aca^my o F sconces] BIOGRAPHY 7 



Geophysical Laboratory is the outgrowth of his work more than that of any one man. 3 His 

 published shorter papers showed an ever-increasing tendency to delve into physical and chem- 

 ical problems and theories and to devise methods for their solution. This is evident in his 

 Finite Homogeneous Strain, Flow, and Rupture of Rocks (1893), Rock Differentiation (1896- 

 97), Experiments on Schistosity and Slaty Cleavage (1904), Torsional Theory of Joints (1913), 

 and numerous other papers. 



Concerning the paper of 1893 Day remarks: 



In this we recognize a splendid attempt to define and formulate in precise terms, some of the relations in 

 the science of rock mechanics. This was a magnificent task of pioneer quality and of extraordinary difficulty, 

 but was not immediately fruitful because clothed in somewhat abstruse form. 



In his discussion of rock differentiation an attempt was made for the first time in America 

 to apply physiochemical laws along the experimental lines of Van't Hoff and others. The 

 conclusions reached can be made clear by quoting his own abstract. 4 



All known processes by which the segregation or differentiation of a fluid magma could take place involve 

 molecular flow. This is demonstrably an excessively slow process excepting for distances not exceeding a few 

 centimeters. Soret's method of segregation, even if it were not too slow, seems inapplicable because it involves 

 a temperature unaccountably decreasing with depth. The normal variation of temperature, an increase with 

 distance from the surface, would be fatal to such segregation. The least objectionable method of segregation 

 would be the separation of a magma into immiscible fractions; but this seems to involve a superheated, very 

 fluid magma, while the law of fusion and the distribution of phenocrysts in rocks indicate that magmas prior 

 to eruption are not superheated to any considerable extent and are very viscous. 



The homogeneity of vast subterranean masses called for by the hypothesis of differentiation is unproved 

 and improbable. The differences between well-defined rock types are more probably due to original and per- 

 sistent heterogeneity in the composition of the globe. Hypogeal fusion and eruption tend rather to mingling 

 than to segregation, and transitional rock varieties are not improbably mere fortuitous mixtures of the diverse 

 primitive relatively small masses of which the lithoid shell of the earth was built up. 



This paper was subjected to a critical review, with only partial agreement by C. F. Tolman, 

 in the Journal of Geology for May-June, 1897. 



In the paper on schistosity and slaty cleavage published in 1896 and already referred to, 

 Becker took issue with the general idea to the effect that a secondary cleavage may be induced 

 under pressure, but argued that "deformation of a solid, homogeneous, viscous, isotropic, not 

 infinitely brittle, mass will develop structure in it on not less than one surface nor on more than 

 four surfaces simultaneously." This he thought to show both mathematically and by experi- 

 ment. In summing up his results he stated: 



In view of the evidence merely outlined above, it appears to me utterly impossible to deny that solid flow 

 does as a matter of fact induce a true cleavage which is parallel to the lines of relative tangential motion or glid- 

 ing, this cleavage not necessarily being accompanied by any actual ruptures however microscopic. 



Again in his paper on Current Theories of Slaty Cleavage (1907), which was largely contro- 

 versial, Becker referred to the prevalent ideas as found in the literature, and then he stated his 

 own views as follows: 



Like Tyndall and Daubree, I consider a parallel arrangement of flattened grains unessential to cleavage. 

 Rupture takes place on planes of maximum slide or maximum tangential strain. Rupture is a gradual process 

 and cohesion is impaired through flow before it is destroyed. Impaired cohesion in my theory is cleavage. 

 Cleavage develops most perfectly when the stress tending to produce it is persistent in direction, because viscous 

 resistance is then small. In a rotational strain there are two sets of mathematical planes on which maximum 

 slide takes place and both sets are parallel to the axis of rotation. They make with the greatest axis of the strain 

 ellipsoid angles given by 



B 



tan = 



(ABC) 1/3 



A being the greatest axis, B the least and C the axis of rotation. The planes of maximum slide contain the cir- 

 cular sections of the ellipsoid only in a limiting case. During the progress of strain these mathematical planes 

 sweep through wedges of the mass, but the two sets of planes sweep at different rates, one set having a relative 

 angular velocity from, say, 20 to an infinite number of times as great as the other. On the planes which sweep 

 rapidly viscosity reinforces rigidity, there is no time for considerable flow to take place, and unless actual rupture 



B See his Project for a Geophysical Laboratory and construction of a geophysical laboratory. Year Book, Carnegie Institution, 1902 and 1904. 

 ' Amer. Jour. Sci., vol. UI, 1897, p. 40. 



