Footnote 398: _Phil. Mag._, vol. ix. (4th series), p. 327.]

[Footnote 399: Spectra may be produced by _diffraction_ as well as by
_refraction_; but we are here only concerned with the subject in its
simplest aspect.]

[Footnote 400: _Astrologia Gallica_ (1661), p. 189.]

[Footnote 401: _Pos. Phil._, vol. i., pp. 114, 115 (Martineau's
trans.).]

[Footnote 402: _Proem Astronomiae Pars Optica_ (1640), _Op._, t. ii.]

[Footnote 403: _Pop. Vorl._, pp. 14, 19, 408.]

[Footnote 404: _Pos. Phil._, p. 115.]

CHAPTER II

_SOLAR OBSERVATIONS AND THEORIES_

The zeal with which solar studies have been pursued during the last half
century has already gone far to redeem the neglect of the two preceding
ones. Since Schwabe's discovery was published in 1851, observers have
multiplied, new facts have been rapidly accumulated, and the previous
comparative quiescence of thought on the great subject of the
constitution of the sun, has been replaced by a bewildering variety of
speculations, conjectures, and more or less justifiable inferences. It
is satisfactory to find this novel impulse not only shared, but to a
large extent guided, by our countrymen.

William Rutter Dawes, one of many clergymen eminent in astronomy,
observed, in 1852, with the help of a solar eye-piece of his own
devising, some curious details of spot-structure.[405] The
umbra--heretofore taken for the darkest part of the spot--was seen to be
suffused with a mottled, nebulous illumination, in marked contrast with
the striated appearance of the penumbra; while through this "cloudy
stratum" a "black opening" permitted the eye to divine farther
unfathomable depths beyond. The _hole_ thus disclosed--evidently the
true nucleus--was found to be present in all considerable, as well as in
many small maculae.

Again, the whirling motions of some of these objects were noticed by
him. The remarkable form of one sketched at Wateringbury, in Kent,
January 17, 1852, gave him the means of detecting and measuring a
rotatory movement of the whole spot round the black nucleus at the rate
of 100 degrees in six days. "It appeared," he said, "as if some
prodigious ascending force of a whirlwind character, in bursting through
the cloudy stratum and the two higher and luminous strata, had given to
the whole a movement resembling its own."[406] An interpretation
founded, as is easily seen, on the Herschelian theory, then st