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Page:Popular Science Monthly Volume 29.djvu/366

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that is wanted, which is dependent upon a very well-defined minimum thickness of the coating. In this is involved a question of interference-colors, the same as is involved in soap-bubbles and the temper-colors of steel, in which there must be an exact difference in the wave-lengths of the light reflected from the upper and lower surfaces of the coating. Many colors, like steel-green, require repeated trials to be brought out in their full beauty. The advance that has been made in this art has been illustrated to me in a specimen-sheet of beads which are designed to make trimmings exactly corresponding in color for silks of a very great variety of shades.

In addition to the glass industry, a very extensive interest has been developed in the manufacture of brass, bronze, pinchbeck, etc., in which use is made of various galvanic coatings of metal. These branches of the art are carefully taught in the industrial school at Gablonz.—Translated for the Popular Science Monthly from Unsere Zeit.


By C. B. WARRING, Ph. D.

THE peculiar climate of geological times has hitherto been treated as if it were a question of temperature only. Scientists have sought the cause of the remarkable warmth in arctic regions, but have left untouched other questions of equal and perhaps greater importance.

One can hardly contemplate the climatic conditions of that remote period without inquiring how there could be other than a great difference of temperature between the summers and winters of lands less than 8° from the pole; and how could circumstances—environments—so unlike as the four or five months of day of those regions, and the twelve-hour day of the tropics, fail to induce great specific differences in their fauna and flora. The questions spontaneously arise: Is it possible that the days and nights in high latitudes were then as they are now? Must not the climate have been warm in January as well as in July? Must not the influences of the solar rays—the actinic force—have been distributed through the year with at least approximate uniformity in high as well as low latitudes? It is these questions, as well as those of temperature, that I shall consider in this paper. I propose to study the record left by the plants and animals which lived in those remote days. Some of their more obvious teachings are startling enough. Regions where now vegetation is of the scantiest character, where no trees exist save a few dwarf willows, where the winters are cold almost beyond endurance, were, as late as

  1. Read before the New York Academy of Science.