— 2.5 



338 ASTRONOMICAL an© 



O's centre pafled the meridian on the 27th of March at 1 1 59 19 A. M. 

 Equation of time + 5' 20". 3 . . . . '25 20.8 



Clock too flow mean time . . . . . 0618 



Ey the paffage of Sirius over the meridian on the 27th') 

 and 28th tlie clock gained on mean Iblar time, about ( 

 10'' per diem, w.liich is equal to about z".§ when l" 

 Sirius was obferved, which is to be deducted J 



Clock too flow mean time when Sirius pafled the meridian o 5 59.3 

 Equation of time . . do. . . o 5 16.1 



Clock too flow apparent time, which differs but i al 



fecond from the error given by Sirius J ^^' 



The tiearefl diftanccs of the limbs of the O . and 5 , were taken twice at this 

 Ration, (as entered in the journal), and may fervc as examples of the accuracy 

 of that method of determining the longitude. — As their altitudes were not 

 taken at the time of the obfervations, they were determined by calculation : 

 The latitude and time being known from oblervation, and the declinations 

 deduced from the Nautical Almanac upon a fuppofition that the longitude 

 was about 5 hours, and 52 minutes, weft from Greenwich. — The method 

 of calculating an altitude ; the latitude, time, and declination being given, 

 may be found in moft books of fpherical trigonometry, and a very eafy one, 

 particulaily adapted to this purpofe, in the requifite tables problems 5, 6 

 and 7 ; but to prevent any errois which might arife from this fource, and 

 affed the determination of the longitude, I would recommend that the al- 

 titudes be determined both ways, as checks upon each other. — Either of 

 the methods bring nut the true altitude of the ©'s, or J) 's centre ; but as 

 die apparent is generally wanted, it will be had by fubftiadling the paral- 

 lax in altitude, and adding the refradion. 



h I II 



The firft obfervation was made by the clock April 8th at 

 Clock too fluw apparent time 



The apparent time of the obfervation was therefore at 



Obferved diftance of the limbs 



O's fcmi-diameter .... 



}>'s do. ..... 



Error of the Sextant .... 



J 's incrcafed femi-diameter for her altitude 



Obferved diftance cf the centres 



O's true 



