The clearest connection between the magnetic movements and the sun-spot changes is seen when we take the mean values of either for considerable periods of time, as, for instance, year by year. But occasionally we have much more special instances of this connection. Some three or four times within the last twenty years an enormous spot has broken out on the sun, a spot so vast that worlds as great as our own could lie in it like peas in a breakfast saucer, and in each case there has been an immediate and a threefold answer from the earth. One of the most remarkable of these occurred in November, 1882. A great spot was then seen covering an area of more than three thousand millions of square miles. The weather in London happened to be somewhat foggy, and the sun loomed, a dull red ball, through the haze, a ball it was perfectly easy to look at without specially shading the eyes. So large a spot under such circumstances was quite visible to the naked eye, and it caught the attention of a great number of people, many of whom knew nothing about the existence of spots on the sun. This great disturbance, evidently something of the nature of a storm in the solar atmosphere, stretched over one hundred thousand miles on the surface of the sun. The disturbance extended farther still, even to nearly one hundred millions of miles. For simultaneously with the appearance of the spot the magnetic needles at Greenwich began to suffer from a strange excitement, an excitement which grew from day to day until it had passed half-way across the sun's disc. As the twitchings of the magnetic needle increased in frequency and violence, other symptoms were noticed throughout the length of the British Isles. Telegraphic communication was greatly interfered with. The telegraph lines had other messages to carry more urgent than those of men. The needles in the telegraph instruments twitched to and fro. The signal bells on many of the railway lines were rung, and some of the operators received shocks from their instruments. Lastly, on November 17, a superb aurora was witnessed, the culminating feature of which was the appearance, at about six o'clock in the evening, of a mysterious beam of greenish light, in shape something like a cigar, and many degrees in length, which rose in the east and crossed the sky at a pace much quicker than but nearly as even as that of sun, moon, or stars, till it set in the west two minutes after its rising. So far we have been dealing only with effects. Their causes still rest hidden from us. There is clearly a connection between the solar activity as shown by the spots and the agitation of the magnetic needles. But many great spots find no answer in any magnetic vibration, and not a few considerable magnetic storms occur when we can detect no great solar changes to correspond.