143 



Finally I wish to inuke a few remarks which refer to another 

 form in which our empirical term can he expressed. 



Prof. E. VAN DE Sande Bakhuizen called my attention to the 

 remarkable fact that the period of the argument x which is added 

 to g agrees, within the errors of ol)servation, with the periodic time 

 of the moon's perigee (the difference in annual motion is 0°.33). As 

 the longitude of the perigee for J 900.0 is 334°.3, our term may be 

 put in the form (if / represents the mean longitude of the moon) 



+ 0"66 sin (/— 89°.l») =: — 0"66 cos L 

 Prof. Bakhuyzen will give a short paper upon the possible signi- 

 fication of our term in connection with this transformation. The new 

 form suggested to me to investigate in how far the term can arise 

 from the circumstance that, following Nevvcomb, my whole investi- 

 gation was based on the tabular errors in right-ascension instead of 

 on those in longitude. 



The great advanttige of this method is that by it the errors of 

 observation in right-ascension are not mixed with those in declina- 

 tion, but we must now pay attention to the systematic differences 

 between the deviations (kt. and öl, therefore also to those [)arts, 

 arising from the tabular errors in latitude. Nevvcomb on pp. 12 and 

 16 of his "Investigation" carefully considers these differences; he 

 finds approximately 



a = l— 2°.r) sin 21 — l°.l sin (2/ ~ 0) -\- l°.l sin 6 



in which S represents the longitude of the node and, as 



da da da 



da = — 61 + —^68 -^ — öi 

 dl do di 



putting 



61 = da — F 



we find : 



P={i- 0.018rf<9 — 0.037 dl) cos {21 — 6) 



— 0.087 di cos 21 

 + 0.0l8d8cos/9 

 -\- 0.2[disin8 



— 0.21 di sin {21 -8) 



Newcomb further points out that P contains no perceptible terms, 

 whose period approaches that of (j, so that their influence upon his 

 and also upon our investigation must be small. 



The value of the term ().018d8 has increased since Newcomb's 

 time, as d8 is now about 10", but its influence may certainly 

 still be disregarded in our investigation. 



