$6 Mr. PiAzzi’s Calculations of Longitudes 
The refult of the obfervation at Greenwich is confirmed in the 
moft fatisfaCtory manner by the obfervations of Oxford andLoam- 
pit-Hill, which Dr. Hornsby and Mr. Aubert have done me 
the honour to communicate to me. Thefe three obfervations 
perfectly agree in the latitude of the moon ; whence it follows, 
that the duration of the eclipfe was judly obferved. And 
whereas the difference of longitude for Oxford, as determined 
by thefe obfervations, is only one fecond, and that of Loam- 
pit- Hill only two feconds, different from that which had been 
determined by means of the beft time-keepers and other mod 
exaCt obfervations, it follows, that thefe three obfervations 
may be confidered as a fingle one, having a treble degree of 
accuracy. In effeCt, if the moment of conjunction found for 
Oxford and Loampit-Hill be reduced to the meridian of Green- 
wich, by adding to the latter 5", 4, and to the former f o 7/ , 
and a mean be taken, it will appear, that this mean differs 
only by 0,6 of a fecond from the conjunction deduced from 
the obfervation made at Greenwich only. This alfo clearly 
proves, that the eclipfes of the fun, when accurately obferved, 
give nearly the fame exaCtnefs as the occultations of the dars, 
which from their nature are confidered as the mod exaCt. 
The obfervation made at Dublin deferves our greated attention, 
particularly fince the edablilhment of a very excellent obferva- 
tory there. Dr. Ussher confeffes, that the longitude of that 
city has not been exaCtly determined (fee the Tran factions of the 
Royal Irifh Academy for the year 1787, p. 86.). He fuppofes 
the longitude of Dublin to be 24/ 58" W. which he determined 
by means of a time-keeper, which Mr. Arnold happened to take 
with him to that city ; whereas I find it to be 25' This 
my determination I believe not to leave the uncertainty of two 
feconds ; 
