TRANSACTIONS OF SECTION A. 795 



the prolonged and feeble shower of clino-Leonids which has been observed. As 

 no such considerable progression of the radiant has been observed, it is plain that 

 these terrestrial clino-Leonids are not what have been chietiy recognised as 

 Leonids. 



We must turn, then, to the planetary clino-Leooids, to those other clino-Leonids 

 which are such because they were acted on dirt'erently from the ortho-Leonids 

 when the great planet Uranus drew the whole swarm into the solar system. 



When we trace out the dynamical consequences of the conditions which then 

 prevailed we find results which are everywhere in agreement with the observations. 

 These planetary cliuo-Leonids are such as had been difterently deflected by Uranus, 

 and were thrown into slightly difiering planes with slightly differing periodic 

 times from the ortho-Leonids. The differences in periodic times have caused them 

 to extend — one set of them backwards and the other forwards — round the whole 

 ring, thus bringing some of them to the earth every jear ; while the variety of their 

 planes and of the deflections which they suH'ered in them has had two effects. It 

 causes the earth to encounter them for some days before and for some days after 

 the ortho-date ; and it occasions a forward shift of the radiant which seems to 

 amount to about ten minutes daily. That the sparse shower presents itself for 

 some days before the ortho-date is owing to the more deflected clino-Leonids 

 having been now for seventeen centuries less acted on by perturbations than the 

 ortho-Leonids. This has led to a shower rate at which their nodes have advanced 

 along the ecliptic, and has also occasioned a gradual shift towards the westward 

 of their radiant, which was originally displaced towards the east. Similarly, the 

 clino-Leonids which were originally less deflected by Uranus than the ortho- 

 Leonids, present themselves now at dates subsequent to the ortho-date, and reach 

 us from radiants which originally lay west of the ortho-radiant, but have since 

 been carried eastward by the quicker advance of their node. It is not likely that 

 these shifts in opposite directions are exactly equal, but the difi'erence is not such 

 as to have attracted the notice of observers. It is therefore of small amount, but 

 may perhaps be detected in observations which have been recorded. Thus in the 

 list of (unfortunately very rough) determinations of radiant points, recently 

 collected by Mr. Denning on page 20 of his pamphlet on the ' Great Meteoric 

 Shower of November,' there are seven determinations which were made on days 

 or groups of days preceding the ortho-date, and six upon days or groups of days 

 after that epoch. The mean of the positions given by the determinations before 

 the ortho-date is 



JR 148° 43' S 22° 51', 



and the mean of the determinations after the ortho-date is 



M 150° 40' b 22° 14', 



which, so far as these observations can be trusted in a matter of so much delicacy, 

 indicates a small shift in longitude towards the eastward accompanied by a slight 

 change in latitude, which also is indicated by the theory. 



Although it is plain that the clino-Leonids which have been recorded as 

 Leonids have been chiefly, perhaps almost exclusively, the planetary clino-Leonids, 

 it is certain that terrestrial cliuo-Leonids also exist, although they probably present 

 themselves in our atmosphere in fewer numbers. They may be distinguished 

 from the planetary clino-Leonids by the greater progress in longitude of their 

 radiants, the position of which (within a degree) depends upon the date, advancing 

 nearly a degree each day. They may probably have been already often observed ; 

 as it is not unlikely that they are some of those meteors which have been recorded 

 as resembling Leonids, but which, nevertheless, have been supposed by observers to 

 belong to other systems because their radiants were not in accordance with what 

 has hitherto been supposed to be exclusively the radiant of the Leonids. 



After dealing in detail with the phenomena of the great Leonid swarm, the 



