Page:Popular Science Monthly Volume 30.djvu/297

Rh Ohio, Indiana, the greater part of Michigan, Northern Illinois, Eastern and Northern Wisconsin, Northern Minnesota, North-Central Iowa, Eastern Dakota, and many parts of Canada. Of valley drift, attention was directed to the moraine-headed valley trains, and the loess tracts. The former show progressively coarser material toward their origin, and merge into expanded heads, blending with the moraines in which they begin. The broad tracts of fine silt, designated "loess," occupy the Mississippi up to East-Central Minnesota, the Missouri up to Southern Dakota, the Illinois and Wabash up to their great bends, and the Ohio up to Southeastern Indiana. Two other assorted deposits considered were those overspreading the great basin of the St. Lawrence and the Winnipeg basin. These often present, among their surest credentials, overflow channels to the southward, crossing divides sometimes hundreds of feet above existing outlets, and varying in altitude among themselves at least two thousand feet.

Durability of Water-Color Drawings.—A controversy, which recently arose in England on the durability of water-color drawings, led to an exhibition of pictures at which visitors were given opportunity to test for themselves the capacity of the specimens shown to hold their colors. The "Saturday Review" draws from the average of the works the conclusions that, in pictures or passages of especially vivid color, little in the way of fading need be apprehended; but, in the delicate, broad, and thin washes of the landscape-painter, "changes of various kinds are apt to take place, capriciously, as it would seem, and from various causes, of which long and continued exposure to light is probably one. Pending more accurate experiments, collectors and managers of public institutions will do well to keep their framed drawings rigorously protected from pure sunlight, and not exposed more constantly than is necessary to ordinary daylight; for which purpose they should be covered with blinds or curtains during the long hours of the summer mornings, and generally when the rooms in which they are hung are disused. Also it will probably be well to vary from time to time the drawings exhibited, and to return each occasionally for a period of rest to the drawer or cabinet. But on the question of frames versus portfolios, it has to be remembered that a well-framed drawing is secure at least from effects of atmosphere; while in portfolios it is only by extreme and constant care that risks can be avoided from dust and rubbing."

Marine Signals.—Sir James Douglass addressed the Section of Mechanical Science of the British Association on lighthouses and marine signals. There are at present not less than eighty-six distinctive characters in use throughout the lighthouses and light-vessels of the world; and as their numbers increase so does the necessity for giving a more clearly distinctive character to each light over certain definite ranges of coast. This important question of affording to each light complete distinctive individuality is receiving the attention of lighthouse authorities at home and abroad, and it is hoped that greater uniformity and consequent benefit to the mariner will result. There are now about seven hundred fog-signals, of various descriptions, on the coasts of the world; and their construction and operation have been the subject of careful experiment and scientific research. Unfortunately, the results thus far have not been so satisfactory as could be desired. This is owing partly to the very short range of the most powerful of the signals under occasional unfavorable conditions of the atmosphere during fog, and partly to the present want of reliable tests for enabling the mariner to determine at any time how far the atmospheric conditions are against him in listening for the signal. The question of utilizing lighthouses and light-vessels as signal-stations in telegraphic communication with each other and with a central station, has received the consideration of lighthouse authorities generally, and has been made of practical effect in Canada. Buoys are illuminated with compressed oil-gas; and automatic lighting apparatus has been applied to those in occasionally inaccessible positions. A comparative test of the merits of electricity, gas, and mineral oil, as lighthouse illuminants, carried on for twelve months, has given the