Page:Popular Science Monthly Volume 34.djvu/589

Rh noticed with the naked eye. When the mirror is cast, the cooling process has the effect of drawing it slightly out of shape, and the impress of the ornamentation on the back of the disk gives a practically indistinguishable variation in convexity on the smooth surface that is only noticed when the reflection is cast upon a screen. The mirrors are not made for the "magic" purpose. They are ordinary mirrors, whose magic properties are the result of chance, and not more than one in a thousand possesses them. The author conceives an application of the principle of these mirrors to the realization of the idea of seeing by telegraph, and suggests that, by the use of electro-magnets and selenium, a metal peculiarly sensitive to light-rays, it might be possible to transfer over hundreds or thousands of miles the reflection of letters, or even faces.

Effects of Tile-Draining.—The influence of tile-draining in flood and drought was thus presented by Prof. R. C. Kedzie, in a paper read at the American Association: "1. Surface ditching in conjunction with deforesting may increase floods and contribute to droughts. 2. Tile-draining may increase floods at the "break-up" in the spring, where the waters accumulated in the surface-soil by joint action of frost and soil capillarity during the winter and surface accumulation in form of snow are suddenly set free by a rapid thaw. 3. During the warm months tile-draining tends to mitigate floods by taking up the excessive rainfall and holding it in capillary form, keeping back the sudden flow that would pass over the surface of the soil if not absorbed by it and escape by flood; and also in mitigating summer drought by increasing the capacity of the soil to hold water in capillary form and draw upon the subsoil water-supply by reason of the increasing capillary power of such soil produced by tile-draining."

International Congress of Hydrology and Climatology.—The second triennial session of the International Congress of Hydrology and Climatology is to be held in Paris near the beginning of October, 1889. The President of the Committee on Organization is M. E. Renou, director of the Meteorological Observatory of the Pare de Saint-Maur. The committee has already arranged that the following questions, among others, shall be discussed: Conditions to be observed in the installation of a meteorological observatory; rules for weather-forecasting, and organization of weather-announcements at sanitary stations; climatology of different sanitary stations; comparison and classification of sanitary stations from the point of view of their climatological conditions; on the action of altitude and climates in affections of the lungs; programme of a course of instruction in climatology. Communications should be addressed to the secretary-general, M. Dr. de Rause, Paris, 53 Avenue Montaigne, from the 1st of October to the 1st of June, and at Neris (Allier), from the 1st of June to the 1st of October.

Mineral Evolution.—Dr. T. Sterry Hunt has asserted that "the transformation of the primitive igneous material of this earth's crust through the action of air and water, aided by internal heat, presents a mineralogical evolution not less regular, constant, and definite in its results than the evolution apparent in the organic kingdoms." Continuing the discussion of this subject in the British Association, he shows that the stability of silicated species under atmospheric influence is very variable, some being readily decomposed, and others very permanent; the indifference or chemical resistance, moreover, increasing with the hardness or mechanical resistance. "These two qualities vary for species of analogous constitution directly as their condensation; while, for species of similar condensation and hardness, the chemical indifference increases as alumina takes the place of the ordinary protoxide base, lime, magnesia, ferrous oxide, and alkalies—a fact readily explained by the comparative insolubility of alumina and aluminous silicates in atmospheric waters." Other changes less well known take place in silicates by the subterranean action of watery solutions, when a greater insolubility determines the formation of certain softer hydrated magnesian and aluminous species by epigenesis from harder and more condensed species, Mr. E. A. Ridsdale has spoken of the production and conservation of more stable species as described by Dr. Hunt as a gradual "selection of inert forms,"