I find, by reference to my note-book, that other changes were visible on the 20th, but unfortunately I was prevented from sketching them. After that, unfavorable weather, and other interruptions, prevented me from sketching the spot, but the sketches that were made cover the period during which the most remarkable changes occurred, as well as that of the greatest magnetic disturbances. In order to
Fig. 3.
obtain a clear notion of the tremendous forces involved in the changes represented in the drawings, it is necessary to consider the enormous size of the spot as measured in square miles. Counting the whole area covered by the various nuclei and the penumbral depression surrounding them, the spot was not less than 60,000 miles long and 40,000 miles wide. In other words, it covered 2,400,000,000 square miles of the solar surface. The area of the whole surface of the earth, land and sea, is less than 200,000,000 square miles, so that if the crust of the earth had been peeled off like the skin of an orange, spread out flat and plastered against the sun, it would have looked like a mere outlying patch beside the great congeries of sun-chasms constituting this gigantic spot. Masses of gaseous matter, many times greater than the earth in volume, must have been hurled and whirled about there with tremendous velocity in order to produce the changes which the telescope revealed. Milton's description of the battling elements of chaos, through which Satan fought his way, will apply, though inadequately, to the scenes of chaotic fury of which such a sun-spot is the theatre.
In Fig. 4 is represented a very remarkable spot which, because it
