COMET OF 1889-1896-1903 221 



3. Lexell's comet underwent its notable disturbance in 

 August, 1779, and, moreover, this disturbance took place in 

 that part of Jupiter's orbit in which the Brooks comet suffered 

 its change of elements in 1886. Between these two appulses 

 there intervened a period of 107 years, which must be accur- 

 ately accounted for in order to establish the identity of these 

 two bodies. That is, during this interv^al the comet must have 

 made two, three or four complete revolutions about the sun, 

 and its period, therefore, must have been one half, a third or 

 some aliquot part of 107 years. Chandler, in the above men- 

 tioned paper,^ found that the period of the Brooks comet pre- 

 vious to 1886 was 26.9 years, very approximately one quarter 

 of the 107 years to be accounted for. The possibility of the 

 comet having made three revolutions during this period can be 

 eliminated, according to Chandler, as this would have brought 

 the comet and Jupiter together in 1815 and 1850, at which 

 times the perturbations would have been enormous. The in- 

 terval can hardly be accounted for upon any other supposition 

 than that of four revolutions of the comet being equal to nine 

 of Jupiter's. 



A comparison of the elements of Lexell's comet, subsequent 

 to its disturbance in 1779, as given by LeVerrier, with those of 

 the Brooks comet previous to 1886, as given by Chandler, show 

 a striking likeness. The longitude of the node is nearly the 

 same for both, 175° for Lexell against 177° for Brooks ; the 

 inclinations differ by less than 4° and the eccentricities are not 

 far apart. Again, the heliocentric longitudes, within which the 

 attraction of the sun was overborne by the influence of Jupiter 

 are nearly the same for both comets. Taking all these points 

 of resemblance into consideration and assuming the substantial 

 correctness of the period (26.9 years) he deduced, Chandler 

 concluded that there is " an overwhelmingly strong presump- 

 tion in favor of the identity of these two comets." 



4. The question of identity was investigated in an entirely 

 different manner by Schulhof,^ who made use of a criterion 



^ Astr. Jour., No. 205. 



^Bulletin Aslrononiique, November, 1889. 



