ELASTIC CONSTANTS OF ROCKS. 9 
In the second experiment the marble lath was longer and at the same time 
somewhat thicker. Its dimensions were as follows : Length, 1 6 inches ; length 
between supports, 15 inches; breadth, i .229 to i .284 inches; thickness, .347 to 
.356 inch. 
Inch. 
Load wjth pan only ,. . . .343 
with pan plus 8 ounces 349 
16 ounces 368 
24 ounces 389 
24 ounces (after i minutes) 392 
28 ounces 401 
32 ounces 416 
32 ounces (after i minutes) 423 
36 ounces 438 
40 ounces 460 
Load with pan only (weight removed, large permanent set) 412 
with pan plus 40 ounces (after 2 minutes) 471 
44 ounces . . . 492 
44 ounces (after a few seconds) 500 
44 ounces (after i minute; broke) 520 
Total deflection 177 
Here it will be noticed that when a certain load is reached a distinct move- 
ment sets in and is maintained without any further increase of load, the 
movement growing in amount as the limit of the strength of the rock is 
approached and producing a permanent set. 
Experiments on the determination of the elastic constants of rocks when 
subjected to twist were also found to be frequently unsatisfactory, owing to 
the low ultimate shearing values of many rocks. 
While a glance at the list of rocks whose elastic constants have been measured 
by Nagaoka will at once show that most of them are rocks whose elasticity 
must be of a very imperfect kind, e. g., weathered clay slate, Schalstein, tuff, 
etc.; the method which he has employed for the determination of Young's 
modulus gives very low results, even in the case of rocks such as marble and 
granite, where the elasticity might be supposed to be of a high order, and 
comparable to that which these rocks have been shown to possess in the 
case of the types selected for investigation in the present paper. This is 
shown by the following figures comprising the values obtained by him for 
each of the marbles and granites contained in his list. 
E 
(Young's 
E 
(Young's 
Paleozoic marble: modulus). Granite: modulus). 
No. IIA 10,120,000 
I IB . 7,950,000 
I2A 5,440,000 
12B 4,770,000 
No. 69 (Shodoshima) 6,140,000 
68 (Hitachi) 2,853,000 
71 (Hitachi) 2,175,000 
56 (Hitachi) 1,588,000 
52 (Hitachi) 3,265,000 
