194 G. F. Becker — Impact Friction and Faulting. 



The group was found loose in the soil and there are no signs 

 of its having been broken off another piece or that there have 

 been any crystals attached after the manner of those in the 

 groups from Reichenstein. 



The only planes that can be definitely recognized are R, 

 — R, ooR. The faces R and — R possess essentially the same 

 luster, so that there is no physical means of distinguishing the 

 one or the other. 



The foregoing article was prepared while the writer held one 

 of the Morgan Fellowships in Harvard College, and this oppor- 

 tunity is taken to express the gratitude he feels to the Director 

 of the Boylston Laboratory, Professor J. P. Cooke, for the 

 unvarying kindness with which Professor Cooke gave aid, 

 counsel and encouragement. 



University of Virginia, May 12th, 1885. 



Art. XXVI. — Impact Friction and Faulting ; by Geo. F. 



Becker. 



(Continued from page 128.) 



The first portion of this article was devoted to a discussion 

 of the distribution of energy in a rod of finite or infinite length, 

 and of elastic or inelastic material, when subjected to an impact 

 in the direction of its axis. It was also pointed out that such 

 a rod might be divided into short portions supposed to remain 

 in contact with one another without affecting the result. It 

 was then shown, that if for such short rods, sheets or plates 

 lying one upon another are substituted, each plate being con- 

 strained to move in its own plane, but presenting on its upper 

 and lower surfaces an indefinite number of extremely small 

 inequalities or teeth interlocking with the similar inequalities 

 of the adjacent plates, the distribution of energy through the 

 system of sheets caused by the impact of these teeth when the 

 uppermost sheet is moved is the same as in a rod subjected to 

 impact except that the axis of distribution is vertical to the 

 line of motion instead of coincident with it. A surface armed 

 with such minute inequalities or teeth, is the conception of a 

 frictional surface temporarily adopted. 



Application of principles of impact to friction. — Considering 

 friction as a form of impact under particular geometrical con- 

 ditions, it is easy to make applications of the results obtained 

 for impact to frictional problems. Were the material of sheets 

 offering frictional resistance perfectly elastic and without elastic 

 limit, the movement of one plate over another would in gen- 

 eral be impossible. The projections on the two surfaces would 



