196 COSMOS. 



discovery of Trans-neptunian planets since the boundary 

 which determines whether a comet is to be called an interior 

 one is changeable, still this term is preferable to that of com- 

 ets of short period, from the fact that it is in each epoch of 

 our knowledge dependent upon something definite. The six 

 interior comets now accurately calculated certainly vary in 

 their periods of revolution only from 3 '3 to 7 '4 years ; but if 

 the return of the comet discovered by Peters at Naples, upon 

 the 26th of June, 1S46 (the 6th comet of the year 1846, with 

 a half-major axis of 6'32). after a period of 16 years, should 

 be confirmed,* it may be foreseen that intermediate members, 

 in reference to the duration of the period of revolution, will 

 gradually be discovered between the Comets of Faye and 

 Olbers. Then it would be difficult in future to fix a limit 

 for the shortness of the period. Here follows the table in 

 which Dr. Galle has arranged the elements of the six interior 

 comets. 



* Galle, in Olbers's Metkode der Cometenbahnen, p. 232. No. 174. The 

 comets of Colla and Bremiker, of the years 1845 and 1840, present el- 

 liptical orbits with ^proportionately not very shoit periods of revolution. 

 (I allude to the 3065 and 8800 years of the Comets of 1811 and 1680.) 

 They appear to have*periods of revolution of only 249 aud 344 years. 

 (See Galle, op. cit., p. 229 and 231.) 



