Click on a cover picture for a larger version.
The front cover of The Practical Surveyor features an 'Improved Compass' made by Andrew Meneely of West Troy, New York. The compass is part of the Charles E. Smart collection, which is owned by the New York State Museum. The photograph was taken by and is copyright 2001 David Manthey.
This compass was manufactured sometime between 1841 and 1850, though based on other Meneely compasses, it is likely that it was made sometime after 1843. Although this is quite some years after The Practical Surveyor was written, the compass is almost the same as the circumferentors made by Jonathan Sisson and discussed in the text.
The limb of the compass is marked to a half a degree, and the Vernier allows it to be read to half a minute. Compasses that were in use during Samuel Wyld's time rarely could be read to an accuracy of better than 5 minutes, despite using the same Vernier technology.
The back cover shows the limb of a semicircumferentor made by John Potter in Brookfield, Massachusetts in the year 1785. This instrument is also part of the Charles E. Smart collection. The photograph was taken by and is copyright 2001 David Manthey,
This semicircumferentor is of much simpler manufacture than the compass on the front cover. It has a wooden base (as opposed to brass), and does not use a Vernier. The limb is a half circle of roughly 12 inches diameter, which can easily be read to 10 minutes of precision, even though it is only marked in degrees. The semicircumferentor has folding sights, which aid in transporting the instrument.
Despite being over two centuries old, the instrument is still in good order, with the needle responding readily when the lifter is retracted.
More photographs of both instruments can be found on David Manthey's personal web site, here.
The Practical Surveyor · by Samuel Wyld · with Notes by David Manthey
ISBN 1-931468-06-0 · Copyright © 2001 by David Manthey · 6x9", 244 pages.
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