and Longitude of the Royal Obfervatory at Greenwich. 1 8 1 
the year 1776, I requeued the late Mr. Wargentin, the 
learned Secretary of the Royal Academy of Sciences at Stock- 
holm, and Author of the Improved Tables for computing 
the Eclipfes of Jupiter’s Satellites, who colle&ed obfervations 
of them from the principal Obfervatories of Europe, in order 
to the further improvement of the- tables, to inform me what 
difference of meridians of Greenwich and Paris refulted from 
my lafl ten years obfervations of the eclipfes of the firft latel- 
lite of Jupiter compared with thofe made by M. Messier at 
Paris. In the anfwer which he favoured me with, inferted in 
the Philofophical Tran factions, Vol. EX VII. p. 162. he let 
down the refult of the companions of eight correfponding im- 
merfions and nine emerfions obferved on both parts, by myfelf 
and M. Messier, from which he deduced the difference of 
meridians of the Royal Obfervatories of Greenwich and Paris 
f 35 // . By two correfponding immerfions and nine correfpond- 
ing emerlions, obferved at both Royal Obfervatories, he found 
f zT'. From the obfervations made between 1761 and 1764 
he found f 28". By the obfervations made before 1700, 
f 2 1 // . And, from a comparifon of mine and the Parifian ob- 
fervations, with the intermediate help of his own made at 
Stockholm, f / i(o" : and from the whole he inferred the dif* 
ference of meridians to be f 2f\ 
Twelve years having elapfed fmce Mr. Wargentin’s com- 
parifon, I was defirous to fee what would relult from the fur- 
ther obfervations made during that time, and applied to the Comte 
Cassini, the refpeftable heir of the late M. Cassini de Thury 
and his fuccclfor at the Royal Obfervatory, and to the celebrated 
M. Messier, to favour me with fuch of their obfervations 
of the eclipfes of the firft fatellite of Jupiter as had been made 
correfpondent to mine. Thefe they immediately lent me in 
the 
