130 HISTOEY OF ASTRONOMY. v^ 



of the present comet, except the inclination, which was 

 too great. Professor Peirce, of Cambridge, has re-com- 

 puted the orbit and obtained a much better coincidence. 

 In short, it appears that the three comets of 1668, 1689, 

 and 1843, all pursued nearly the same path, and presented 

 somewhat similar appearences. What are we to infer ? 

 Mr. Walker inferred that these were different appearances 

 of the same comet, with a period of 2l years, the comet 

 having made seven revolutions from 1689 to 1843. But 

 why was it not seen at either of the intermediate returns? 

 Because (it is said) the position of the comet was unfavor- 

 able for observation. From the position of its orbit, the 

 comet will always have considerable southern declination, 

 which is unfavorable to its being seen in the northern 

 hemisphere. This answer is not entirely satisfactory, as 

 it is improbable that so prodigious a tail should pass un- 

 noticed during six successive returns. 



Professor Schumacher is inclined to regard this comet 

 as identical only with that of 1668, giving it a period of 

 175 years. Professor Peirce has made a comparison of 

 all the best observations, and his result is that an ellipse 

 of short period is inadmissible. The observations may 

 all be represented by a parabola within the usual limits 

 of the errors of cometary observations. An ellipse of 

 about 180 years represents them a little better. Profes- 

 sor Hubbard, of the Washington Observatory, has re- 

 cently undertaken a thorough discussion of all the ob- 

 servations of this comet, and has computed the effect due 

 to the perturbations of the planets. He finds the most 



