114 WEATHERBY, BORN; AND HARDING 
Table II gives the values found for the two samples. 
TABLE II 
Sample r Sample 2 Average 
Dimensions 1.13 in. X1.13 in. X11.31in. 1.13 in. X1.13 in. Xg.oin. 
Natural frequency 7,108 cycles/sec. (av.) 9,182 cycles/sec. (av.) 
Rod velocity 13,3909 s5o0it./sec. 13.773 100 ft./sec. 13,586 ft./sec. 
Density 2.62 grams ce. 2.68 grams per cc. 2.65 grams cc. 
Young’s modulus 4.37 X10"! dynes/cm.? 4.72 X10 dynes/cm.? 4.55 X1oUdynes/c . 
Deeee dsuy!¥ 
} ie } fetes 



Young’s modulus is the only elastic constant which may be di- 
rectly obtained by this method. The longitudinal rod velocity ob- 
served is characteristic of the material in the form of a rod only, and 
is therefore not directly comparable with the bulk velocity deter- 
mined in the field measurements. If, however, the value of Poisson’s 
ratio for the material is known, the corresponding bulk velocity may 
be calculated by means of the relationship 
= 
Vis = Vir V 
I—o— 202 
636 
