ASTRONOMICAL OBSERVATIONS. 49 



A number of the eclipfes of the firfi: Satellite of Jupiter, 

 together with a great proportion of my notes relative to the 

 city of Wafliington, were privately taken from my lodgings iii 

 Georgetown, otherwife they iliould have appeared in this 

 paper. 



As the city of Wafliington from its fliortly becoming the 

 permanent feat of the government of the United States, mufl: be 

 an objeft of importance, I prelume it will not be unacceptable 

 to give fome account of the method ufed in laying out the ten 

 miles fquare, and executing the plan of the city. — Preparative 

 to beginning the ten miles fquare, a meridian was traced at 

 Jones's Point on the weft fide of the Potomak : from this 

 meridian an angle of 45" was laid off north-weft erly, and a 

 ftraight line continued in that direction ten miles ; from the 

 termination of this line making a right angle with it, a ftraight 

 line was carried north-eafterly ten miles : from the termination 

 of this fecond line, a third making a right angle with it was 

 carried fouth-eafterly ten miles ; and from the beginning on 

 Jones's Point, a fourth was carried ten miles to the termination 

 of the third. Thefe lines were meafured with a chain which 

 was examined and corrected daily, and plumbed wherever the 

 ground was uneven, and traced with a tranfit and equal altitude 

 inftrument which I conftrufted and executed in 1789, and 

 ufed in running the weftei-n boundary of the State of New 

 York. This inftrument was fimilar to that defcribed by M. 

 Le Monnier in his preface to the French Hiftoire Celefte ; ex- 

 cept in being accommodated to a firm portable triangular frame. 

 The tranfit and equal altitude inftrument is of all others the 

 moft perfeft, and beft calculated for running ftraight lines, and 

 when the different verifications are carefully attended to, may 

 fafely be confidered as abfolutely perfeft. The lines of the ten 

 miles fquare were opened forty feet wide, and a mile-ftone fet 

 up at the termination of each mile where the ground would 

 admit of it, and marked with the magnetic variation at that 

 particular fpot. 



In order to execute the plan of the city, a meridional line 

 was drawn through -he area intended to be occupied by the 

 Capitol, and croffed at right angles by another line paffmg 

 through the fame area : the^e lines ,were continued to the ex- 

 tremities of the city, and became the bafts on which the moft 



coniidcrable 



