392 Scientific Intelligence. 



placed opposite the insulated metallic plate, the electrical equi- 

 librium was destroyed and a deviation of 84 scale divisions was 

 obtained from the electrometer. A plate of brass or other metal 

 produced no effect.— Phil. Mag., March, 1898, 277-278. j. t. 



II. Geology and Mineralogy. 



1. U'echelle r'eduite des experiences geologiques permet-elle leur 

 application aux phenomenes de la nature? Par W. Prinz. 

 (Revue de l'universite de Bruxelles, tome II, pp. 550-547, figs. 

 1-49. 1897.) — Professor Prinz in this paper has brought together 

 a series of experiments to show the close similarity of the effects 

 produced by a variety of modes of application of mechanical 

 pressure upon various substances differing very greatly in dimen- 

 sions and in physical consistency. The experiments of Daubree 

 and James Hall, and later of Cadell and Willis and others, with 

 clay and wax models of geological strata, are familiar to all geol- 

 ogists. The folding and faulting of mountain regions are thus 

 reproduced on a small scale. The experiments of Malloc are 

 cited to show that the materials of the thin layer of steel, removed 

 from the surface as the tool advances in a planing machine, be- 

 have in the same way as do the wax and clay models, and like- 

 wise the rock layers in faulting and sliding over each other. 



The law that cleavage planes form at oblique angles, and schist- 

 osity planes at right angles to the direction of the compressing 

 force, is illustrated by geological sections, by cylinders of wax 

 and clay, by the fractures appearing in a pile of setting and set- 

 tling mortar, by the cracking of walls broken by the jar of earth- 

 quake ; and complex effects produced by bending an elongated 

 cylinder of clay illustrate the same principle. The relation of the 

 direction of the planes of fracture to the duration of the passage 

 of the pressure is illustrated by another series of experiments 

 bringing out the fact that the relationship between these two 

 factors is independent of the nature of the material and of the 

 size of the fractures. 



The familiar crevasses of glaciers are first put in evidence. 

 The same law is traced by the author through the following 

 diverse experiments: The cracks diverging from a line made by 

 drawing a cane through the snow, a needle drawn across a thin 

 layer ot plaster, a pencil in raggedly tearing a sheet of paper, a 

 stick drawn through the mud of a road. Added to these are the 

 effects produced by a steel roulette used in cutting glass, the like 

 effect of a cart-wheel running through a muddy road. Micro- 

 scopic examination of the scratch of a diamond upon a glass plate 

 shows the same disposition of the fracture planes as in the other 

 cases. 



In these several cases it appears that the fractures produced in 

 substances of greatly varying constitution, when pressed beyond 

 the limit of elasticity by a hard tool either passing through it, 

 pressing over the surface, or rolling on the surface, are alike in 



