COMETS. 101 



forms, as the breaking forth or extinction of a single volcano 

 has in our less extensive sphere. 



A third planetary comet of short period was discovered 

 on the 22d of November, 1843, at the Paris Observatory, 

 by M. Faye. Its elliptic path approaches much more nearly 

 to a circle than that of any of the comets previously known 

 to us, and is included between the orbits of Mars and 

 Saturn; passing, according to Goldschmidt, beyond the 

 orbit of Jupiter. This comet is therefore one of the very 

 few whose perihelia are beyond the orbit of Mars ; its period 

 of revolution is 7*29 years, and the present form of its 

 path may perhaps be due to the near approach which it 

 made to the great mass of Jupiter at the end of the yeai 

 1839. 



If we consider all comets moving in elliptic orbits as mem- 

 bers of our solar system, and class them by the lengths of 

 their major axes, the amount of their excentricities, and the 

 duration of their periods of revolution, it seems probable 

 that in the last-named respect, the three comets of Encke, 

 Biela, and Paye, are most nearly approached by the comet 

 which Messier discovered in 1766 (regarded by Clausen as 

 identical with the third comet of 1819), and by the fourth 

 comet seen in the same year (1819), discovered by Blan- 

 pain, and thought by Clausen to be identical with the 

 comet of 1743. The orbits of the last-mentioned comet, 

 as well as that of LexelPs, seem to have undergone great 

 alteration by the proximity and attraction of Jupiter ; their 

 periods of revolution appear to be only from five to six years, 

 and their aphelia take place near the orbit of Jupiter. 

 Among comets whose periods range from seventy to seven ty- 

 six years, we should name, first, Halley's which has been 



