The motions which tend to the support and the destruction of created things are balanced by one another: there must be an equilibrium in these opposing forces-- Sic aequo geritur certamine principiorum Ex infinito contractum tempore bellum.[383] Death and birth succeed one another, as now the vitalising, now the destructive forces gain the upper hand. Further, the great diversity in Nature is to be accounted for by diversity, not only in the original forms of matter, but also in their modes of combination. No existing thing is composed solely of one kind of atoms. The greater the variety of forces and powers which anything displays, the greater is the variety of the elements out of which it was originally composed. Of all visible objects the earth contains the greatest number of elements; therefore it has justly obtained the name of the universal mother. There is however a limit to the modes in which atoms can combine with one another: each nature appropriates elements suitable to its being and rejects those unsuitable. All existing things differ from one another in consequence of the difference in their elements and in their modes of combination. The different modes of combination give rise to many of the secondary properties of matter, which are not in the original elements. Colour, for instance, is not one of the original properties of atoms: for all colour is changeable, and all change implies the death of what previously existed. Moreover, colour depends on light, and the atoms never come forth into the light. The atoms are also devoid of heat and cold, of sound, taste, and smell. All these properties must be kept distinct from the original elements-- Immortalia si volumus subiungere rebus Fundamenta quibus nitatur summa salutis; Ne tibi res redeant ad nilum funditus omnes.[384] Further, although they are the origin of all living and sentient things, the atoms themselves are devoid of sense and life, otherwise they would be liable to death. All living things are merely results of the constant changes in the primordial elements contained in the heavens and the earth. Hence the heaven is addressed as the father, the earth as the mother, of all things that have life. Finally, from the infinity of space and matter, it may be inferred that there are infinite other worlds and systems beside our own. Many elements were added from the infinite universe to our system before it reached maturity: and many indications prove that the period of growth is now past, and that we are living in the old age of the world.