144 HISTORY OF ASTRONOMY. 



Thus it appears that these two bodies, during the entire 

 period of their visibility, remained at a distance from 

 each other less than the mean distance of the moon from 

 the earth; nevertheless, the perturbations arising from 

 their mutual attraction, did not change their positions be- 

 yond a very small number of seconds at the utmost, from 

 which we nlust infer that their masses were excessively 

 small. 



Biela's comet reappeared August 25, 1852, and con- 

 tinued visible till the 28th of September. The changes 

 of relative brilliancy of the two comets were similar to 

 those observed in 1846. For convenience of distinction 

 we will call the most southern comet A, and the most 

 northern B. The comet A was observed from August 

 25th to September 25th. The comet B was not noticed 

 until September 15th and was followed until September 

 28th. On the 15th of September, A was fainter than B ; 

 on the 19th A was brighter than B ; on the 20th both 

 comets had the same brightness ; while on the 23d and 

 25th A was fainter than B. 



The apparent distance of one comet from the other dur- 

 ing the whole time of their visibility was about half a 

 degree. The absolute distances of the comets from each 

 other according to the computation of Professor D' Arrest 

 were as follows : 



Distance. 



1852, Aug. 27, 1,501,000 miles. 



31, 1,531,000 " 



Sep. 4, 1,559,000 " 



8, 1,582,000 " 



12, 1,601,000 " 



Distance. 



1852, Sep. 16, 1,616,000 miles. 

 20, 1,624,000 " 

 24, 1,625,000 " 

 28, 1,619,000 



