( J03* ) 
The life of the foregoing TABLES. 
' H E Eclipfes of the firft Satellite of Jupiter j as 
Jl^ has been already faid, afford the beft means of 
determining the Longitude of places on the Land, 
where Telefcopes of a convenient length may be ufed ; 
thirteen of thefe Eclipfes happening every x3 Days; 
but it is requifite that the Obferver know near the 
matter when thefe opportunities offer themfelves, 
leaft on the one hand he let them flip, or elfe grow 
weary by a too long attendance on them. 
Thofe therefore who are curious to obferve them, 
may readily compute the times of the Immerfions 
or Emetfions of this Satellite, and that with great 
exadnefs, by the following very fliort Precepts, which 
admit of no Exception or Caution, viz. 
Out of the firft Table take the Epoche for the Year, 
with its correfponding tJumb. A and Numh B ; and to 
them add, out of the Tables of Months, the Day, 
Hour, Minute and Second, neared lefs than the time 
of the Eclipfe you Peek for, together with its Nam, 
A and B: the Sum of the times is the mean time of 
the middle of the Eclipfe. a. With Nam, A thus coL 
lefled take out the fird ^Equation of the Conjun- 
tdions ; as alfb the iEquaxion of Num. B. always to be 
added to Num. B. before found, j. With Num. B. fb 
equated, take out the fecond /Equation of the Con- 
lundions ; and in the lad Table, the third /Equation, 
as alfb the Semi-duration of the Eclipfe anfwering to 
Num. A. 4. To the mean time of the middle of the 
Eclipfe, add all thofe three /Equations ; the Sum fhall 
be the true equated time of the middle of the Eclipfe 
fought. 5. If Num. B. equated be lefs than 500^ fubdradl 
