Notice of the Periodical Comet o/^1819. 277 



the other elements as proportional to its first power. How- 

 ever, we should observe that, if it were necessary to have re- 

 gard to higher powers of this variable quantity, that the for- 

 mulas which the author has given for this purpose in the be- 

 ginning of his memoir would J|ot be exact, and that it would 

 be necessary to recur to the ordinarv formulas of quadratures. 

 Although the interval of time comprehended between the ap- 

 pearance of 1805 and that of 1819 comprises four revolu- 

 tions of the comet, M. Damoiseau, in calculating the distur- 

 bances which have taken place in the course of that period, 

 has always retained the same values of the primitive elements. 

 It would nevertheless have been proper to change them, at 

 least every revolution, taking into consideration each time the 

 preceding disturbances. This is a point which it will be suffi- 

 cient merely for us to mention to the author, if he proposes to 

 review and complete his work. 



' In the period of twenty-four years which the author has ob- 

 served he has constantly computed the action of Jupiter, and 

 the action of the Earth and Venus only in that part of the 

 period in which the comet is so near that this action is per- 

 ceptible. As to the other planets, he has thought he might 

 neglect their action, which he has regarded as imperceptible 

 on account of their distance, o^ the smallness of their size. 

 He thought, moreover, that he had no occasion to extend his 

 calculations to the epochs of 1795 and 1786, in which the 

 same comet had been observed, because he considered those 

 observations not very exact, or not sufficient to determine the 

 elements of the orbit. M. Encke, on the contrary, was desir- 

 ous to represent these early observations ; but he discovered 

 that in the observed right ascensions and declinations, it would 

 be necessary to suppose errors, the mean of which would 

 amount to twenty-four minutes, and this he judged to be in- 

 admissible. To explain these differences between the results 

 of calculation and observation, M. Encke thought that it 

 would be necessary to recur to the resistence of ether ; and he 

 has announced in a late number of M. de Zach's Astronomi- 

 cal Correspondence, that by taking into account this tangen- 

 tial force, and making a suitable supposition in relation to its 

 intensity, these great differences might be made to disappear. 



