Ras Algethi, or [alpha] Herculis, is also beyond the limits of the map,
but may be easily found by means of Map 2, Frontispiece. It is, properly
speaking, a multiple star. Considered as a double, the arrangement of
the components is that shown in Plate 3. The larger is of magnitude
3-1/2, the smaller of magnitude 5-1/2; the former orange, the latter
emerald. The companion stars are small, and require a good telescope to
be well seen. Ras Algethi is a variable, changing from magnitude 3 to
magnitude 3-1/2 in a period of 66-1/3 days.

The star [rho] Herculis is a closer double. The components are 3"·7
apart, and situated as shown in Plate 3. The larger is of magnitude 4,
the smaller 5-1/2; the former bluish-white, the latter pale emerald.

There are other objects within the range of our map which are well
worthy of study. Such are [mu] Draconis, a beautiful miniature of
Castor; [gamma]^{1} and [gamma]^{2} Draconis, a wide double, the
distance between the components being nearly 62" (both grey); and
[gamma]^{1} and [gamma]^{2} Coronæ, a naked-eye double, the components
being 6' apart, and each double with a good 3-inch telescope.

We turn, however, to another region of the sky. Low down, towards the
south is seen the small constellation Corvus, recognised by its
irregular quadrilateral of stars. Of the two upper stars, the left-hand
one is Algorab, a wide double, the components placed as in Plate 3,
23"·5 apart, the larger of magnitude 3, the smaller 8-1/2, the colours
pale yellow and purple.

There is a red star in this neighbourhood which is well worth looking
for. To the right of Corvus is the constellation Crater, easily