ASTRONOMY, PROGRESS OF, IN 1890. 



39 



wise visible the comet was constantly immersed 

 in the sun's rays. No doubt is felt about its pe- 

 riodicity, though it has been observed at only 

 one return. At its next appearance, in 1899, it 

 will be better placed for observation. 



The following periodic comets were expected 

 at perihelia in 1890, but up to Oct. 1 not one of 

 the three has been found: Barnard's 1884 II, 

 Brorsen's of 1846, and Coggia's of 1873. The 

 elements of the first of these strongly resemble 

 those of De Vice's comet of 1844 I, and also 

 those of Finlay's comet 1886 VII. Brorsen's 

 was diligently sought by many astronomers with 

 large telescopes, but without success. It was 

 seen in 1846, 1857. 1868, 18.73, and 1879, but 

 eluded observation in 1851, 1862, 1884, and 1889. 

 At its recent return it was well situated for ob- 

 servation. Coggia's, which is supposed to be 

 identical with Pons's comet of Feb. 23, 1818, was 

 not searched for. It has not been seen since 

 1873, though a period of five and a half years 

 has been assigned to it. 



Barnard's comet e 1888 = Comet I 1889, is 

 at this writing still visible as an exceedingly 

 faint and small object, even with the Lick glass 

 of a yard in diameter. It was first found on 

 Sept. "2, 1888, and has, therefore, a visibility of 

 more than two years' duration, the longest of 

 any comet on record. 



Identity of Periodic Comets. In the " As- 

 tronomische Nachrichten," No. 2,964, M. Schul- 

 hof, of Paris, has an instructive paper entitled 

 " Notes on Some Comets of Short Period." It 

 discusses the probable identity of several pairs 

 of periodic comets of short period, and also the 

 possible identity of several, as Finlay 1886 VII 

 and De Vico 1884, Denning 1881 V and Pigott 

 1783, Blanpain 1819 and Grischaw 1743 I, Cog- 

 gia 1873 VII and Pons 1818 I, and others. Prof. 

 Seth C. Chandler, in " Gould's Astronomical Jour- 

 nal," Nos. 204 and 205, has proved to the satis- 

 faction of a majority of astronomers that Comet 

 V, 1889 (Brooks) is identical with the long-lost 

 Lexell comet of 1770; but M. Schulhof regards 

 as more probable the identity of the Lexell comet 

 with Comet 1886 VII (Finlay's). When it is re- 

 membered that the orbit of Lexell's comet, by 

 its near approach to Jupiter in 1767, was changed 

 from a parabola to an ellipse with a short peri- 

 helion distance, thus rendering it visible, and 

 that in 1770 it was again perturbed and made 

 invisible by a still closer approach to that planet, 

 which caused an increase of perihelion distance, 

 and, also, that Jupiter has several times exerted 

 his powerful attraction in changing its orbit, 

 the question rises whether there are none among 

 the large number of known comets of short pe- 

 riod identical with this lost one. 



It is highly improbable that of all the short-pe- 

 riod comets, or even a tithe of them, are or ever 

 will be known to astronomers. The facts of the 

 division of Biela's comet into two perfectly 

 formed comets which for at least six and a half 

 years maintained their cometary character and 

 individuality, the separation of the great comet 

 of 1882, the recent division and subdivision of 

 Brooks's comet of 1889, and, furthermore, the 

 remembrance that this process has been going 

 on since the solar system has existed, filling it 

 with subdivided comets too faint to be detected 

 by any known optical means, carry us into a 



realm of the wildest speculation as to the num- 

 ber of these bodies in the solar system. 



Synchronical Revolution and Rotation of 

 the Planet Mercury. Signer Schiaparelli, of 

 Milan Observatory, Italy, has given astronomers 

 a surprise somewhat akin to the discovery of 

 Neptune and of the satellites of Mars. He an- 

 nounces, as the result of a discussion of one hun- 

 dred and fifty drawings of Mercury, covering 

 seven years of observation, that that planet com- 

 pletes but one rotation during a revolution around 

 the sun, exactly as the moon rotates on her axis 

 once while she revolves round the earth. He 

 arrives at the conclusion that Mercury completes 

 a rotation on its axis in 87,969 days, which is the 

 exact time of his period of revolution around the 

 sun. If his deductions be true, it follows that 

 one Mercurial hemisphere is constantly bathed 

 in sunlight, while the other is enveloped in per- 

 petual darkness. Observations of this planet are 

 always unreliable and unsatisfactory and must 

 always be made under difficulties, because he is 

 ever in direct sunlight or in strong twilight (in 

 the latter case at a low altitude), and hence the 

 conclusions of this distinguished astronomer re- 

 quire strong confirmation from other observers. 

 Were his assumption true, it does not follow 

 that an exact half of the planet is forever devoid 

 of sunlight, as, owing to his small size compared 

 with that of the sun and also to his nearness to 

 that luminary, there will be exposed to his direct 

 beams in excess of one half of his surface a belt 

 nearly twenty miles in width entirely around the 

 planet, whose breadth must be still further in- 

 creased by refraction from an undoubtedly ex- 

 isting atmosphere, and (because of the great 

 eccentricity of his orbit) by greatly extended 

 librations, and from these, and perhaps other 

 causes, it may be that not much over one fourth 

 of the planet is in unending darkness. The 

 same astronomer claims to possess evidence to 

 warrant the declaration that Venus also rotates 

 on her axis, but once during a revolution around 

 the sun, or in 224*7 days. 



Oxygen in the Sun. Since the invention of 

 the spectroscope, the presence of oxygen in the 

 sun has been denied by many spectroscopists, 

 while others have testified to having obtained 

 unmistakable evidences of it. By a series of ob- 

 servations of the spectrum of an electric light 

 placed on the Eiffel Tower in Paris, as examined 

 from his observatory at Meudon, M. Jansen has 

 confirmed the conclusion he drew from his ob- 

 servations made in 1888, that the supposed oxy- 

 gen lines in the solar spectrum are due wholly 

 to the influence of our own atmosphere. This, 

 if true, is of great importance ; for while more 

 than half of the earth and its atmosphere con- 

 sists of oxygen, it is indeed remarkable that this 

 should be entirely absent from the sun in which 

 twenty or more other telluric elements exist, as 

 proved by spectrum analysis. Its absence from 

 that body affords a strong argument against the 

 theory of the earth's having originally been 

 evolved from the sun. 



Sun-Spots. In 1889 the sun was free from 

 spots for 211 days, the longest spotless period 

 being from Oct. 23 to Dec. 11. There were also 

 eight others of more than two weeks' duration. 

 The mean daily area, however, for the latter half 

 of the year was nearly twice as great as for the 



