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S. Wales) by Tebbutt and 18 occiiltations observed by Ellery in 

 1874 and '75 at Melbourne. He applied to the ephemerides of the 

 moon of the Nautical Almanac the corrections of Nkwcomb's Investi- 

 gation and took for the relation between the moon's radius and 

 the horizontal parallax the value ^-rrr 0.27264 found b.y me. {VersL 

 en Meded. Ahad. Amsterdam Afd. Nat. 1^^ Reeks, Vol X p. 25). 



But as nevertheless a constant error might occur in the obtained 

 results, he calculated, as a test, a large number of occultations, 

 which had been observed either at Greenwich or at places of 

 which the longitude had been determined by telegraph, viz : 31 

 observed at Greenwich, 25 at Washington, 40 at Nikolajef, 44 at 

 Oxford, 30 at Luxor, 46 at Strassburg, 13 at Jjcipzig, 7 at Vienna, 

 2 at Königsberg, 2 at Moscow, 2 at Pulkowa and 1 at Kiel. 



Thus he was able to derive the correction to be applied to a 

 longitude determined by a disappearance at the dark limb, and found 

 for this after a graphical compensation : 



I have on purpose given this table in full to show how constant 

 is the positive sign of the correction. For the reappearances Auwers 

 found a correction which in the mean was larger by -\- 0%23. (Although 

 this value has been found iiaving regard to weights, it yet seems to 

 me rather uncertain ; I tind for its mean error =t 0%64). It appears 

 from this that this correction is due not to an erroneous value of 

 the moon's radius, but to a slowly varying error still left in the 

 tables of the moon. 



Now if we want to apply this correction — and I consider this as 

 quite justified — we must also take for the relation k between the 

 apparent radius of the moon and the horizontal parallax the same 

 value as Auwers has used and hence apply the necessary corrections 

 to our longitude. 



The formulae required for this could be easily derived. Let the 

 diiference in right ascension between the moon's centre and the place 



