ical
purposes, and the meridian of Greenwich shall be adopted for all
nautical purposes." The execution of this law necessarily involves the
question, "What shall be considered astronomical and what nautical
purposes?" Whether it was from the difficulty of deciding this
question, or from nobody's remembering the law, the latter has been
practically a dead letter. Surely, if there is any region of the globe
which the law intended should be referred to the meridian of
Washington, it is the interior of our own country. Yet, notwithstanding
the law, all acts of Congress relating to the territories have, so far
as I know, referred everything to the meridian of Greenwich and not to
that of Washington. Even the maps issued by our various surveys are
referred to the same transatlantic meridian. The absurdity culminated
in a local map of the city of Washington and 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