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Meantime M. Rudolf Wolf, transferred to the direction of the Zürich Observatory, where he died, December 6, 1893, had relaxed none of his zeal in the investigation of sun-spot periodicity.
That is to say that if anything important took place in the sun the formation of a new sun-spot, for instance an astronomer who was watching the orb through his telescope at the time would be quite unaware of the incident while it was happening, since the ray of light bearing the news would not reach him until more than eight minutes later.
Similar phenomena to that which is now interesting us have been observed before, and so, until we have proof to the contrary, it is more sensible to believe it is a sun-spot than to listen to sensational tales of a new world running wild through space.
During the times of minimum sun-spot activity the spectrum shows, for example, the presence of large quantities of iron in these spots of course in a state of vapor.
But the result, so far, has been to negative the ascription to them of any systematic direction. Uprushes and downrushes are doubtless, as Father Cortie remarks, "correlated phenomena in the production of a sun-spot"; but neither seem to predominate as part of its regular internal economy. The same kind of spectroscopic evidence tells heavily against a theory of sun-spots started by Faye in 1872.
They occur in greatest numbers in periods of about eleven years apart, and astronomers and geologists agree that periods of rainy and dry seasons seem to correspond with the sun-spot periods. When the greatest number of spots are visible on the sun, scientists agree that the climatic conditions on the earth are normal and even.
Lockyer also detected displacements of the spectrum lines in the spots, such as would be produced by a rapid motion in the line of sight. It has been found that both uprushes and downrushes occur, but there is no marked predominance of either in a sun-spot. The velocity of motion thus indicated in the line of sight sometimes appears to amount to 320 miles a second.
The explanation of this phenomena, if Professor Lockyer reads the signs aright, is that during times of minimum sun-spot activity the temperature of the sun-spots is relatively cool, and that in times of activity the temperature becomes greatly increased.
Considering that once it must have been more radiantly powerful than at present, one is tempted to wonder if that could have been the time when tropical life flourished within the earth's polar circles, sustained by a vivific energy in the sun which it has now lost. The corona, as we have said, varies with the sun-spot cycle.
In 1870, Mr. Ranyard whose death, December 14, 1894, was a serious loss to astronomy acting upon an earlier suggestion of Sir William Huggins, collected records of unusual appearances on the disc of Jupiter, with a view to investigate the question of their recurrence at regular intervals. He concluded that the development of the deeper tinges of colour, and of the equatorial "port-hole" markings girdling the globe in regular alternations of bright and dusky, agreed, so far as could be ascertained, with epochs of sun-spot maximum. The further inquiries of Dr. Lohse at Bothkamp in 1873 went to strengthen the coincidence, which had been anticipated
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