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    CN and Mason-Dixon line
    From: Bruce J. Pennino
    Date: 2013 Nov 26, 19:30 -0800

    Hello:

    I recently stumbled on and now reading "Drawing the Line " by Edwin Danson. The book is meticulous and fascinating for anyone interested in boundary surveys, geodesy, surveying and navigation instruments, time keepers etc. Basically the book describes how two English Surveyors (Astronomers, navigators and mathematicians) surveyed and resolved a boundary dispute between Pennsylvania and Maryland. Mason and Dixon used many CN skills. But the book also brings together so many familiar CN topics and characters. Harrison,Maskelyne, astronomer royal Bradley. Briefly, Mason worked under Bradley, and Dixon was an assistant to Mason. Maskelyne, Mason and Dixon were all involved with developing instruments and taking data for the 1761 transit of Venus.

    I've always been curious about the historical background of dip measurement data, and assumed the basic work was done by British astronomers. I guess you know if you are a close student of "dip", as Danson states, James Bradley published in 1720 a table of refraction "for the correction of astronomical measurements for the light bending effects of the atmosphere". That is really early! Amazing to me. Maskelyne assisted Bradley in preparing a table of refractive indexes that were published in the 1767 Nautical Almanac. I checked the 1802 Bowditch & Kirby Table VII Depression Dip of the Horizon (and also Bowditch 1837), and the dip table is basically the same as present. I conclude the original astronomical work and calculations for dip were done in early to mid 1700s. Really astounding the excellence of the early astronomers and mathematicians.

    Best regards

    Bruce
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