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THE POPULAR SCIENCE MONTHLY. 



Van Diense, and others. The present writer has elsewhere * called 

 attention to the close agreement of the elements of the comets of 1812 

 and 1846. These coincidences are seen at a glance in the following 

 figure, where the dotted ellipse represents the orbit of the comet of 

 1812, and the continuous curve that of the fourth comet of 1846. 



It seems difficult to regard this general similarity as accidental. 

 A possible explanation may be found in the hypothesis of an ancient 

 comet's separation into parts a phenomenon known to have oc- 

 curred in the case of Biela's comet. It has also been pointed out 

 that the paths of both comets very nearly intersect the orbit of Ve- 

 nus ; that of 1812 in true anomaly 341, and that of 1846 in 347. 



On the hypothesis of a common origin it is obvious that these bod- 

 ies must have entered the solar system at a remote epoch. It seems, 

 therefore, quite remarkable that neither is known to have been ob- 

 served before 1812. The period of De Vico's comet of 1846 is still 

 too uncertain to be traced backward through former returns ; but, 

 with a mean period of the Pons-Brooks comet equal to the interval 

 between the two observed apparitions, we find the dates of former 

 perihelion passages to have been approximately as given below. The 



* u Comets and Meteors," Chapter III. The nodal lines are nearly coincident, but the 

 ascending node of the one is at the descending node of the other. 



