DUE TO THE WEIGHT OF CONTINENTS. 
215 
Table VII.—Limiting stress-difference. 
. 
Produced by tension. 
Produced by crushing. 
Material. 
Breaking 
stress- 
difference in 
metric tonnes 
per square 
centimeter. 
Stress-difference at which 
permanent set begins in— 
Material. 
Breaking stress-difference 
in— 
Metric tonnes 
per square 
centimeter. 
British tons 
per square 
inch. 
Metric tonnes 
per square 
centimeter. 
British tons 
per square 
inch. 
Sheet lead.... 
•28 
•23 
1-46 
Strong red brick . 
•077 
•49 
Cast tin .... 
•416 
•417 
2-64 
Strong sandstone . 
•39 
2-45 
5 ? .... 
■325 (R) 
• « 
2-06 (R) 
(F) Strong lime- 
Wood (ash) . . . 
1-20 
1-20 
7-61 
stone .... 
•60 
3-80 
Cast brass.... 
1-27 
1-27 
8-05 
Marble .... 
•39 
2-45 
,, iron .... 
•94 to 2'04 
1T4 to 1-87 
7-23 to 11-86 
Granite .... 
•39-to -77 
2-45 to 4-91 
Drawn copper 
4T0 
4-00 
25-36 
(F) Granite (Mount 
English steel piano- 
Sorrel) .... 
•905 
5-74 
forte wire . 
23-62 
23-56 
149-6 
(F) Grauwacko. 
1T9 
7-54 
(R) Brick, cement . 
•020 to -021 
• • 
•125 to -134 
Ash (along the grain) 
•63 
4-02 
(R) Glass .... 
•66 
. , 
4-20 
Cast brass . . . 
•73 
4-60 
(R) Slate .... 
•68 to ‘90 
• • 
4-3 to 5-7 
Wrought iron . . 
2-52 to 2-84 
16 to 18 
Note. —The second and third columns give the product of Young’s modulus into greatest elastic exten¬ 
sion, and this should give the stress-difference when permanent set begins. Rankine does not give the 
data for this quantity, but the breaking stress-difference is given in both metric and British units, the 
latter being in the third column. 
In the second half of the table the results marked F are from Sir William Fairbaien’s experiments. 
The only cases in these two tables in which we have the opportunity of comparing 
the strength for resisting the stress-difference, when produced in the two manners, is 
for the materials cast brass and ash; in both cases we see that the substance is 
considerably weaker for crushing than for tension. 
I should be inclined to suppose that the crushing strength is more nearly the datum 
we require for the case of the stresses in the earth. 
In the first half of the table we probably see the effect of permanent set in the 
cases of copper and pianoforte wire (compare TOO with 4’10, and 23'56 with 23*62), 
but it is surprising that the contrast between the two columns is not more marked. 
§ 10. On the case when the elastic solid is compressible. 
It appears desirable to know how far the results of the preceding investigation may 
differ, if the elastic solid be compressible. According to the views of Dr. Ritter, 
referred to in the summary, this must be largely the case. 
As I did not examine this point until after the above was completed, it seemed 
preferable to make a fresh beginning, rather than to modify the whole investigation. 
