NavList:

Greg, you wrote:
"It sounds a little odd that the Sumner method would not yield the same accuracy."

You're right: it does yield the same accuracy, but only if a few conditions are met. Back in the late 19th century, Sumner lines and other methods that used LOP plots were only just becoming popular. There was a real bias against plotting back then, and it seems that there was little advice offered to students and other potential users. It takes a sharp pencil and careful work with dividers to get the plotting done correctly. Even the simple aid of ruled graph paper was a rare thing back then. Also, the accuracy of a true "Sumner" fix degrades as the spacing between the latitudes increases because the approximation of the actual circles of position as straight lines starts to fail.

In general, Sumner lines and other plotting methods were considered some sort of "child's play" in that era. Real men calculated. Examples of Sumner line calculations are few and far between in actual logbooks. There are some hints in earlier decades but they may just be tentative steps. The earliest reference I've found to Sumner lines in primary navigation sources, as opposed to textbooks dates from 1859 (and even that just a single experiment on one day in the mid-Pacific). Poor old Sumner went mad waiting for navigators to realize that those lines of his were a revolutionary solution to the problem of celestial navigation. It didn't really happen until decades after he died.

-FER

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