[407], 
ftinguifii one Satellit horn auotlier, and that Tables or 
ther contrivaaces for fliewing their Mutual pofitions are 
here wanting i to which 1 anfwer. 
Thatif it be not praxflicable at Sea they: c imot deny 
but it is at land ; That t]xQX,x\xQ. lon^ituds of remote Coajls 
from us are the firft thing defired for the correc^tion of 
their Charts j let them attempt thefe firfl, and I doubt not 
but the fuccefs will encourage them fo much, that they 
will readily find means to put it in practice at Sea. That 
the French haveaifed this method luccesiully both in Den- 
mark^ and their own Country; That 2. TehjcQpe of 14 
foot long at moft, or for need one B foot, with broad 
eyeglaffes, will be fufBcient for this purpofe; that the di- 
ficultycanot be known till it be tried, and that uie ren» 
ders many things eafie which our firft thoughts concea- 
ved unprad:icable. 
That tht Satellits may bediftinguifhed by their Magni- 
tudes^ the third from ^ being the biggeftj the firft fome- 
thing lefs, the fecond yet lefs than the firft, and the 
fourth or outermoft the fmalleft. And to their laft ob- 
jedlion, that if I find this method heeded by tliem, I fhall 
take care to publifli eafie T^W^-f for finding their Configu-- 
rations and £i:/^^y>j in good time. I delay it at prefent 
on no other account, then that by further Obfervations 
I may get a better knowledge of their Motions^ for tho 
thefe Satellits were difcovered ,74. years agone, yet have 
we no obfervations of x\\^ Ecltffes^ that we may rely on, 
hQ^OTQ Hodiernas^ and.the firft of his is fcarce 42 years 
old as yet : I hope ne^^erthel^fs my preleat Tables 
will not erre fenfibly for half a, dozen years farther , and 
that in the mean time I may give them a further corre- 
dtion by the help of fuch Obfervations, as if God. fpare 
me life and health, I intend to make, whereby they may 
be rendred ferviceable for a much longer time, without 
any confiderable faults. 
As for the C/s^r^3^^^z^^ itfelf I give init firft the Moneth, 
then the day, and to avoid miftakes 1 have prefixed the 
H h h Tla- 
