290 



Reduction of the Olscrvation of the 



** From 12^ 50"" to 13^ 40"" per clock, or from 21^ 56"^ to 

 25^ 46"^ apparent time, I measured the horizontal diameter 

 of Mercury, which, from a- mean of 26 observations upon 

 the scale, amounted to 1 1-646 of the vernier; and from a 

 mean of 27 off the scale, it amounted to 15*255 parts of the 

 vernier; the mean of both amounts to 11*646 parts of the 

 vernier, or 8^'*1 7 ; aild the correction of the vernier is— 0"-95 

 of its parts, or — 0^^*73. 



"By a mean of 21 measures the Sun's horizontal diameter 

 was 5 inches 0^- tenths 8*253 vernier, which diminished 

 by 0'95 the correction of adjustment leaves 5 inches Of 

 tenths 7*3' vernier = 5*0646 inches, answering to 32' 25 "*4, 

 the apparent diameter of the Sun ; from which we derive 

 the value of the scale. 



*' At 14^ 51"" 36'*8, or 23^ 57"* 2r*4 apparent time, I 

 observed with the 46-inch achromatic telescope the thread 

 of light between Mercury and the Sun's limb to break, or 



the 



