sted by the more powerful instruments
which his ingenuity succeeded in constructing, to discern in them
innumerable groups of worlds, in various stages of formation! A new
light was thrown upon the history of the Universe. Man was able to
assist, as it were, at the process of creation, and to watch the
development of a mass of incoherent matter into a perfect star. This
alone was a discovery which might well have immortalised the name of
Herschel.

But we owe to him the elements of our knowledge of the Sun's physical
constitution. He swept aside the erroneous theories and conjectures
which had previously prevailed, and guided the astronomical inquirer
into the right path. He convinced himself, by long and patient
researches, that the luminous envelope of the great "orb of day" was
neither a liquid nor an elastic fluid; that it was in certain respects
analogous to the clouds which wreathe our mountain-summits and fertilize
our plains; that it floated in the solar atmosphere. Thence he came to
the conclusion that the Sun has two atmospheres, endowed with motions
quite independent of each other. An elastic fluid, now known as the
_photosphere_, is in course of continual formation on the dark rugged
surface of the solar mass; and rising, on account of its specific
lightness, it forms the _pores_ in the stratum of reflecting clouds;
then, combining with other gases, it produces the irregularities or
furrows in the luminous cloud-region. When the ascending currents are
powerful, they create those appearances which astronomers designate the
_nuclei_, the _penumbrae_, the _faculae_.

Such was Herschel's explanation of the mode of formation of the solar
spots; and allowing it to be well-founded, we must expect to find--what
is, indeed, the case--that the Sun does not always and regularly pour
forth equal quantities of light and heat. It is true that Herschel's
hypothesis has been modified by later astronomers; but his is the credit
of having directed them into the right course of inquiry and
observation.

* * * * *

The physical constitution of the Moon was a subject which also engaged
the attention of our indefatigable enthusiast. As early as 1780 he
attempted the measurement of the lunar mountains, and came to the
conclusion that few of them exceeded 2600 feet in height. Later
research, however, has proved these figures to be inadequate. Next he
addressed himself to a study of the lunar volc