Early surveyor’s transits like this one were used to lay out the course of the original Erie Canal across New York State. Though cutting-edge for their day, these instruments were primitive by modern standards, and were prone to errors due to careless use and to rough handling (e.g. being carried on horseback).
Even without errors, the task of finding a level route for a canal in that day was a daunting one. Transits were “line of sight” tools and New York State was a wilderness of trees then. Survey teams consisted of a few men to survey, and a dozen or more axe-men to clear a path through the foliage ahead of them. Their job was to not only find as level a route as possible, but also to make sure there was an adequate water supply that could flow down to the canal to supply its needs. Their success is one of the great engineering feats in American History.
The Original Erie Canal had three high-spots.
Can you find them on this 1832 profile?
Each of those three high-spots needed a source of water that was higher than they were. There are no pumps in the Erie Canal today, and there were certainly none in 1825. Finding those sources – and estimating their ability to provide enough water – was one of the most important jobs of the early surveyors of the canal!