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594 SWEDENBORG AS A MAN OF SCIENCE. [Doc. 203.
and likewise the time of the place where I am, the astronom
ical tables must tell me what time it is at the same moment
in the various meridians for which the tables have been com
puted. We thus become acquainted with the difference of
time and consequently of the meridians. We all agree in this
main principle ; but the question now is, in the first place,
how shall I find the apparent position of the moon at a given
time upon the sea, and how shall I afterwards discover its
true position.
These questions you are accordingly pleased to answer
thus, “The time when the moon comes into line with the
above-mentioned stars is observed ; and from this observation
the apparent, and afterwards the true, position of the moon
will appear.” In considering the method of finding the ap
parent place of the moon by such an observation, i. e. when
two fixed stars are in the same degree of longitude, in the
first place, one insurmountable difficulty occurs to me. For
suppose E L to be the ecliptic, Q its pole, Z the zenith, s
and t two " fixed stars in the same longitude, and consequent
ly in the same largest circle Q s t," I am indeed able to
know that the apparent longi
2
tude of the moon is at a, which
is the same as that of the stars;
but if the latitude of the moon,
or ) a is unknown, most un
doubtedly no " apparent place of
the moon" will result " without
any observation of the altitude,"
Ен K
as is said on p. 4, for the ap
parent place of the moon is determined conjointly by the ap
parent longitude and latitude.
With regard to the first argument on p. 4, I have the
honour to observe, that the moon’s distance ) b taken in the
vertical circle 2 ) I, from the point b, where the moon’s
vertical meets the ecliptic, can never be called the parallax of
altitude, except in the sense that the moon has no true latitude;
wherefore b a also cannot be called the parallax of longitude.
I have myself tried to resolve these difficulties (where I
was aided by the printed figures, in which, however, I found
a
I
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