Page:Popular Science Monthly Volume 21.djvu/881

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diate of Arkansas and Tennessee to that of New Jersey. A radius of from 18° to 24° takes in the marine tertiaries of the East and the West; one of 24° marks the main outlines of the continent; while one of 36° takes in the extreme points of the continent in all directions. The rule is applied with almost literal similarity to the other continents. Professor Owen furthermore maintains that the western Alps became a dynamic focus at about the beginning of the Cenozoic period, and that Monte Rosa is nearly the center of the dry land of the globe, whence a great circle of immense seismic activity may be traced nearly parallel with the Asiatic continental trend to the Himalayas and thence around to the Andes and the South American earthquake-region. Another great circle is nearly parallel to the North American trend, and includes the volcanoes of Central America and the geysers of Iceland, and incloses and probably aids to heat our Gulf Stream.

Value of Disinfectants.—Dr. George M. Sternberg, surgeon in the United States Army, has reported upon the results of experiments he has made with various disinfectants and vaccine virus, the conclusion drawn from which is that chlorine, nitrous acid (nitrogen dioxide), and sulphurous acid (sulphur dioxide), are reliable disinfectants in the proportion of one volume to one hundred volumes of air. Probably a considerably smaller proportion of these disinfectants would be efficient in destroying the potency of thin layers of virus in a moist state, or of virus exposed to the action of the disinfectant in an atmosphere saturated with moisture. Experiments with carbolic acid, on the other hand, "show that the popular idea, shared perhaps by some physicians, that an odor of carbolic acid in the sick-room or foul privy is evidence that the place is disinfected, is entirely fallacious, and, in fact, that the use of this agent as a volatile agent is impracticable, because of the expense of the pure acid and the enormous quantity required to produce the desired result."

A Selenium Photometer.—M. Léon Vidal has devised a photometric apparatus of selenium, for measuring the intensity of natural or artificial light by means of an action purely physical and mechanical, and in a manner analogous to that by which we measure the temperature and the amount of atmospheric pressure with the thermometer and the barometer. The difference in conductibility which results from the action of light on selenium produces deviations in the needle of the galvanometer which correspond in extent with the intensity of the luminous source. In this manner we may determine, at a glance, the intensity of light at any instant. The principle is applied to the construction of meteorological photometers, for which elements of selenium of equivalent conductibility are provided, to be substituted for each other as their molecular condition becomes modified; the plates may be restored to their normal condition by heating them, and used again. This instrument may be employed for the rapid and visible record of the instantaneous changes in luminous intensity, at all heights and depths, the observer reading the indications of the galvanometer at the place which may be most convenient for him.


The American Public Health Association will hold its tenth annual session at Indianapolis, Indiana, October 17th to 25th. Papers will be presented on the different action of disease in the white and black races, the removal of excreta, heredity, sanitary associations, vaccination, intermittent fever in New England, sanitary organization, cattle-disease, etc., etc., with reports of committees on the prevention of venereal disease, compulsory vaccination, the management of epidemics, statistics, cattle-diseases, National Museum of Hygiene, incorporation of the Association, and necrology.

The American School of Classical Studies at Athens, Greece, under the direction of a committee of the Archæological Institute of America, is to be opened on the 2d of October. Its object is to promote the study of classical literature, art, and antiquities, by graduates of American colleges, and to prosecute and aid original and co-operative research in those subjects. The school is open, free of fees, to bachelors of arts, properly recommended from co-operating colleges. Nine colleges in New England, New York, New Jersey, and Baltimore, have contributed annual subscriptions of $2,250, most of them for ten years, in aid of the school.