Not till well toward the close of the eighteenth century was an attempt made to substitute a scientific guess at the riddle of creation for the old poetic ones, and yet another century elapsed before the new explanations availed fully to supplant the old ones. It was Laplace, the great French mathematician, who elaborated toward the close of the eighteenth century a so-called nebular hypothesis, which may fairly be considered the first measurably scientific attempt ever made to explain the origin of the world. The hypothesis conceives that, at a time indefinitely remote, the entire solar system and space far beyond it was filled with a “fire mist,” consisting of the material in a gaseous state which now forms the sun and planets. This gaseous body, contracting through loss of heat, and rotating on its axis, left behind from time to time, successive rings of its own substance, that, consolidating, became the planets; the remaining core of substance contracting finally to constitute the body that we call the sun. Nineteenth century science elaborated, without essentially modifying, this nebular hypothesis. Elaborate attempts have been made by Dr. Croll and by Sir Norman Lockyer to explain the origin of the “fire mist” itself, from which per hypothesis our solar system and an infinity of like stellar systems were formed. The meteoritic hypothesis of Lockyer supposes that the primeval fire mist was due to the collision of swarms of meteors; Croll’s theory postulates the smashing together of dark stars: but the two theories are essentially identical in their main thought, which is, that previously solidified bodies of the universe are made gaseous through mutual impact, thus affording material for the operation of those changes outlined in the nebular hypothesis of Laplace. True or false, this hypothesis stands to-day as the expression of the profoundest cosmogonic scientific guess that modern thought has been able to substitute for the poetic guesses of antiquity.