ASTRONOMY: HALE AND LUCKEY 
389 
or arch on one side of the Hne joining the two 'spots/ with the very 
different structure just described on the opposite or following side. 
Such an appearance of asymmetry would seem to be faithfully repro- 
duced on some of our photographs of the hydrogen flocculi surrounding 
bipolar spot groups. If this resemblance should prove to be other than 
superficial, it would apparently indicate that in these cases the hydro- 
dynamic influence of the spot vortices outweighs their electromagnetic 
effect in determining the structure of the floccuH. It may be added 
that the inward (nearly horizontal) flow of the smoke at high levels, the 
downward flow at intermediate levels and the outward flow at low levels 
is in harmony with solar observations.' But no final conclusions can 
be drawn before the experiments have been multipHed, and the necessary 
magnetic influence introduced, if possible, by means of magnets within 
the liquid vortices, acting on the moving smoke particles, ionized by an 
X-ray discharge, and separated electrostatically. As other photographs 
of the hydrogen floccuH surrounding bipolar spots seem to show a more 
nearly symmetrical structure, resembhng the Hnes of force about a bar 
magnet, it may be true that in such cases the electromagnetic influence 
predominates, since we have no evidence that one spot may be regarded 
as a source and the other as a sink. The possible effect of electric fields 
in and about sun-spots must also be considered.^ 
It has been shown in this paper that some of the phenomena of single 
and multiple sun-spots can be imitated by simple laboratory experiments, 
which may also assist in explaining certain characteristic structures and 
motions of the solar atmosphere. The full details of the investigation 
will be published in the Astrophysical Journal. 
1 The vertical tube shown at the bottom of the tank, used for another experiment, has 
no effect on this result. 
2 See these Proceedings, 1, 382 (1915). 
2 Observations of Solar Spots, p. 222. 
4 London, Mon. Not. R. Ast. Soc, 73, 687 (1913). 
^ Kelvin, Mathematical and Physical Papers, vol. 4, p. 67. 
^ See Mach, Ann. Physik, Leipzig, 68, Plate III, j5g. 13. A better resemblance is afforded 
by a photograph of a smoke ring by Wood, reproduced in Nature, 63, 418, fig. 1. 
^ The stream-hnes in different planes, either vertical or horizontal, are most clearly shown 
by a narrow beam of sunlight, admitted through the glass wall of the tank by means of a 
sUt, which can be set in any desired position. In this way it is easy to imitate phenomena 
observed with the spectroheliograph in plan on the sun's disk and in elevation at the limb, 
where Slocum and others have photographed prominences while being drawn into sun-spots. 
Radial stream-lines in the horizontal plane, like those often indicated by the hydrogen floc- 
culi about single spots, are well shown by the smoke at high levels. 
8 An error occurs in a paper by Hale and Babcock in a recent number of these Proceed- 
ings (March 1915, p. 125). Having in mind the hnes of force between the separated charges 
in the vortex, the electric lines of force in the spot were described as tangential to the solar 
surface. This statement is more likely to apply only to the edges of the spot. At its center 
the lines of force are probably nearly radial. 
