The great body of the sun is gaseous, though it is impossible for us to conceive of the condition of the gaseous core, subjected, as it is, at once to temperature and pressure both enormously great. Probably it is a gas so viscous that it would resist motion as pitch or putty does. Nor do we know much of the nature of either the sun-spots or the solar corona. Both seem to be produced by causes which lie within the sun; both undergo changes that are periodical and connected with each other. They exercise some influence upon the earth's magnetism, but whether this influence extends to terrestrial weather, to rainfall and storms, is still a matter of controversy. The sun itself is distant from the earth in the mean, about 92,885,000 miles, but this distance varies between January and June by 3,100,000 miles. The diameter of the sun is 866,400 miles, but perhaps this is variable to the extent of some hundreds of miles. It would contain 1,305,000 times the bulk of the earth, but its mean density is but one-quarter that of the earth. The force of gravity at its surface is 27-1/2 times that at the surface of the earth, and it rotates on its axis in about 25 days. But the sun's surface does not appear to rotate as a whole, so this time of rotating varies by as much as two days if we consider a region on the sun's equator or at a distance from it of 45°. The intensity of sunlight at the surface of the sun is about 190,000 times that of a candle-flame, and the effective temperature of the solar surface is eight or ten thousand degrees centigrade. Such are some of the facts about the sun that are received, or, as it would be technically expressed, "adopted" to-day. Doubtless a very few years will find them altered and rendered more accurate as observations accumulate. In a few hundred years, knowledge of the constitution of the sun may have so increased that these data and suggestions may seem so erroneous as to be absurd. It is little more than a century since one of the greatest of astronomers, Sir William Herschel, contended that the central globe of the sun might be a habitable world, sheltered from the blazing photosphere by a layer of cool non-luminous clouds. Such an hypothesis was not incompatible with what was then known of the constitution of the heavenly bodies, though it is incompatible with what we know now. It was simply a matter on which more evidence was to be accumulated, and the holding of such a view does not, and did not, detract from the scientific status of Sir William Herschel. The hypotheses of science require continual restatement in the light of new evidence, and, as to the weight and interpretation to be given to such evidence, there is continual conflict--if it may so be called--between the old and the new science, between the science that is established and the science that is being established. It is by this conflict that knowledge is rendered sure.