May 22, 1896.] 



SCIENCE. 



787 



strata from the main river ; thus Perm's creek is 

 almost captured by a lougitudiual subsequent 

 stream that enters the Susquehanna at Win- 

 field ; North Mahantaugo creek is likewise 

 nearly diverted by a longitudinal subsequent 

 branch of Middle creek that flows by Freeburg; 

 and perhaps the direct longitudinal course of 

 White Deer creek, further north, may be ex- 

 plained as a return to its normal attitude ; its 

 former southward deflection being suggested by 

 the occurrence of a large nupiber of Medina 

 boulders on the col by which it is now divided 

 from a south-flowing, transverse branch of 

 Buflulo creek. 



Among numerous points of interest noted 

 during the trip may be mentioned : The superb 

 view of the Delaware watergap, deep cut in 

 level-crested Kittatinny mountain, as seen from 

 the edge of Pocono plateau; the monotonous 

 surface of this plateau, over 2,000 feet above 

 tide, nearly stripped of its timber, almost unin- 

 habited, and yielding little more than the win- 

 ter ice crop of its numerous ponds; the alluvial 

 fans, locally known as 'bulges,' formed on the 

 low valley floors beneath various notches in the 

 Medina ridges of the Seven mountains, one fan 

 at Glen Iron having a radius of half a mile and 

 a height of about three hundred feet, now some- 

 what trenched by its stream; the Pocono syn- 

 clinal coves west of the Susquehanna, opposite 

 Millersburg and Dauphin; the long straight 

 boulder-strewn valley floor of Stony creek, 

 east of the Susquehanna between Second and 

 Third mountain, the boulders having crept 

 down from the crests of Pocono and Pottsville 

 sandstone and conglomerate, producing an irre- 

 deemable veneer over the otherwise fertile 

 Mauch Chunk red shales; and the immediate 

 transition from this uninhabitable valley to 

 fertile fields on passing through Fishing creek 

 gap to the more open country between First 

 (Blue) and Second mountain. 

 (2) April recess excursion to Gay Head, Martha's 



Vineyard : By J. B. Woodward. 



T. A. Jaggab, Je., 

 Recording Secretary. 



NEW YORK ACADEMY OF SCIENCES. 



At the meeting of the Section of Astronomy 

 and Physics on May 4th Prof A. M. Mayer 



presented a paper on a heliostat with small 

 mirrors, giving an intense beam of light and 

 forming an image at its focus. It consists in 

 mounting a convex lens so as to concentrate 

 the beam of sunlight upon one surface of a 

 total reflection prism, the lens being mounted 

 to rotate upon a polar axis so as to keep the 

 sunbeam continually upon the mirror. A neg- 

 ative lens near the prism renders the beam 

 parallel again. A second total reflection prism 

 sends the beam in any desired direction. The 

 advantages of this heliostat are a very power- 

 ful beam of light which can be made to emanate 

 practically from a point, and from which the 

 heat rays have been almost entirely absorbed 

 by its passage through the various pieces of 

 glass. It is especially adapted to work with 

 the solar microscope and experiments on the in- 

 terference of light. The paper was discussed 

 by Prof E. S. Woodward. 



The following notes were presented by Mr. 

 Wallace Goold Levison. (1) On photographs 

 of Geissler and Crookes' radiant matter tubes. 



Mr. Levison presented a very interesting 

 sferies of photographs of Geissler and Crookes' 

 tubes taken by their own light. Many of these 

 showed very beautifully the stratification in the 

 Geissler tubes and the difierence between the 

 phenomena at the anode and at the cathode. 

 He also showed a series illustrating the disturb- 

 ances in the stratification produced by plung- 

 ing the cathode to various depths in water. 

 The photographs of the Crookes' tubes showed 

 not only the fluorescent spot opposite the ca- 

 thode, but also very distinctly the pale bundle 

 of cathode rays which are almost invisible to 

 the unaided eye. (2) In this connection Mr. 

 Levison pointed out the resemblance between 

 the succession of colors with varying pressure 

 in Geissler tubes and the color variation in the 

 aurora, and suggested that the experiments de- 

 scribed bore out the idea that the aurora is an 

 electric discharge through the atmosphere at 

 various heights and pressures. A possible con- 

 nection between these phenomena and the 

 solar corona and comets was also pointed out. 



The third note was the description of simple 

 apparatus for obtaining X-ray photographs by 

 long exposure with small (6-inch) induction 

 coil and four Bunsen cells. The fourth note 



