346 On the Collision of two Comets. 



Art. XVll. — 0?i the Collision of two Comets, and the Comet of 

 July, 1831 ; by J. J. Littrow. (Zeitschrift fiir Physik.) 



Of all the comets which are known to astronomers, that of Biela 

 is the only one whose orbit is such as to admit of its ever coming in 

 contact with the Earth. This is a circumstance which renders that 

 body an object of deep and peculiar interest'to the inhabitants of our 

 globe. Another very remarkable fact, in relation to Biela's comet, 

 is, that its orbit passes very near to that of Encke's comet, so that in 

 course of time, it will not only make its appearance in the vicinity of 

 our Earth, but will also pass very near, perhaps even come in con- 

 tact with the comet of Encke. This possibility of a collision be- 

 tween two of the bodies of the solar system does not appear to have 

 engaged the attention of astronomers hitherto, and is, so far as our 

 knowledge extends, an anomaly in the celestial motions. 



The point of space at which it is possible for this encounter to 

 happen, is situated at a distance from the nearest point of the terres- 

 trial orbit of little more than half the semi-diameter of this orbit : it 

 is then by no means impossible that it may fall to our lot to witness 

 the interesting spectacle of the conflict of these two comets in the 

 heavens, and at a distance which is inconsiderable when compared 

 to that of some other bodies in the solar system. Should such an 

 event not result in the destruction of the two comets, it would at least 

 occasion a great derangement in their motions, indeed a total change 

 in their orbits ; so that we should perhaps have little cause to fear, 

 for the future, the long dreaded encounter of Biela's comet with the 

 Earth. 



The following calculation, founded on the elements given by Encke 

 and Damoiseau for the year 1832, will serve to show the possibility 

 of the event alluded to : the elements are as follows : — 



Eiicke's comet. Biela's. 



Longitude of the ascending node, 334° 32' 5.2^' 248° 12' 24'' 

 Inclination to the ecliptic, 13° 22' 12.3" 13° 13' 13" 



Semi-transverse axis, 2.222212 3.53683 



Angle of eccentricity, 57° 43' 6.3" 48° 44' 30.4" 



From these data we find, by the well known formulae of spherical 

 trigonometry, that the common intersection of the planes of the two 

 orbits, makes with the line of the nodes of Encke's comet on the 

 ecliptic an angle of 47° 15' 52.4", and with that of Biela's comet 



