Scientific Serials

Abstract

American Journal of Science, October.—Notes on the Colorado Canyon District, by W. M. Davis. The Kaibab section of the canyon discloses the nearly even floor on which the horizontal Palæozoic strata rest. The floor is of complex structure. The fundamental schists with granitic dikes are overlaid in the eastern section by the heavy Unkar and Chuar series dipping eastward. The wedge in which the tilted formations, terminate westward is a most remarkable geological structure, alike for its distinctness and for its significance.—Determination of minerals in thin rock sections by their maximum birefringence, by L. V. Pirsson and H. H. Robinson. The method described is an adaptation of Michel-Levy's colour diagram. The thickness of the rock section having been determined, the highest colour given in any of the numerous sections of the unknown mineral is observed, and by means of the diagonals the numerical value is noted which corresponds to the given colour in a section of the determined thickness. The maximum birefringence having thus been determined, the table of birefringences is referred to and the mineral usually found to be one of a group of several, among which it is easily distinguished by cleavage, colour and other optical properties. The authors add a table of birefractive powers, ranging from 0.287 (rutile) to 0 001 (chlorite).—Experiments on high electrical resistance, by N. Rood. An electric current travelling along a bad conductor has many analogies to a stream of pitch. It attains the end of the channel after a considerable interval, and if the resistance is very high, the potential at the end remains at zero. The author describes a number of experiments carried out with glass, silk, mica, jade, guttapercha, ebonite, amber and rosin. When glass, silk and mica were connected with one coating of a charged Leyden jar, it was found that within fifteen minutes the part farthest from the jar had assumed its potential. This was not the case with the other substances. Ebonite showed a slight change of the opposite sign at the furthest end, probably due to prolonged inductive action.—New occurrences of corundum in North Carolina, by J. H. Pratt. The new occurrences are in an amphibole schist and a quartz schist respectively.—Products of the explosion of acetylene, and of mixtures of acetylene and nitrogen, by W. G. Mixter. Acetylene and ammonia yield hydrocyanic acid at a much lower temperature than is required to cause nitrogen to combine. It may be that ammonia is the first compound of nitrogen formed in the bomb, but the fact that a little ammonia is found among the products is not conclusive, as that may have resulted from the decomposition of hydrocyanic acid.