166 Observation on the Flanet Venus. 



rays. The top of the upper sash of the window of the place 

 of observation was likewise so adjusted as to intercept the 

 greater part of the sun's rays from entering the tube of the 

 telescope. The sun's declination at that time was 3° 26' south, 

 and that of Venus 2° 12^ south ; consequently the difference of 

 declination was 1^ 14'= the distance of Venus from the sun's 

 centre ; and as the sun's semidiameter was about 16', Venus 

 was then only 58' distant from the sun's northern limb, or & 

 less than two diameters of the sun. 



This is the nearest approximation to the sun at which I 

 have ever beheld this planet, and it demonstrates that Venus 

 may be seen even when within a degree of the sun's margin ; 

 and it is perhaps the nearest position to that luminary in which 

 this planet can be distinctly perceived. It shews that the 

 light reflected from the surface of Venus is far more brilliant 

 than that reflected from the surface of our moon ; for no trace 

 of this nocturnal luminary can be perceived, even when at a 

 much greater distance from the sun, nor is there any other 

 celestial body that can be seen within the limit now stated. 

 This is the first observation, so far as my information extends, 

 of Venus having been seen at the time of her superior con- 

 junction. 



The practical conclusion from such observations is, that at 

 the superior conjunction of this planet, when its distance from 

 the sun's margin is not less than 58', its polar and equatorial 

 diameter may be measured by a micrometer, when it will be 

 determined whether or not Venus be of a spheroidal figure. 

 The Earth, Mars, Jupiter, and Saturn are found to be not 

 spheres but spheroids, having their polar shorter than their 

 equatorial diameters. But the true figure of Venus has never 

 yet been ascertained, because it is only at the superior con- 

 junction that she presents a full enlightened hemisphere, and 

 when both diameters can be measured, except at the time 

 when she transits the sun's disk, which happens only twice in 

 the course of 120 years. Thomas Dick.* 



BiiouGHXY Ferry, near Dundee, 

 November 1843. 



* The planet Venus has been, at the superior conjunctions, seen several times 

 at less angular distances from the sun than that mentioned by Dr Dick. On De- 

 cember 30, 1798, it was observed by M. Vidal at Mirepoix, in France, at 19' dis- 

 tance from the sun's limb. — Connaissance des Terns pour I'An. xi. p. 240 ; pour 

 I'An. xii. p. 333. 



In a memoir by Dr Wollaston, " On the Finite Extent of the Atmosphere," 



