56 



ASTRONOMICAL PROGRESS AND DISCOVERY. 



inences has been constant. The prominences 

 had decreased in number. The heights of the 

 largest prominences were much diminished. 

 Some preliminary investigations in- regard to 

 the surface-currents of the sun seem to indi- 

 cate: 1. That the direction at the poles is gen- 

 erally vertical to the limb ; 2. That there is a 

 decided current crossing the equator, some- 

 times in a northerly, and at other times in the 

 southerly direction ; 3. That changes of direc- 

 tion occur most frequently in mid latitudes. 



Spectroscopy. Prof. Griinwald, of Prague, 

 has propounded a theory, according to which 

 the wave-lengths of the lines due to a certain 

 element in a given compound are to the wave- 

 lengths due to that same element, when the 

 first compound is combined with some further 

 body, as the volume the element occupies in 

 the first case is to the volume it occupies in 

 the second. Examining the low temperature 

 spectrum of hydrogen, he finds that the wave- 

 lengths of its several lines are just double 

 those of the lines of the water spectrum, line 

 for line. Similar, but less simple relationships 

 are given for other spectra, and Prof. Griin- 

 wald concludes from them that hydrogen and 

 oxygen are compound bodies, and are dissoci- 

 ated in the sun. Hydrogen is inferred to have 

 a composition of the form A 4 b ; of which the 

 supposed element A is associated with the line 

 of the corona 1474 K ; and b with the ' helium ' 

 line D 3 . Louis Bell, Fellow of Johns Hopkins 

 University, has given, in the " American Jour- 

 nal of Science," a paper describing his careful 

 determination of the wave-lengths of the Da line 

 of sodium. The result is to increase slightly 

 Thalen's correction of Angstrom's value, the 

 wave-length finally adopted being 5,896-08 

 tenth-metres. Prof. Rowland has followed 

 this with a table of the relative wave-lengths 

 of about 450 standard lines, based upon the 

 above determination, and designed to be used 

 in connection with his photographic map of 

 the normal spectrum. R. Copeland considers 

 that he has discovered a line in the spectrum 

 of the Great Nebula of Orion corresponding to 

 the place of D s . He remarks that "the oc- 

 currence of this line in the spectrum of a neb- 

 ula is of great interest, as affording another 

 connecting link between gaseous nebulae and 

 the sun and stars with bright-line spectra, es- 

 pecially with that remarkable class of stars of 

 which the first examples were detected by 

 MM. Wolf and Rayet in the constellation of 

 Cygnus." The Astronomer Royal of England, 

 at the January, 1888, meeting of the Royal 

 Astronomical Society, called special attention 

 to two points of interest in the spectroscopic 

 determinations of the motions of stars in the 

 line of sight. One point referred to the mo- 

 tion of Sirius. This star has shown a complete 

 reversal of motion since Dr. Huggins's first re- 

 sults. In 1868, Dr. Huggins found the motion 

 to be 29 miles a second receding from the earth ; 

 in 1872, 18 to 22 miles a second. The Green- 

 wich observations in 1875-'76, showed a mo- 



tion of 24 miles a second. Subsequent years 

 gave the following result: 1876-'77, 12 miles; 

 1877-'78, 23 miles; 1879-'80, 15 miles; 1880-'81, 

 11 miles; 1881-'82, 2 miles; thus showing a 

 decreasing recessional motion. In 1882-'83 

 the motion was 5 miles a second, approach- 

 ing the earth ; 1883-84, 19 miles, approaching 

 1884-'85, 23 miles, approaching ; 1885-'86, 24 

 miles, approaching; 1886-'87, 1 mile approach- 

 ing; and for the year 1887, 6 miles receding. 

 These results are to be accepted with great 

 caution, as astronomers are not yet fully satis- 

 fied that an apparent change in the displace- 

 ment of the F. line indicates a real motion in 

 the line of sight. The change of motion indi- 

 cated by the above figures is very much larger 

 than any that would appear probable from the 

 known motion of Sirius in its orbit. The sec- 

 ond point of interest referred to the orbital 

 motion of Algol. The spectroscopic observa- 

 tions seem to show that this interesting vari- 

 able is revolving about a primary, and that the 

 system to which it belongs is, as a whole, ap- 

 proaching the earth. Further observations are 

 necessary to establish anything definite. Prof. 

 H. C. Vogel, in a communication to the Royal 

 Prussian Academy, says that photography has 

 been successfully employed to overcome the 

 effect of atmospheric tremors, so noticeable in 

 spectroscopic work investigating stellar mo- 

 tions. The time of exposure employed is from 

 half an hour to two hours. 



The Constant of Aberration. Prof. Hall has pub- 

 lished the results of his reduction of the ob 

 servations made in the years 1862-'67 upon 

 a Lyrse by Profs. Hubbard, Newcomb, Hark- 

 ness, and himself, with the prime - vertical 

 transit-instrument of the Naval Observatory, 

 for the purpose of determining the constants of 

 nutation and aberration. He obtained as the 

 most probable value of the constant of aberra- 

 tion, 20-4542" 0-0144". This, with Michel- 

 son and Newcomb's determination of the ve- 

 locity of light, gives for the solar parallax a 

 value of 8-810" 0-0062". 



Resisting Medium. Freiherr v. Haerdtl, a pu- 

 pil of Oppolzer, lately read a paper at Kiel Uni- 

 versity on the periodic comet of Winnecke. 

 He found no indication of any influence on the 

 comet's motion due to a resisting medium. On 

 the other hand, O. T. Sherman considers that 

 the variations in the motion of Encke's comet, 

 other than those produced by planetary attrac- 

 tion, are caused " by a resisting medium con- 

 nected with , the sun, and disturbed by those 

 forces which produce and are produced by sun- 

 spots." He considers tl that the zodiacal light 

 is intimately connected with these disturbing 

 forces, being in fact a locus of condensation of 

 matter driven from the sun similarly to the tail 

 of a comet from the nucleus, and after conden- 

 sation again precipitated upon the solar sur- 

 face." 



Catalogues. Le Verrier, on becoming Direct- 

 or of the Paris Observatory in 1854, planned 

 to reobserve Lalande's catalogue of 47,390 



