hile the
average interval from one maximum to the next is eleven years, the period
of each distinct wave of agitation is twelve or fourteen.[426] Curious
evidence of the retarded character of the maximum of 1883-4 was to be
found in the unusually low latitude of the spot-zones when it occurred.
Their movement downward having gone on regularly while the crisis was
postponed, its final symptoms were hence displaced locally as well as in
time. The "law of zones" was duly obeyed at the minima of 1890[427] and
1901, and Spoerer found evidence of conformity to it so far back as
1619.[428] His researches, however, also showed that it was in abeyance
during some seventy years previously to 1716, during which period
sun-spots remained persistently scarce, and auroral displays were feeble
and infrequent even in high northern latitudes. An unaccountable
suspension of solar activity is, in fact, indicated.[429]

Gustav Spoerer, born at Berlin in 1822, began to observe sun-spots with
the view of assigning the law of solar rotation in December, 1860. His
assiduity and success with limited means attracted attention, and a
Government endowment was procured for his little solar observatory at
Anclam, in Pomerania, the Crown Prince (afterwards Emperor Frederick)
adding a five-inch refractor to its modest equipment. Unaware of
Carrington's discovery (not made known until January, 1859), he arrived
at and published, in June, 1861,[430] a similar conclusion as to the
equatorial quickening of the sun's movement on its axis. Appointed
observer in the new Astrophysical establishment at Potsdam in 1874, he
continued his sun-spot determinations there for twenty years, and died
July 7, 1895.

The time had now evidently come for a fundamental revision of current
notions respecting the nature of the sun. Herschel's theory of a cool,
dark, habitable globe, surrounded by, and protected against, the
radiations of a luminous and heat-giving envelope, was shattered by the
first _dicta_ of spectrum analysis. Traces of it may be found for a few
years subsequent to 1859,[431] but they are obviously survivals from an
earlier order of ideas, doomed to speedy extinction. It needs only a
moment's consideration of the meaning at last found for the Fraunhofer
lines to see the incompatibility of the new facts with the old
conceptions. They implied not only the presence near the sun, as glowing
vapours, of bodies highly refractory to heat, but that these glowing