Astronomy and 18th Century surveying

[Bob Norton]

>Sez here in the New columbia encyclo that Charles Mason and Jeremiah 
>Dixon were astronomers.  I admit I'm ignorant.  Surveying have a heck 
>alot to do with astronomy in the 18th C?

Surveyors often found themselves in situations in which they knew neither
the time nor their location. They would observe events of the four Galilean
moons of Jupiter and check contact and eclipse times against the ephemeris
from the Paris Observatory. This would give them the exact time. Once they
knew the time, their location could be calculated by using stellar transit
times, checked against a freshly reset chronometer.