Page:Popular Science Monthly Volume 52.djvu/588

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its use is attended with no harmful results to the patient. The complete address, with some interesting illustrations, appeared in the American Journal of the Medical Sciences for December, 1897.

Artesian Wells in Iowa.—The artesian field of Iowa is described by Mr. W. H. Norton as being only a part of an extensive basin which may be termed the artesian area of the upper Mississippi Valley. It includes a part of Missouri, a large part of Illinois, southern Wisconsin, and southern Minnesota. The intake of the whole field lies in the two States last mentioned. The size of the intake area is roughly estimated at about fourteen thousand five hundred square miles. With the whole Iowa field, it lies within a region of abundant rains, enjoying a mean annual rainfall of not less than thirty-two or thirty-three inches. On the basis of De Rance's estimate that one inch of rainfall per year is equivalent to 14,555,280 imperial gallons to the square mile, or a daily average of 40,000 gallons to the mile, the total annual rainfall of the collecting area of the Iowa artesian field may be estimated at about 475,000,000 gallons to the square mile, a daily average of 1,280,000 gallons or a total annual precipitation for the entire collecting area of 6,887,500,000,000 gallons. Only what of this water does not go into the streams and escape by evaporation is available for the artesian reservoir, but there is every reason for believing that that which falls over the collecting area is more than sufficient to meet all the demands made upon it by the Iowa wells.

Submarine Land Slides and Telegraphic Cables.—While the general result of denudation on the land is to bring material to a lower level, and, by gradually wearing away excrescences like mountain heights, to render such forms more stable, beneath the sea, as Prof. John Milne pointed out at the British Association, such materials are accumulated in slopes, which become unstable as the deposits grow, and facial slidings take place from time to time. The movements are caused by gravity, by subterranean springs, and by submarine earthquakes, the effects of which are at least equal to those we see produced on land, and probably greater. These slidings, occurring along the edges of submarine banks and of the submerged continental frontier, are very damaging to telegraphic cables, which are apparently buried under large bodies of material. Sometimes two or three cables, ten or fifteen miles apart, have been destroyed by such slides. Earthquakes have been felt on land at the same moment that a cable has been broken, and the ocean has been thrown into a state of agitation for one or two days. Under very great disturbances of this kind the resultant earth movement might be recorded, with suitable instruments, at any point on the surface of the globe. In the most remarkable disturbances recorded, changes of depth up to two hundred fathoms have taken place over considerable areas. The study of these dislocations should be established on all the continents and oceanic islands.

School Sessions and Health.—In order to obtain a consensus of opinion on the subject, eight questions bearing upon the influence of our school system on the health and development of the child were addressed by Dr. E. Stuver, of Rawlins, Wyoming, to about one hundred and fifty educators and physicians of the country. Twenty-nine out of sixty-three educators and thirty out of thirty-five physicians did not think our present comprehensive course of study best calculated to develop the highest physical and intellectual powers of the child, and some of the respondents condemned these courses severely. Eighteen educators and one physician were doubtful. Respecting the proper length of continuous school sessions, the average of one hundred opinions were in favor of not longer than one hour or an hour and a half. While considerable divergence appeared concerning the limit of length of a single recitation, the majority of respondents advocated from ten to twenty minutes in the primary and from twenty to thirty minutes in the grammar grades; but much was thought to depend upon the nature of the subject of the lesson, the method of instruction, and the kind of teacher. Frequent recesses met much favor, and many respondents advised one every hour. Of one hundred and five opinions expressed as to the relative merits of open-air recesses with spontaneous play and of formal indoor exercises, all except