570 



THE POPULAR SCIENCE MONTHLY. 



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. 



POPULAR MISCELLANY. 



The Ice Age. At a meeting of tbe 

 Academy of Natural Sciences of Philadel- 

 phia, Professor Heiiprin advanced the opin- 

 ion 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 po- 

 lar "ice-cap." 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. Pre- 

 cipitation 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. Haye3, but 

 not yet sufficiently appreciated, namely, that 

 the rate of increase in the thickness of the 

 glacier diminished northward. Recent ob- 

 servations 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 dis- 

 tance of 100 miles, and 5,000 feet at 300 

 miles from its termination. Rejecting sev- 

 eral 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 Ileilprin 

 replied that no laws of glacial action were 

 known which would account for the indis- 

 criminate 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 calcu- 

 lations 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 progres- 

 sion 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 di- 

 ameter, and the polar ice-cap of glacial 

 times, and mentioned Croll's estimate that 

 the former is twelve miles thick at its cen- 

 ter. 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 final- 

 ly 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 ex- 

 perimented 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 unfavor- 

 ably affected from the first day of the ex- 

 periment. From June 22d to September 

 6th none of the plants died except the car- 

 bolic-acid plant, although the nitric-acid 

 plant succumbed shortly after the experi- 

 ment terminated. Of the rest the sulphuric- 

 acid plant was most thriving, then the hy- 

 drochloric-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 in- 



