ASTRONOMY: HALE AND LUCKEY 
385 
SOME VORTEX EXPERIMENTS BEARING ON THE NATURE 
OF SUN-SPOTS AND FLOCCULI 
By George E. Hale and George P. Luckey 
MOUNT WILSON SOLAR OBSERVATORY, CARNEGIE INSTITUTION OF WASHINGTON 
Read be fore the Academy. April 20. 1915. Received. May 22. 1915 
The following working hypothesis of sun-spots was first proposed, in 
a somewhat different form, in the Annual Report of the Director of the 
Mount Wilson Solar Observatory for 1912: 
As the result of an eruption, or some other cause tending to produce rapid 
convection, a gaseous column moves upward from within the sun toward the 
surface of the photosphere. Vortex motion is initiated by differences in ve- 
locity of adjoining surfaces or by irregularities of structure and is maintained 
by convection. The circulation in the vortex is vertically upward and then 
outward along the photosphere, as in a terrestrial tornado. Expansion pro- 
duces cooling at the center of the vortex, and a comparatively dark area (the 
umbra) results. As in Harker's electric furnace experiments, a rapid flow of 
negative ions sets in toward the cooler gases at the center from the hotter 
gases without. These ions, whirled in the vortex, produce a magnetic field, 
plainly indicated by the widened and resolved lines of the sun-spot spectrum. 
Hitherto we have assumed the spot to be single. The typical sun-spot 
group is double, though either or both of the principal members may be re- 
placed by several smaher spots. The axis of the group makes a small angle 
with the solar equator, and the magnetic polarities of the preceding and fol- 
lowing members are opposite in sign. Such a group may result from the 
tendency of any columnar vortex to turn up toward the photosphere, thus 
forming a semi-circular vortex ring. 
A secondary vortex, caused by the influence of the low-lying spot vortex on 
the gases of the solar atmosphere above it, partially determines the structure 
of the hydrogen flocculi, which are drawn inward at high levels, then down- 
ward and outward at the upper levels of the spot vortex. The hydrodynamic 
structure thus developed may be more or less modified by the influence of the 
spot magnetic field on the trajectories of the moving ions within it. 
The presence of magnetic fields in all sun-spots and the spectroscopic 
observations of Evershed and St. John on the revolution of the spot 
vapors at various levels, seem to prove beyond doubt that sun-spots are 
vortices. The object of the present paper is to describe some recent 
experiments bearing on the suggested explanation of 'double or multi- 
ple spots, and the floccuh associated with them. 
A closely wound helix of brass wire, with disks of wood threaded on 
it to increase friction, is hung vertically from the shaft of an electric 
motor, and spun at moderate velocity in water. A columnar vortex is 
