observed; seven have taken place unperceived. But the elliptic orbit is now determined with precision. Observers are numerous and vigilant, and the comet will doubtless no longer escape the researches of astronomers, except when its apparent proximity to the sun and its distance from the earth are such as not to admit of its being seen. The period of the revolution of Winnecke's comet is 2,042 days, only forty days more than that of Brorsen's comet; the eccentricity of its orbit is somewhat less. In perihelion the comet is situated at a distance from the sun equal to fourfifths of the distance of the earth; in aphelion it exceeds the orbit of Jupiter by about one-fifth of this distance. SECTION X. TEMPEL'S SHORT PERIOD COMET. Calculation of the elliptic elements of the second comet of 1867, discovered by Tempel-Perturbations due to Jupiter, and corsequent delay in the return of the comet to its perihelion in 1873-Remarkable agreement of observation and calculation. THE second comet of 1867, discovered by M. Tempel, was found by several astronomers to have elliptic elements. It passed its perihelion on May 23, 1867, and its period had been calculated at 2,064 days. But Dr. Söllinger, taking into account the perturbations its passage in the vicinity of Jupiter would produce in the elements of its orbit, assigned a retardation of 117 days in the date of its return to perihelion in 1873. It was, in fact, seen again in the course of that year, and its perihelion passage took place on May 9, which gives for the duration of the revolution performed in the interval between the two apparitions a value of very nearly six years, or 2,178 days, three days less than the number determined by calculation. Tempel's comet of short period is, therefore, the ninth periodical comet whose return has been verified by observation; that is to say, which really forms an integral part of our solar system. Observed in May 1873, at Greenwich, by Messrs. Christie and Carpenter, it appeared in the telescope like an elongated nebulosity, about 40" in diameter, with a central nucleus, which shone like a star of the twelfth or thirteenth magnitude. |