58 On the Iron Meieoritc 



Time of revolution — 6 3'ears and one-half, ^ivcvs for the greater 

 semi-axis 3.482. I'hat of the comet was: 1806—3.567; 1826—^ 

 3.560; 1832—3.537; 1846— 3.520 ; 1852— 3.527. There wms 

 therefore a constant diminntion of the major axis of the ellipse, 

 which is confirmed by the orbits of the Bielid meteors. 



The small number of meteors seen to fall at Zacatecas, com- 

 pared with those seen in Europe, may be easily explained. Eu- 

 ]-()pean observe! s agiee in fixing the time of maximum fall at 6 

 P. M. of tiie 27th, Paris time. The corresponding time at Zaca- 

 tecas was 11 A. M. of the same day. At this hour, Andromeda 

 was below the horizon at Zacatecas, while at Paris it was at the 

 zenith ; so that observations at Zacatecas was made seven hours 

 after the maximum as determined in Europe. 



As already stated, the number of meteors counted in 9 

 hours was 2,720 ; whereas among the Euro]-)ean observers. Abbe 

 Denza, for example, estimate those counted by him in four hours 

 at 39,546 ; on the other hand the observations are quite in accord 

 with those of Consul Labadie, at Nogales, made at the same 

 time, since he estimates 115 meteors in 20 minutes, and Pro. Bo- 

 nilla and his assistants, 24:0 in 30 minutes. 



Let us consider the possibility of one of these shooting-stars 

 reaching the earth's surface. It is certain that three different 

 velocities are possessed by a meteor befoi'e and during its fall, 

 i. e. : Its velocity in its orbit ; its acquired velocity Avhen at- 

 tracted by the earth, and its velocity in falling. We can easily 

 estimate its orbital velocity, since we know the elements of its 

 orbit. From calculations made by Alexander Herschel (Lec- 

 tures on Astronomy, Vol. 5, p. 222), it is known that such bodies 

 enter into the atmosphere of the earth with a minimum velocity 

 of 19,000 metres per second. From the moment that terrestrial 

 attraction affects them, they are comjielled to abandon their 

 original orbits and follow a new path (the curve made being 

 parabolic), which is equal to the velocity of the earth through 

 space multiplied by the square root of 2. As the mean velocity 

 of our planet, in its orbit, is 29,640 metres per second, that of 

 the meteor is 42,570. As these bodies have a direct motion, that 

 is to say, the same as that possessed by the earth, their relative 

 sjoeed diminishes to 13,000 metres per second. But, on entering 

 our atmosphere, these small bodies that have the temperature of 



