A RECENT STAR SHOWER. 211 



from interstellar space. We come next, however, to 

 a really crucial test (suggested to me by Professor 

 Herschel, to whose consideration I had submitted 

 the new theory). If Jupiter were to introduce a 

 number of comets into our system 'by his action on 

 matter arriving from without, we should recognise in 

 these comets the signs of their extra-planetary origin, in 

 a diversity of motion and direction corresponding to that 

 recognised in the great comets which from time to time 

 visit our system from without. Some of the 'Jovian 

 family would travel forwards (that is, in the same direc- 

 tion as the planets), others would travel backwards, 

 some would travel nearly in the level of the planetary 

 motions, others on paths more or less considerably 

 inclined, and some few on paths nearly square to that 

 level. But, if the Jovian comet-family were originally 

 expelled from Jupiter, inasmuch as they would all 

 (besides the motion he gave on ejecting them) partake 

 in his rapid forward motion, we should find them all 

 travelling forwards and all on paths not greatly in- 

 clined to the level on which Jupiter himself travels. 

 Precisely as when a bomb explodes in mid-air, the 

 fragments all travel in the general direction which the 

 bomb had before pursued, even though the bursting 

 force acts backwards on some and sideways on others, 

 so it would be with the matter expelled from Jupiter. 

 Those cometic masses which we recognise as Jovian, 

 may indeed (as suggested above) be masses hurled by 

 Jupiter almost directly rearwards, yet that would still 

 leave a balance of the forward motion they had shared 



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