According to this theory,—if all the planets are of the same substance as the earth on which we live, and of the greater sun from which they have ages since been separated,—there must once have been material heavy as rock and earth after condensation, filling the space around our sun in every direction for 3,000 millions of miles. If we could learn _how_ this material of fire-mist originated we could better understand the mystery of world-making. A theory that would explain the formation of our own solar system should explain the formation of all the suns in space, a state of fire-mist for one implying the same for all. Let us consider whether there may not be other explanations of the phenomena in question fully as credible as the one given, and quite as consistent with all the known laws of nature. CHAPTER I. EXPANSION AND CONTRACTION. 1st. _Expansion._ It is supposed by the nebular hypothesis that the planets were all formed from rings of condensing vapor thrown off from a contracting sun which once filled space to, and beyond, Neptune’s distance. Let us imagine them again expanded to a like dimension, or even greater, reaching half way to the next nearest sun, Alpha Centauri, whose distance from our sun is computed as about twenty trillions of miles. Assuming this to be the true distance there could be placed between the two stars fifteen septillions of suns, each with a diameter of 800 thousand miles. Were it possible to expand the earth a million and a quarter times its present size, that is as large as the sun now is, it would then be but one fifteen-septillionth the size necessary to fill the space between the sun and Alpha Centauri. What we know of earth, air, water, rocks, and the metals would not lead us to suppose that these substances could be increased by expansion even a million of times. Could there be such an expansion they would then exist as mere atomic particles of dust incapable of holding heat with the outside element space 300° below zero. Nearly all known substances expand on being heated, though not often to any great extent; as, for example, iron and the metals. But anything that is greatly expanded cools rapidly. Then may we suppose that earth to-day could be expanded into a body large enough to fill the great space it must once have occupied in the state of fire-mist claimed for it? or, if thus expanded, that it would take one year, or even one day, to cool such a body?