ON THE VISIBILITY OF VENUS — CAMERON. 153 



interior conjunction. If this were the limit of eye-visibility 

 there would be 91 days out of every 292 during which she would 

 be in\isible, and 200 during- which she would be visible. If then 

 there are any eyes so poor that they can't see Venus when nearer 

 than 20° to the sun, even those eyes can see her foi* more than 

 two-thirds of the time, that is for eight months out of every 

 twelve on the average. 



I have no particular reason for selecting 20" elongation as 

 the upper limit of perfectly easy visibility except that 20 is a 

 nice round number, and that something of this sort may be found 

 convenient to refer to afterwards. As to tlie " perfectly easy " 

 character affirmed of Venus in this position, that is a matter that 

 every one can verify for himself. The first opportunity to do so 

 will occur on the evening of June 25, and the next on the morn- 

 ing of Jul}' 22 this year. On these dates Venus will l)e 20° out 

 from inferior conjunction. This is the easier of the tAvo 20° 

 positions. In general the phase is then only j^^ but the brilliancy 

 is 45. At 20" from superior conjunction the phase is, in general, 

 ,^, but the brilliancy is only 27. The first opportunity for an 

 observation of this last kind will occur on the morning of 

 February 10, and the next on the evening of July 14, 1893. 



Our business now is to see how much nearer to conjunction 

 than 20° the naked e3''e can see Venus, and at how small a phase 

 and how low a brilliancy. 



I shall take up the observations near superior conjunction 

 first. 



In 1888 Venus was in superior conjunction on July 11. About 

 a month later I began trying to pick her out in the sunset sky, 

 but the weather was against me and it was August 23 before I 

 got the first glimpse of her. That was 43 days after conjunction. 

 The elongation was then 12|°, the phase ^, and the brilliancy 

 24.4. The observation was made at 7.30 p.m., 15 minutes after 

 the sun had dropped below the sea-horizon and when Venus was 

 3° above it. I learned afterwards that M. Bruguiere had seen 

 her at Marseilles on August 12. This was only 32 days after 



