ischich took place on September 7, 1820. 39 



The Rev. Dr. Pearson measured the diameters of the sun 

 and moon not only with one of Doilond's divided object-glass 

 micrometers, but also M'ith one of Troughton's line-microme- 

 ters. By means of the former he made the moon's semi- 

 diameter equal to 14-' 44", 6; and with the latter, equal to 

 14' 44", 7: the semidiameter of the sun being considered as 

 the standard for the scale. These measures correspond with 

 my own, prior to their reduction. Dr. Pearson also measured 

 the luminous portion of the sun, vi'hen most obscured, by means 

 of one of his compound prismatic eye-pieces with variable 

 powers, attached to a 2^ feet achromatic telescope, and found 

 it to be 3' 58",24. This measure would indicate an error in 

 the Itmar tables ; as the eclipse ought not to have been of this 

 magnitude even at Greenwich ; and much less ought it to be . 

 so at the place where the observation was made. The distance 

 between the cusps at 1'' 53' was 28' 53",8 by Doilond's mi- 

 crometer: and the distance of the cusps was exactly equal 

 to the diameter of the moon, on its leaving the sun's disc at 

 2" 2' 25". The end of the eclipse took place at 3" 13' 20" 

 mean time at the place: the beginning was not observed. 

 Dr. Pearson's obsenatory is situated at East Sheen, in N. lat 

 51° 27' 35",7, W. long, l' 3',7 in time from Greenwich. 



Mr. William Allen observed the eclipse at Stoke Newington 

 N. lat. 51° 33' 40", W. long. 22" in time from Greenwich. 



Beginnhig = 0" 22' 31" 



End ... = 3 13 59 



Duration = 2 51 28 



Mr. Isaac Wiseman wrote to me from Norwich (N. lat. 

 52° 38', E. long. 5' lO" in time from Greenwich), stating that 

 the eclipse began there at 0" 28' 45", and ended at 3" 21' 40", 

 mean time at the place. The observation was made with a 

 three feet reflecting telescope, with a power of 1 80 ; and tiie 

 time was deduced from a meridian of his own construction, 

 This gentleman lias also sent me the result of some ex})erir- 

 ments on the power of the burning lens on diflerent substances, 

 during the time of the eclipse. Having procured a ])iece of 

 pasteboard, he affixed thereto four ecjual pieces of dilT'ercnt ct>- 

 lourcd cloths; vi/. black, blue, yellow, antl red; and placed 

 them successively in the focus of a burnhig lens, on the day 

 precedin<r the eclipse. The ibllowing are the periods at which 

 they respectively took lire: viz. 



He 



