3 S Chronicles of Science. [ July , 



bestrewn with meteors as to give a yearly recurrence of showers 

 besides the great displays occurring at intervals of 33J years. 



Leveirier, however, calculated the orbit on the supposition of a 

 period of 33J- years. It is easily shown that the orbit has a mean 

 distance exceeding that of Saturn ; and that, owing to its eccen- 

 tricity, its aphelion extends beyond the orbit of Uranus. 



But the difficulty lay in deciding between this orbit and that 

 adopted provisionally by Professor Xewtoru and supported by the 

 strongly-expressed opinion of Sir John Hersehel. There was but 

 one phenomenon available for the decision of this question — but 

 the consideration of this phenomenon brought the question imme- 

 diately into the class of the abstrusest mathematical problems. On 

 examining the dates upon which the shower appeared in former 

 years, it is seen that these dates fall later and later in the year at 

 each successive recurrence. Thus in the year 902 aj>.. when the 

 earliest recorded shower took place, it occurred on Oct. 12th o.s., 

 or Oct. 17th srjs.. four weeks earlier than the present date of the 

 shower. This corresponds to an annual displacement of the node 

 of the meteors orbit by 102 '6. with respect to the equinox, or 

 • r 2 4 with respect to the fixed stars. Njpw it is possible to calcu- 

 late the secular motion of the node for an orbit of given period, 

 though the problem has peculiar difficulties, either when Professor 

 Newton's assumed period is taken, or when the eccentric orbit 

 corresponding to the period of 33 J years is considered. Profe- 

 Adams has calculated the nodal motion for both cases. In the first 

 case he obtained an annual retrogression of only 21 instead of 

 52"*1. In the latter he obtained a retrogression of 28' in 33^ 

 years, or about 50"*5 in one year, a result according so closely 

 (considering the circumstances) with observation, as to leave no 

 doubt that _ " years is the true period of the meteoric orbit. 



A result yet more interesting appears to flow from Adams's 

 researches. When the orbit of the meteors is calculated, it appears 

 that its elements agree in the most remarkable manner with those 

 of a periodic comet discovered in January, 1866. The following 

 table exhibits this agreement : — 



\":-^'-::M^:^. Comet L, 1S66. 



Period .... 53*25 rears 'assumed) 33-18 years. 



Mean distance . . - 10-3402 . v . . 10-3248 



Eecentricitv . . . 0'9047 . . . 9054 



Perihelion distance . . 0"9855 ... 9765 



Inclination. . . . 16° 46' . . . il° 18* 



Longitude of node . . 51* fg . . . 51- . ' 



Longitude of perihelion . 57 c 19" . . 60° 28' 



Direction of motion . . Eetrograde . . Betrograde. 



Close as the approximation appears, it would be yet closer if we 

 assumed (as we are free to do) that the period of the meteors is 

 33*18 years instead of 33£, a professedly rough approximation. 



Singularly enough this particular comet is the only one which 



