156 ON THE VlS[HlLITV OF VENUS — CAMERON. 



a general limit near superior conjunction an interval of 40 days 

 and an elongation of 10''. Thus no one who wishes to have a 

 daily glimpse of Venus need wait longer than 40 days after 

 superior conjunction to begin having it, and in favorable con- 

 ditions he ma}' hope to be al»le to l:>egin as early perhaps as 20 

 days after. Having once begun, the daily glimpse may be con- 

 tinued, weather permitting, for the next eight months or more, 

 until Venus gets near inferior conjunction. 



Nearer than 13 days certainly, for that is the interval of time 

 that corresponds here to an elongation of 20° ; and we have 

 already found this elongation to be quite unnecessarily large in 

 the case of superior conjunction, although there the brilliancy is 

 only 5 of what it is at 20*^ out from inferior conjunction. 



Let us now see how near to inferior conjunction the observa- 

 tions at hand show that Venus can be seen. 



Owing to several unfortunate circumstances I have never been 

 able to do justice to Venus near an}- of these conjunctions. Be- 

 fore them, the sky has been cloudy or the early evenings have 

 been required for other engagements ; after them, the early 

 mornings have been pa.ssed in the unconscious condition and the 

 horizontal position common to most of us at those hours. As will 

 be seen presently, this last unfortunate circumstance seems to 

 have affected other observers as well as myself, and to it may be 

 largely attributed the fact that there are no observations as near 

 to inferior conjunction after it as there are before it. Then there 

 is the other disadvantage already mentioned in connectien with 

 observations made after superior conjunction : at such a time the 

 observer has no previous day's observation of the same oljject to 

 help him in selecting the right spot in the sk}- to look at. He 

 can get over this of course by taking observations of stars hav- 

 ing the same declination and the same hour-angle as the planet 

 to be observed, but there still remains the other disadvantage of 

 the inconvenient and uncomfortable hour at which planets must 

 be caught earl}^ after passing to the west side of the sun. 



The only observation of mine after inferior conjunction that I 

 have kept a record of was made after an interval of 18i days 



