Sir J. W. Lubbock, Bart., on Shooting Stars. 331 



ing to ascertain how much the perihelion distance of such a body 

 might be lengthened under given circumstances of the action of 

 Jupiter ; or whether, under any hypothesis of the confio-uration of the 

 planets, the perihelion distance of any known comet could be brought 

 under •004G47. Le Verrier suggests, that some of the comets may 

 have become fixed to our system, and retained by the action of Jupi- 

 ter ; and that in consequence of the same action, they may again 

 wander in space, and cease to belong to this system.* But may not 

 such bodies owe their origin to the same forces of which the existence 

 is indubitable, which operate on the surface at any rate of the sun's 

 mass ? And if so, it is by no means impossible, that, by calculatino- 

 the perturbations of some comet for the past, especially one whose 

 perihelion distance is small, it may be traced back to its origin, and 

 the very year ascertained when it left the solar mass. 



The phenomena of shooting stars may possibly throw lioht upon 

 the question of the extent to which an atmosphere extends, capable 

 of affording any sensible resistance to the motion of such bodies, and 

 may thus afford an interesting illustration of the connexion which 

 exists between different branches of physical science. In my treatise 

 on the Heat of Vapours, p. 43, I have given a table, shewing, upon 

 the hypothesis I there adopted, the density and temperature for a 

 given height above the earth's surface. According to that hypothesis, 

 at a height of 15 miles the temperature is 240°-6 F., below zci-o 

 the density is 03573, and the atmosphei-e ceases altogether at a 

 height of 22-35 miles. In the Comptcs Renclus des Seances dc 

 V Acadamie des Sciences, torn. viii. p. 95, M. Biot has verified a cal- 

 culation of Lambert, who found from the phenomena of twilio-ht, the 

 altitude of the atmosphere to be about 18 miles. The constitution 

 of the higher regions of tlie atmosphere, according to the hypothesis 

 adopted by Ivory is very different, and extends to a much greater 

 height. See p. 3, of the Supplement to my Treatise on the Heat of 

 Vapours, where I have given a table, shewing the construction of the 

 atmosphere according to Ivory. Such a table for the constitution 

 due to Laplace's hypothesis is still wanted. — (The Philosophical Ma- 

 gazine, Third Series, vol. xxxii. p. 170, March 1848.) 



* " Dans un certain nombre de siecles toutefois, ellc atteindra de nouveau 

 I'orbite de .Jupiter, dans une direction opposee a celle par laquelle elle a par 

 arriver dans le systetne planctaire ; et son cours sera certainement encore fois 

 alt^r6-Peut-etre raeme Jupiter la rendra-t-il aux espaces aux quels il I'avnit 

 d^robee." — Le Verrier, Comptes Rendus, Dec. 20, 1847, p. 925. 



