His was a somewhat mystical view, but later mathematical developments found it quite useful, and today we refer to such a region of space as a magnetic field. Some speculate that the unusually cold weather during those years was related to their disappearance, but in any case, by the time they returned, the attention of astronomers had moved elsewhere. For the fuller account of Schwabe's discovery,see here . The nature of sunspots remained unclear until 1908, when George Ellery Hale, using an instrument that observed the Sun in narrow ranges of color emitted by selected substances, reported that the light from sunspots was modified in ways that indicated it was produced in intense magnetic fields. Yet even there the instruments of spacecraft such as Voyager 2 still measure it reliably.
Sunspots display many interesting features.
The general magnetic field, producing the Sun's north and south magnetic poles, also reverses polarity at each cycle, the reversal typically occuring 3 years after sunspot minimum. All these suggest that the 11-year cycle is a magnetic phenomenon. Such methods also made possible limited observations of the inner corona, outside times of total solar eclipses. And they revealed changes much faster than those previously noted in sunspots, some of which cause interesting magnetic effects at the Earth. The most remarkable aspect of such activity is the speed with which it takes place.