Harold E. Nelson
14 Hill Avenue,
Newport, ME 04953
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The attached images were taken by myself
with Steve Randall's digital camera. Here are Steve and Casey
Brennan all the way up from NOAA Headquarters with a Trimble 4000 SSE
GPS receiver. The receiver collects satellite data every 15
seconds as the satellite configuration changes. Satellites are
always rising and setting and move much faster than the stars do.
Attached is an image from the book "The Coast Mappers" by Taylor Morrison, which shows George Davidson taking astronomical readings on stars as they pass over. Actually, Davidson is using a Zenith Telescope to determine latitude, but in the background is an Astronomical Transit used to measure stars for longitude determination. Both instruments were used in Calais, the Zenith Telescope in 1857 to determine latitude, and the Astronomical Transit for longitude between Bangor and Calais. In 1866, only the Astronomical Transit was needed for longitude work between Calais and Heart's Content, Newfoundland, latitude having already been determined.
Although Morrison's book details the adventures of George Davidson mapping the Pacific Coast during the Gold Rush era, it is entirely appropriate to show it here. This is the best glimpse of what it might have looked like in the Calais Observatory. Davidson though, had to measure time with a chronometer, as telegraph lines had not reached the west coast. The men at Calais had the luxury of time transmitted via telegraph wires. Note the oil lamps on the sides of the instrument that illuminated the cross hairs in the eyepiece. George Davidson did go to Calais in 1866 to head the longitude operations at the Calais Observatory, but took ill and had to leave.
"The Coast Mappers" is available online through Walmart.com, and probably other sites. This is a great juxtaposition of determination of latitude and longitude between the 1800's and late 1900's.
Click image for enlarged view.
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