. Discovery. Science. DISCOVICKY 171) lower hydrogen clouds. This gave strong support to the hypothesis of the vortical nature of sun-spots. " We know now," said Hale in November 1908, " that they are caused by vortices in the solar atmosphere, and the various theories which do not recognise this fact may be laid ; At that time. Hale inclined to the view that " in the case of sun-spots we see a phenomenon somewhat analogous to a tornado or waterspout on the earth. If the gases at high levels conducted b}- Rowland at Baltimore as far back as 1S75 indi
. Discovery. Science. DISCOVICKY 171) lower hydrogen clouds. This gave strong support to the hypothesis of the vortical nature of sun-spots. " We know now," said Hale in November 1908, " that they are caused by vortices in the solar atmosphere, and the various theories which do not recognise this fact may be laid ; At that time. Hale inclined to the view that " in the case of sun-spots we see a phenomenon somewhat analogous to a tornado or waterspout on the earth. If the gases at high levels conducted b}- Rowland at Baltimore as far back as 1S75 indicated that, if electrically-charged bodies existed at all in the solar atmosphere, their revolution in sun-spot vortices would produce a mag- netic field ; and in 1S96 Zeeman, of Amsterdam, showed that the light from a luminous vapour is altered in a remarkable way when under the influence of a strong magnetic field—the lines of the spectrum being widened or broken up into several constituents (the Zeeman-. PHOTO OF SU-NSPOTS T.\KEN' .4T GREENWICH , MAV (By kind permission ol the Astronomer Royal.) whirl with sufficient velocity, they develop a tube-like extension which reaches down through the compara- tively undisturbed gases at lower levels. At the centre of the storm the expansion of the gases due to their rapid rotation cools them and thus produces a compara- tively dark cloud which we see in the ; At that time Hale believed the disturbances giving rise to the spots to have their origin in the upper regions of the solar atmosphere. This view he modified later. effect). With the aid of the 30-foot spcctroheliograph of the Mount Wilson Observatory, Hale, in 1908, closely scrutinised the spectra of sun-spots for traces of the Zeeman-effect, and his scrutiny was soon re- warded by the discovery that the double and triple lines in these spectra are exactly similar to the lines produced by the presence of a magnetic field. In the annual report of the
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