[BuRTON] YOUNG’S MODULI OF METALS 19 
vernier so that the distance between the edge of any dust heap and 
the nearest division of the standard yard could be accurately deter-” 
À . 
mined. The mean of 24 observations on the value of = iain gave 
7-1757 cms., the greatest divergence from this number being the 
values 7-1788 and 7-1723 cms. 
The mean of three readings of the length of the rod gave 75-0484 
ems. The specific gravity of the rod was determined by finding its 
volume and weight, corrections being carefully made for the very small 
holes made in the rod in attaching the dise on the end inserted in the 
dust-tube. The average of 15 readings on the diameter of the rod 
gave 1.2675cms. ‘The corrected volume of the rod was 94.6949 ces.; the 
weight of the solid rod was 805-19 grams, which brings the density 
equal to 8-503. 
If V, denotes the velocity of sound in brass, V,, that in air, À,, the 
wave-length in brass, 4,, the wave-length in air, 
À 75-0484 
This gives from the above results V, = V,X——— 
oli obs 
The results given for the value of V, for air in tubes are as follows:— 
Kayser (1877): 1200 ..882-5 metres per sec. at O°C. 
Waller: CLSTS) i Mn, .331. 9 Fa * a 
1 EO GY 119 [0 7.8 ae es ae 331-9 . 72 a - 
One is doubtless justified in taking as the most probable value of 
V,, 331-9 metres per second. We have still to correct for the tempera- 
ture as the above result refers to air at 0° C. and the equation 
connecting the velocity at 0° C. and t° C. is, for small values of t, 
V, = V, (1 + 4 at), where “a” is the coefficient of expansion of 
air. Therefore the value of V,, the velocity of sound in air at 15° C., 
the temperature at which the above experiments were carried out, is 
34105 cms. per second. 
Introducing this value in the equation for V,, we get as the value for 
the velocity in the brass rod at 15° C.—358,080 cms.per second. 
From the equation q — V’,.d, we obtain q’ —10-902 X 10" 
dynes per square centimetre. 
