292 POOR. 



periodic time of the comet, previous to 1827, was approximately 

 24 years then the comet and Saturn would have been in the 

 same parts of their respective orbits in longitude 300° for many 

 months in 1 786-87, and large disturbances in the comet's motion 

 would have resulted. Slightly different values of the period 

 would have caused the comet to have approached Saturn in 

 longitude 0° in 1790, or in longitude 70° in 1795. We thus 

 see that with elements differing but little from the definitive 

 values a close approach to Saturn is indicated. 



46. While an approach to Saturn at some time between 1786 

 and 1794 is not improbable, yet the uncertainty of the problem 

 is such that we cannot form any idea as to the effect of such 

 approach. In accordance with Tisserand's criterion such an 

 approach, with resultant large disturbances, is necessary to 

 establish the identity of comets Brooks and Lexell. From 

 what we have seen it is, therefore, not impossible that the dis- 

 turbances by Saturn were of such a character as to satisfy this 

 criterion and it is not impossible, therefore, that the two comets 

 are identical. The numerical results of the present investigation 

 are not conclusive, therefore, as to the non-identity of these 

 two comets. These results indicate the probability of large 

 perturbations by Jupiter in 1827 ; the possibility of a close ap- 

 proach to Saturn in 1786-94 and a consequent faint possibility 

 of the comet having been in 1779 in the neighborhood of Jupi- 

 ter at the time when Lexell's comet underwent its notable dis- 

 turbance. Even if the numerical results showed that the comet 

 was in the vicinity of Jupiter in 1779, when Lexell's comet 

 disappeared, this would not of itself prove the identity of the 

 two bodies, although it would render such identity highly prob- 

 able. In this connection it would be well to recall the re- 

 searches of Schulhof on the path of Comet Swift (1895 II) and 

 the possibility of its identity with that of Lexell. 



47. In this paper Schulhof^ showed that the elements of 

 Comet Swift, as deduced from observations, were slightly inde- 

 terminate. He showed that the comet had suffered disturb- 



1 Recherches sur I'orbite de la Comete Swift (1895, II), avant 1S84. Bulletin 

 Astronoraique, March, 1897. 



