I 5° 2 ] 
XXjXHL A Letter from Jofeph Willard to the Rev . Dr. 
Mafkelyne, Afronomer Royal \ concerning the Longitude of 
Cambridp'e in New England. 
Read July 5, 1781. 
R K V. SIS, 
r difference of meridians between Greenwich and 
A Cambridge has been generally reckoned 4I1. 44'. This 
was what the late Dr. wjnthrop made ufe of; but I do 
not find mat he determined it by adtual obfervations, made by 
him at Cambridge, compared with correfponding ones, made 
at the Royal Obfervatory at Greenwich. It appears, that' in 
1769,; at the time of the tranfit of Venus, the doctor was not 
entirely certain of the longitude of Cambridge. He mentioned 
4 h. 44' as near the truth ; but for better fixing it, he gave 
feveral of his obfervations of the eclipfes of Jupiter’s fatellites 
to be compared with thofe made at Greenwich > but there were 
■'v ■■■.V . , . 
too few correfponding ones to determine the point with preci- 
fion ; and as modern aftronomers do not make abfolute depen- 
deuce upon the difference of meridians deduced from the eclipfes 
of JupiteCs fatellites, unlefs there has been a feries of obfer- 
yations, both of immerfions and emerfions, I have wifhed to 
find fome obfervations of folar eclipfes and occultations of fixed 
ffars by- the moon, made at Cambridge, of which correfpond- 
ing ones were made at Greenwich. I have met with no obfer- 
vations of occultations made by Dr. winthrop; but a folar 
2 eclipfe 
