ABSTRACT
One well-known astronomical writer of the time was Thomas Dick, and in his book The Solar System, published in 1799, we read: "[Conclusions are] that the central part of the spots, i.e. beneath the level of the Sun's surface, or, in other words, that the spots are excavations in the body of this lurnillary, and that the umbra, or shade, which surrounds ir is the shelving sides of this excavation in the luminous matter." Yet in the same year there appeared a book by Margaret Bryan Lectures in Astronomy, which gave a rather different explanation: "Less bright spots arc perceived on the surface, the shape of which is variable, as well as the situation and number of them. These appearances arc at first obscure, and then become brighter by degrees, so that at last they exceed the other pans of the Sun in brilliancy. Their obscurity is supposed to be produced by the smoke of the volcanoes previous to rhc eruption." This might be a reference to faculae, but the idea of sunspots as the tops of erupting volcanoes was quite common at the time.
