512 FRANK D. ADAMS 



marble and embedding material in these experiments was 30,500 

 pounds. 



The column after deformation, when removed from the parafhne, 

 displays a very characteristic shape, and one which is quite different 

 from that shown by the rock when deformed in alum. The move- 

 ment set up in the column commences at one end and gradually 

 extends toward the other end of the column, not however as a general 

 rule reaching this before the experiment has to be brought to a close 

 on account of the impending rupture of the copper tube. 



This movement results in the development of a symmetrical 

 enlargement of that part of the column affected, the greatest diameter 

 being a short distance from the end of the column. The deformed 

 portion of the column thus swells out into a more and more pro- 

 nounced bell-shaped form, which fades away into the unaffected 

 portion of the column, which latter retains not only its form but also 

 the original polish of the surface. 



Crossing the smooth, bell-shaped surface, in that portion of the 

 column in which movement has taken place, are certain faint lines 

 which when the deformation is slight are just barely perceptible, but 

 which become more pronounced as the deformation increases. 

 These lines, which are uniformly spaced, or nearly so, are due to a 

 very slight displacement along their course and are, as is well known, 

 developed when any solid body is strained above its elastic limit. 

 They are known as Cooper's or sometimes as Luder's lines. As 

 seen on any one part of the lateral surface of the cylinder, they are 

 arranged in two series which cross one another at an angle which, as 

 nearly as it can be measured by an application goniometer, is 72 

 degrees. That is to say, each line makes with the vertical, which is 

 the direction in which the pressure is applied, an angle of 36". Along 

 this multitude of intersecting planes, in the early stage of deformation, 

 movement takes place with approximate uniformity, and as a result 

 the cylinder slowly shortens, widening at the same time as described 

 into a symmetrical, bell-shaped form which tapers down into the 

 undeformed portion of the cylinder. 



As the deformation goes forward and becomes more pronounced 

 the movement, while still taking place simultaneously along a great 

 number of these planes, becomes more pronounced along certain of 



