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h。 They have taught us that for the deciphering of the past and the predicting of the future； no hypotheses are admissible which are not based upon the actual behaviour of things in the present。 Once there was unlimited facility for guessing as to how the solar system might have come into existence； now the origin of the sun and planets is adequately explained when we have unfolded all that is implied in the processes which are still going on in the solar system。 Formerly appeals were made to all manner of violent agencies to account for the changes which the earth's surface has undergone since our planet began its independent career； now it is seen that the same slow working of rain and tide； of wind and wave and frost； of secular contraction and of earthquake pulse； which is visible to…day； will account for the whole。 It is not long since it was supposed that a species of animals or plants could be swept away only by some unusual catastrophe； while for the origination of new species something called an act of 〃special creation〃 was necessary； and as to the nature of such extraordinary events there was endless room for guesswork； but the discovery of natural selection was the discovery of a process； going on perpetually under our very eyes； which must inevitably of itself extinguish some species and bring new ones into being。 In these and countless other ways we have learned that all the rich variety of nature is pervaded by unity of action； such as we might expect to find if nature is the manifestation of an infinite God who is without variableness or shadow of turning； but quite incompatible with the fitful behaviour of the anthropomorphic deities of the old mythologies。 By thus abstaining from all appeal to agencies that are extra…cosmic； or not involved in the orderly system of events that we see occurring around us； we have at last succeeded in eliminating from philosophic speculation the character of random guesswork which at first of necessity belonged to it。 Modern scientific hypothesis is so far from being a haphazard mental proceeding that it is perhaps hardly fair to classify it with guesses。 It is lifted out of the plane of guesswork； in so far as it has acquired the character of inevitable inference from that which now is to that which has been or will be。 Instead of the innumerable particular assumptions which were once admitted into cosmic philosophy； we are now reduced to the one universal assumption which has been variously described as the 〃principle of continuity；〃 the 〃uniformity of nature；〃 the 〃persistence of force；〃 or the 〃law of causation；〃 and which has been variously explained as a necessary datum for scientific thinking or as a net result of all induction。 I am not unwilling； however； to adopt the language of a book which has furnished the occasion for the present discussion； and to say that this grand assumption is a supreme act of faith； the definite expression of a trust that the infinite Sustainer of the universe 〃will not put us to permanent intellectual confusion。〃 For in this mode of statement the harmony between the scientific and the religious points of view is well brought out。 It is as affording the only outlet from permanent intellectual confusion that inquirers have been driven to appeal to the principle of continuity； and it is by unswerving reliance upon this principle that we have obtained such insight into the past； present； and future of the world as we now possess。
The work just mentioned＇1＇ is especially interesting as an attempt to bring the probable destiny of the human soul into connection with the modern theories which explain the past and future career of the physical universe in accordance with the principle of continuity。 Its authorship is as yet unknown； but it is believed to be the joint production of two of the most eminent physicists in Great Britain； and certainly the accurate knowledge and the ingenuity and subtlety of thought displayed in it are such as to lend great probability to this conjecture。 Some account of the argument it contains may well precede the suggestions presently to be set forth concerning the Unseen World； and we shall find it most convenient to begin； like our authors； with a brief statement of what the principle of continuity teaches as to the proximate beginning and end of the visible universe。 I shall in the main set down only results； having elsewhere＇2＇ given a simple exposition of the arguments upon which these results are founded。
＇1＇ The Unseen Universe； or； Physical Speculations on a Future State。 ＇Attributed to Professors TAIT and BALFOUR STEWART。＇ New York： Macmillan & Co。 1875。 8vo。 pp。 212。
＇2＇ Outlines of Cosmic Philosophy； based on the Doctrine of Evolution。 Boston： J。 R。 Osgood & Co。 1875。 2 vols。 8vo。
The first great cosmological speculation which has been raised quite above the plane of guesswork by making no other assumption than that of the uniformity of nature； is the well…known Nebular Hypothesis。 Every astronomer knows that the earth； like all other cosmical bodies which are flattened at the poles； was formerly a mass of fluid； and consequently filled a much larger space than at present。 It is further agreed； on all hands； that the sun is a contracting body； since there is no other possible way of accounting for the enormous quantity of heat which he generates。 The so…called primeval nebula follows as a necessary inference from these facts。 There was once a time when the earth was distended on all sides away out to the moon and beyond it； so that the matter now contained in the moon was then a part of our equatorial zone。 And at a still remoter date in the past； the mass of the sun was diffused in every direction beyond the orbit of Neptune； and no planet had an individual existence； for all were indistinguishable parts of the solar mass。 When the great mass of the sun； increased by the relatively small mass of all the planets put together； was spread out in this way； it was a rare vapour or gas。 At the period where the question is taken up in Laplace's treatment of the nebular theory； the shape of this mass is regarded as spheroidal； but at an earlier period its shape may well have been as irregular as that of any of the nebulae which we now see in distant parts of the heavens； for； whatever its primitive shape； the equalization of its rotation would in time make it spheroidal。 That the QUANTITY of rotation was the same then as now is unquestionable； for no system of particles； great or small； can acquire or lose rotation by any action going on within itself； any more than a man could pick himself up by his waistband and lift himself over a stone wale So that the primitive rotating spheroidal solar nebula is not a matter of assumption； but is just what must once have existed； provided there has been no breach of continuity in nature's operations。 Now proceeding to reason back from the past to the present； it has been shown that the abandonment of successive equatorial belts by the contracting solar mass must have ensued in accordance with known mechanical laws； and in similar wise； under ordinary circumstances。 each belt must have parted into fragments； and the fragments chasing each other around the same orbit；