314 The Nebular Hypothesis of Laplace. 



and a transport of matter which would be deposited in hori- 

 zontal layers at the bottom of the vast basins in which the 

 waters would congregate. These phenomena would continually 

 be reproduced through the successive evaporations and con- 

 densations which the water would experience through the 

 high temperature of the surface of the globe, and through the 

 continual refrigeration of the atmosphere. Thus the successive 

 formations on the terrestrial globe, which it belongs to geology 

 to elucidate, would arise naturally out of the circumstances we 

 have considered." 



c ' The comets which from time to time pass near the sun 

 cannot be regarded as arising from the nebula which we have 

 supposed to be the origin of the sun and planets, and of their 

 satellites. These comets must be regarded as small nebulae 

 moving in immensity, and which on approaching our system 

 are drawn into it by the sun's attraction, and which after 

 coming near him, recede, often never to return. When a comet 

 thus journeys near our sun and planets, their actions upon it 

 may modify the line in which it moves, so as to convert it into 

 an ellipse with a major axis not extravagantly great ; and thus 

 the comet may become periodic, and an integral part of our 

 system. Four known periodical comets seem to be in this 

 condition, but it may happen that the disturbing actions of the 

 planets, near which they pass, may so modify their orbits as to 

 elongate them indefinitely from us, without absolutely pre- 

 venting their return ; and there are instances of comets whose 

 movements have been effected by actions of this kind." 



" The zodiacal light is readily explained according to the 

 hypothesis of Laplace. It cannot be regarded as due to the 

 atmosphere of the sun, as it extends beyond the orbits of 

 Mercury and Venus, and thus exceeds the limits within which 

 the solar atmosphere must be circumscribed through the 

 volocity of the sun's rotation; but we might conceive that 

 some of the matter successively abandoned by the nebula 

 which formed our planetary system, might not be totally con- 

 densed into the various masses out of which the planets were 

 formed. Small quantities of this matter might remain and 

 form a very diffuse lenticular nebula, such as the zodiacal light. 

 Many examples of such elongated nebula are found in the 

 heavens. It may also happen that nebular matter diffused in 

 the space surrounding the sun might be condensed into an 

 immense number of little planets, and in this way we may 

 explain the origin of shooting stars, whose periodical return 

 gives some countenance to such a theory." 



