more stringent methods, must lead to great advances in knowledge. The explanation of the operation of the magnet, inadequate as it may otherwise be, affords us a view of the exact and consequent carrying out of hypotheses which is characteristic of the whole natural philosophy of the Epikureans. Lucretius reminds us, to begin with, of the continual extremely rapid and tempestuous motions of the subtle atoms which circulate in the pores of all bodies, and stream out from their surfaces. Every body, on this view, is always sending out in every direction streams of such. atoms, which produce a ceaseless interchange amongst all the objects in space. It is a theory of universal emanation. as against the vibration theory of modern physical science. The relations of these interchanges in themselves, apart from their form, have been in our own days not only demonstrated by experiment, but have had an incomparably greater importance assigned to them in their kind, quantity, and rapidity than the boldest imaginations of the Epikureans could have conceived. Lucretius tells us that from the magnet there proceeds such a violent stream outwards, that it produces through the driving out of the air a vacuum between the magnet and the iron, into which the iron rushes. That there is no idea here of a mystically acting 'horror vacui' is, of course, obvious, if we consider the physical philosophy of this school. The result is rather produced because every body is constantly assailed on every hand by blows from atmospheric atoms, and must therefore yield in any direction in which a passage opens itself, unless its weight is too great, or its density is so slight that the air-atoms can make their way unhindered through the pores of the body. And this explains why it is iron of all things that is so violently attracted by the magnet. The poem refers it simply to its structure and its specific gravity; other bodies being partly too heavy, as in the case of gold, to be moved by the streams, and so carried through the void space to the mag net, and partly, as in the case of wood, so porous, that the streams can fly through them freely without any mechanical collision. This explanation leaves much still unexplained, but the whole treatment of the subject advantageously contrasts with the hypotheses and theories of the Aristotelian school by its vividness and clearness. We first ask, how is it possible that the currents from the magnet can expel the air without repelling the iron by the same force? 76 And it might have been readily ascertained by an easy experiment that into the void created by rarefied air, not iron alone, but all other bodies, are carried. But the fact that we can raise such objections shows that the attempt at an explanation is a fruitful one, whilst the assumption of secret forces, specific sympathies, and similar devices, is hostile to all further reflection. This example also shows us, it is true, why this fashion of natural inquiry could make so little progress in antiquity. Almost all the real achievements of physical science among the ancients, are mathematical, and therefore in astronomy, in statics and mechanics, and in the rudiments of optics and acoustics. There was further a valuable mass of materials accumulated by the descriptive sciences; but everywhere, where what was needed was the attainment by the variation and combination of observations to the discovery of laws, the ancients remained in a backward condition. To the Idealist was lacking the sense for and interest in concrete phenomena; the Materialists were always too much inclined to stop short with a single observation, and to content themselves with the first explanation that offered itself, instead of probing the matter to the bottom. 76 We may compare the well-known experiment in which a plate which is held over the opening of a vessel through which a stream of air is flowing, is attracted and held fast because the air, which streams rapidly sidewards, is rarefied between the vessel and the plate (Müller's Physik., i. 9, 96). Even though we cannot assume that the Epikureans were acquainted with this phenomenon, yet they may have conceived in a similar way the expulsion of the air by the currents proceeding from the stone. SECOND SECTION. THE PERIOD OF TRANSITION. CHAPTER I. THE MONOTHEISTIC RELIGIONS IN THEIR RELATION THE disappearance of the ancient civilisation in the early centuries of the Christian era is an event the serious problems of which are in great part still unexplained. It is difficult enough to follow the intricate events of the Roman Empire in all their extent, and to grasp the important facts; but it is incomparably more difficult to estimate in their full extent the workings of the slight but endlessly multiplied changes in the daily intercourse of nations, in the hearts of the lower orders, by the hearth of humble families, whether in the city or the countryside.1 And yet, so much at least is certain, that from the lower 1 A very valuable insight into the physiology of nations has been recently afforded us by the consideration of history from the standpoints of the natural sciences and of political economy, and the light thus kindled extends into the poorest hevels; yet it shows us only one side of the matter, and the changes in the intellectual condition of peoples remain still covered with darkness, so far as they cannot be explained from the social changes. Liebig's theory of VOL. I. the exhaustion of the soil has been carried by Carey (Principles of Social Science, vol. i. chaps. iii. ix., vol. iii. chap. xlvi., &c.) to wrong and exaggerated conclusions, and been fused with entirely absurd doctrines (comp. my essay, Mill's Ansichten über die sociale Frage u. d. angebl. Umwälzung der Socialwissensch. durch Carey, Duisb. 1866), but the correctness of this theory in its main features, and its applicability to the civilisation of the old world, cannot be doubted. L |