_Facts tending to illustrate and prove the existence of a_ mid-plane-space, _situated between the concave and convex surfaces of the sphere._ According to Symmes's Theory, each sphere has an intermediate cavity, or _mid-plane-space_, of considerable extent, situated between the convex and concave surfaces of the sphere, filled with a very light and elastic fluid, rarified in proportion to the gravity, or condensing power of the exposed surfaces of the respective spheres: and also, various other less cavities or spaces between the larger or principal one, and the outer and inner surfaces of the spheres, each filled with a similar fluid or gas, most probably partaking much of the nature of hydrogen. This fluid is lighter than that in which the sphere floats; and has a tendency to poise it in universal space. The spheres, in many parts of the unfathomable ocean, is believed to be water quite through from the concave or convex surfaces to the great mid-plane-space, and probably the earthy or solid matter of the sphere, may in many places extend quite through from one surface to the other, tending, like ribs or braces, to support the sphere in its proper form. Such a formation of spheres appears to be supported by various facts and phenomena; amongst the most prominent of which are Volcanoes and Earthquakes. Many volcanic mountains burst out and burn for ages, discharging from the bowels of the earth immense quantities of lava, pumice, and various substances of various kinds. Some of these mountains have been burning for thousands of years, at least as far back as the records of history have been made known to us.