58 PROCEEDINGS OF THE AMHERST MEETING 



thinks that it imposes too great labor on the teacher, and consequently 

 will not be largely used in the class-room. 



SUGGESTED APPARATUS 



The reply of Fred E. Wright, 2 of the Geophysical Laboratory, is espe- 

 cially suggestive. He says : 



"Practically all the phenomena which the geologist has to consider involve 

 spacial relations. Thinking in terms of space dimentions is not easy, and any 

 models which aid the student to visualize and interpret three dimensional re- 

 lations are welcome. It is for this reason, I take it, that the body of your 

 letter is devoted to the consideration of models illustrating geological struc- 

 tural relations. Fainted models of this sort do aid the purely geometric con- 

 cepts, but they do not illustrate geological processes, and it is with the prin- 

 ciples underlying these processes that the student should be most concerned. 

 The geological structure is, in a measure, the end-product of a series of geo- 

 logical processes, and it is in the interpretation and history of these processes 

 that we are most interested rather than in the formal description of structural 

 relations as depicted in models." . . . "Experiments may be used to illus- 

 trate, for example, the mechanical behavior of rocks (elastic properties of 

 materials, et cetera), the thermal behavior (thermal conductivity, diffusivity. 

 et cetera), the physical-chemical behavior at different temperatures and pres- 

 sures." 



A. Under the heading of mechanical and elastic properties experiments may 

 be set up to illustrate — 



1. Formation of joint cracks. 



(a) By mechanical means (Daubree's torsion experiment). 



(b) By thermal means (rapid chilling of heated glass plates). 



(c) By drying out (mud-cracks). 



By volatilization (drying of rosin). 



2. The elastic constants of rocks and materials. 



(a) Compressibility (bulk modulus). 



(&) Rigidity (shear). 



(c) Tensile and crushing limits. 



Phenomena of fracture. 

 {d) Plastic flow, 

 (e) Viscous flow. 



(/) Behavior of bodies under hydrostatic pressure or tension. 

 (g) Behavior of bodies under load. 

 (70 Use of polarized light to show distribution of stresses in 



strained samples of glass, celluloid, or other transparent 



material. 

 (i) Elastic after-effect. 

 0) Influence of temperature on these properties. 



The importance of a thorough training in the principles of mechanics and 

 the engineering attitude toward the elastic properties of materials, especially 

 rocks, can not be over-emphasized. 



- Letter received Augusl 30. 1021. 



