be in the same proportion greater than at the earth, but this may be modified ( 

 by many causes in operation on the planet and in its atmosphere. 



The distance of the earth from the sun is greater than that of Venus in the 

 ratio of 10 to 7 nearly, and consequently the apparent diameter of the sun as 

 seen from Venus will be greater in the same ratio than as seen from the earth. 

 If E represent the apparent magnitude of the sun as seen from the earth, V will 

 represent its apparent magnitude as seen from Venus. 



The intensity of the sun's light at Venus will be about twice its intensity at 

 the earth. 



TWILIGHT ON VENUS AND MERCURY. 



The existence of an extensive twilight in these planets has been well ascer- 

 tained. By observing the concave edge of the crescent which corresponds to 

 the boundary of the illuminated and dark hemispheres of the planets, it is found 

 that tl e enlightened portion does not terminate suddenly, but there is a grad- 



