The constancy of the supply of heat furnished by the sun and the division of the year into definite seasons was one of the first phenomena which attracted the attention of man at the dawn of history, and in the many accounts of the creation which we find in literature we see the feeble attempts of man to account for what he observed. Although the knowledge which we have at the present time is not complete enough to warrant any feeling of pride, yet we do know enough to say, with certainty, some things concerning the solar system. We know that our sun cannot forever radiate away its heat into space without sometime becoming as cold or colder than we are, unless the energy which it is losing in the form of heat be restored to it by some means not at this time known. Sir William Thomson (Lord Kelvin) has calculated that at the present rate of solar radiation, which amounts to about twenty-eight calories per minute, per square centimeter, at the distance of the mean radius of the earth's orbit, it would have taken somewhat more than fifteen million years for the heat generated by the contraction of the sun's mass from the orbit of the outer planet, Neptune, to its present size, to have been radiated away into space. This means that gravity, as a source of heat development, at the rate of solar radiation now known, would account for, perhaps, twenty million years' expenditure of energy in reducing the sun's diameter to but one-thirteen-thousandth part of what it once was. Not only does the nebular hypothesis fall short of accounting for the facts, as will subsequently be shown in this one particular of the length of time during which our solar system has existed, but it does not account for the variation in the obliquity of the poles of the planets, which are the attendants upon the sun; nor does gravitative attraction alone enable us to account for the tremendous velocities of some of the stars through space, such as Arcturus,--so that it may be safely assumed that we shall be forced to modify our ideas as to the value of the nebular hypothesis as a working basis, before we can harmonize our deductions from astronomical and geological grounds. Fortunately, the study of the spiral nebulæ has done much to elucidate our conceptions of the formation of the planetary systems, and from the discoveries made concerning these highly attenuated bodies of matter, a new hypothesis has been formed which will completely harmonize, perhaps, with these above stated facts, which could not be made to accord with the nebular theory as previously held.