But besides the direct action of outward things on the senses, he admits the power of certain images to make themselves immediately present to the mind (iv. 722-822), and also a certain immediate apprehension or intuition of the mind (iniectus animi) into things beyond the cognisance of sense[395]. Thus there is no actual inconsistency with his principles in claiming the power of understanding the properties and configuration of the atoms, which are represented as lying below the reach of our senses-- Omnis enim longe nostris ab sensibus infra Primorum natura iacet. But of the mode of operation of this 'intuition of the mind' there is no criterion. The doctrine of the properties, shapes, motions, etc. of the atoms is a creation of the imagination, suggested by certain analogies from sensible things, but incapable of being verified by the senses, which he regards as the only sure foundations of knowledge. But even on the supposition that the existence and properties of the atoms had been satisfactorily established, no adequate explanation is offered of their relation to the facts of existence. The same difficulty is encountered at the outset of this as of all other ancient systems of ontology, viz. how to pass from the eternal and immutable forms of the atoms to the variety and transitory nature of sensible objects. This is the very difficulty which Lucretius himself urges against the system of Heraclitus,-- Nam cur tam variae res possint esse requiro, Ex uno si sunt igni puroque creatae. The order of Nature now subsisting is declared to be the result of the manifold combination of the atoms through infinite time and space, but the intermediate stages by which this process was effected are assumed rather than investigated. We seem to pass 'per saltum' from the chaos of lifeless elements to the perfect order and manifold life of our system. This wide chasm seems as little capable of being bridged by the help of the atoms of Democritus, as by the watery element of Thales or the fiery element of Heraclitus. But in Lucretius this difficulty is partially concealed, by a poetical element in his conception, really inconsistent with the mechanical materialism on which his philosophy professes to be based.--It is to be observed that while the Greek word ἄτομα implies merely the notion of individual existences, the words used by Lucretius, 'semina,' 'genitalia corpora,' really indicate a creative capacity in these existences. In conceiving their power of carrying on and sustaining the order of Nature, his imagination is thus aided by the analogy of the growth of plants and living beings. A secret faculty in the atoms, distinct from their other properties, is assumed. Thus he says-- At primordia gignundis in rebus oportet Naturam clandestinam caecamque adhibere.[396]