DBCEMBBB28, 1900.] 



SCIENCE 



1007 



tan Island retains more or less structural evi- 

 dence of having begun its existence as a vein, 

 segregated from a magma or igneo-aqueous 

 emulsion. Even the notable dike near 205th 

 Street, crossing the dolomite, retains the vein 

 structure, perfectly in places and imperfectly 

 throughout. 



3. Contact phenomena are confined mainly 

 to the earlier alteration along seams, to projec- 

 tion of veinlets rather than intrusion pophyses, 

 and, at one dolomite intersection, to a thin sel- 

 vage of phlogopite and tremolite. 



4. The vein structure presents distinct lami- 

 nation, correspondent deposits on the two walls, 

 comb structure, passage from less to more acid 

 minerals toward the center, and final concen- 

 tration of minerals of the rarer elements in 

 association with the significant matrix, smoky 

 quartz, along lenticular bands, often near a 

 central suture. 



5. Some of the most prominent features are 

 the results of pressure upon the original veins 

 through erogenic movements of the stratum of 

 schists, viz., fissuring, faulting, crushing, shear- 

 ing with development of aplite, refusion and 

 development of new phenocrysts (granite-por- 

 phyry), and generation of reaction borders out- 

 side of each wall of a vein. Where fiowage 

 has taken place and some transferrence of the 

 crushed vein material along the plane of the 

 vein, the appearances of a dike begin. Many 

 of these results may be distinguished along the 

 course of the same vein at short intervals, but 

 in the most characteristic dikes the vein struc- 

 ture is rarely, if ever, completely obliterated. 



Theodore G. White, 



Secretary. 



SECTION OF ASTRONOMY, PHYSICS AND CHEM- 

 ISTRY. 



A MEETING of the Section was held at 12 West 

 31st Street, New York, on the evening of De- 

 cember 3, 1900. 



Professor E. E. von Nardroff presented a 

 paper with an experimental illustration, on 'The 

 Determination of the Wave-Length of Sound by 

 the Grating Method.' As a source of sound the 

 author used a miniature steam whistle made of 

 brass and operated by a current of air from a 

 tank of compressed air. The sound produced 



in this way was inaudible on account of its high 

 pitch, the wave length being only about three- 

 eighths of an inch. The whistle was placed at 

 one of the conjugate foci of a parabolic metallic 

 mirror, a sensitive flame being placed at the 

 other conjugate focug. A transmission grating 

 made of wood, and resembling somewhat a 

 portion of a picket fence, was then interposed 

 in the path of the reflected sound waves, and it 

 was found that when the sensitive flame was 

 shifted to one side, as many as four positions of 

 maximum effect were obtained on each side of 

 the central direct beam of sound. With this 

 apparatus, the wave-length of sound, when the 

 waves were short like those used, could be 

 measured to within one per cent. 



Mr. W. G. Levison read a paper on ' A 

 Method of Photographing the Entire Corona on 

 One Plate,' employed at Newberry, S. C, for 

 the total solar eclipse of May 28, 1900. The 

 method consisted in the employment of a 

 specially constructed color screen most dense 

 at the center and fading off to clear glass at the 

 edges, which was placed close to the photo- 

 graphic plate. The size and density of the 

 screen were adjusted as nearly as possible so 

 that the image of the inner corona made by a 

 suitable lens fell on the part of the plate cov- 

 ered by the screen, while the image of the outer 

 corona passed through the clear glass. The 

 color screen was made from a lens of colored 

 glass with sharp edges which was cemented into 

 a recess in a plate of clear glass, ground to re- 

 ceive it. Two screens were made, one of orange- 

 yellow glass and one of dark greenish-blue 

 glass. In testing these screens at the time of 

 the eclipse, an arrangement of telephoto-lenses 

 was used, but unfortunately the exposure was 

 not long enough to give any image at all of the 

 outer corona through the clear glass, although 

 a considerable impression of the inner corona 

 was produced through the orange-yellow glass, 

 but none through the bluish-green glass. This 

 should give some idea of the relative actino- 

 metric intensity of the light from the inner and 

 from the outer corona. 



Mr. Levison also presented a short note on 

 ' The Action of Canada Balsam on Photographic 

 Plates.' In making the experiments with the 

 color screens he noticed that Canada balsam 



