The first or innermost of Saturn’s satellites is nearer to the central body than any other of the secondary planets. Its distance from the centre of Saturn is 80,088 miles; from the surface of the planet 47,480 miles; and from the outmost edge of the ring only 4916 miles. The traveller may form to himself an estimate of the smallness of this amount by remembering the statement of the well-known navigator, Captain Beechey, that he had in three years passed over 72,800 miles. According to very recent observations, Saturn’s ring is divided into _three_ separate rings, which, from the calculations of Mr. Bond, an American astronomer, must be fluid. He is of opinion that the number of rings is continually changing, and that their maximum number, in the normal condition of the mass, does not exceed _twenty_. Mr. Bond likewise maintains that the power which sustains the centre of gravity of the _ring_ is not in the planet itself, but in its satellites; and the satellites, though constantly disturbing the ring, actually sustain it in the very act of perturbation. M. Otto Struve and Mr. Bond have lately studied with the great Munich telescope, at the observatory of Pulkowa, the _third_ ring of Saturn, which Mr. Lassell and Mr. Bond discovered to be _fluid_. They saw distinctly the dark interval between this fluid ring and the two old ones, and even measured its dimensions; and they perceived at its inner margin an edge feebly illuminated, which they thought might be the commencement of a fourth ring. These astronomers are of opinion, that the fluid ring is not of very recent formation, and that it is not subject to rapid change; and they have come to the extraordinary conclusion, that the inner border of the ring has, since the time of Huygens, been gradually approaching to the body of Saturn, and that _we may expect, sooner or later, perhaps in some dozen of years, to see the rings united with the body of the planet_. But this theory is by other observers pronounced untenable. TEMPERATURE OF THE PLANET MERCURY. Mercury being so much nearer to the Sun than the Earth, he receives, it is supposed, seven times more heat than the earth. Mrs. Somerville says: “On Mercury, the mean heat arising from the intensity of the sun’s rays must be above that of boiling quicksilver, and water would boil even at the poles.” But he may be provided with an atmosphere so constituted as to absorb or reflect a great portion of the superabundant heat; so that his inhabitants (if he have any) may enjoy a climate as temperate as any on our globe. SPECULATIONS ON VESTA AND PALLAS.