Page:A Voyage in Space (1913).djvu/242

222 the gist of the matter is that a sunspot is an electric whirlpool, which is as good as a magnet. Many of you know already what an electro-magnet is; if we take a coil of wire and send a current round and round it, the coil will attract iron filings in the same way as our little bar magnet. The wire may be made of copper and need not have any iron in it at all, though usually an iron "core" is added to make it stronger; but it would still act as a magnet if there were only the copper wire and the electricity circling round in it. Similarly, if we can get an electric whirlpool in any other way we shall have something which behaves like a magnet, and Professor Hale has shown that the sunspots behave in this way. Some of them are whirling in one direction and some in the other—he can detect the direction by the magnetic action. You know there are two ends to a magnet, often called the north and south poles, a whirlpool in one direction acts like a north pole and in the other like a south pole.

We shall not be able to describe Professor Hale's experiments, but I can show you some beautiful pictures taken by his assistant, Mr. St. John, with the spectro-heliograph, which show that a spot has the sucking action of a whirlpool. Have you ever read about the Maelstrom, the great Norwegian whirlpool? A boat which gets caught in it circles slowly round and round at first in the outer parts, but is always being drawn nearer and nearer to the centre, in a spiral. It is whirled more and more rapidly and ultimately sucked down at the centre, as though by some great octopus which waved its