610 FRANK D. ADAMS AND J. AUSTEN BANCROFT 



every 15 seconds instead of every 30 seconds till they remained 

 constant for at least 5 consequent readings. This change was 

 necessitated in order to standardize the conditions in the two series 

 of experiments, since, when the tube was filled with tallow, the 

 whole load was applied to overcome the resistance of the tube, 

 while, when the place of the tallow was taken by marble, a portion 

 of the load was applied to overcome the internal friction of the 

 rock, and the movement was slower. By modifying the procedure, 

 as above mentioned, in the case of the tubes filled with tallow an 

 identical deformation was secured in both cases. 



When columns of rock are inclosed in the steel tubes and 

 deformation is carried out in the manner described, the impending 

 rupture of the steel tube, which marks the conclusion of the experi- 

 ment, is indicated by the appearance of a series of sharply marked 

 vertical lines on the bulged wall of steel which inclosed the deformed 

 rock. If the experiment is continued, the tube splits along one of 

 these vertical lines, and the inclosed rock becomes visible, and, if 

 the pressure is still maintained, the resistance along the line of 

 rupture being removed, the rock along this line crumbles and is 

 forced out of the fissure in the form of a powder. 



In the case of the experiments in which tallow was employed in 

 place of a column of rock, the completion of the test is marked by 

 the development of a vertical fissure in the thin portion of the steel 

 tube in the usual manner. So soon as this appears, however, and 

 usually before the load can be taken off the testing machine, a 

 fragment of the thin steel wall, bounded on one side by the fissure 

 in question and at the top and bottom by the thicker portion of the 

 steel tube, opens out like a door on its hinges and is instantly torn 

 off and with a loud report is shot across the room with great violence. 

 It therefore was necessary in the case of these experiments that the 

 observer should always be protected from these projectiles, the 

 importance of this protection being emphasized in the case of one 

 of the experiments by the fact that the piece of steel struck and 

 split in two the piece of hard wood, a quarter of an inch thick, 

 which protected the observer's head. 



In order to make quite sure that the form and outline of the 

 bulge assumed by the tube in the case of the experiments with the 



