JANUAKY 13, 1911] 



SCIENCE 



75 



following list were read by the authors during 

 the three sessions of Section A. 



1. " The Relations between Jupiter and the 

 Asteroids" (vice-presidential address), E. W. 

 Brown. 



2. " The Contributions of Astronomy to Mathe- 

 matics," F. R. Moulton. 



3. " On some possible Bases for the Spectral 

 Classification of Stars," B. B. Frost. 



4. " Apparent Photographic Star-streams and 

 their Relations to some of the Vacant Regions of 

 the Sky," E. E. Barnard. 



5. " Photographic Observations of the Surface 

 of the Planet Mars," B. E. Barnard. 



6. " An Integrable Case in the Problem of three 

 Bodies," W. D. MacMillan. 



7. " Photographic Position of 127 Stars within 

 Ten Minutes of the Ring Nebula of Lyra," F. P. 

 Leavenworth. 



8. " Preliminary Report on the Evidences of 

 Circulation in the Atmosphere of the Sun, Derived 

 from the Study of Solar Prominences," Frederick 

 Slocum. 



9. " On the Choice of Standard Stars in Photo- 

 graphic Stellar Photometry," J. A. Parkhurst. 



10. " The Oblateness of the Earth," J. E. Siebel. 



11. "Dials for Calculations," H. E. Wetherill. 



12. " Parallax of Ring Nebula of Lyra from 

 Photographs taken at the Lick Observatory," B. 

 L. Newkirk. 



13. " Spectrum of Ring Nebula of Lyra," K. 

 Burns. 



14. " The Sun as a Star," Percival Lowell. 



The addresses by E. W. Brown and F. R. Moul- 

 ton will appear in Science. Abstracts of the 

 other papers follow, the numbers preceding these 

 abstracts correspond to the titles in the list given 

 above. 



3. There are numerous possibilities in the selec- 

 tion of a basis for the establishment of a system 

 of stellar classification according to spectra. 

 Emphasis may be laid upon the differences of a 

 physical sort between stars, such as temperature, 

 as inferred from the extension of the spectrum 

 toward the violet, or from measurements of the 

 radiation at different wave-lengths or differences 

 of a chemical sort may be made the criterion, 

 according to the elements found in the spectra. 

 Again, theoretical reasons based upon the dynam- 

 ics of the case may be regarded as especially 

 important; or deductions from some hypothesis 

 of stellar evolution may be considered as the most 

 logical basis for discrimination. Even the mo- 

 tions of the stars, or the space within which they 



are found, may have a bearing upon the subject, 

 as, for instance, in the case of the streams of 

 stars recently discovered and lately much dis- 

 cussed. 



The paper gives a brief general discussion of 

 some of these points, with lantern illustrations 

 of different celestial spectra. 



4. There are frequently seen, on wide field pho- 

 tographs of the sky, lines of stars either straight 

 or curved, and sometimes in the form of more or 

 less complete ellipses with a brighter star iu a 

 focus of the ellipse. It is probable that most of 

 these stars are not physically connected, and 

 appear so only by perspective. But it does not 

 seem probable that all these appearances are due 

 to fortuitous circumstances alone. 



Besides these lines and curves of stars, so 

 striking in some parts of the sky, there are ap- 

 parently broad streams of stars which seem to 

 have a common trend. This appearance usually 

 occurs in a very dense region, and resembles that 

 which might be produced by the sweep of a giant 

 broom. In some cases these " sweeps " are ap- 

 parently connected with vacant regions, as if 

 there were a common drift of the stars away from 

 these places. A striking case of this kind occurs 

 in Scutum, where the appearance is that of 

 streams of stars diverging away from or converg- 

 ing to a vacant region at this point. 



5. During the opposition of Mars in 1909 ef- 

 forts were made to secure photographs of its sur- 

 face features with the 40-inch refractor and a 

 negative enlarging lens made by Brashear. For 

 this purpose a yellow color screen, made espe- 

 cially for the work by Mr. Wallace, with Cramer 

 instantaneous isochromatic plates, was used. 

 Though the exposures were short (three or four 

 seconds), it was found necessary to guide on the 

 planet during the exposure. In the eyepiece of 

 the long- focus (61 J feet) guiding telescope two 

 cross-wires (spider threads) were inserted. In 

 making the photographs the polar cap of the 

 planet was bisected by these cross-lines, and the 

 telescope held firmly in this position by pressure 

 exerted at the eye-end of the 40-inch. The cross 

 wires are on a perforated strip of sheet brass 

 (with an opening a couple of inches in diameter) 

 that can be shoved back and forth through a slit 

 in the adapter carrying the eyepiece. It is also 

 arranged to move in position angle. 



For photographing Jupiter and Saturn, where 

 there is nothing definite to guide on, the inter- 

 section of the wires can be made to bisect a 

 satellite, after the image of the planet has been 



