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♦ KNOWLEDGE ♦ 



[December 1, 1886. 



and sun. Moons will gravitate to their planets, planets to 

 their suns, and so on, until the matter of the universe, with 

 intermediate outbursts of energy, becomes cold, inert, and 

 solid, and Force will have subdued all things unto itself. 

 The molecular energy likewise passes, but more rapidly, 

 into the ethereal medium, throbbing ceaselessly in all 

 directions to the farthest marge of space, if any marge there 

 be. Small portions of it are intercepted by each mass, but 

 of these the larger proportion is reflected back, the remainder 

 setting up sepai-ative motions on the surface, as, e.g., in the 

 fomiliar case of the fiction of the sun's radiant heat on the 

 earth. Of this solar energy, which is radiated equally in 

 every direction, the earth does not intercept much more 

 than the two thousand millionth part. And of this the larger 

 proportion is reflected back, only a fraction, to be itself 

 finally dissipated, being used to maintain the earth as the 

 theatre of changes whose highest result is life. 



Such, with much detail left out for clearer presentment 

 of the subject, is the mode in which the shining hosts of 

 stellar systems, as the sand by the sea-shore innumerable, 

 appear to have been evolved from nebulous matter. In 

 this exposition students of astronomy will recognise the 

 '• nebular theory " of Kant and Laplace, but with important 

 modifications due to the doctrine of the Conservation of 

 Energy, which was unknown in their day.* 



EvohUion of the Solar System. — We may now leave the 

 general for the particular, and apply the theory to the 

 evolution of the stellar system to which we belong, and to 

 that portion of it which we call our earth. If the explana- 

 tion of the origin of the sun and planets repeats somewhat 

 of the foregoing, it will only bring home to us the uniformity 

 of the pi'ocess, and show that what is true of the whole 

 holds good for every part, and for the parts of every part 

 down to the indivisible and unseen atoms of which all things 

 consist. 



Two striking pieces of evidence of the common origin of 

 the sun and planets may be cited at the outset: — (1) They 

 ai-e made of like materials ; (L') they have like motions. 



1. The spectroscope has revealed to us the chemical con- 

 stitution of several of the fixed stars, their enormous dis- 

 tance not aflfecting the trustworthiness of the analysis. It 

 evidences to the existence of substances in the glowing 

 vapours of their atmospheres akin to those which feed the 

 lires of the sun ; and if such identity of stuflf is proved to 

 exist between the sun and other stars, we may with reason 

 look for still closer identities of material lietween him and 

 his family of planets, moons, and erratic bodies. 



2. The planets and, with rare exceptions, their satellites, 

 revolve round him in the .same direction ; they also, so far 

 as is known, rotate on their axes in the same direction, and 

 very nearly coincide in the .shape and planes of their orbits, 

 which are almost in a plane with the sun's equator. Now, 

 since the consequences would be the same were these 

 motions, both on axis and in orbit, in the reverse direction, 

 the inference is obvious that there was an uniform motion 

 of lotation of the mass from which they were severally formed. 



As with the primitive nebula from which that mass was 

 detached, so with the mass itself; there were differences of 

 density throughout. On no other theory is its .segregation 

 into a multitude of bodies explicable. As the rotation of 

 the mass quickened with the indrawing of the particles 

 towards the common centre of gravity, the energy of molar 

 separation acted most powerfully in the region of tlie bulging 

 equator, and, overcoming the force of cohesion along the line 



* For a lucid criticism of the defects of Laplace's theorv, more 

 especially in its failiu-e to account for the peculiar distribution 

 of the larger and smaller planets, the reader may study with 

 advantage Mr. Proctor's ess.iy on "How the Planets Grew" in his 

 " Expanse of Heaven." 



of least resistance, detached certain portions one after another 

 at irregular intervals from the central mass as it retreated 

 within itself. These portions were the nuclei of the planetary 

 groups, in which the like processes of contraction and rupture 

 were repeated, the masses detached becoming moons, or, as 

 in the case of Saturn, rings of satellites. In respect of the 

 diflased and highly energised fugitive masses, as comets and 

 meteors, Mr. Proctor has adduced cogent reasons in support 

 of the theory that they are " products of expulsion from suns, 

 from giant planets, and from orbs like our earth when in 

 the sun-like state." 



The origin of the planets and their moons being found 

 in the mode described above, it is obvious that in their 

 primitive state they were molten, and shone by their own 

 light. The smaller the body, the sooner would its molecular 

 energy be dissipated ; in other words, the quicker it lost its 

 heat. The present in a large degree interprets the past, and 

 explains the several stages of the membars of our system, 

 according to their bulk. The sun, whose mass exceeds the 

 combined mass of all the planets more than 700 times, is 

 still slowly contracting, and therefore still radiating energy. 

 The cloud-laden atmospheres of the larger planets, as Jupiter 

 and Saturn, are torn by cyclones only second to those of the 

 sun in their fury, and the molten centres feed volcanic 

 outbursts to which those of Vesuvius and Krakatoa are 

 squibs. But as for the smaller bodies, their turmoil is calmed 

 and their light extinguished ; the store of energy is exhausted ; 

 the forces of aflinity and cohesion have gained the upper 

 hand and drawn the particles together into the solid form. 

 Thus it is with the moon, on whose dead and barren surface 

 we may read the future of the giant planets and the sun 

 himself. For the history of one is the history of all ; each 

 has passed, or is passing, from the indefinite nebulous state, 

 through numberless modifications, to the definite and solid 

 state ; by decrease in volume and increase in density. What 

 the earth is, the moon was ; what the moon is, the earth 

 will be. 



Evolution of the Earth. — To this passage from the sun-like 

 to the solid state the earth bears witness. Its flattened 

 poles, its bulging equator, its spheroidal shape, are the eflects 

 of rotation on a fluid or viscous mass ; whilst the geologically 

 oldest parts of the crust — for there is no primogeniture in 

 matter — are of a structure which is producible only by the 

 fusion of particles under intense heat. As that crust, thin 

 and mobile at the outset, continued to cool and thicken, 

 it evidenced more strikingly to the play of forces and 

 energies within and of energies, and, in lesser degree, 

 of forces without. The cooling and shrinking of the 

 internal mass, as the stored-up energy slipped away, caused 

 tension of the crust, which, yielding to the force of gravi- 

 tation, was drawn inwards, and cracked and crumpled 

 into mountains and valleys, and into the deep depressions 

 which the great oceans have filled since the time when their 

 waters were first condensed from the thick primitive 

 vapours that swathed the cooling earth. Then the con- 

 tinuous action of the sun's radiant energy, operating 

 through air and water upon the increasingly rigid crust, 

 dissolved its superficial particles, and re deposited them 

 as stratified rocks, in endless beauty and variety, over 

 the surface of the globe. And herein lies the major 

 cause of our earth's present condition as a possible abode 

 of life. For its native supply of energy — that of posi- 

 tion derived from the momentum given it when thrown 

 off from the parent mass; and the still unspent, but always 

 lessening, store of internal heat manifest in the volcano and 

 the earthquake — would not sufiice to arrest effeteness and 

 the wrapping of the globe in a winding-sheet of ice. It is 

 the imported supply from the sun which alone does that, for 

 in its absence the trivial tidal energy due to the moon would 



