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[[left margin]] Solar eclipses not proper for determining the Longitude of places upon the earth. [[/margin]]

MR URBAN,

I shall endeavour to shew that solar [[strikethrough]] E [[/strikethrough]] [[insertion]] ^ e [[/insertion]]clipses, tho' recommended for ascertaining longitude, upon examination, will be found very erroneous, though the times be taken with the greatest exactness. It may not be improper to consider, what are the requisites proper for this prospose viz. that the beginnings and endings of observations made for this purpose, be seen in the same moment of time in all places where visible. Examine this in a solar eclipse; suppose the sun totally eclipsed, and upon the same meridian in a different degree of latitude, it may be beheld but just barely eclipsed, so that the beginning and end is but a few minutes, likewise on the same meridian (to wit in the intermediate spaces between the two places) the quantity of the eclipse will be very different, and consequently the beginnings and endings of the eclipse as different and variable in time, th[[strikethrough]] at [[/strikethrough]]at is, in the the places where the eclipse is total it is seen to begin first, and end last, and in the other case, the beginning will be later and the end sooner. 
This shews that solar eclipses will not be sufficient to determine the same meridian, much less any other. But in eclipses of the moon and satellites, the times of their going in, and coming out of the shadow of their primary is seen in all places where visible at the same moment of time, and therefore capable of determining the difference of meridians with great exactness. Those that have a correspondent observer in a different meridian, and are minded to make the most of a lunar eclipse, may take the times of the beginning and end, and (if total) the beginning and end of total darkness, also the times of the shadow passing over the principal or most remarkable spot. (Gents. Mag. Oct. p. 472)    J. R   

[[left margin]] The same refuted [/margin]]

Mr. URBAN,

By attempting to prove that longitudes deduced from observations of solar eclipses [[underlined]] 'will be very erroneous, though the times be taken with the greatest exactness' [[/underlined]], J.R. has shewn that he is ignorant of the method of determining the longitudes of places from such observations. It is not, as his objection supposes, by immediately comparing the observations at one place, with those at another; but the time of the [[underlined]] true conjunction [[/underlined]] at each place is deduced from the observations at that place, and from the difference of the times thus deducted, the difference of the meridians of the places of observation is inferred. Now [[underlined]] this [[/underlined]] method is so far from being very erroneous, that, in the opinion of the ablest astronomer, it is [[underlined]] at least [[/underlined]] as accurate, as any we have. (Gents Mag. Nov. p. 522.) W.