604 FRANK D. ADAMS AND J. AUSTEN BANCROFT 



of the research in these units. In presenting the final results, 

 however, the data for the conversion of these into a unit more 

 generally employed in physical investigations are given. 



The extensometer employed for the purpose of measuring the 

 expansion of the tube under pressure was a simplified form of the 

 type designed by Professor Coker and described in the Proceedings 

 of the Royal Society of Edinburgh, XXV (1904-5). It was affixed 

 to the opposite points of the steel tube on the plane of maximum 

 deformation and showed the expansion, multiplied by two, by 

 means of a fine line moving over a graduated scale, which was read 

 by a telescope placed at a distance of several feet. 



In a number of experiments two extensometers were employed, 

 which were applied to the tube in the plane of maximum deforma- 

 tion, but in directions at right angles to one another. In this way 

 it was ascertained that the bulge which the steel tube displayed 

 under pressure was nearly symmetrical, but in order that any error 

 which might arise from a single measurement might be eliminated, 

 in almost all cases the two extensometers employed were affixed to 

 the tube at right angles to one another, and the mean of the two 

 readings was secured. By means of this form of extensometer and 

 by reading with a telescope, it was possible to measurean increase 

 on the diameter of the tube amounting to only 0.0005 inch. The 

 steel tube inclosing the rock column, with the extensometers in 

 position, the whole set up in the press ready for the application of 

 pressure, is shown in Fig. 2. 



The method adopted for measuring the internal friction devel- 

 oped in the rock by deformation was as follows: 



A column of rock, Carrara marble, first was taken, having the 

 dimensions already referred to. This was inclosed in a tube of 

 nickel steel, as above described; the tube had a wall thickness of 

 0.25 centimeter at its thinner portion. As will be seen from Fig. 1, 

 the middle portion of the marble column is inclosed by the thinner 

 portion of the tube, while the ends of the column are held by the 

 thicker portion of the tube wall. In this way the rock is prevented 

 from flowing up between the tube and the pistons and thus from 

 escaping from the tube. With a tube of this shape and these 

 dimensions, the movement of the rock under pressure is confined 



