ON COMPARATIVE 



Observations 

 of the suii'5 

 diameter. 



1795. 

 March SOth and 31st. Day very favourable; various, sets, 

 of measures taken with divided object-glass 

 and wire micrometers. The extremes of the 

 divided object-glass micrometer measures never 

 exceeding I". Those of the wire microme- 

 ter 0. 



S. Dr.0. 



D. O. G. Micr. 

 * Wire Micr. . 



.\\6'. 2"A5\ 

 . j 16'. 1",9 5 



June 8th. The two different micrometers were applied (o 

 the 42-inch achromatic telescope, and the 

 scales verified. 



Same day, 



D- O. G. Micr. 



Wire Micr. . . 



Semidiameters of©, as given 

 in the Nautical Almanack. 



^15'.46W) , 



June 9, 



D. O. G. Micr 



Troughton's sextant 



int + 3", I 13'. 46",0 j ^^ '^^ >** 



June 15, 



D- O. G. Micr. 



Wire Micr. . . 



. . .•)15'.45",9 7. ,5, 47. 

 . . .5 15'. 46",7 S ' 



June 19. The measures, with the different micrometers, 

 were taken with tlie greatest care ; and a mean 

 of internal and external contacts, of the sun's 

 limb to the micrometer wires, was used as the 

 ♦ measure of the sun's disk by the , wire viwcro* 

 meter. 



* This curtation of the sun's s«nidiameter is the effect of the 

 difference of refraction of the L. L. of the sun from the upper. 



