Page:Popular Science Monthly Volume 59.djvu/353

Rh experiments of Hertz, we must still admit that the ultimate nature of electricity remains wrapped in mystery. It is true, we discard the material effluvium of Gilbert, but only to substitute for it an ethereal ripple, a quiver, a wave motion in the hypothetical ether with which we fill all space.

From 1580 to 1600, we find Gilbert spending in his workship all the leisure he can snatch from his professional duties. He notes down his experiments, his failures as well as his successes, discusses them, reasons on them, and pursues his inquiry further and further. In a word, we find him toiling in his workshop at Colchester as Faraday toiled more than 200 years later in the low, dark rooms of the Royal Institution of Great Britain. Both were actuated by the same calm, persevering, experimental spirit. Gilbert founded and christened the science of electrics; he left it in its infancy, it is true; but with sufficient vitality to enable it to survive the neglect of years, until at last it was taken up and fondly cared for by our Franklins and Faradays.

The science of magnetism is even more indebted to Gilbert than that of electricity. The ancients spoke of the lodestone as the Magnesian stone, from its being found in Magnesia, in Asia Minor. Gilbert constantly uses the adjective magnetica; and it is to his use of that word that we owe the terms magnet, magnetic and magnetism. He showed that a great number of bodies could be electrified; but he maintained that those only could exhibit magnetic properties which contain iron. He satisfies himself of this by rubbing with a lodestone such substances as wood, gold, silver, copper, zinc, lead, glass, etc., and then floating them on corks, quaintly adding. that they show 'no poles, because the energy of the lodestone has no entrance into their interior.'

To-day we know that nickel and cobalt behave like iron, whilst antimony, bismuth, copper, silver and gold are susceptible of being influenced by powerful electromagnets, showing what has been termed diamagnetic phenomena. Even liquids and gases, in Faraday's classical experiments, yielded to the influence of his great magnet; and Professor Dewar, in the same Royal Institution, exposed some of his liquid air and liquid oxygen in the presence of the writer to the influence of Faraday's electromagnet and found them to be strongly attracted, thus behaving like the paramagnetic bodies, iron, nickel and cobalt.

Gilbert observes in all his magnets two points, one near each end, in which the force, or, as he terms it, 'the supreme attractional power,' is concentrated. He terms these poles by analogy to the earth; and he will have it understood that these poles are not mathematical points, as