might therefore be expected 

 generally, the adverse wind were assumed to be a little stronger 

 at the elevation than at the surface, such a result would at once 

 follow. " The explanation of this phenomenon as suggested by the 

 hypothesis of Professor Stokes is founded on the fact that in the 

 case of a deep current of air the lower stratum or that next the 

 earth is more retarded by friction than the one immediately above, 



the upper currents of air are frequently five or six times more rapid than the 

 surface currents. (Travels in the Air, p. 9.) Prof. Cleveland Abbe remarks: "From 

 seven balloon ascensions made on July 4th, 1871, at different points in the United 

 States, I have deduced the velocity of the upper currents as about four times that 

 of the surface wind prevailing." (Bulletin Philosoph. Soc. Washington, Dec. 16, 1871, 

 vol. i. p. 39.) And M. Peslin states in general terms : " It is certain according to 

 ali observations made both in mountains and in balloons, that the force of the 

 wind increases considerably as we ascend in the atmosphere." (Bulletin Inter- 

 national de I'Observ. de Paris et de VObserv. Phys. Cent. Montsouris, July 7, 1872.) 



