258 DELAUNAY'S EXPRESSION FOR THE MOON'S PARALLAX. [30 



Since the errors affecting Delaunay's coefficients of parallax are com- 

 paratively large, it will be necessary to determine the factors by which 

 these errors are multiplied in the equations of condition with a much 

 greater degree of accuracy than is required in the case of the factors by 

 which the errors of the coefficients of longitude and latitude are multiplied 

 in the same equations. Otherwise, it will not be possible to deduce these 

 last-mentioned errors from the equations with the requisite degree of pre- 

 cision. It will be necessary to take special precautions in order to determine 

 with accuracy the corrections of the assumed coefficients in the inequalities 

 of longitude which have long periods. 



