98 



SCIENCE. 



[Vol. I., No. 4. 



covering the nortU flank of the Kittatinny Mountain; 

 and a bowlder of limestone perched on the summit, 

 which, within a distance of three miles, had been 

 carried up eight hundred feet of vertical distance. 



Referring to a paper recently published by Mr. W. 

 J. McGee, who found difficulties similar to those of 

 Professor Heilprin in the assumption of a polar ice- 

 cap of great thickness, and who imagined the glacier 

 to increase by additions to its outer rim, Professor 

 Lewis held, that the single fact of the transportation 

 by the glacier of far-travelled bowlders to its terminal 

 moraine was a fatal objection to any such hypothesis. 

 Nor did he believe that the hypothesis adopted by 

 Professor Dana and others, of a great elevation of 

 land in the north, was a probable one. The facts 

 •now in the possession of geologists do not indicate 

 ■such a great and local upheaval as required by that 

 ihypothesis. 



An explanation therefore must still be sought for 

 the southward flow of a continuous ice-sheet, — a 

 flow in some regions up-hill. The action of gravity 

 was certainly not sufficient. Even in the case of the 

 downward flow of the steeply inclined Swiss glaciers, 

 it had been shown that gravity was more than coun- 

 terbalanced by friction of the sides and bottom, and 

 those glaciers moved by reason of an inherent moving 

 power of the molecules of the ice. It was probable 

 that a similar action occurred in the great conti- 

 nental glacier. He suggested, therefore, a hypoth- 

 esis whtch, while preserving the unity of the glacier, 

 as indicated by observed facts, neither assumed an 

 unreasonable land-elevation in polar regions, nor re- 

 quired a thickness of ice so great as to be open to 

 the objections of the last speaker. He suggested 

 that the ice-cap flowed south simply because it flowed 

 toward a source of heat. Such flow does not depend 

 upon gravity, but would occur in a flat field of ice, or 

 possibly even up a slight incline toward a warmer 

 temperature. Upon this hypothesis the ice need not 

 to have been more than a few times its present tliick- 

 ness in Greenland to account for all existing phe- 

 nomena. 



AN EARLY STATEMENT OF THE DE- 

 FLECTIVE EFFECT OF THE EARTH'S 

 ROTATION. 



A coEKECT knowledge of the deflective effect of the 

 earth's rotation on the motion of bodies on its sur- 

 face is generally accounted the result of studies made 

 witlrin the last twenty-five years. First in 1856, and 

 more fully in 1859, Mr. William Ferrel of Nashville, 

 Tenn., now of Washington, made the general state- 

 ment, that, " in whatever direction a body moves on 

 tlie surface of the earth, there is a force arising from 

 the earth's rotation which deflects it to the right in 

 the northern hemisphere, but to the left in the soutli- 

 ern" (Math, monthly, 1859, i. 307); and gave, by a 

 rigorous analytical treatment of the question, a quan- 

 titative measure of this force, showing that it de- 

 pended on the sine of the latitude of the body, but not 

 at all on the direction of its motion. A similar but 

 less comprehensive result was arrived at about the 

 same time by Babinet and others (Comptes rendus, 

 xlix. 1859) ; and since then the subject has been 

 treated by many wi'iters, among whom may be men- 

 tioned Buff, Finger, Guldberg and Mohn, and Sprung. 

 It has, however, also been disputed by some authors, 

 as Bertrand and Benoni, who erroneously hold to the 

 old idea, first suggested by Hadley (1735), and recalled 

 (it would seem independently) by De Luc (1779), Dal- 

 ton (1793), and Dove (1835), that the deflective effect 

 is greatest on motions in the meridian and nothing 



on east-and-west lines ; and this incorrect view is but 

 slowly disappearing from the text-books in general 

 use. 



It is the object of this note to call attention to an 

 early statement of the law of deflection, tliat has 

 never, so far as I can learn, received due credit. In 

 1848 Mr. Charles Tracy, now of New Tork, read a 

 paper ' On the rotary action of storms ' before the 

 Utica (N. T.) society of natural history; this was 

 publislied in the American journal of science (xlv. 

 1843, 65-72), and the paragraphs quoted below are 

 taken from it. It will readily be perceived that this 

 explanation is far in advance of Dove's; although it 

 lacks the consideration of the effect of centrifugal 

 force and of the preservation of areas, to be a full 

 statement of the matter. Mr. Tracy thought, in ac- 

 cordance with Espy's theories, that there must exist 

 "a qualified central tendency of tlie air, in both the 

 general storms and the smaller tornadoes" (p. 67); 

 and in order to develop a uniform rotary movement 

 in tliese centripetal winds, he looked to " the forces 

 generated by the earth's diurnal revolution " (p. 66). 

 In every storm, "the incoming air may be regarded 

 as a succession of rings taken oif tlie surrounding 

 atmosphere, and moving slowly at first, but swifter 

 as they proceed towards the centre." In virtue of 

 the law of deviation, every ring "begins to revolve 

 when far from the centre, turns more and more as 

 it draws near it, and finally as it gathers about the 

 central spot all its forces are resolved into a simple 

 whirl" (p. 69). The law of deviation is illustrated 

 by appropriate figures for the two hemispheres, and 

 is explained as follows. (Its direct application to the 

 tornado and water-spout is probably incorrect, as 

 Mr. Ferrel lias shown.) "The relative motions of 

 the parts of a small circular space on the earth's 

 surface, by reason of the diurnal revolution, are pre- 

 cisely what they would be if the same circular space 

 revolved upon an axis passing through its centre 

 parallel to the axis of the globe. If such space be 

 regarded as a plane revolving about such supposed 

 axis, then the relative motions of its parts are the 

 same as if the plane revolved about its centre upon 

 an axis perpendicular to the plane itself; with this 

 modification, that an entire revolution on the axis 

 perpendicular to the plane would not be accomplished 

 in twenty-four hours. Such plane daily performs 

 such part of a full revolution about such perpendic- 

 ular axis as the sine of the latitude of its centre is 

 of radius. The plane itself — the field over which a 

 storm or a tornado or a water-spout is forming — is in 

 the condition of a whirling table. Hence the tend- 

 ency to rotary action in every quarter of the storm is 

 equal, and all the forces which propel the air toward 

 the centre co-operate in harmony to cause the revolu- 

 tion " (p. 72). The special value of this statement 

 lies in the proof that motions in all directions are 

 deflected equally; but on account of the omissions 

 above named only one-half of the total deflective 

 force is accounted for. W. M. Davis. 



LETTERS TO THE EDITOR. 

 'Mother of petre ' and ' mother of vinegar.' 



Chemists were not a little interested a few years 

 since by the discovery, first announced by Alexander 

 MuUer in Germany, and afterwards by Schloesing 

 and Muntz in France, that the formation of saltpetre 

 in nature, and of other nitric compounds as well, is 

 in some way connected with the presence and action 

 of a living ' ferment,' much in the same way that 

 the formation of alcohol in the brew-house or distil- 



