(7.) Giacobini's Second Periodical Comet (1900, iii.).
On Dec. 20, 1900, Giacobini at Nice discovered a small comet which was found to be moving in an elliptic orbit with a period of about 634 years. The elements bear a considerable resemblance to those of the comets of Wolf and Barnard (1892, v.). The comet had passed its perihelion when discovered, and its increasing faintness, and unfavourable position in the sky, rendered observation of it very difficult towards the end of the 8 weeks during which it was in view. It was not seen at its expected return in 1907, so we shall have no chance of knowing anything more about it until 1914.
(8.) Swift's Second Periodical Comet (1889, vi.).
This comet, discovered by L. Swift on Nov. 16. 1889, presented the ordinary appearance of a telescopic comet without pronounced nucleus or tail. The ellipticity of its orbit soon became evident, and a period of about 7 years was assigned to it. It ought to have returned in 1898 but escaped notice; and we can only say now that as the character of its orbit is so very uncertain no forecast of its future career is possible.
(9.) Borelly's Comet (1905, ii.).
On Dec. 28, 1904, Borelly at Marseilles discovered a small comet which remained visible for 5 months. Its orbit was found to be elliptic, with a period of about 7 years. It has been suggested that this cornet was identical with the Comet of 1783 (i.), for which a period of 5⋅9 years was assigned by C. H. F. Peters. Its expected return in 1911, or 1912, will be awaited with interest.
(10.) Swift's First Periodical Comet (1885, ii.).
On Aug. 20, 1885, L. Swift detected a faint comet in Pisces which during its whole period of visibility of about 2 months was never very conspicuous. Observation soon showed that the comet was a periodical one, and a strong suspicion was
