280 CARNEGIE INSTITUTION OF WASHINGTON. 



VORTEX EXPERIMENTS. 



Mr. Hale and Mr. Luckey have been engaged in a series of vortex 

 experiments bearing on the nature of sun-spots and floccuh. Accord- 

 ing to the tentative hypothesis employed, a single spot is represented by 

 a columnar vortex, descending for some distance into the photosphere. 

 To accoimt, however, for the rapid decrease in the strength of the 

 magnetic field above sun-spots, it is supposed that the electrons 

 whose motion produces the field are confined to the upper portion of 

 the vortex. As sun-spots are usually associated in pairs of opposite 

 magnetic polarity, the experiment was tried of spinning a flexible 

 wire helix, threaded with wooden disks to float most of the weight and 

 increase friction, at high velocity in a tank of water. After some 

 wandering, the lower extremity of the columnar vortex thus produced 

 gradually turns up until it meets the surface, resulting in a semi- 

 circular vortex ring, the two extremities of which are assumed by the 

 hypothesis to represent the two spots of a bipolar group. 



Kelvin's approximate formula for the motion of translation of a 

 vortex was tested in water by the use of a semicircular vortex ring, 

 with paddles which can be driven at any desired velocity, suspended 

 from a balanced pendulum. As already mentioned (p. 259) sun-spots 

 in high and low latitudes are found to move in opposite directions, as 

 the opposite directions of rotation of bipolar groups in such latitudes 

 would require.^ But their velocities, as calculated from Kelvin's for- 

 mula, should apparently be much greater than the observed solar 

 motions, and a study of the velocity of vortex rings in gases at various 

 pressures is being made to test this point. 



As might be expected from the above experiment, a straight, hori- 

 zontal, flexible vortex, suspended below the surface of water and driven 

 by a pulley at its middle point, turns up to the surface at both of its 

 free ends. Thus any columnar vortex not far below the surface of the 

 photosphere would tend to form a bipolar spot if spinning at a suffi- 

 ciently high velocity. 



A semicircular vortex ring, supported so that the paddles at its two 

 ends come just below the surface of the water, may be used to set up 

 secondary vortices in the air above. To render these visible the space 

 over the water is tightly inclosed in a glass case and filled with smoke. 



The circulation observed and photographed in the smoke is inward 

 and downward at high and intermediate levels, then outward along the 

 surface of the water and upward at some distance from the vortex. 

 The horizontal pattern thus produced when a semicircular ring is used 

 (the two paddles at its extremities will serve equally well) closely re- 

 sembles a side view (in the plane of the ring) of a colored vortex ring 

 rising tlii'ough water. The structure is decidedly asymmetrical, the 



'See footnote, page 25S. 



