4l!j 



Rev, Mr, Emmett^s Observations 



PDec. 



reflector of the same aperture and power, but every achromatic ; 

 indeed the quantity of light is astonishing. I have often com- 

 pared two telescopes ; one a triple achromatic by Dollond, fitted 

 for terrestrial observations of 1-^ inch aperture, which is a very 

 fine instrument ; the other consists of two convex lenses ; the 

 object glass has an aperture 0*5 inch, and the same power as 

 the former ; the light is as nearly equal as possible, and in point 

 of distinctness there is little difference. These remarks will 

 show that no imperfections in the instruments employed in 

 viewing Venus can have introduced any errors. 



The first time I observed any appearance of spots on Venus 

 was Feb. 21, 7'' ; I used the reflector, having six inches aperture, 

 and powers from 120 to 400. There were two narrow duskish 

 iiTegular lines, which were best seen with 200. On the 22d, 

 7*" 30™, the spots occupied a different part of the disc to what 

 ihey did the day before, having moved according to the order 

 of the signs. They were very faint, and ill defined. I saw no 

 more spots until March 11, beginning a little before sunset, and 

 continued to 9'' ; the same instru- 

 ment and powers as before. The 

 air was in a very unfavourable 

 Mate. The spots were very con- 

 spicuous, as in fig. ] , still they 

 were not well defined ; during 

 the short time in which observa- 

 tions could be made, this even- 

 ing, no conclusion could be drawn respecting the rotation of the 

 planet. Dr. Wasse observed Venus with the same instrument, 

 and made a drawing of the spots, which coincided with mine. 

 The weather was so uniformly cloudy that no observations could 

 fee made before April 4 : on that evening, from 8'' to IV\ I had 

 an imperfect view of spots ; but the air was so extremely tremu- 

 lous that I could not see them well defined, or perceive any change 

 in their position. April 7, from 7'' to 9'', I had a better view. 

 At 7*', the light was so strong that stars of the first magnitude 

 were not visible. At 7'' the spots 

 were as in fig. 2 ; at 8'' 30™, they 

 appeared to have sensibly ad- 

 Tanced, as in fig. 3 ; the spots 

 a b were not in view before 

 S** 30™. The horns projected 

 considerably beyond the semi- 

 circle, which probably is owing 

 to the planet's atmosphere. 

 Reflector six inches aperture ; 

 powers 120 and 200. 



April 8, 8*'. The air in a good 

 state. Venus appeared as in 



