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XIX. On the Visihiliiy of the Planet Venus during the Dai/y 

 and the Use that may be made of this Fact in determining 

 Longitude. » 



To Mr. Tilloch. 



_ January 18, 1821. 



SiBj — It is very well known that some of the planets, and the 

 fixed stars to the second or third magnitude, may be seen in full 

 daylight with hut small telescopes ; but I am not certaui whether 

 it is generally known, that Venus can be seen during a great por- 

 tion of her revolution around the sun, in full sunshine with tlie 

 naked eye. As the Moon's distance from the planets may at 

 some future period be employed in deducing the longitude at 

 sea, and Venus is easily found in the daytime, she maybe of more 

 service in that operation than those planets which are slower and 

 less bright. If you think the following extract from my diary 

 worth insertion 'in the Philosophical Magazine, as bearing upon 

 this point, I shall be much obliged by your making use of it. It 

 appears to me, that if ever Venus is employed in deducing the 

 longitude, she affords a ready means of extending the advantage 

 of taking the moon's distance from a planet, through a great por- 

 tion of the day, when it might not have been expected. 

 I am, Sir, 



Your very obedient humble Servant, 



^. 

 1820. li. m. 



May 16 1 P.M. Venus near the 5 . O shining very 

 bright; seen w'\th the naked eye; with 

 power 40 was distinctly seen through 

 flying clouds which obscured the }) ; 

 also distinct with 170. 

 June 24 12 Noon. Again in bright sunshine, zf/Mwo^e J tye. 

 July 10 9 30 A.M. Ditto ditto ditto 



15 2 P.M. Ditto ditto (about 23'^ dist. from©) 

 19 10 45 A.M. Ditto, with power 40 distinct, but 7ioi 



with naked eye. 

 22 1 1 A.M. Ditto ditto through flying clouds, 



but not with naked eye. 

 25 9 A.M. Ditto very beautiful with 40 and 90, 

 ditto. 

 Ditto ditto 70, ditto. 



Ditto very bright, with 40 and up- 

 wards, ditto was in 6 yesterday. 

 August 5 9 30 A.M. Ditto, very distinct with 40 and up- 

 wards, not with naked eye. 

 Ditto ditto ditto ditto. 

 Ditto ditto passing merid. ditto. 



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