the District of Columbia, issued by private parties, in 1861, in
which we find even the meridians passing through the city of
Washington referred to a supposed Greenwich.

This practice has led to a confusion which may not be evident at
first sight, but which is so great and permanent that it may be
worth explaining. If, indeed, we could actually refer all our
longitudes to an accurate meridian of Greenwich in the first
place; if, for instance, any western region could be at once
connected by telegraph with the Greenwich Observatory, and thus
exchange longitude signals night after night, no trouble or
confusion would arise from referring to the meridian of Greenwich.
But this, practically, cannot be done. All our interior longitudes
have been and are determined differentially by comparison with
some point in this country. One of the most frequent points of
reference used this way has been the Cambridge Observatory.
Suppose, then, a surveyor at Omaha makes a telegraphic longitude
determination between that point and the Cambridge Observatory.
Since he wants his longitude reduced to Greenwich, he finds some
supposed longitude of the Cambridge Observatory from Greenwich and
adds that to his own longitude. Thus, what he gives is a longitude
actually determined, plus an assumed longitude of Cambridge, and,
unless the assumed longitude of Cambridge is distinctly marked on
his maps, we may not know what it is,

After a while a second party determines the longitude of Ogden
from Cambridge. In the mean time, the longitude of Cambridge from
Greenwich has been corrected, and we have a longitude of Ogden
which will be discordant with that of Omaha, owing to the change
in the longitude of Cambridge. A third party determines the