nis, &c. &c.

In order that future generations might be able to ascertain what changes
were taking place in the face of the sky, astronomers have from time to
time drawn up catalogues of stars. These lists have included stars of a
certain degree of brightness, their positions in the sky being noted
with the utmost accuracy possible at the period. The earliest known
catalogue of this kind was made, as we have seen, by the celebrated
Greek astronomer, Hipparchus, about the year 125 B.C. It contained 1080
stars. It was revised and brought up to date by Ptolemy in A.D. 150.
Another celebrated list was that drawn up by the Persian astronomer, Al
Sufi, about the year A.D. 964. In it 1022 stars were noted down. A
catalogue of 1005 stars was made in 1580 by the famous Danish
astronomer, Tycho Brahe. Among modern catalogues that of Argelander
(1799-1875) contained as many as 324,198 stars. It was extended by
Schoenfeld so as to include a portion of the Southern Hemisphere, in
which way 133,659 more stars were added.

In recent years a project was placed on foot of making a photographic
survey of the sky, the work to be portioned out among various nations. A
great part of this work has already been brought to a conclusion. About
15,000,000 stars will appear upon the plates; but, so far, it has been
proposed to catalogue only about a million and a quarter of the
brightest of them. This idea of surveying the face of the sky by
photography sprang indirectly from the fine photographs which Sir David
Gill took, when at the Cape of Good Hope, of the Comet of 1882. The
immense number of star-images which had appeared upon his plates
suggested the idea that photography could be very usefully employed to
register the relative positions of the stars.

The arrangement of seven stars known as the "Plough" is perhaps the most
familiar configuration in the sky (see Plate XIX., p. 292). In the
United States it is called the "Dipper," on account of its likeness to
the outline of a saucepan, or ladle. "Charles' Wain" was the old English
name for it, and readers of Caesar will recollect it under
_Septentriones_, or the "Seven Stars," a term which that writer uses as
a synonym for the North. Though identified in most persons' minds with
_Ursa Major_, or the Great Bear, the Plough is actually only a small
portion of that famous constellation. Six out of the seven stars which
go to make up the well-known figure are of the second magnitude, while
t