The stadium is equal to one hundred and twenty-five of our Roman paces, or six hundred and twenty-five feet. Posidonius supposes that there is a space of not less than forty stadia around the earth, whence mists, winds and clouds proceed; beyond this he supposes that the air is pure and liquid, consisting of uninterrupted light; from the clouded region to the moon there is a space of two million of stadia, and thence to the sun of five hundred million. It is in consequence of this space that the sun, notwithstanding his immense magnitude, does not burn the earth. Many persons have imagined that the clouds rise to the height of nine hundred stadia. These points are not completely made out, and are difficult to explain; but we have given the best account of them that has been published.