ions" of spots
were, however, recognised by Schroeter,[419] and utterly baffled
Laugier,[420] who despaired of obtaining any concordant result as to the
sun's rotation except by taking the mean of a number of discordant ones.
At last, in 1855, a valuable course of observations made at Capo di
Monte, Naples, in 1845-6, enabled C. H. F. Peters[421] to set in the
clearest light the insecurity of determinations based on the assumption
of fixity in objects plainly affected by movements uncertain both in
amount and direction.

Such was the state of affairs when Carrington entered upon his task.
Everything was in confusion; the most that could be said was that the
confusion had come to be distinctly admitted and referred to its true
source. What he discovered was this: that the sun, or at least the outer
shell of the sun visible to us, has _no single period of rotation_, but
drifts round, carrying the spots with it, at a rate continually
accelerated from the poles to the equator. In other words, the time of
axial revolution is shortest at the equator and lengthens with increase
of latitude. Carrington devised a mathematical formula by which the rate
or "law" of this lengthening was conveniently expressed; but it was a
purely empirical one. It was a concise statement, but implied no
physical interpretation. It summarised, but did not explain the facts.
An assumed "mean period" for the solar rotation of 25.38 days
(twenty-five days nine hours, very nearly), was thus found to be
_actually_ conformed to only in two parallels of solar latitude (14 deg.
north and south), while the equatorial period was slightly less than
twenty-five, and that of latitude 50 deg. rose to twenty-seven days and a
half.[422] These curious results gave quite a new direction to ideas on
solar physics.

The other two "elements" of the sun's rotation were also ascertained by
Carrington with hitherto unattained precision. He fixed the inclination
of its axis to the ecliptic at 82 deg. 45'; the longitude of the ascending
node at 73 deg. 40' (for the epoch 1850 A.D.). These data--which have
scarcely yet been improved upon--suffice to determine the position in
space of the sun's equator. Its north pole is directed towards a star in
the coils of the Dragon, midway between Vega and the Pole-star; its
plane intersects that of the earth's orbit in such a way that our planet
finds itself in the same level on or about the 3rd of June and the 5th
of December, when a