ORBIT ELEMENTS COMET I., 1899, (SWIFT). 185 



T being some date which is about a mean of the dates correspond- 

 ing to n n etc. The values of a and the coefficients b, c, have been 

 found from equations of condition formed with the values of n n' 

 etc. between the dates 1899 May 17, 1899 May 29. 



The computed values of these quantities being placed in equation 

 1 we have the following 



n<x = + 8*747 + [0-46350]t + [9-35631]r 2 

 The quantities within brackets are logarithms, and the initial date 

 ^equals 1899 May 24. 



The values of n a n' etc. being subtracted from the residuals 

 n n' etc. corresponding to the dates tt' etc., then small differences 

 will result, which are weighted and applied to the value of n 

 corresponding to the date desired. 



The value of the definitive co-ordinate in declination has been 

 found as in the case of Normal I. 



The method just described will be made explicit by the example 

 given in the case of Normal VI. 



Normal VI. — From a number of values of n, between the dates 

 1899 June 8, 1899 June 15, see next page, the following equations 

 have been obtained, 



n o .= + 31-610 - [0-07584]r - [7-86053]r 2 

 n 8 = + 108"583 + [0-95095]r - [8-37020]r 2 

 the initial date being 1899 June 12. 



[p(n-n a )] = _ o - i4 



[P] 

 This normal has been constructed for the date 1899 June 12, 

 therefore r equals o, so that we have 



rc a = + 31-61 

 The value of n to be applied to the ephemeris position for the 

 date 1899 June 12 is therefore 



n = + 31-47. p = 16 

 The value of n to be applied to the declination, has been found 

 in the same manner. 



