﻿276 Bancs and Strouhal — Hydro-electric 



its cup. In some of the octahedrons the effect caused by the 

 repeated interruption of the tendency to form the faces (m-m) 

 on the face (1) is often quite striking, producing step-like 

 formations (figs. 9, 11). Another point observed was that in 

 some of the combinations of the cube and octahedron the faces 

 of the latter were unequally developed, while those of the cube 

 were elongated into rectangles (figs. 13, 22). It was found 

 that the development took place in alternate faces of any half 

 of the octahedron, that is, that the large and small faces alter- 

 nated above and below, and it was also found that the cubic 

 faces which were parallel were elongated in directions at right 

 angles to each other. As elongation or distortion of the octa- 

 hedron could not produce either of these effects, the conclusion 

 is that the octahedron is composed of plus and minus tetrahe- 

 dra, notwithstanding the fact that all the faces (1) are the same 

 in general appearance. In this combination the edges of the 

 tetrahedron whose faces are more largely developed are replaced 

 by cubic faces. These faces (H) have luster, while the faces (1) 

 have not. 



The distortions occurring in these crystals produce singular 

 effects (figs. 9, 10, 11). In some of the octahedrons, one of the 

 axes will be so much inclined that a crystal is produced decid- 

 edly monoclinic in appearance. In others two axes are inclined, 

 giving a triclinic appearance. Some of the cubes have been dis- 

 torted into prisms apparently tetragonal or orthorhombic. One 

 of the latter (fig. 12) has two of its diagonally opposite angles 

 replaced by large faces (1), and the other angles by very small 

 faces or none at all. In some of the crystals fossils are found 

 (figs. 14, 15, 16, 17), sometimes in the crystal, sometimes on a 

 face, the fossils being composed of limonite. Most of the crys- 

 tals examined were obtained from Col. J. H. Morrison, Adjunct- 

 Professor Chemistry, etc., who has collected them in large 

 numbers. 



Yirginia Military Institute, Jane 12th, 1886. 



Art. XXXII. — Note on the hydro-electric effect of Temper, in case 

 of Steel ; by C. Barus and V. Strouhal.* 



Our original object in writing these papers was that of elu- 

 cidating questions having reference to the carburation of steel 

 from a purely physical standpoint. The reasoning available 

 to the physicist is, however, of an analogical kind, and there- 

 fore as dangerous as it is fascinating. Hence, in view of the 

 time already spent, it seemed to us expedient to endeavor to 



* Communicated with the permission of the Director of the Geological Survey. 



