lO BROWN : 



quot part of another arc which measures another angular 

 opening, namely, the sun's angular semi-diameter. The arc, 

 then, of which V'V" is the chord is computed in the manner 

 following : — 



If the moment when the planet is in contact with the sun 

 at i (ingress) be noted with great exactness, and also that at 

 e (egress), this interval of time will be an enlarged measure 

 of the choi'd ie as seen from the more southerly station C. In 

 like manner the observer at S, making the same observations 

 at i' and e', we shall have obtained the relative lengths of the 

 two chords ; and if their relative lengths, then their distances 

 from the centre in aliquot parts of the sun's semi-diameter. But 

 the angular value of the sun's semi-diameter is known, though 

 not accurately ; hence, the angle M, under which the differ- 

 ence of the solar parallax and that of Venus appears becomes 

 known, and, so the others, as set forth. 



It is true the difficulty of the imperfectly known angular 

 semi-diameter of the sun has not yet been gotten over, but the 

 substance of Dr. Halley's paper, referred to above, has been 

 given, and the original may now be quoted. 



The communication is entitled : 



"A new Method of determining 

 the Parallax of the Sun or 

 his distance from the Earth, 

 by Dr. Halley, Sec'y R. S. 

 No. 348 ; p. 454. Translated 

 from the Latin." 



In the abridged Philosophical Transactions, London, C. & 

 R. Baldwin, it is to be found, Vol. VI, pp. 243, et scq. 



"There remains, therefore, Venus' transit over the sun's 

 disk, whose parallax being almost 4 times greater than that of 

 the sun will cause very sensible differences between the times 

 in which Venus shall seem to pass over the sun's disk in dif- 



