VENUS IN DAYLIGHT — CAMERON. 349' 



much farther out than on that (lay. This was partly the fault 

 of fog, partly of cloud, but mostly of white sky and heat-haze. It 

 was on the I7th at 11.15 a. m., S days after conjunction and 11 

 days after my last ej'e-observation. My note-book says, — 

 " Venus in eye at last, very easy, sky l)lue : what a difference 

 between the white sk}^ accompanying the hot weather of last 

 w^eek and the blue one coupled with the cool bracing air of to- 

 day. Can pick her up easily again and again, and hold her 

 with eye even thro' clouds, light ones of course." 



And so it turned out that the prediction of " a fortnight or so" 

 during which Venus might not be visible to the naked eye in 

 daylight in 1892 had not been made too rashly. If the last sen- 

 tence of the Visibility article were to be re-written now, it w^ould 

 read thus, — " On every clear day in 1892 she could have been 

 seen in this latitude, even at noon, by any eye of average ijuality 

 that knew w^here to look for her, excepting onh" on the ten days 

 between the 6th and the l7th of July." And this other sentence 

 might be added—" And of these ten days five were cloudy or 

 fopfp-y, either all dav or at the best time of dav for seeing Venus; 

 while on three of the other five the sky near the sun was white." 

 ******** 



After Venus passes the limit of visibility on the west side of 

 inferior conjunction, her elongation increases fast and her bril- 

 liancy very fast. And therefoi'e it becomes easier and easier for 

 the eye to see her in daylight. About 36 days after inferior con- 

 junction she is at greatest brilliancy (100 for mean conditions), 

 and her elongation is then about 40". In 36 days more she 

 reaches greatest elongation (about 46'') and her brillianc}^ is then 

 73. Then she begins to swing slowly back tow^ards the sun. It 

 takes her more than three times as long to swing in to superior 

 conjunction as it does to swing out from inferior. Her brilliancy 

 decreases during all this time, l)ut very slowly, and the more 

 slowly the more nearly she approaches conjunction. At inferior 

 conjunction the brilliancy may go down to 0, and usually does 

 go down to very nearly that, but at superior it cannot get nmch 

 below 24. It ought therefore to be possible to see her at a less 



