1897,] ApproacJiing Itetnrn of ihe November Bleteorp, 337 



WEEKLY EVENING MEETING, 

 Friday, February 19, 1897. 



8tr Frederick Abel, Bart. K.C.B. DXIL. LL.D. F.R.S, 



Vice-President, in the Chair, 



G. Johnstone Stoney, Esq. M.A. D,Sc. F.R.S. 3I.B.L 



The Approaching Beturn of the Great Swarm of November Meteors. 



The present discourse was intended to supplement one delivered 

 eighteen years before, in the Theatre of the Royal Institution, oil 

 * The Story of the November Meteors,' of which a copious extract 

 will be found in vol. ix, of the Proceedings of the Institution. 



Orbit of the Leonids. 



In the earlier discoui'se an account was given of the successive 

 steps which led up to the great discovery by the late Professor J. 

 Couch Adams of the orbit of these meteors. They novr pursue, and 

 have been for several hundreds of years pursuing^ a long oval path in 

 the heavens, round which they travel three times in each century. 

 This orbit near its distant end intersects the orbit of Uranus and 

 very close to its perihelion it intersects the orbit of the earth. It 

 does not intersect the orbits of the intermediate planets, of which 

 the principal are Jupiter and Saturn, since the plane in which the 

 meteors move is so much inclined to the planes of the orbits of those 

 planets that the meteors are carried above and below their orbits in 

 each revolution. The swarm is extended like an immense procession 

 many millions of miles in length, though only some 100,000 miles 

 wide, along a portion of its orbit. During one half of each revo- 

 lution the stream is for sixteen years lengthening out as it approaches 

 the sun, and during the other half of the revolution,' while receding 

 from the sun, it shortens again, not, however, quite to the same size 

 as it had at the commencement of the revolution, since one revolution 

 after another there is a gradual increase in the length of the pro- 

 cession. 



Entrance of the Leonids into the Solar System^ 



After the lapse of a sufficient time the swarm will of necessity 

 have so lengthened out as to extend the whole way round its orbit • 

 and the consideration that it is at present of limited lent^th, viewed 

 in connection with the dynamical certainty that it must ever keep 

 steadily extending, carries our thoughts bask to that past time, which 

 cannot be very remote from the cosmical standpoint, when that 

 which is now a long stream was a compact cluster. It was then, 



