Page:On the Magnet - Gilbert (1900 translation of 1600 work).djvu/80

water. For we see one drive towards another, and the quicker the nearer they are. Solids are impelled towards solids by the medium of liquid: for example, touch the end of a versorium with the end of a rod on which a drop of water is projecting; as soon as the versorium touches the top of the droplet, immediately it is joined * strongly by a swift motion to the body of the rod. So concreted humid things attract when a little resolved into air (the effluvia in the intermediate space tending to produce unity); for water has on wet bodies, or on bodies wet with abundant moisture on the top of water, the force of an effluvium. Clear air is a convenient medium for an electrical effluvium excited from concreted humour. Wet bodies projecting above the surface of water (if they are near) run together so that they may unite; for the surface of the water is raised around wet substances. But a dry thing is not impelled to a wet one, nor a wet to a dry, but seems to run away. For if all is dry above the water, the surface of the water close to it does not rise, but shuns it, the wave sinking around a dry thing. So neither does a wet thing move towards the dry rim of a vessel; but it seeks a wet rim. A B is the surface of the water; C D two rods, which stand up wet above the water; it is manifest that the surface of the water is raised at C and D along with the rods; and therefore the rod C, by reason of the water standing up (which seeks its level and unity), moves with the water to D. On E, on the other hand, a wet rod, the water also rises; but on the dry rod F the surface is depressed; and as it drives to depress also the wave rising on E in its neighbourhood, the higher wave at E turns away from F; for it does not suffer itself to be depressed. All electrical attraction occurs through an intervening humour; so it is by reason of humour that all things mutually come together; fluids indeed and aqueous bodies on the surface of water, but concreted things, if they have been resolved into vapour, in air;—in air indeed, the effluvium of electricks being very rare, that it may the better permeate the medium and not impel it by its motion; for if that effluvium had been thick, as that of air, or of the winds, or of saltpetre burnt by fire, as the thick and foul effluvia given out with very great force, from other bodies, or air set free from humour by heat rushing out through a pipe (in the instrument of Hero of Alexandria, described in hisbook