Sir J. W. Lubbock on Shooting Stars. 87 



1 70° per minute. Tliis is equivalent to a velocity of about five 

 miles per second; according to M. Quetelet, their observed 

 velocity is, on the average, about twenty miles per second. 



If the body move in space round the sun, and is not to be 

 considered as a satellite of the earth, ^ 



If §X' is the angle described by the earth in ^t, 



If the body move in a circle 8x = 8x', if 8^=1", this gives 



8x'= [3-03491] - (in degrees, p being in miles), the number 



P 

 between brackets being a logarithm. If p = 100, this gives 8x' 

 about 10°, and the velocity about eighteen miles per second, 

 agreeing with the observed velocity. 



The angular velocity in this case, as seen by the spectator, 

 would depend partly upon the motion of the earth in its orbit, 

 and uponits direction relatively tothatoftheother movingbody. 

 Perhaps it may be found upon investigation, thai some 

 shooting stars belong to one class and some to the other. The 

 periods of satellites would necessarily be so short, that the 

 appearances might be satisfied by a small number of such 

 bodies, because their apparitions would recur so frequently. 

 But if the shooting stars are bodies revolving in space, the 

 same body would be seen so seldom, that the conclusion seems 

 in that case unavoidable, that the number of such bodies must 

 be very great. Experience leads to the conclusion, that, 

 under favourable circumstances, there is scarcely a night in 

 which several are not visible. Nor is there any reason apriori 

 for supposing tliat such bodies abound more in orbits nearly 

 intersecting the orbit of the earth than in any other part of 

 the planetary system. It seems natural to suppose, that, coming 

 so very near the earth, the attraction of the earth would in 

 some cases overcome the attraction of the sun, and cause the 

 body to revolve in future as a satellite. If we adopt the fol- 

 lowing data, 



Distance of the sun = 95,000,000 miles, 

 Distance of the moving body from the centre of the earth 

 = 4000 miles. 



Mass of the earth ^r^^^, the attraction of the earth would 

 351'93o 

 be about 3000 times greater than that of the sun. 



