Recovering, reinstalling and rededicating the Calais Observatory.

Each temporary observatory had an astronomical transit. An astronomical clock and chronograph register were wired together with a battery and connected to the nearby commercial telegraph line, which was usually used free of charge after 9 p.m. A local true north meridian was established and a point set upon which to point the transit, then it was aimed skyward through a slit in the roof of the observatory building. The pendulum of the clock was dipped in a pool of mercury, which made second beats on the chronograph drum. The electromagnetic pen was also wired to a telegraph key. When a particular star passed the crosshair, the observer tapped the key, which made an "out of sync" mark on the chronograph register. An etched glass plate could then be placed over the chronograph paper to read time to the hundredth of a second. The surveyor-measurer would then subtract the west station time from the east station time for a particular star, and have longitude in hours, minutes and seconds, which easily converted to DMS (degrees, minutes, seconds) format. These "pie pieces" of longitude spread south in the winter and north in the summer from Harvard College Observatory, the cardinal point of longitude in North America. By 1851, the work had progressed to Thomas Hill Observatory at Bangor, Maine.