392 



SCIENCE. 



[Vol. II., No. 33. 



HI. Relative level of the land and sea. 



I have examined carefully along southern 

 New England for proofs of the quaternarj' 

 submergence which the iceberg theory' assumes 

 to have existed in the glacial era. I thought 

 at one time that I saw evidence about New 

 Haven of a submergence of 45 to 50 feet. But 

 the terrace that afforded the evidence was 

 situated six miles back from Long Island 

 Sound, adjoining the rivers ; and on further 

 examination I found that the deposits had 

 precisely the structure of those along the river- 

 valle3-s farther north, and that, in fact, the}' 

 were nothing but fluvial formations. The 

 highest terraces on or near the shores of the 

 sound, in the vicinity of New 

 Haven, have a height above 

 mean tide of 23 to 26 feet ; 

 and on Milford bay, nine 

 miles west, a similarlj' situ- 

 ated terrace has a height of 

 30 to 33 feet. Along the 

 hills facing the waters, and 

 the southern extremitj' of 

 the valle3's, no traces of an}' 

 higher level exist. Twent\'- 

 five to thirtj'-five feet is the 

 greatest amount of submer- 

 gence the facts sustain. Sea- 

 border deposits exist at a 

 higher level on the coast of 

 Maine and on the shores of 

 the St. Lawrence, and show 

 what was the position of the 

 shore-line in those regions. 

 But the level along southern 

 New England is not proved 

 bj' the facts there gathered, 

 neither is it established by 

 the demands of the iceberg theorj-. 



In conclusion, if icebergs, or floating masses 

 of ice, were not capable of covering with 

 scratches great continuous areas, and would 

 have had a chance for little rock-abrasion on 

 account of the covering of detritus ; if they 

 could not have made, in their hitching and 

 swinging way of action, when touching bottom, 

 scratches over great areas, that had the even 

 course and parallelism characterizing those of 

 drift regions, or could not have ploughed out 

 the deep furrows ; if thej' could jiot have gath- 

 ered the great bowlders for transportation ; 

 and if the sea along the sound did not cover 

 the land, in anj' part of the era of ice, to a 

 greater depth than 30 or 35 feet, — the iceberg 

 theory of the drift ma}' be reasonably pro- 

 nounced unsatisfactory for southern New Eng- 



land ; and similar facts show tliat it is equally 

 unsatisfactory for the rest of New England. 



James D. Dana. 



THE MAGNETOPHONE.^ 



The experiments of Bell,'- Preece,^ Merca- 

 dier,'' and others on the radiophone, suggested 

 to me the possibility of interrupting, or at 

 least periodically modifying, the lines of force 

 proceeding from the poles of a magnet, by 

 means of a disc of sheet iron, perforated with 

 a series of equidistant holes, and rotated so 

 that the holes should pass directly in front of 

 the magnetic pole. It is well known that an 

 armature, placed on the poles of a permanent 

 magnet, diminishes the 

 strength of the external field 

 of force by furnishing supe- 

 rior facilities for the forma- 

 tion of polarized chains of 

 particles from pole to pole. 

 This is the case even when 

 the armature does not touch 

 the poles, but is in close 

 proximity to them. 



If a piece of sheet iron be 

 placed over the poles of a 

 magnet without touching, 

 and the magnetic curves be 

 developed on paper above 

 the iron, they will be found 

 to exhibit less intense and 

 less sharply defined mag- 

 netic action than when the 

 sheet iron is removed. If, 

 however, a small hole be 

 drilled directly over each 

 magnetic pole, the screen- 

 ing action of the sheet iron 

 is modified in much the same way as when 

 a hole is made in a screen opaque to light ; 

 for the developed curves show distinctly the 

 outline of the holes. If, therefore, the sheet 

 iron in the form of a circular plate, pierced 

 with a number of holes, be rapidly rotated 

 between the pole of a magnet and a small 

 induction bobbin, the action of the magnet 

 on the core of the bobbin will be periodi- 

 cally modified because of the passing holes ; 

 and hence induced currents will flow through 

 a circuit including the bobbin. A disc of sheet 

 iron was pierced with two circles of quarter- 



^ Read at the Minneapolis meeting of the American assooia* 

 tion for the advaneement of science. 



- Proceedings Ainer. assoc. adv. sci., sxix. 115. Smithsonian 

 misc. col., XXV. 143. 



■' Proifeedines Uoyal society, xxxi. 506. 



* Journ. phys. x. 53. 



