extending over
more than a century. But it has never extended its operations far
outside the field of observation, reduction, and comparison with
existing tables. It shows clearly, from time to time, the errors of the
tables used in the British Nautical Almanac, but does nothing further,
occasional investigations excepted, in the way of supplying new tables.
An exception to this is a great work on the theory of the moon's
motion, in which Professor Airy is now engaged.

It will be understood that several distinct conditions not yet
fulfilled are desirable in astronomical tables; one is that each set of
tables shall be founded on absolutely consistent data, for instance,
that the masses of the planets shall be the same throughout. Another
requirement is that this data shall be as near the truth as
astronomical data will suffice to determine them. The third is that the
results shall be correct in theory. That is, whether they agree or
disagree with observations, they shall be such as result mathematically
from the adopted data.

Tables completely fulfilling these conditions are still a work of the
future. It is yet to be seen whether such co-operation as is necessary
to their production can be secured under any arrangement whatever.

XIV

THE WORLD'S DEBT TO ASTRONOMY

Astronomy is more intimately connected than any other science with the
history of mankind. While chemistry, physics, and we might say all
sciences which pertain to things on the earth, are comparatively
modern, we find that contemplative men engaged in the study of the
celestial motions even before the commencement of authentic history.
The earliest navigators of whom we know must have been aware that the
earth was round. This fact was certainly understood by the ancient
Greeks and Egyptians, as well as it is at the present day. True, they
did not know that the earth revolved on its axis, but thought that the
heavens and all that in them is performed a daily revolution around our
globe, which was, therefore, the centre of the universe. It was the
cynosure, or constellation of the Little Bear, by which the sailors
used to guide their ships before the discovery of the mariner's
compass. Thus we see both a practical and contemplative side to
astronomy through all history. The world owes two debts to that
science: one for its practical uses, and the other for the ideas it has
afforded us of the immensity of creation.

The practical uses of astr