62 O. C. LESTER, JR. 
of sound in air, as the air became present in larger and larger propor- 
tions near the surface. The few profiles in which velocities lower than 
that of sound in air had been indicated, were considered interesting 
but somewhat anomalous, and were strongly suspected of contain- 
ing some unseen error. A discussion of sound velocities in air-water 
mixtures,! which was pointed out by E. E. Rosaire, was the direct 
cause of the experiment here discussed. This experiment was carried 
out in the Gulf Coast region near Houston, Texas. 
On the assumption that Gulf Coast gumbos may be treated as 
fluids, within limits, calculation of theoretical velocities to be ob- 
tained from earth-air mixtures in varying proportions were carried 
out from the equations given in the article mentioned,” namely: 
iY yee 
Fe Aces, re 
Where: 
P,=density of air=.oo1r2 
E,=elasticity of air=1.2X 10° 
P.,=density of earth, assumed as 1.9 
E,=elasticity of earth, computed as 5.58X10'° 
X = proportion air to total by volume 
1— X =proportion earth to total by volume 
V =velocity of sound in mixture 
If the values of the composite velocities be plotted against pro- 
portions of air to earth, a curve of the form in Figure 1 is obtained. 
Though this curve should perhaps be considered only qualitatively 
because of the assumption of earth as a fluid, it indicates the prob- 
ability of obtaining velocities from earth-air mixtures, whose magni- 
tudes may be actually less than that of sound in air alone. This pre- 
diction has been verified experimentally by shooting a short detailed 
refraction profile, extreme precautions being taken to muffle the shot 
point and hence eliminate any effect of the air wave. The recording 
was begun at a distance of 5 feet from the shot point and carried out 
on the surface to a distance which definitely indicated the ‘“‘un- 
weathered”’ velocity on the time-distance curve. This curve is shown 
as curve (A) in Figure 2. 
1 A. B. Wood, A Textbook on Sound, pp. 327-28. 
2 A. B. Wood, op. cit. 
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