366 
DR. EVERETT ON THE RIGIDITY OF IRON AND COPPER. 
piece was weighed in air and water, the weights found being 100485 and 87-400 grammes. 
The temperature of the water was 10-4 Cent., at which temperature the expansion of 
water is 1-0003. From these data the volume of the rod in centimetres is found to be 
13-085 x 1-0003=13-089, 
and the specific gravity 100-485 -v-13-089 = 7-6771. Dividing the volume by the length, 
which was 29-27, we find the sectional area 5 rr 2 = -44566, r= -37664. Hence we have 
M (Young’s modulus)=^ =1,999,400,000, 
n (Rigidity) =^ = 783,790,000, 
TYT 
k (Incompressibility) = 3 ^ 77 = ^ =1,484,100,000, 
M 
a (Poisson’s ratio) =— — 1 = -275 as above. 
Experiments on Cast-Iron Bod. 
These experiments gave the following values for T and F : — 
Pointer- • 
Pointer- 
reading. 
T. 
F. 
reading. 
T. 
F. 
0 ° 
311-2 
245-8 
90° 
311-8 
245-2 
o 
o 
CO 
310-7 
245-3 
120 ° 
310-8 
245-0 
60° 
311-8 
244-7 
150° 
311-7 
245-3 
Combining positions at right angles, we have — 
From 0° and 
90° . . 
T=311-5 
F=245-5 
„ 30° „ 
120 ° . . 
„ 310-8 
„ 245-2 
„ 60° „ 
150° . . 
„ 311-7 
„ 245-0 
Here no correction is required for difference of arms, as the cross-piece was turned 
through a right angle in passing from the third to the fourth position. 
The values of corrected for difference of scale-divisions by subtracting one part in 
266, are 1*264, 1-263, and 1-267, which are first approximations to l+<r. 
To find the mechanical correction, we have length between mirrors 28-69, length 
subjected to torsion and flexure 43*5, height of scale above mirrors 222-8, as before. 
From these data, together with the above values of T and F, we have — 
Torsion in portion of rod between mirrors . . . . • -0098 
Flexure „ „ „ „ -0077 
which numbers being multiplied by ffy X’729, give -0108 and -0085. Hence the me- 
chanical corrections are 
+ -0108T and + -0085F; 
and the optical corrections being the same as before, the total corrections are 
+ -0061 T and +-0044F. 
