Gilbert has been stiled the father of modern electricity; and when we consider how little was known of the subject prior to his time, and the merit that belongs to himself, not only from his own experiments, but also from turning the attention of philosophers to a new branch of natural science, we cannot but allow that he eminently deserves the title.
Cabeus followed Gilbert, but did little else than add to the list of electrics, wax, gum elemi, Gum guaiaci, Pix Hispanica and Gypsum.
Thirty years after the publication of Gilbert’s work, the celebrated Sir Kenelm Digby, in his “Treatise of the nature of Bodies,” touches upon electricity: but as the age in which he lived was still busying itself with the hypothetical philosophy of Aristotle, so this philosopher in what he says of electricity, appears to be rather amusing himself in inventing theories, to explain the manner in which electric attraction is performed, than in advancing the science by new facts and experiments. His theory of electric attraction is, however, of some celebrity: it was allowed by his contemporary Des Cartes, in his principles of philosophy, and was embraced by the chief writers of his age; though it does not differ essentially from that of Gilbert.
“Attraction (says he) is made by a tenuious emanation, or continued effluvium, which after some distance retracteth into itself, as is observable in drops of syrups, oil and seminal viscosities, which spun at length, retire to their dimensions. Now these effluviums advancing from the body of an electric, in their return do carry back the bodies whereon they have laid hold, within the sphere or circle of their continuities; and these they do not only attract, but with their viscous arms, hold fast a good while after. And if any shall wonder why these effluvium issuing forth, impel and protrude not the straw before they can bring it back; it is because the effluvium passing out in a smaller thread, and more enlengthened filament, stirreth not the bodies interposed; but returning into its original, falls into a closer substance and carrieth them back into itself.”
Sir Thomas Brown succeeded to Sir Kenelm Digby. In his “Inquiry into Vulgar Errors,” this inquisitive philosopher has a chapter on electricity, in which he corrects some mistakes into which his predecessor had fallen, adds some new experiments of his own, and gives us a summary view of the state of electrical knowledge at the time he wrote.
“By electrical bodies, (says he) I understand not such as are metallical, mentioned by Pliny, and the ancients; for their electrum was a mixture made of gold, with the addition of a fifth part of silver; a substance now as unknown as true Aurichalcum, or Corinthian brass, and set down among things lost by Pancirollus. Nor by electric bodies do I conceive such only as take up shavings, straws, and light bodies, in which number the ancients only placed Jet and Amber; but such as conveniently placed unto their objects attract all bodies palpable whatsoever. I say conveniently placed, that is, in regard of the object, that it be not too ponderous, or any way affixed; in regard of the agent, that it be not foul or sullied, but wiped, rubbed, and excitated; in regard of both, that they be conveniently distant, and no impediment interposed. I say, all bodies palpable, thereby excluding fire, which indeed it will not attract, nor yet draw through it; for fire consumes its effluxions by which it should attract.”
Brown augmented the list of electrics, and found attraction not only in simple bodies, but in such also as were compounded. He observed, that the attractions of bodies were different. Resinous bodies, he says, attract most vigorously, and “good hard wax so powerfully, that it will convert the needle almost as actively as the load-stone. Gums easily dissolved in water, draw not at all; no metal attracts, nor wood, though never so hard and polished. “Glass, (he says,) attracts but weakly, though clear: and some slick stones, and thick glasses but indifferently.”
These experiments on the electricities of bodies, he performed by means of a needle, “settled freely upon a well pointed pin, so that the electrics might be applied to it without disadvantage;” he tried them also in straws and paleous bodies, powders of wood and iron, in gold and silver foliated.
How the attraction of electrics is performed, he acknowledges is not easily determined; though, he says, “that it is performed by effluviums is plain, and granted by most; for electrics will not commonly attract, except they grow hot and perspirable. For if they be foul and obnubilated, it hinders their effluxion; nor if they be covered, though but with linen or sarsenet, or if a body be interposed, for that intercepts the effluvium. If also a powerful and broad electric of wax or anime be held over fine powder, the atoms or small particles will ascend most numerously unto it; and if the electric be held unto the light, it may be observed that many thereof will fly, and be as it were discharged from the electric to the distance sometime of two or three inches. Which motion is performed by the breath of the effluvium issuing with agility; for as the electric cooleth, the projection of the atoms ceaseth.”
Sir Francis Bacon in his “Physiological Remains,” has inserted a catalogue of bodies attractive and not attractive; but he differs in nothing worth mentioning from his predecessors.