DR. EVERETT ON THE RIGIDITY OE IRON AND COPPER. 
369 
The following Table contains the collected results of all my experiments, the figures 
I., II., III. indicating the paper in which the experiments are described and the results 
deduced. The values of M, n , and k are given in millions of grammes weight per square 
centimetre. 
M 
(Young’s mo- 
dulus). 
(Rigidity). 
Tc 
(Resistance to 
compression). 
a 
(Poisson’s 
ratio). 
Specific gravity. 
Glass, flint (I.) .... 
614-3 
244-2 
423-0 
•258 
2-942 
„ „ (II.) .... 
585-1 
239-0 
353-3 
•229 
2-935 
Brass, drawn (II.) . . 
1094-8 
372-9 
5701 (?) 
•469 
8*471 
Steel (II.) 
2179-3 
834-1 
1875-6 
•310 
7-849 
Iron, wrought (III.) 
1999-4 
783-8 
1484-1 
•275 
7-677 
„ cast (III.) .... 
1374-1 
542-3 
982-2 
•267 
7-235 
Copper (HI.) 
1255-8 
455-6 
1716-4 
•378 
8-843 
The values of M and n are derived directly from the observed amounts of flexure and 
torsion respectively, and their probable errors (estimated as percentages) may be con- 
sidered equal. 
Again, the comparison between flexure and torsion is so direct (with the exception of 
the first set of results for glass), that the probable error of ^ may be considered about 
equal to that of M or n. 
The values of <r and k are deduced on the hypothesis that the substances operated on 
are isotropic ; and on this hypothesis, if e denote the probable error of the probable 
error of a is e, and that of k is - 1 -— e nearly. 
<r l — o- 
. 1 -f- <r . 
For all the substances in the Table except brass, the value of the coefficient is 
from 5 to 11, but for brass it is 47 ; hence the enormous value of k found for brass 
cannot be depended on. 
The tendency of anything like fibrous structure in the rods operated on, the fibres 
being supposed to run in the direction of the length, is to make <r and k come out too 
large. This follows from the theoretical considerations adduced on page 152 of my last 
paper, and I have verified it by experiments on a rod of wood which gave values of T 
T 
four or five times greater than those of F, whereas the ratio p for isotropic substances 
must always lie between 1 and T5. 
As the intention was expressed in my last paper of introducing a modification of the 
apparatus with the view of diminishing the mechanical correction, I should state by way 
of explanation that the experiments here described were nearly completed before that 
intention was expressed. 
