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Astronomy. — "Inresthjalion of tl te eri-ot'.s of the tahles of tlie moon 

 of Hansen — Newcomb for the i/ears 1895 — J 902". By Dr. E. F. 



VAN DE SaNDE BaKHUI./ZEN. 



(Communicatfd in the meeting of June '■11, 1903). 



/. Iidrodiirfion. 



1. In the years 1901 — 1902 ^Ir. C. Sanders has made a longitude 

 determination on the West-coast of Africa by means of liie moon. 

 The investigation descril)ed in the following pages was undertaken in 

 order to furnish liini witli accurate data for the moon's places. 



Especially with regard to the systematic errors which aftect all 

 the observations of the moon's limbs, it is desirable to use for this 

 purpose not only a fe\v observations made in the neighbourhood of 

 the days for which the places of the moon are required, but to 

 make a more extensive investigation of the errors of the tallies. 

 There was still another reason foi' doing so. For when I first 

 undertook the \^ork, for which the observations at Greenwich had to 

 form the Imsis, I could dispose only of those up to the year 1899, 

 so that a direct determination of the required corrections was entirely 

 impossible. 



So at first I employed only the observations of the years 1895 — 

 1899, but later I was able to extend my investigation also over the 

 3 following years. For this I am indebted to the courtesy of Mr. Christie, 

 who sent me a complete copy of the observations of the moon made 

 at Greenwich during the years 1900 — 1902 and who thus enabled me 

 to render my results much more reliable. In the same letter, however, 

 Mr. Christie told me that a similar invcstigaticm for a similar pur- 

 pose had been undertaken at Greenwich ^) and at first this made 

 me doubt whether in this circumstance it would not be better to 

 stop my ^vork. But as my calculations for the period 1895 — 1899 

 were rather far advanced, I ultimately resolved to continue them. 

 I considered that perhaps in this case it might be useful when two 

 independent investigations should confirm each other. 



2. It is well-known that the motion of the moon offers many 

 unsolved problems. Quite recently Newcomb in a paper read at the 

 March-meeting of the English Royal Astronomical Society '), (when I 

 had already begun my work), once nu)re cleaily pointed out the 

 deficiencies of the theory which chiefly his investigations had brought 

 to light. Let us shortly recapitulate those investigations. 



1) Comp. Report of the Astronomer Royal .... read VM)'i June 0, p. 9. 



2) Monthl. Not. R. Astr. Soc. Vol. 03, p. 316. 



