5S0 PHILOSOPHICAL TRANSACTIONS. [anNO 1721. 



north or south belonging to the points marked ; the great letters signifying the 

 points the loadstone was applied to, and the small letters showing the conse- 

 quential poles. 



There are two other experiments described in the same letter, relating to the 

 attraction of fluids, one of which, viz. that of the hyperbola made by the sur- 

 face of the water between two glass-planes, being already described in N° 336, 

 we shall only give the account of the other, as follows : viz. 



I took several very thin pieces of fir-board, and having hung them suc- 

 cessively in a convenient manner to a nice pair of scales, I tried what weight 

 was necessary, over and above their own, after they had been well soaked in 

 water, to separate them at once from the surface of stagnating water. I found 

 50 grains to separate a surface of one inch square; and the weight in every trial 

 being exactly proportional to the surface, I was encouraged to think the experi- 

 ment well made. The distance of the under surface of the board from the 

 surface of the stagnating water, at the time they separated, I found to be -jVr 

 of an inch ; though I believe it would be found greater, if it could be measured 

 at a greater distance from the edge of the board than I could do it, the water 

 rising a little before it came quite under the edge of the board. 



On the Method of determining the Places of the Planets by observing their near 

 Appulses to the Fixed Stars. By Edmund Halley, LL. D. N° 369, p. 209. 



Of all the celestial observations that have hitherto been made, none are so 

 capable of perfect exactness, as the near appulses of the moon and planets to 

 the fixed stars ; for though the places of the stars have not as yet attained an 

 ultimate precision, yet these sorts of observations are ever good, and the places 

 of the planets ascertained, in proportion to the correctness of the catalogues 

 that may hereafter be made : but the ordinary number of the stars, with which 

 the planets may be thus compared, being small, the opportunities of observing 

 are consequently rare : whence appears the great use of a full catalogue of 

 telescopical stars, at least within the limits of the zodiac, viz. that these oppor- 

 tunities may be more frequent : and wherever such observations have formerly 

 been made on these small stars, we may be enabled to find them out, and by 

 determining their places, to be certain of the places of the planets also : of 

 which I have given a notable instance in finding the place of the great comet of 

 1 680, in its first appearance, even before it had a tail visible to the naked eye, 

 of which an account is given in N° 342 of the Transactions. And since the 

 Royal Observatory at Greenwich has been put under my care, I have endea- 

 voured to put myself into a condition to supply the many and great vacancies to 



