H. A. Newton— Biela Meteors of Nov. 27th, 1885. 413 



Following a similar process of reasoning to that of the arti- 

 cle referred to, we may compare the number N of meteor tracks 

 which are visible during a given time at one place whose mid- 

 dle points are within 10° of the zenith, with the number N' of 

 tracks visible during the same time (not necessarily visible all 

 at one place) whose middle points are in a right cylinder of 

 circular base whose radius is r, and whose axis proceeds from 

 the observer in the direction of the radiant. The following 

 proportion is readily formed : 



N:N' :: I n px* tan 2 10° dx: I re p r 2 seczcfe::tan 2 10°/ p-x 2 dx; 



r 2 sec zl p dx, 



in which x expresses the height from the ground of middle 

 points of meteor tracks, a and b the limiting values of x, z the 

 zenith distance of the radiant, and p a factor proportional to 

 the mean density of the meteor tracks at different altitudes, 

 which is assumed to be a function of x only. 



If we further assume that the values of p in the present 

 shower are equal to those used in the memoir cited, and which 

 were obtained from all the measured altitudes of shooting stars 

 then available, we shall have for p at elevations of 45, 75, 105, 

 135 and 165 kilometers the several values 114, 243, 277, 106 

 and 57. 



Using finite summation for integration we have, 



2 pAx= f I97 Ax, and tan 2 10° .Sec 2 pz/ ^=252930 Ax; 



hence the above proportion gives N' = "00315 Nr 2 sec z where r 

 is to be expressed in kilometers. 



The radiant at the time of the maximum of the shower was 

 vertical over the Caucasus, and the value of sec z for the sev- 

 eral stations varied from 1*02 to 1*15. I shall use the value 

 1*08 for sec z, and 1500 for N for an hour. This gives N 7 = 

 5"lr 2 for one hour, in other words, at the maximum of the 

 shower there were 5 - l meteors per hour, the middle points of 

 whose visible paths were in a fixed right cylinder whose axis 

 was parallel to the relative motion of the meteoroids, and 

 whose radius was one kilometer. But such a cylinder evi- 

 dently received all the meteoroids of a cylinder of nearly equal 

 radius located in the meteoroid group, and whose length was 

 the hourly motion of the meteoroids relative to the earth before 

 the earth began sensibly to attract them. 



The velocity of the Biela meteoroids relative to the earth 

 (using the orbit of 1852), is found by Weiss to be "53484. 

 (Beitrage zur Kenntniss der Sternschnuppen I, p. 11.) The 

 earth's velocity being 29*8 kilometers per second, we get 



