A second edition of this useful work having been called for, I have, at the publishers' request, in consequence of the lamented death of the Author, corrected some errors which had been observed in the previous edition, and have otherwise carefully revised the work. In order to render the present Edition still more worthy of the reputation the work has so long enjoyed, I have also taken the Opportunity of mak ing several additions, consisting of descriptions of new and improved surveying and other instruments; and an Index has been added.
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