A geodetic transit observes the transit of a celestial body over the
meridian. In the early 19th century, geodetic transits were used primarily to
determine local time. In the 1860s the United States Coast Survey began using
these instruments, in connection with an electric telegraph, to determine
longitudes. In the late 1870s, the Survey began using transits equipped with
striding levels and micrometer eyepieces to determine latitude, in the same way
that had been done with a zenith telescope.
C. A. Schott, "Determination of Time by Means of the Transit
Instrument," United States Coast Survey Annual Report (1866),
Appendix No. 9.
George Davidson, "Description of the Davidson Meridian Instrument,"
United States Coast and Geodetic Survey Annual Report (1879), Appendix