hould never be ignored. But as the outcome of
the enormous development given to the powers of the telescope in recent
times, together with the swift advance of physical science, and the
inclusion, by means of the spectroscope, of the heavenly bodies within
the domain of its inquiries, much knowledge has been acquired regarding
the nature and condition of those bodies, forming, it might be said, a
science apart, and disembarrassed from immediate dependence upon
intricate, and, except to the initiated, unintelligible formulae. This
kind of knowledge forms the main subject of the book now offered to the
public.

There are many reasons for preferring a history to a formal treatise on
astronomy. In a treatise, _what_ we know is set forth. A history tells
us, in addition, _how_ we came to know it. It thus places facts before
us in the natural order of their ascertainment, and narrates instead of
enumerating. The story to be told leaves the marvels of imagination far
behind, and requires no embellishment from literary art or high-flown
phrases. Its best ornament is unvarnished truthfulness, and this, at
least, may confidently be claimed to be bestowed upon it in the ensuing
pages.

In them unity of treatment is sought to be combined with a due regard to
chronological sequence by grouping in separate chapters the various
events relating to the several departments of descriptive astronomy. The
whole is divided into two parts, the line between which is roughly drawn
at the middle of the present century. Herschel's inquiries into the
construction of the heavens strike the keynote of the first part; the
discoveries of sun-spot and magnetic periodicity and of spectrum
analysis determine the character of the second. Where the nature of the
subject required it, however, this arrangement has been disregarded.
Clearness and consistency should obviously take precedence of method.
Thus, in treating of the telescopic scrutiny of the various planets, the
whole of the related facts have been collected into an uninterrupted
narrative. A division elsewhere natural and helpful would here have been
purely artificial, and therefore confusing.

The interests of students have been consulted by a full and authentic
system of references to the sources of information relied upon.
Materials have been derived, as a rule with very few exceptions, from
the original authorities. The system adopted has been to take as little
as possible at second-hand. M