longitudes of, let us suppose, St. Louis from Washington, he adds
the assumed longitudes of Washington from Greenwich which may not
agree with either of the longitudes of Cambridge and gets his
longitude. Thus we have a series of results for our western
longitude all nominally referred to the meridian of Greenwich, but
actually referred to a confused collection of meridians, nobody
knows what. If the law had only provided that the longitude of
Washington from Greenwich should be invariably fixed at a certain
quantity, say 77 degrees 3', this confusion would not have arisen.
It is true that the longitude thus established by law might not
have been perfectly correct, but this would not cause any trouble
nor confusion. Our longitude would have been simply referred to a
certain assumed Greenwich, the small error of which would have
been of no importance to the navigator or astronomer. It would
have differed from the present system only in that the assumed
Greenwich would have been invariable instead of dancing about from
time to time as it has done under the present system. You
understand that when the astronomer, in computing an interior
longitude, supposes that of Cambridge from Greenwich to be a
certain definite amount, say 4h 44m 30s, what he actually does is
to count from a meridian just that far east of Cambridge. When he
changes the assumed longitude of Cambridge he counts from a
meridian farther east or farther west of his former one: in other
words, he always counts from an assumed Greenwich, which changes
its position from time to time, relative to our own country.

Having two meridians to look after, the form of the American
Ephemeris, to be best adapted to the wants both of navigators and
astronomers was necessarily peculiar. Had our navigators referred
their longitudes to any meridian of our own country the