After the observations of these two fortunate persons were known, the attention of the scientific was directed to this phenomenon. Scheiner supposed the spots to be _planets_ which revolved very near the sun. In process of unwearied observations, it was ascertained that these spots changed their positions. Sometimes two would blend together, and thus run into each other. Sometimes one large one would divide into two or three smaller ones. They were observed to dilate, and contract; and to have umbræ, or shades attending them.
From these phenomena Galileo and others supposed the solar spots were _schoria floating on the burning liquid matter_, of which they supposed the sun composed. M. de la Hire, and La Lande supposed them to be eminences which occasionally rose above the rolling tides of fire, as islands rise above the sea. All these theories were on the supposition that the sun was an igneous body, in a high state of combustion, by which means he dispenses heat and light to the surrounding planets.
Dr. WILSON, Professor of practical astronomy in the University of Glasgow, was the first to conjecture that these spots were _depressions_ rather than elevations. This was about the year 1769. The Doctor rendered this conjecture very probable, by his close and lucid observations and illustrations.
These spots attracted the attention of the celebrated Dr. Herschell in 1779, who continued to observe them closely until 1794, and by means of his immensely large and powerful telescopes, he clearly established Dr. Wilson's conjectures, _that these spots are openings in the luminous surface of the sun, through which his opake body appears_.
Dr. Herschell regards the real body of the sun to be an _opake nucleus_, fit for the habitation of intellectual creatures: that he has an atmosphere suited in density and height to his own magnitude: that in the higher regions of this atmosphere there are _two_ sets of clouds surrounding the sun, which are permanently and essentially luminous, being _phosphoric_ in their nature. The lower set of these clouds, which are _next_ the sun, are less bright, and more dense than the upper set. They are designed to serve as a _curtain_ to the sun's body, to prevent a too great intensity of light at his real surface; the higher set of clouds, which are visible to us, being the principal source, or rather _agent_, of light.