CORRESPONDANCE. ï66p.

450

When you nrit let your Watch by the Sun, you are to fubduct from thé time
obferved by the Sun, the Aequation adjoyned to that day of the Month in the
Table, and to fet thé Watches to the remaining hours, minuts and feconds, that
is, the Watches arc to be fet fo much (lowcr, than the time of the Sun, as (in the
Table) is thé Aequation of that day; fo that the Aequation of the Day, added to
the time of the C!ock, is the true time by thé Sun. And when after fome days,
you deiïre to know by the Watch the time by thé Sun, you are to add to the
time, fhew'd by thé Watch, the Aequation ofthat day; and the Aggregate fhall
be -the time by the Sun, if thé Watch hath been perfeétly weU adjuHed after the
meafure of the 7~M// days; for the doing of which, this will be a Conve-
nient way

Draw a Meridian line upon a floor (the manner of doing which is fufficiently
known; and note, that the utmoU exa~tneis herein is not necenary :) and then hang
two plummets, each by a fmall thred or wire, direétly over the faid Meridian, at
the diftance of fome 2. feet or more one from the other as the fmalnefs of thé
thred will admit. When the middtë of the Sun (the Eye being placed fb, as to
bring both the threds into one line) appears to be in the famé line exa~Hy (for
the better and more fecure difcerning whereof, you muft be furnifh't with a glafs
of a dark colour, or fomewhat blackt with the fmoak of a Candle,) you are
then inmediately to fet the Watch, not precifety to the hour oft2. but by fo
much lets, as is the Aequation of the day-by thé Table. E. g. If it were the 2. of
March, the Aequation of thaï day being by thé Table, 8 min. 3 fec.; thefe are
to be tubduc~ed from !2. hours, and thé rcmainderwittbe n.hours.gï.min.
g~. fec.; to which hours, minutes, and feconds you are to fet the Index of the
Watch refpe~tive!y Then after fome days you arc to obferve again in the (âme
manner, and likewife to note the hour, min. and fec. of the Watch; to which you
are to add the Aequation of thefe days, taken oui ofthe Table, And if thé Ag-
grcgate doe luit make 12. hours, the Watch is fet adjuited to the right mea-
fure but if it differ, you are to divide the minutes and feconds of that difference
by the number of the days between both the Observations, to gct thé daily dif-
ference. Let us fuppo~E this fecond Obier vation to have been made the 20. of
M~'cA viz. 8. days after the nrit, and nnding, thaï thé Midd!e of the Sun being
ieen in the Meridian in the line with the two threds, as before thé Watch

h. m. ièc.

points n 1 $!
The Aequation of the 20 of 7~'cA, by the Table, is. o t o ~o
Which being added [o thc time, i'how'd by thé

Watch,gives. t2

tfthis had heen luit !2 hours, thé Watch woutd hâve bccn weH anjutted, but
heing t. min. iec. more than !2, it hach gone fb mueh too tatt inS.days.