30* 



TRANSIT. OF MERCURY* 



XIIL 



Tranfit of Mer- 

 c»ry. 



Mercury fecn 

 on the fun's 

 diflc, perfectly 

 round j 



Obfervations of the Tranfit of Mercury over the Difk of the Sun; 

 to which is added, an Invcftigation of the Caufes which oftejt 

 prevent the proper ASlion of Mirrors, By William H e r - 

 schel, ZL.D.F.R.S.* 



JL HE following obfervations were made with a view to at- 

 tend particularly to every phenomenon that might occur during 

 the paflage of the planet Mercury over the fun's body. My 

 folar apparatus, on account of the numerous obfervations I 

 have lately been in the habit of making, was in great order for 

 viewing the fun in the Jiigheft perfection ; and, very fortu- 

 nately, the weather proved to be as favourable as I could pof- 

 fibly have wifhed it. 



The time at which the obfervations were made, not being 

 an object of my inveftigation, is only to be confidered as de- 

 noting the order of their fucceffion. 



November 9, 1802. About 40' after feven o'clock in the 

 morning, I directed a telefcope, with a glafs mirror of (even 

 feet focal length, and 6,3 inches in diameter, to the fun ; and 

 perceived the planet Mercury. It was eafily to be diftin- 

 guiflied from the openings in the luminous clouds, generally 

 called fpots, of which there were more than forty in number. 

 Its perfect roundnefs Would have been fufficient to point it out, 

 had I not already known where to look for it. 



10 h 0'. When the fun was come to a fufficient artftude to 

 fhow objects on its furface with diftinctnefs, I directed my 

 attention to the contour of the merculial difk, and found it$ 

 termination perfectly (harp. 



. , • From the Philofophical Tranfactions for 1803. 



(To be continued. J 



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