350 VENUS IN DAYLIGHT — CAMERON 



elongation when near superior conjunction than when near in- 

 ferior, and M. Trouvelot gives 5° as the limit for the former case 

 as against 10° for the latter. But in the latter case the elonga- 

 tion is changing very much faster than in the former, so much so 

 that while the time interval corresponding to 10" near inferior 

 conjunction is only 6h days on the average, that corresponding 

 to 5'^ from superior conjunction is nearly 20. As Venus has been 

 seen with the naked eye in daylight when only 3 days and only 

 7*^ from inferior conjunction, it should be possible to see her when 

 less tlian 20 days and less than 5*^ from superior conjunction. 



Whether she has ever been so seen I don't know. I have 

 tried my eye on her at such times, but have never had the sky 

 and the air in the best seeing condition. Before I knew of M, 

 Trouvelot's 5° limit, the best I had done near superior conjunc- 

 tion was to see her distinctly on March 19, 1890, ten minutes 

 after sunset. This was 26| days after conjunction, and the 

 elono-ation was 6i°. I have done nothing better since, and I 

 know of nothing better having been done by any other observer. 

 But of course M. Trouvelot must have made a better observation, 

 or must know of a better one having been made, — unless his 5 ° 

 limit is an inference from what has been done, under conditions 

 of much lower brilliancy, at the other conjunction. I have a 

 record of one that would have been a little better if it were 

 more trustworthy. The date is May 24th, 1893, when Venus 

 was 22| days past her last superior conjunction, and when her 

 elongation was 6"^. My note says that from 2 to 17 minutes 

 after the disappearance of the sun I had " several glimpses with 

 eye (?) — not distinct." The "glimpses" and the " not distinct" 

 would not spoil this as an observation, but the (?) does and I 

 don't count it. 



There is another objection to counting either it or the previous 

 one here. They were made after sunset. It is true that it was 

 only a few minutes after sunset, and that at the time il faisait 

 grand jour ; and perhaps a Frenchman might feel justified in 

 saying that it was " en plein jour." I have read in a French 

 astronomical journal of a shooting-star that was seen 34 minutes 

 after sunset, and the heading of the item was " Etoile fileante en 



