238 Original Articles. [April, 



affected by their different distances from the sun, any conclusion 

 arrived at concerning one of them would be equally applicable to the 

 rest. With respect to heat, there seems clear evidence of a compensa- 

 tion for diminished solar radiation. The same cannot, however, as yet 

 be certainly said of light. But even on the ordinary law of radiation, 

 and not considering the small but appreciable effect from the four, 

 if not more, moons of Uranus, and the two of Neptune, the amount of 

 light at the distance of the latter must be far beyond the limits en- 

 joyed by many terrestrial creatures. The light from brightest sun- 

 shine has been calculated by Wollaston to be equal at the Earth to 

 805,072 full moons, and as Neptune is thirty times more distant than 

 it from the sun, he would receive wboth the amount, or an equivalent 

 to that of 890 full moons, if his atmosphere exerted the same ab- 

 sorptive effect as ours. The average day of the exterior planets is ten 

 hours, their years varying in length from nearly 12 of ours on Jupiter 

 to I64f on Neptune. The specific gravity, compared with that of the 

 Earth, varies from ■ 24 for Jupiter to ■ 14 for Saturn. 



Between Mars and Jupiter are from 75 to 80 small planets, of 

 which more is unknown than known. We will merely observe that 

 their aggregate mass is much smaller than their number would seem 

 to imply, as Le Verrier concludes, from its producing no perceptible 

 variation in the heliocentric longitude of the perihelion of Mars that 

 it cannot equal one-third that of the Earth.* 



On summing up this subject we find that on our own planet every 

 element, every region, and nearly every foot of space swarms with 

 living creatures possessing an endless diversity of organization to suit 

 an endless variety of condition ; that throughout all geologic ages 

 " the systems of life have been varied from time to time, but never 

 extinguished ;" that from microscopic creatures only the millionth of 

 an inch to the immense Dinotherium giganteum, or the Megalosaurus, 

 seventy feet long, there has been every gradation of size ; that beyond 

 our planet there are evidences of adaptation, first on one and then on 

 another member of the series to which it belongs, of a character such 

 as to render them probably habitable; that, furthermore, there are 

 indications of a great number of such series in the existence of bodies 

 resembling the sun as independent sources of light, heat, and chemical 

 and attractive power, and, like him, abounding in elements which, 

 under the influence of these forces, seem specially susceptible of 

 ministering to the organization of living creatures ; that many of these 

 greatly surpass our own sun in some of these qualities, their light 

 being so intense as to penetrate to the base of our atmosphere, while 

 themselves are often so distant as to afford no sensible parallax ; that 

 one of them at least is ascertainably of a much greater mass ;f and, 

 lastly, that their great distances from him and from one another would 

 be explicable on the supposition that they had secondary systems 

 revolving round them, which these distances preserved from destruc- 



* 'Month. Not. Astro. Soc. for 1853 to 1855,' p. 63. 



t The binary system, 70 Qphiucfai, is said by Sir J. Herschel on the authority 

 of M. Kriiger to be '3^ 6 times the mass of the Sun. 



