95 
finite extent of the atmosphere. 
the motion of Venus can be perceived in her progress toward 
the sun, as would occur from increasing refraction; and by 
comparison of her motion in the interval between his last ob- 
servation and my own, with her change of place for the same 
interval given in the Nautical Almanac, there seems no 
ground whatever to suppose that her apparent position has 
been in the least affected by refraction through a solar atmos- 
phere, although the distance at the time of Captain Kater’s 
last observation was but 65' 50" from the sun’s centre, and at 
the time of my own only 53' 15''. 
Although these distances appear small, I find that Venus has 
been seen at a still less distance by Mons. Vidal of Mont- 
pellier in 1803.* On the 30th of May, he observed Venus 
3 m 16 s after the sun, when their difference of declination was 
not more than i', so that her distance from the centre was 
about 46 minutes of space. Since his observations also accord 
with the calculated places of Venus, they might have super- 
seded the necessity of fresh observations, if I had been duly 
aware of the inference to be drawn from them. 
The same skilful observer has also recorded an observa- 
tion of Mercury on the 31st of March of the same year, when 
he was seen at about 65' from the sun’s centre. 
If I were to describe the little telescope with which my 
observations were made, without taking due care to explain 
the precautions adopted, and the grounds of their efficacy, it 
might perhaps be scarcely credible, that with an object glass 
less than one inch in aperture, having a focal length of only 
seven inches, I could discern an object not to be seen by 
telescopes of four and five inches aperture. We know, how- 
* Conn, des Terns. 1808. 
