204 
Dr. Herschel's Observations 
February 21, 1780. No spot on the disk of Venus; diameter 
i5",9, mean of three measures. 
May 2, 1780. No spot ; power 449; diameter 17", 2. 
May 28, 1780. No spot; power 268 and 449; diameter 
22", 8. 
May 29, 1780. I viewed Venus with a 20-feet Newtonian 
reflector ; power 447. The edge of the disk was so sharp and 
well defined, that there can be no wish to see it better. 
There was 110 spot of any kind. 
I could see no projections of any mountains, though the 
phase of Venus is now such as would be most favourable for 
shewing them. 
June 19, 1780. There is, on Venus, a bluish, darkish spot, 
&dc; and another, which is rather bright, red; they meet 
in an angle at c, the place of which is about one-third of the 
diameter of Venus from the cusp a. See Tab. XXII. fig. 1. 
June 21, 23, 24, 25, 2 6, 28, 29, 30, and July 3, 1780. Con- 
tinued observations were made upon these, and other faint 
spots, and drawings of them annexed. The instrument I 
used was a 20-feet Newtonian reflector, furnished with no 
less than five different object specula, some of which were in 
the highest perfection of figure and polish ; the power ge- 
nerally 300 and 450. But the result of them would not give 
me the time of the rotation of Venus. For the spots assumed 
often the appearances of optical deceptions, such as might 
arise from prismatic affections ; and I was always very un- 
willing to lay any stress upon the motion of spots, that 
either were extremely faint and changeable, or whose situa- 
tion could not be precisely ascertained. 
However, that Venus has a motion on an axis cannot be 
