Page:History of the Royal Astronomical Society (1923).djvu/189

 1860-70] ROYAL ASTRONOMICAL SOCIETY 161 recognise in 1799 that the meteors radiated from a point fixed in relation to the stars. It was Olmsted, of Yale University, who first in 1834 recognised the significance of this point as indicating the direction of the meteors in their approach to the earth, and he regarded them as a form of comet describing an elliptical orbit with a period of about 182 days, and meeting the earth near aphelion. Erman, of Berlin, discussing in 1839 the similar problem presented by the August meteors (Perseids), found it necessary to assume that the meteors in that case formed a con- tinuous stream along their orbit. Olbers, in 1839, was ted to predict a fine display of Leonids in 1867 November. But fortunately H. A. Newton, Professor in Yale University, published in 1864 hi g well-known discussion of ancient records of November meteors, dealing with thirteen showers since A.D. 902, and indicating the existence of a cycle of 33*25 years. Considering the phenomena to be caused by a ring of meteoroids revolving round the sun, he showed that in one year the meteoroids must describe either 2^V S or i^, or ^ revolutions. He further pointed out that the longitude of the node of the orbit is gradually increasing, and that its observed motion would afford a method for deciding which of the five periods is the correct one, if only the perturbations by the various planets were calculated. He predicted a fine display of meteors for 1866 November, a year earlier than Olbers's date. When Newton's prediction was verified, the problem became a very attractive one. It was made all the more attractive by Schia- parelli's discovery that the cosmical orbit of the Perseid meteors coincided closely with the orbit of the retrograde comet which was discovered by Swift in 1862, and which reached perihelion on August 22 of that year. The spring of 1867 is made memorable by a display of striking Memoirs following one another with almost meteoric rapidity. In January Le Verrier published his Memoir showing that a swarm of meteors with a period of 33-25 years would intersect the orbit of Uranus, but from its inclined position indicated by the radiant's latitude 10 it would not intersect the paths of Saturn, Jupiter, or Mars. His calculations showed that in A.D. 126 there would have been a close approach of Uranus to such a swarm, and that that date might be the epoch of the capture of the swarm for the solar system by their diversion into a retrograde elliptic orbit of period 33-25 years. In 1867 February, C. F. W. Peters and Oppolzer pointed out the close resemblance of Oppolzer's orbit for the comet discovered by Tempel in 1865 December, which reached perihelion on 1866 January n, to Le Verrier's orbit of the meteors. ii