Page:Popular Science Monthly Volume 53.djvu/739

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ure. . . . In some cases the system has been adopted sparingly and timidly, as if under stress of competition. More often it has been received heartily up to a certain limit." The method of its application has, however, been very diversified, resulting in a great variety of schemes, a considerable number of which are reviewed and analyzed by the author. "No two colleges agree as to what studies are 'essential for all who are candidates for a liberal degree.' As to the working of the elective plan, the author believes that its risks are overestimated." No candid observer of college life can deny that free choice has promoted vital scholarship and hastened the growth of manly judgment in college students. It has revolutionized college teaching by sealing the doom of the lazy instructor. It has steadily extended its conquests, and is pushing its way into more colleges and over wider areas of the college course. That it should stand without important checks few would contend, but that the college student does not often abuse the elective privilege is, in the belief of the author, capable of proof. And a contribution to this proof is made from the records of the author's own college, Colgate University. Professor Bingham regards his study, as a whole, as indicating the sobriety, earnestness, and intelligence of the college man, and has no question that, "for the average man, sound habits of steady endeavor grow best in fields of choice."


By availing himself of the properties of surface tension, M. Charles Henry has discovered a method of producing permanent coloration by the use of light-colors, without the aid of any pigment. Liquids having a superficial tension less than that of water are deposited on water in thin layers, where they reflect the colors of the spectrum. By whistling over this layer we obtain for each tone a vibration which is responded to by a special coloration, and a kind of molecular landscape is produced. The liquid, however, soon evaporates, and the play of colors vanishes. In order to preserve the colors, a fixed excipient is introduced into the liquid, which will retain the thickness of the pellicular layer, and the colors as well, after the essence has evaporated. Some resin or coal-tar substance is used for this, giving permanence to the pellicle and the picture. M. Henry has further devised a process for producing this pellicle and picture upon a solid foundation, as of wood, glass, or paper, and even for accomplishing it by mechanical processes. The nature of the ground in which the picture-pellicle is laid has much to do with its character. Dark grounds give intense colors, white grounds lighter ones, and grounds of intermediate colors various shades. The process is called iri chromatime.

The images left by uranium upon a sensitive plate locked up with it in the dark may be regarded as an effect of the fluorescent property that metal is known to possess. Dr. Russell has, however, described to the Royal Society experiments from which it appears that mercury, zinc, magnesium, cadmium, aluminum, nickel, pewter, bismuth, lead, tin, antimony, and cobalt give out radiations capable of affecting the sensitive plate, and will leave images of themselves after standing upon one in the dark for about a week, although they possess no evident luminosity. Gold, platinum, and iron exhibit little or no power of the kind. A figure scratched upon the polished face of a sheet of zinc repeated itself. The interposition of a coat of varnish between the metal and the plate served to increase the effect, while glass, which makes no difference when uranium is applied, stopped the action with the other metals. Some non-metallic substances, such as straw, wood, charcoal, and printer's ink, presented the same property of leaving images. A section of young larch wood printed its formation clearly on a plate, so that the rings and bark could be made out. In many cases the activity was increased by heating the body, and diminished by cooling it.

A silicified tree is described by Lewis Woolman in the Report of the Geological Survey of New Jersey which lies in the orange-colored sand near Lindenwold in that State. The farmer of the land having regularly plowed up pieces of silicified wood, Mr. Woolman and his friends dug for the