LAC TCHAD. — NOTICE ASTRONOMIQUE. 2%J 
M. Christie, directeur de l'Observatoire de Greenwich, estime que «l'adop- 
tion de la valeur la plus probable de la correction aux coordonnées de la Lune 
dans le Natitical Almanac pour un jour donné est une cbose qui demande un 
jugement dans chaque cas particulier» et nous adressait un tableau des erreurs 
qui, d'après son jugement, devaient être adoptées pour chacun desjours de nos 
occultations 
C'est une opinion analogue que nous exprimait M. Newcomb en nous disant 
et que les résultats des observations méridiennes faites dans les observatoires ne 
répondent pas bien à ce que nous nous proposons »; et l'illustre savant qui 
devait malheureusement disparaître quelques jours plus tard ajoutait «que nous 
avions uniquement besoin des corrections qui seront déduites des tables qu'il 
espérait publier dans trois ou quatre mois* 2 '??. 
"> Lettre de M. Christie à M. le capitaine cTintauterie coloniale Tillio, commissaire français, 
Paris : 
iqoij, July sa. 
SlR, 
VVith référence to your lelter o( Line f> , I would explain lliat the adoption of tlie niost probable 
value of Ihe correction to the Nautical Almanac place of the Moon for a given day is a matter whicli 
reipiires judgment as to the particular eircumslances, bearing in niind that the observations with 
the transit circle and the altazimuth are each liahle to error and that the corrections to the Moon's 
tabular place change from day lo day. Where observations of the Moon's linib and of Mosting A bave 
been obtained both with the transit circle and altazimuth on the day for which the correction is 
requiredl consider the best course would be to take tbe simple mean of the four resulls wilh 
equal weight. In other cases judgment lias to be exercised. 
Under thèse eircumslances 1 liavc thought il best to send you the enclesed table of the errors 
which in my judgment should be adopted for the days on which you require thoni. In some cases 
there is uecessarily mue h iiiuerlainly, r. >j. Myt'.i Oelnber y/j and a."» and December •->••, Ihere being 
no observations at (ircenwich siillicienlly near your dates, but in any case 1 think it will be bélier 
to apply corrections for the errors adopted rather than to use the uncorrected Xaalical Almanac 
place. 
I am, Sir, 
Your obedient servant, 
W. H. E. Christie, 
Aslronomcr Royal. 
Lettre de M. Newcomb à M. le rapilaiiie d'infanterie coloniale Tilho, commissaire français. 
1 am in receipt of your letter of Juue h, and will take pleasme in doing ail that I can toward 
promoting the objects of your inlcrnational commission. 
As regards the publication of matters pertaining to Ihe occultations they will be issued by the 
(Jllice of tbe Xaittical Almanac in Un; Naval Observatory. The same is true of the tables of correc- 
tions to Hansen's tables of tbe Moon which will probably appear bofore the discussion of occultations. 
But I take tbe liberly of repeating what I said to you before, that the results of meridian obser- 
vations as îuade at observatories will not well answer \our [inrpose. AH (bal you need are corrections 
to l)e derived from the tables which 1 bope to publish within three or four months. 
Ilot it is not even necossary foi' you to await the publication of thèse tables. Il is qnile possible 
mission Tii.no. — i. 1 6 
