Page:Popular Science Monthly Volume 24.djvu/586

570 Electrical Directory and Advertiser: British, American, and Continental. By J. A. Berly. New York: George Gumming. Pp. 664. $2.50.

Tertiary History of the Grand Canon District. By Clarence E. Dutton. Washington: Government Printing-Office. Pp. 264, with an Atlas containing Twenty large Plates and Panoramas.



The Ice Age.—At a meeting of the Academy of Natural Sciences of Philadelphia, Professor Heilprin advanced the opinion that the enormous sheet of ice which extended over a large portion of North America and Europe during the Glacial period could not have originated from a polar "icecap." He deemed it doubtful that there could have accumulated in the Arctic regions sufficient snow and ice to propel a glacier probably several thousand feet thick over hundreds of miles, and up slopes to heights of five or six thousand feet. Precipitation in polar regions takes place mainly in a low atmospheric zone; hence it would be impossible for so great a mass of snow to accumulate at so great an elevation as would be necessary to propel southward a glacier of the extent required by geologists. Professor Lewis called attention to a point observed some time ago by Dr. Hayes, but not yet sufficiently appreciated, namely, that the rate of increase in the thickness of the glacier diminished northward. Recent observations of his own showed the glacier to have been 800 feet thick five miles from its southern limit, and 2,030 feet thick at a point eight miles from its edge, while it was only about 3,100 feet in thickness at a distance of 100 miles, and 5,000 feet at 300 miles from its termination. Rejecting several hypotheses, Professor Lewis suggested that the ice-cap flowed south simply because it flowed toward a source of heat. Such a motion not being caused by gravity, would take place in a nearly flat field of ice, and upon his supposition the ice need not have been more than a few times its present thickness in Greenland. Professor Heilprin replied that no laws of glacial action were known which would account for the indiscriminate progression of an ice-sheet toward a source of heat, and that the molecular expansion theory, as applied to the Alpine glaciers, took no cognizance of the direction of the heat-power, but merely of that of least resistance (the trend of the slope). At a subsequent meeting he supported his views previously communicated by statistics of precipitation at different elevations on the Alps, and presented some curious calculations in regard to the rate of progression of the great ice-sheet. Allowing for it the average rate of the Alpine glaciers, one foot a day, it would have required a period of no less than 25,000 years to move from the sixty-fifth parallel of latitude to the line of its terminal moraine. But it may well be questioned if the conditions allowed progression at more than one fifth of this rate. Professor Lewis remarked that arguments, drawn from meteorological conditions as they now exist, will not in all cases apply in considering the Glacial epoch. He further suggested a probable analogy between the Antarctic ice-cap, some 25,000 miles in diameter, and the polar ice-cap of glacial times, and mentioned Croll's estimate that the former is twelve miles thick at its center. In speaking of a polar ice-cap, he did not mean to imply, however, that the ice was necessarily thickest on the pole, but that in Greenland, Labrador, the Hudson Bay region, or elsewhere, there may have been centers from which glaciers grew finally to coalesce into one mass of ice, the top strata of which flowed southward to the great terminal moraine.

Effect of Watering Plants with Acids.—Mr. L. P. Gratacap, of New York city, has published a report of experiments he has made to determine the effect of watering with solutions of acids upon plants. He experimented upon the silver-leaved geranium with hydrochloric, nitric, carbolic, formic, salicylic, sulphuric, tartaric, and citric acids, and water. The plants watered with the first six acids except salicylic were unfavorably affected from the first day of the experiment. From June 22d to September 6th none of the plants died except the carbolic-acid plant, although the nitric-acid plant succumbed shortly after the experiment terminated. Of the rest the sulphuric-acid plant was most thriving, then the hydrochloric-acid plant, and last, and just alive, the plant treated with formic acid. Analyses of the ashes of the plants showed that the acid waters tended to introduce 