OBSERVATIONS OF LUMINOUS METEORS. 49 



may have transformed the original orbits of many of the former as well as of 

 the latter into ellipses. It is an interesting fact that the motions of some 

 luminons meteors (or cometoids, as, perhaps, they might be called) have been 

 decidedly indicative of an origin beyond the limits of the planetary system. 

 But how are the phenomena of periodic meteors to be accounted for in ac- 

 cordance with this theory? 



" The division of Biela's comet into two distinct parts suggests several 

 interesting questions in cometary physics. The nature of the separating 

 force remains to be discovered ; ' but it is impossible to doubt that it arose 

 from the divellent action of the sun, whatever may have been the mode of 

 operation. A signal manifestation of the influence of the sun is sometimes 

 afforded by the breaking up of a comet into two or more separate parts, on 

 the occasion of its approach to the perihelion ' *. No less than six such in- 

 stances are found distinctly recorded in the Annals of Astronomy, viz. : — 1. 

 Ancient bipartition of a comet. — Seneca. 2. Separation of a comet into a 

 number of fragments, 11 B.C. — Dion Cassius. 3. Three comets seen simul- 

 taneously pursuing the same orbit, a.d. 896. — Chinese Records. 4. Probable 

 sejDaration of a comet into parts, a.b. IQIS.—Hevelius. 5. Indications of 

 seimration, 1661. — HeveVms. 6. Bipartition of Biela's Comet, 1845-46. 



" In \dew of these facts it seems highly probable, if not absolutely certain, 

 that the process of division has taken place in several instances besides that 

 of Biela's Comet. May not the force, whatever it is, that has produced one 

 separation again divide the parts ? And may not this action continue until 

 the fragments become invisible ? According to the theory now generally 

 received, the periodic phenomena of shooting-stars are produced by the inter- 

 section of the orbits of such nebulous bodies with the earth's annual path. 

 Now there is reason to believe that these meteoric rings are very elliptical, 

 and in this respect wholly dissimilar to the rings of primitive vapour which, 

 according to the nebular hypothesis, were successively abandoned at the solar 

 equator ; in other words, that the matter of which they are composed moves 

 in cometary rather than in planetary orbits. May not our periodic meteors 

 be the debris of ancient but now disintegrated comets, whose matter has be- 

 come distributed round their orbits ? " 



These views, announced in the year 1861, were afterwards completely 

 established by the calculations of Professor Newton and Professor Schia- 

 pareUi regarding the real orbital velocities of shooting-stars, proving them 

 to move, generally, in parabolic, or cometic, rather than in planetary orbits ; 

 and by the astonishing discovery in the year 1866, by Professor Schiaparelli, 

 of the almost absolute identity of the orbit of Tuttle's Comet (III. 1862) with 

 that of the August, and of the orbit of Temple's Comet (I. 1866) with that 

 of the November meteor-stream, supposing (as the researches of Professor 

 Newton and Professor Adams amply prove) that the latter, and presumably 

 also the former of those meteor-clouds revolve in elliptic orbits of such 

 considerable length, as not to differ much from the comets in their times 

 of revolution. In his communication to the American Philosophical Society, 

 Professor Kirkwood retraces the recent researches of Hoek, Leverrier, and 

 SchiapareUi respecting the probable circumstances of the introduction of 

 comets and periodical shooting-stars ab extra into the limits of the planetary 

 system. The disturbing force by which their cosmical orbits were converted 

 into elliptic ones of short periods (it is found in harmony with the preceding 

 theory) was probably the overpowering attraction of one of the larger planets 

 near to which the cosmical bodies first entered the limits of the solar system. 



* Grant's ' History of Physical Astronomy,' p. 302. 

 1871. I 



