On the Orbit of Part of the Leonid Stream. 



321 



" On the Orbit of the Part of the Leonid Stream which the Earth 

 encountered on the Morning of 1898, November 15." By 

 Akthur A. Eambaut, M.A., D.Sc., Eadcliffe Observer. Com- 

 municated by G. Johnstone Stoney, M.A., D.Sc, F.E.S. 

 Eeceived June 14, — Eead June 15, 1899. 



For an accurate prediction of the return of the Great Leonid swarm 

 of meteors, it is of the highest importance to determine as accurately 

 as possible the orbit in which each part of the swarm is moving. 



As has been pointed out by Drs. Stoney and Downing, * the denser 

 part of the stream, with which we are chiefly concerned, being now 

 drawn out to such a length that it takes more than two years to pass 

 any point of the orbit, it results that the perturbing effect of the 

 several planets will not be the same on different parts of the stream. 



Hence it follows that the orbit deduced from the observations made 

 during the great shower of 1866, however reliable they may have been, 

 must not be assumed to represent accurately the track of the meteors 

 which we shall meet when we pass through the node of the orbit next 

 November, even when allowance is made for the perturbations which 

 that part of the stream has suffered in the meanwhile. 



But although the determinations of the radiant point of the shower 

 made in 1866 are entitled to a high degree of confidence, owing to the 

 large number of meteors upon which they depend, yet the discrepancies 

 existing between the results of different observers, and the fact that 

 the varying effect of the earth's attraction upon the position of the 

 radiant at different zenith-distances was generally overlooked by the 

 observers at the time, introduce an element of uncertainty into the orbit. 



The extent of these discrepancies may be estimated from the " List 

 of Observed Places of the Eadiant Point in 1866," as given by Professor 

 A. S. Herschel in the 'Monthly Notices of the Eoyal Astronomical 

 Society,' vol. 27, p. 19, and the effect of this uncertainty on the 

 resulting orbit may be illustrated by comparing the two sets of 

 elements deduced by Adams and Schiaparelli, respectively, from English 

 observations of the radiant point on that occasion. These are — 







Ada 



ms.f 



Schiaparelli. X 



Period (assumed) 



P = 



33*25 years. 



33*25 years 



Mean distance 



a =» 



10-340 



10-340 



Eccentricity 



e = 



0-9047 



0-9046 





i - 



16° 



46' 



17° 44'-5 





v — 



51° 



28' 



51° 28' 



Longitude of perihelion... 



7T = 



58° 



19' 



56° 26' 



* ' Eoy. Soc. Proc.,' No. 410. 

 ' f 'Monthly Notices,' vol. 27; 'The Scientific Papers of John Couch Adams, 

 vol. 1, p. 269. 



X ' Entwurf einer Astronomischen Theorie der Sternschnuppen,' von J. Y. Schia- 

 parelli, p. 57. 



