ASTRONOMICAL PROGRESS AND PHENOMENA. 



43 



bcinj* R. A. = 15 1 ll m ; decl. = 30 36'. On May 



13 it" was described by Prof. Boss as having a starlike 

 nucleus of the 1 1 '5 magnitude j it increased somewhat 

 in brightness till about the middle of June, without, 

 however, changing its general appearance. Mr. 

 Chandler has combined all the observations at present 

 available into four normal places, and finds that they 

 are rather more satisfactorily represented by an ellipse 

 than by a parabola. 



Comet 1887 V is Olbers's periodic comet, rediscov- 

 ered by Mr. Brooks on Aug. 24, 1887. This comet 

 was originally discovered by Olbers at Bremen, on 

 March 6, 1815, and in 1816 Bessel predicted that it 

 would return to perihelion about Feb. 9, 1887. In 

 1881 Dr. Ginzel. of Vienna, published an elaborate 

 rediscussion of tne orbit, using 346 observations from 



14 observatories, and taking account of perturbations. 

 He obtained a period of about 74 years, with an uncer- 

 tainty of 1-6 years, and gave Dec. 16, 1886, as the 

 most probable date of perihelion passage. An ex- 

 tensive sweeping cphemeria was prepared by him, 

 and for months a search for the comet was kept up 

 by several astronomers, resulting in its discovery by 



Mr. Brooks, who was also the first to detect Pons's 

 comet at its return in 1883-' 84. Especial interest at- 

 taches to Olbers's comet as the third member of the 

 group of comets having a period of about 75 years 

 (Halley's, Pons's, and Olbers's) which has returned to 

 perihelion in conformity with prediction. Early in 

 September the comet showed some slight traces of a 

 tail, in spite of its considerable distance from the 

 earth. The nucleus was cnrite well defined, its bright- 

 ness being from the eighth to the tenth magni- 

 tude. 



Dr. Krueger's corrected orbit of the comet discov- 

 ered by Mr. Finlay on Sept. 26, 1886 (1886 VII) 

 shows that it can no longer be regarded as identical 

 with De Vico'slost comet of 1844. However, Finlay's 

 comet is moving in an ellipse whose period is about 

 6 '7 years, and as it passed its perihelion on Nov. 22, 

 1886, another return will be due in the summer of 

 1893. 



The approximate elements of the new comets 

 are as follows, the dates being in Greenwich 

 mean time : 



Prof. Daniel Kirkwood has suggested the 

 probability that certain comets of short period 

 may have originated within the solar system. 

 For example : before its last near approach to 

 Jupiter, Wolf's comet, 1884 III, had an ec- 

 centricity of - 28, which is exceeded by twelve 

 known asteroids, and a period of revolution of 

 3,619 days, or five sixths that of Jupiter. It 

 was then an asteroid too distant to be seen 

 even at perihelion. Again : the orbit of Tern- 

 pel's comet, 1867 II, lies between Mars and 

 Jupiter, and its elements do not differ greatly 

 from those of an eccentric asteroid. 



Dr. Bredichin has made a study of Fabry's 

 comet, and of Barnard's two comets of 1886, 

 with respect to their bearing upon his new 

 theory of comets' tails. The tail of Fabry's 

 comet belongs undoubtedly to type II, and the 

 principal tail of Barnard's first comet ( 1886 

 II ) to the same type. The secondary tail of 

 this comet, noticed by Backhouse, seems to 

 have been merely an elongation of the head, a 

 phenomenon observed in other comets. Bar- 

 nard's second comet (1886 IX) had two tails 

 distinctly visible for a month, which belonged 

 respectively to types I and III, and after pass- 

 ing perihelion it furnished further confirmation 

 of Bredichin's theory by throwing out a third 

 tail belonging to type II. 



Stellar Photometry. From a comparison of the 

 star-magnitudes of the Oxford Uranometry 

 with those of Wolff's second catalogue, and with 

 those of the Harvard Photometry, Prof. Pick- 

 ering has found that the Oxford magnitudes 

 are, on the average, less than the Harvard mag- 

 nitudes for stars down to the third magnitude, 

 but greater for the fourth and fifth, and less 

 again for stars below the sixth. The Harvard 

 catalogue differs less from those of Wolff and 

 Pritchard than the two latter do from each 



other. The "wedge photometer," constructed 

 under the direction of Prof. Pritchard for Prof. 

 Pickering, has been submitted to a careful ex- 

 amination by Profs. Langley, Young, and Pick- 

 ering, and it appears from Prof. Langley 's ob- 

 servations of the wedge by means of his bo- 

 lometer, that there is a selective absorption of 

 light throughout the wedge; feeble in the more 

 luminous portion of the spectrum, but of such 

 a character that, broadly speaking, the trans- 

 missibility always increases from the violet to- 

 ward the red, increasing very greatly in the 

 infra-red. These results have been confirmed 

 by Prof. Pickering's experiments, and they 

 emphasize the danger, already recognized by 

 Prof. Pritchard, of employing an instrument 

 of this kind in the observation of deeply-colored 

 stars. 



The magnitudes of the standard stars of the 

 British, French, German, Spanish, and Ameri- 

 can nautical almanacs, have been rediscussed 

 by Prof. Pickering, and his results will proba- 

 bly be adopted in future issues of the French, 

 Spanish, and American works. The plan pro- 

 posed was, that the magnitude adopted for 

 each star should be the mean of those derived 

 from the Harvard photometry, the photometric 

 observations of Wolff, the Uranometria Oxoni- 

 ensis, and the Uranometria Argentina. The list 

 published by Prof. Pickering embraces 800 

 stars, and of these the magnitudes of all but 

 64 depend upon at least two and generally 

 upon three authorities ; 132 stars being com- 

 mon to all four of the adopted standard cata- 

 logues of brightness. 



Variable Stars. Several new variable stars 

 have been detected by Chandler, Sawyer, Es- 

 pin, and others, and among them are two of 

 more than ordinary interest, as they appar- 

 ently belong to the well-known " Algol" type. 



