150 Royal Astronomical Society, 



and it is for this purpose I have undertaken the present series of 

 charts. . . . The stars included in Weisse's Catalogue from Bessel's 

 Zones were first laid down for 1825 as points of reference. All 

 other stars, to the tenth magnitude inclusive, were then entered by 

 estimation of their positions with respect to the neighbouring mem- 

 bers of Weisse's Catalogue. . . . The charts for the hours of right 

 ascension in which the ecliptic falls beyond the declination limits of 

 the Berlin maps ( — 15°) are in a state of forwardness, and will be 

 published as soon as they are completed. They are regularly com- 

 pared in their present state with the heavens, so that the search for 

 planets and the formation of the charts are going on at the same 

 time. ... I take this opportunity of expressing my warmest thanks 

 to Mr. J. R. Hind, for the great care and indefatigable zeal he has 

 displayed in the formation of this chart, which, to my knowledge, 

 he has examined with the heavens from fifty to sixty times ; but the 

 success of his research, as shown by the discovery of two planets, 

 speaks for itself, and will, I am sure, dispose astronomers to receive 

 these charts with confidence." 



Extract of a Letter from Lieut. Giliiss*, U.S.N. 



" The computations for the longitude of Washington, from cor- 

 responding moon-culminations observed by me between 1838-1842, 

 are nearly completed. The results for 1839 and 1840 give the fol- 

 lowing corrections of the (hitherto received) longitude : — 



8 



1st Limb —5-39 by 182 comparisons. 



2nd Limb — 4'41 by 74 comparisons. 



Mean . . — 4'84 by 256 comparisons according to weight. 

 The European observatories with which the comparisons are made, 

 are Edinburgh, Oxford, Greenwich, Cambridge, and Hamburg : the 

 individual results very accordant ; those from Cambridge strikingly so. 

 Comparisons have also been made with the observations of Copen- 

 hagen, Kremsmunster, Cracow, and Wilna, which seem to show 

 considerable errors in the longitudes assigned to those observatories." 



XX. Intelligence and Miscellaneous Articles. 



ON THE EQUIVALENT OF FLUORINE. BY M. LOUYET. 



TN some previous experiments the author had deduced the equiva- 

 ■■- lent of fluorine from the quantity of sulphate of lime yielded by a 

 certain weight of the purest natural fluoride of calcium, and also by 

 artificial fluoride. As the two series of experiments agreed perfectly, 

 M. Louyet had presumed that the results to which they led were 

 sufficiently correct. Nevertheless he decided with some reserve ; 

 for having demonstrated that sulphuric acid did not completely de- 

 compose fluoride of lead, it occurred to him that this acid might act 

 in an analogous manner on fluoride of calcium. His doubts were 

 * Lieut. Giliiss became very favourably known to many members of this 

 Society on his visit to England a few years ago. The observations made 

 at Washington were published in 1846 by the order of the Senate, and 

 have been very freely distributed here and on the continent. They are a 

 proof of what may be done with moderate means by a skilful and conscien- 

 tious observer. 



