5 i8 THE POPULAR SCIENCE MONTHLY. 



He assumes that our globe was once very much smaller than it is at 

 present, and that independent masses of matter, perhaps other planets, 

 have fallen upon it, the shock of collision generating an enormous de- 

 gree of heat. This is an effect of the " crush of worlds " not common- 

 ly apprehended. If two bodies, conjointly equal to the bulk of the 

 earth, were rapidly traveling through space, and should violently 

 come together, their collision would evolve enough heat to convert the 

 united mass into lava, or heated vapor. An asteroid falling upon the 

 sun would generate from 4,600 to 9,200 times as much heat as would 

 come from the combustion of an equal mass of bituminous coal, the 

 force of velocity changing into caloric. This view, though adequate 

 to explain the origin of the nebula, does not account for the existence 

 of the colliding bodies. It might be consistent with the doctrine of 

 the eternity of matter, in which case the colliding planets may have 

 been coursing about the sun for myriads of ages as aggregations of 

 matter corresponding to the last term of the great cosmic cycle — in- 

 organic sterility. Could we understand how all the planets might 

 eventually fall into the sun, we might suppose the present series of 

 changes is only one of several cycles, in agreement with the specula- 

 tions of certain writers. 



Dr. Mayer carries his theory much farther. He does not confine 

 these cataclysmic unions to the ante-nebulous periods. It is suggested 

 that there may have been similar accretions to the surface of our planet 

 after the introduction of life. A luxuriant vegetation, or a thickly- 

 peopled continent, may have been often buried beneath the fiery d&bris 

 resulting from the conflict. There are frequent occurrences of a simi- 

 lar character at the present day, but of trifling influence upon the gen- 

 eral temperature. Every solid meteor that falls from the sky develops 

 heat ; and it cannot be denied that, were these bodies of large size, 

 the calamitous occurrences depicted by Dr. Mayer would be expe- 

 rienced. Each one of these cataclysms would interrupt the cycle of 

 progress as set forth above, and carry the order of the mutations back 

 to the beginning. 



When we study the scheme of worlds revolving around the sun, 

 we discover that they all rotate on their axes in the same direction ; 

 that they all proceed from west to east, their orbits being nearly cir- 

 cular, and in almost the same plane, which is nearly coincident with 

 that of the sun ; that the sun moves on his axis in less time than any 

 of the planets, and each planet rotates more quickly than its satellite. 

 These and other facts point out a community of origin and develop- 

 ment inexplicable by chance or the law of gravitation. We suppose, 

 then, that the sun and all the planets and their satellites composed 

 originally a single mass of luminous fog, with a diameter exceeding 

 that of the orbit of Neptune, the remotest planet, or not less than 

 three thousand million miles. This would correspond well with the 

 supposed dimensions of the smaller nebulae now seen in the skies. The 



