554 I'HiLOSormcAL transactions. [anno 1J84. 



thing of either atmosphere or nebulosity about Mercury during all the time of 

 the transit; and yet he is persuaded that such an atmosphere really exists. 



Mr. W. calculated the places of the sun and of Mercury by Halley's tables for 

 2i h , 3i h , and 4-i- h , a space of time including the whole duration of the transit, 

 whence he found as follows, in true time. 



at 2" 3(T at 3 h S0 m at 4 h 30 m 



The longitude of the sun 7 s 20° 22' 43".6 7 s 20° 25' 14".8 7 s 20° 27' 45".9 



His right ascension 7 17 55 55.3 7 17 58 28.4 7 18 1 1.5 



His declination, south 17 51 49 .6 17 52 29-9 17 53 10.1 



« 's geocentric longitude 7 20 32 2-9 7 20 28 40.8 7 20 25 18.4 



His latitude, north 14 31.0... 15 22.6.. . 16 13.8 



Which gives between 2i h and 3| h . . between 3i h and &\*. 



§ 's relative horary motion in the ecliptic ° 5' 33". 3 ° 5' 53".5 



Inclination of his orbit to the ecliptic 8 IS 33 .8 8 14 28 .5 



Horary motion in his orbit 5 57-05 5 57.19 



The diameter of the sun used in the calculations was 32' 24".5, and that of 

 Mercury 9".535 as found above; and the sun's parallax 8".7 at its mean distance 

 from the earth. Whence Mr. W. concludes the difference of the horizontal 

 parallaxes of the sun and Mercury for the day of the transit, Nov. \1, to be 

 4 / '.088. With these elements he calculated the observations of the contacts, the 

 chief results of which are as in the following table. 



Table of the Results of the Calculation of the Observations of the Contacts and of the Centre of Mercury. 



Interior contacts. Exterior contact. Centre of £ . 



„ e .. K , (-beginning 3 h 2 m 3 s . 8.. 2" 56"' n 28\ 8. . 2"58 n, 2S ! .8 



True tune of the observed { en * » 4 l? ^ 4 4 ^ 53 4 _ 4 2Q ^ 



Duration given by observation 1 15 14 . 6. . 1 26 24 . 6". . 1 22 7.6 



Least dist. of the cent, seen from the earth's surf. 15 41. 2.. 15 42. 5.. 15 41.0 



True time of observation at the C beginning 3 5 3.25.. 2 59 3.11.. 3 1 1 1 .7 



earth's centre I end 4 14 31.70.. 4 20 31.13.. 4 18 5.7 



Duration for the earth's centre 1 9 28.45.. 1 21 28.02.. 1 16' 54.0 



Time of the 6 of and g . 4 2 53 . 2. . 4 2 5 4 . 8. . 4 2 44 . 1 



Latitude of $ in die 6 by observation s ° 15' 55". 1 . . s ° 15' 56'".4 . . s ° 15'54".8 



Longitude of the © or § in the 6 7 20 26 37 .6 . . 7 20 26 37 .7 .. 7 20 26 37 .2 



Longitude of g in the 6 allowing for aberration 7 20 27 8 .4 .. 7 20 27 8 .3 .. 7 20 27 8 .9 



L atitude of g in the 6 by the tables, north 15 50 .7 . ■ 15 50 .7 ■ ■ 15 50 .5 



7- r .u ■ ui ( in longitude — 30.8 - 30.6 - 31.7 



Error of the tables j 1n]ati f ude + 44 + &Jf + ^ 



Adopting the lat. of J at the d given by the interior contacts 15' 55". 1, Mr. W. finds the place of 



the S of 5 to be 



r 15° 45' 22".8 supposing the inclin. of the orbit 7° 0' 0" with Cassini, 

 1 15 44 57 .7 6 59 20 with Hatley. 



It appears by this table that the interior contacts give the time of the middle 

 of the transit within -fo of a second of the same by the exterior contacts; the 



