lly charged particles, should give rise to a
magnetic field. This hypothesis at once suggested that the double
lines observed by Young might really represent the Zeeman effect.
The test was made, and all the characteristic phenomena of radiation
in a magnetic field were found.

Thus a great physical experiment is constantly being performed
for us in the sun. Every large sunspot contains a magnetic field
covering many thousands of square miles, within which the spectrum
lines of iron, manganese, chromium, titanium, vanadium, calcium,
and other metallic vapors are so powerfully affected that their
widening and splitting can be seen with telescopes and spectroscopes
of moderate size.

THE TOWER TELESCOPE

Both of these illustrations show how the physicist and chemist,
when adequately armed for astronomical attack, can take advantage
in their studies of the stupendous processes visible in cosmic
crucibles, heated to high temperatures and influenced, as in the
case of sun-spots, by intense magnetic fields. Certain modern
instruments, like the 60-foot and 150-foot tower telescopes on
Mount Wilson, are especially designed for observing the course
of these experiments. The second of these telescopes produces at
a fixed point in a laboratory an image of the sun about 16 inches
in diameter, thus enlarging the sun-spots to such a scale that
the magnetic phenomena of their various parts can be separately
studied. This analysis is accomplished with a spectroscope 80 feet
in length, mounted in a subterranean chamber beneath the tower. The
varied results of such investigations cannot be described here.
Only one of them may be mentioned--the discovery that the entire sun,
rotating on its axis, is a great magnet. Hence we may reasonably
infer that every star, and probably every planet, is also a magnet,
as the earth has been known to be since the days of Gilbert's "De
Magnete." Here lies one of the best clues for the physicist who
seeks the cause of magnetism, and attempts to produce it, as Barnett
has recently succeeded in doing, by rapidly whirling masses of
metal in the laboratory.

[Illustration: Fig. 33. Sun-spot vortex in the upper hydrogen
atmosphere. (Benioff).

Photographed with the spectroheliograph. The electric vortex that
causes the magnetic field of the spot lies at a lower level, and
is not shown by such photographs.]

Perhaps a word of caution should be interpolated at this point.
Solar magnetism in no wise acc