Among the various properties of bodies, however, there were two which Demokritus recognised as not merely relative to the observer, but also as absolute and belonging to the body in itself. These were weight and hardness--primary qualities (to use the phraseology of Locke and Reid), as contrasted with the secondary qualities of colour, taste, and the like. Weight, or tendency downward, belonged (according to Demokritus) to each individual atom separately, in proportion to its magnitude: the specific gravity of all atoms was supposed to be equal. In compound bodies one body was heavier than another, in proportion as its bulk was more filled with atoms and less with vacant space.[208] The hardness and softness of bodies Demokritus explained by the peculiar size and peculiar junction of their component atoms. Thus, comparing lead with iron, the former is heavier and softer, the latter is lighter and harder. Bulk for bulk, the lead contained a larger proportion of solid, and a smaller proportion of interstices, than the iron: hence it was heavier. But its structure was equable throughout; it had a greater multitude of minute atoms diffused through its bulk, equally close to and coherent with each other on every side, but not more close and coherent on one side than on another. The structure of the iron, on the contrary, was unequal and irregular, including larger spaces of vacuum in one part, and closer approach of its atoms in other parts: moreover these atoms were in themselves larger, hence there was a greater force of cohesion between them on one particular side, rendering the whole mass harder and more unyielding than the lead.[209] [Footnote 208: Theophrastus, De Sensu, s. 61. [Greek: Baru\ me\n ou)=n kai\ kou=phon tô=| mege/thei diairei= Dêmo/kritos], &c. Aristotel. De Coelo, iv. 2, 7, p. 309, a. 10; Gen. et Corr. i. 8, p. 326, a. 9. [Greek: Kai/toi baru/teron ge kata\ tê\n u(perochê/n phêsin ei)=nai Dêmo/kritos e(/kaston tô=n a)diaire/tôn], &c.] [Footnote 209: Theophrastus, De Sensu, s. 62.] [Side-note: All atoms essentially separate from each other.] We thus see that Demokritus, though he supposed single atoms to be all of the same specific gravity, yet recognised a different specific gravity in the various compounds of atoms or material masses. It is to be remembered that, when we speak of contact or combination of atoms, this is not to be understood literally and absolutely, but only in a phenomenal and relative sense; as an approximation, more or less close, but always sufficiently close to form an atomic combination which our senses apprehended as one object. Still every atom was essentially separate from every other, and surrounded by a margin of vacant space: no two atoms could merge into one, any more than one atom could be divided into two. [Side-note: All properties of objects, except weight and hardness, were phenomenal and relative to the observer. Sensation could give no knowledge of the real and absolute.]