radually increased in accuracy as the tables of
the celestial motions were improved from time to time. At first they
were not regular, annual publications, issued by governments, as at the
present time, but the works of individual astronomers who issued their
ephemerides for several years in advance, at irregular intervals. One
man might issue one, two, or half a dozen such volumes, as a private
work, for the benefit of his fellows, and each might cover as many
years as he thought proper.

The first publication of this sort, which I have in my possession, is
the Ephemerides of Manfredi, of Bonn, computed for the years 1715 to
1725, in two volumes.

Of the regular annual ephemerides the earliest, so far as I am aware,
is the Connaissance des Temps or French Nautical Almanac. The first
issue was in the year 1679, by Picard, and it has been continued
without interruption to the present time. Its early numbers were, of
course, very small, and meagre in their details. They were issued by
the astronomers of the French Academy of Sciences, under the combined
auspices of the academy and the government. They included not merely
predictions from the tables, but also astronomical observations made at
the Paris Observatory or elsewhere. When the Bureau of Longitudes was
created in 1795, the preparation of the work was intrusted to it, and
has remained in its charge until the present time. As it is the oldest,
so, in respect at least to number of pages, it is the largest ephemeris
of the present time. The astronomical portion of the volume for 1879
fills more than seven hundred pages, while the table of geographical
positions, which has always been a feature of the work, contains nearly
one hundred pages more.

The first issue of the British Nautical Almanac was that for the year
1767 and appeared in 1766. It differs from the French Almanac in owing
its origin entirely to the needs of navigation. The British nation, as
the leading maritime power of the world, was naturally interested in
the discovery of a method by which the longitude could be found at sea.
As most of my hearers are probably aware, there was, for many years, a
standing offer by the British government, of ten thousand pounds for
the discovery of a practical and sufficiently accurate method of
attaining this object. If I am rightly informed, the requirement was
that a ship should be able to determine the Greenwich time within two
minutes, after being six months at