117 



of micrometers they used to deduce their respective semi- 

 diameters. 



It is unnecessary to extend these observations any farther, 

 I shall, therefore, only add to this paper, that it will appear, 

 by comparing the divided object-glass micrometer's mea- 

 sures of the sun's diameters, of December 15, 1794, and of 

 June 19, 1795, that the difference of the perigeal and apo- 

 geal diameters of the sun was found to be 65",14. De 

 la Lande found this difference 64",8. but he calls it, in 

 round numbers, db". 



Note. Where no notice is taken of the time of obser- 

 vations, it is to be understood they were taken very near 

 to noon, and as soon after each other as micrometers could 

 be changed. 



The originals of these observations, and several others, 

 are to be seen in the registry of observations kept at the 

 Observatory, Armagh, for the years 1794 and 1795. 



I have the honor to be, 



DEAR SIR, 



Your faithful and obedient servant, 

 JAMES A. HAMILTON. 



VOL. X. 



