354 VENUS IN DAYSIGHT — CAMERON. 



I think it is likely that luy failure to see Venus On May 31 

 and June 1, 1898, when the sky was in good condition, was 

 chiefly due to want of proper eye-adjustment. It was certainly 

 not due to Venus being too difficult, or to my not knowing 

 where to look. This I was sure of, and very exactly, for each 

 of those days ; but, for several weeks before, my eye had been 

 unpracticed in far-off focussing. 



* * * * 



The star-gazer who has only his naked eye to work with can 

 see Venus in daylight in a clear sky, on at least 84 days out of 

 every 100, on the average. The astronomer with his telescope 

 can see her every day. How near to the astronomer's record 

 may the star-gazer push his if he is provided with a small optical 

 instrument ? 



If the instrument is like an opera-glass that I often use in 

 making observations, he may hope, under favorable conditions, 

 to make a record of 97 days out of the 100. 



This glass — which I call N. when making notes — has a magni- 

 fying power which I estimate at 2f diameters. Its object-glasses 

 have a clear aperture of 1| inch. Its length over all, when 

 focussed, is 4f inches. A larger binocular — one of the kind 

 called field-glasses — should, of course, do better than this, but the 

 one I use has no better Venus record than the above, although, 

 at the limit of visibility, it always found and held the planet 

 more easily than the opera-glass did. I call my field-glass A. 

 Its length when focussed is 7| inches, the aperture 2|, its power 

 4 diameters. It bears the name of Dufourmantel of St. Cloud, 

 and was bought there for 75 francs. (Bardou, of Paris, offers 6- 

 diameter ones for 55 francs.) 



At the inferior conjunction of July, 1892, my eye failed to find 

 Venus on the ten days between the 6th and the 17th. On three 

 of these days neither sun nor Venus could be seen here. Five 

 others were not good days, but my field-glass managed to pick 

 up Venus on each of them. Two were good days, and one of 

 them was the 9th, the day of conjunction. I had not intended 

 to try any observation with these small glasses on this day, takiuo- 



