“Very many electric bodies do not attract at all, unless they are first rubbed. An ordinary piece of amber does not attract by heat, even when brought to the flaming point, but it attracts by friction, without which latter few bodies give out their true natural electric emanation and effluvium. By friction, the amber is made moderately hot and also smooth; these conditions must in most cases concur; but a large polished piece of amber or of jet attracts even without friction, though not so strongly; yet, if it be carefully brought nigh to a flame or a red coal, it does not attract corpuscles; further, the sun’s heat heightened by means of a burning-glass imparts no power to amber, for it dissipates and spoils all the electric effluvia. Again, flaming sulphur and burning sealing-wax (of lac) do not attract. “The loadstone, though susceptible of very high polish, has not the electric attraction. The force does not come through the lustre proceeding from the rubbed and polished electric; for the vincentina, diamond and pure glass attract when they are rough. Effluvia that attract but feebly when the weather is clear produce no motion at all when it is cloudy. For the effluvium from rock crystal, glass, diamond--substances very hard and very highly compressed--there is no need of any notable outflow of substance. Such an electric as sound cypress-wood, after a moment’s friction, emits powers subtle and fine, far beyond all odours; but sometimes an odour is also emitted by amber, jet, sulphur, these bodies being more readily resolved; hence it is that, usually, they attract after the gentlest friction because their effluvia are stronger and more lasting. “Rock crystal, mica, glass, and other electric bodies do not attract if they be burned or highly heated, for their primordial humour is destroyed by the heat, is altered, is discharged as vapour. All bodies that derive their origin principally from humours and that are firmly concreted attract all substances whether humid or dry; but bodies consisting mostly of humour and not firmly compacted by nature, wherefore they do not stand friction but either fall to pieces or grow soft or are sticky, do not attract corpuscles. “Electrical movements come from the matter (_materia_) but magnetic from the prime form (_forma_). Moist air blown from the mouth, moisture from steam, or a current of humid air from the atmosphere chokes the effluvium. But olive oil that is light and pure does not prevent it; and, if a sheet of paper or a linen cloth be interposed, there is no movement. But loadstone, neither rubbed nor heated, and even though it be thoroughly drenched with liquid, and whether in air or water, attracts magnetic bodies, and that though solidest bodies or boards or thick slabs of stone or plates of metal stand between.