|*Swift | 10 3 | D | 1896 | |*Brooks (1889)| 6 4 | D | 1896 | | Faye | 11 20 | D | 1896 | |*Denning | 6 51 | D | 1899 | |*Peters | 30 24 | R | ? | | Tuttle | 54 19 | D | 1899 | |*Tempel (1866)| 17 18 | R | 1899 | |*Stephan | 18 13 | D | 1900 | |*Westphal | 40 59 | D | 1920 | | Pons | 74 3 | D | 1955 | | Olbers | 44 35 | D | 1960 | |*Di Vico | 84 57 | D | 1919 | |*Brorsen | 19 8 | D | 1922 | | Halley | 17 45 | R | 1912 | +——————————————+——————-+————-+——————-+ _Halley’s Comet._—A fine comet with a tail about 15° long appeared in the summer of 1682, and Halley computed the orbit according to the method explained by Newton. He then consulted observations of previous comets, and discovered a great similarity in the paths of large comets seen in 1531 and 1607 to that of the one he himself had observed in 1682. He thereupon suspected the three bodies to be one and the same, and advised posterity to maintain a strict watch for the comet’s return in about 1758 or 1759. On pursuing his investigations still further, he alighted upon records of comets in 1305, 1380, and 1456, which greatly strengthened his opinion that the comet of 1682 moved in an elliptical path with a period of about 75½ years. He termed this body “the Mercury[42] of comets, revolving round the Sun in the smallest orbit,” and said that, should it reappear according to his prediction in about the year 1758, “impartial posterity must needs allow this to be the discovery of an Englishman.” As the time drew near for the return of the comet, interest became intensified, and computations were made by Clairaut with a view to determine the precise epoch when it would arrive at perihelion. He found that the comet would be retarded by the action of Jupiter and Saturn, but that perihelion would be reached at the middle of April 1759, subject to an uncertainty of 30 days. The comet was rediscovered on Dec. 25, 1758, by Palitzch, an amateur astronomer at Politz, near Dresden, who employed a telescope of 8 feet focal length, and appears to have anticipated Messier and others who were on the alert for it. It arrived at perihelion on March 12, 1759, and within a month of the date announced by Clairaut. Early in May it had a tail nearly 50° long, and presented a fine aspect in the heavens. Thus the sagacity of Halley had revealed a periodical comet—the first known. It duly returned again in 1835, and received all the attention which a body so replete with historical associations deserved. [Illustration: Fig. 47. Comet 1862 III. (Aug. 19, 1862).] [Illustration: Fig. 48. Sawerthal’s Comet, 1888 I. (March 25, Brooks).]