CONDITION OF THE LARGER PLANETS. 183 



important to notice this, because many who, k in ex- 

 amining a series of arguments, recognise, or suppose 

 they recognise, some weakness in the evidence of one 

 or other argument, are apt to infer that the conclusion 

 is to the same degree invalidated as it would be if the 

 arguments were dependent, and therefore each one 

 essential to the establishment of the conclusion. 



The first argument for the theory is that derived 

 from the now accepted hypothesis of the growth or 

 development of the solar system. It is rendered to all 

 intents and purposes certain, as well from the evidence 

 of the earth's crust as from that given by the move- 

 ments of the sun, planets, asteroids, and satellites, that 

 the solar system was developed from a former nebulous 

 condition. The process of development may have been 

 that conceived by Laplace in his nebular hypothesis, 

 which may be described as the contraction theory, or 

 that recently suggested by meteoric discoveries, which 

 may be called the accretion theory, or, far more 

 probably, the solar system was formed by combined 

 processes of contraction and accretion. But in any 

 case the planets as severally formed were intensely 

 heated, partly vaporous, partly liquid bodies, the larger 

 being the more heated. It is no longer supposed, as 

 in Laplace's time was the case, that the outermost 

 planets were fashioned first. They may have begun 

 to be formed first this, indeed, is altogether probable 

 but the vastness of their bulk suggests that they 

 went on gathering in matter and contracting (forming 

 in the process their systems of moons) long after such 



