. 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. eff
. 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 observatory for 1909, Hale was able to announce that the existence of magnetic fields in sun-spots " has been placed beyond doubt through
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