longitude, but one in latitude forty-five degrees (say), the other on the equator, the latter will advance farther and farther in longitude from the former, gaining daily about two degrees, so that in the course of about one hundred and eighty days it will have gained a complete revolution. That is to say, the sun's equator makes about two revolutions more per annum than regions in forty-five degrees north and south solar latitude." The sun is about 850,000 miles in diameter; its density is one-fourth that of the earth; its mass is 316,000 times greater, and its volume 1,253,000. Gravity at its surface is 27.1 times that of the earth; its distance is approximately 92,000,000 miles; it rotates upon its axis, which is inclined to the planetary plane at an angle of seven degrees, once in twenty-five and one-third days, apparently increased to thirty days by the earth's orbital advance in the same direction around the sun; and it has a motion around its center,--a true orbital motion,--due to displacement by gravity of the planetary masses, which, however, is always within its own mass. The above, in brief, is, so far as we know, the constitution of the sun and its appendages. Its internal globe is surrounded by a glowing gaseous envelope, the photosphere, which is the visible orb, composed of cloud masses of glowing hydrogen gas intermingled with vapors of many of our terrestrial elements, all in a state of apparent disassociation. Of the constitution of the sun's mass, Professor Ball says, "Professor Rowland has shown that thirty-six terrestrial elements are certainly indicated in the solar spectrum, while eight others are doubtful. Fifteen elements have not been found, though sought for, and ten elements have not yet been compared with the sun's spectrum. Reasons are also given for showing that, though fifteen elements had no lines corresponding to those shown in the solar spectrum, yet there is but little evidence to show that they are really absent from the sun. Dr. Huggins epitomizes these very interesting results in the striking remark, 'It follows that if the whole earth were heated to the temperature of the sun, its spectrum would resemble very closely the solar spectrum.'" Outside the photosphere is the simpler chromosphere, composed largely of hydrogen, and merging into the corona at a distance of hundreds of thousands of miles from the sun's apparent surface, and this corona extends outward to a vast distance, and is itself largely composed of self-luminous matter, the action of gravity being counterbalanced by the centrifugal force of orbital rotation, or more probably by electrical repulsion. The metallic vapors in the sun's photosphere are suspended in glowing hydrogen, which vastly preponderates over all the others in mass and volume, the incandescence of which is the principal source of solar light and heat. The planets revolve in elliptical orbits around this central sun, and crossing these