204 ASTRONOMICAL and 



veyor, I have likewife to acknowledge my obligations, 

 for the promptitude with which they executed the orders, 

 they received, and the aid they gave me in making the 

 obfervations. 



An Account of the Apparatus uftd on the boundary be- 

 tzveen the United States and His Catholic Majejly. 



On behalf of the United States we had, 



iftly, One zenith fe£lor of nearly fix feet radius fimi- 

 lar to the one made by Mr. Graham for Dr. Bradley 

 and Mr. Molyneux, with which the aberration of the 

 ftars, and nutation of the earth's axis were difcovered, and 

 the quantities determined. 



adly, Another zenith fedtor of 19 inches radius to 

 be ufed when the utmoft accuracy was not neceflary, 

 and where the tranfportation of the large one could not 

 be effected without great expenfe and difficulty. Thefe 

 inftruments were principally executed by my late worthy, 

 and ingenious friend Mr. Rittenhoufe, except fome ad- 

 ditions which 1 have made myfelf. The plumb lines of 

 both feftors are fufpended from a notch above the axis 

 of the inftruments, in the manner defcribed by the Rev. 

 Dr. Mafkelyne the prefent Aftronomer Royal at Green- 

 wich, in the introdudion to the firft volume of his 

 Aftronomical Obfervations. A particular defcription of 

 thofe inftruments is rendered unneceflary, by being ac- 

 curately done in a number of fcientific works, particularly 

 by M. de Maupertuis in his account of the meafurement 

 of a degree of the meridian under the ardic circle. The 

 fedtor is of all inftruments the heft calculated for mea- 

 furing zenith diftances which come within its arch. The 



large 



