1871.] 



Mr. J. R. Hind on Transits of Venus. 



423 



April 20, 1871. 

 Dr. WILLIAM HUGGINS, Vice-President, in the Chair. 



The following communications were read : — 



I. " Note on the circumstances of the Transits of Venus over the 

 Sun's Disk in the years 2004 and 2012." By J. R. Hind, 

 F.R.S. Received March 1, 1871. 



While preparations are being made by astronomers of various nations for 

 the observation of the approaching transit of Venus over the sun's disk in 

 December 1874, it may be of interest to know under what conditions the 

 pair of transits in the twenty-first century will take place. This conside- 

 ration has induced me to make a careful calculation of the circumstances 

 of the transits in 2004 and 2012, from M. Leverrier's Tables of the Sun 

 and Planet, which at present are extremely accurate, and which, there can 

 be little doubt, will closely represent the phenomena to be witnessed in 

 those years. The calculations have been made entirely by myself, but 

 with every precaution to avoid error, and I have confidence in the results. 

 The following are the resulting elements of the transit in 2004 : — 

 Greenwich mean time of conjunction in right ascension 2004, June 

 7 d 20 h 51 m 28 s -8. 



O I II 



Right ascension of Sun and Venus .... 76 50 28*6 



Declination of Sun +22 53 20'4 



Venus . . +22 42 52*3 



Horary motion in R.A Sun .... 2 35*07 



Venus .. -1 37*40 



Horary motion in declination. Sun .... +0 13*00 



„ „ Venus .. -0 43*83 



Semidiameter of Sun .... 15 45*74 



„ Venus . . 28-75 



Horizontal parallax Sun .... 8*78 



Venus . . 30-85 



Log. distance of Venus from the Earth. . 9"46069 



Equation of time . . l m 15 s, 6 (additive to mean time). 

 Hence, for the centre of the earth, — 



d h m s 

 First external contact ... June 7 17 3 43 at 115-0 from N. towards E. 



„ internal „ „ 17 22 35 at 118-0 ,, 



Second internal „ „ 23 5 40 at 214-6 „ 



„ external „ „ 23 24 32 at 217*5 „ 



And / being the geocentric latitude, p the radius of the earth at any place, 

 VOL. xix. 2 L 



