Volltext: Collected Papers On Acoustics

rear seat forward one centimeter. This distance is so slight that 
without moving in his seat, in fact, without moving his shoulders, 
a slight inclination of the head would accomplish an equivalent 
gain. Thus, while the effect is in the right direction, it is of entirely 
imperceptible magnitude. If we take into account the sound re¬ 
flected from walls and ceiling, the gain is even less. 
But the suggestion which is the text of the present paper was 
not made by one, but by several gentlemen, and is based on the 
well-recognized fact that one can hear better, often very much 
better, with the wind than against it, and better than in still air. 
Therefore, the suggestion is not groundless and cannot be disposed 
of thus summarily, certainly not without submitting to the same 
calculation the out-of-door experience that gave rise to the thought. 
In the nomenclature of the United States Weather Bureau a 
wind of from “1 to 5 miles an hour is called light, 6 to 14 miles 
fresh, 15 to 24 miles brisk, 25 to 37 miles high, and a wind of from 
40 to 59 miles is called a gale.” Taking the case of a “high wind” 
as a liberal example, its average velocity is about 14 meters per 
second, or about one twenty-fifth the velocity of sound. In such 
a wind the sound 1000 meters to leeward would be louder than in 
still air only by an amount which would be equivalent to an ap¬ 
proach of 40 meters, or 8 per cent. Similarly, to windward the sound 
would be less loud by an amount equivalent to increasing the dis¬ 
tance from 1000 to 1040 meters. This is not at all commensurate 
with general experience. The difference in audibility, everyone will 
agree, is generally greater and very much greater than this. The 
discrepancy, however, can be explained. The discrepancy is not 
between observation and theory, but between observation and a 
very incomplete analysis of the conditions in the out-of-door ex¬ 
perience. Thus, the ordinary view is that one is merely hearing 
with or against the wind and this wind is thought of as steady and 
uniform. As a matter of fact, the wind is rarely steady, and partic¬ 
ularly is it of different intensity at different altitudes. Fortunately, 
the out-of-door phenomenon, which in reality is very complex, has 
been carefully studied in connection with fog signals. 
The first adequate explanation of the variation in loudness of a 
sound with and against the wind was by the late Sir George G.


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