Plücker, the celebrated geometer already mentioned, who pursued experimental physics for many years of his life with singular devotion and success, visited Faraday in those days, and repeated before him his beautiful experiments on magneto-optic action. Faraday repeated and verified Plücker’s observations, and concluded, what he at first seemed to doubt, that Plücker’s results and magnecrystallic action had the same origin.
MAGNETISM AND CRYSTALLISATION.
At the end of his papers, when he takes a last look along the line of research, and then turns his eyes to the future, utterances quite as much emotional as scientific escape from Faraday. “I cannot,” he says at the end of his first paper on magnecrystallic action, “conclude this series of researches without remarking how rapidly the knowledge of molecular forces grows upon us, and how strikingly every investigation tends to develop more and more their importance and their extreme attraction as an object of study. A few years ago magnetism was to us an occult power, affecting only a few bodies. Now it is found to influence all bodies, and to possess the most intimate relations with electricity, heat, chemical action, light, crystallisation, and through it with the forces concerned in cohesion. And we may, in the present state of things, well feel urged to continue in our labours, encouraged by the hope of bringing it into a bond of union with gravity itself.”
In 1848 Faraday gave five Friday night discourses, three of them on the “Diamagnetic Condition of Flame and Gases.” In 1849 he gave two, one of them on Plücker’s researches. In 1850 he gave two, one of them being on the electricity of the air, the other on certain conditions of freezing water. He had meanwhile continued to work at magnetism. The twenty-third series dealt with the supposed diamagnetic polarity. It incidentally discussed the distortion produced in a magnetic field by a mass of copper in motion across it. The twenty-fourth series was on the possible relation of gravity to electricity. The paper concludes with the words: “Here end my trials for the present. The results are negative. They do not shake my strong feeling of the existence of a relation between gravity and electricity, though they give no proof that such a relation exists.” The next series (the twenty-fifth) was on the “Non-expansion of Gases by Magnetic Force” and on the “Magnetic Characters of Oxygen [which he had found to be highly magnetic], Nitrogen, and Space.” He had found that magnetically substances must be classed either along with iron and the materials that point axially, or else with bismuth and those that point equatorially, in the magnetic field. The best vacuum he could procure he regarded as the zero of these tests; but before adopting it as such, he verified by experiment that even in a vacuum a magnetic body still tends from weaker to stronger places in the magnetic field; while diamagnetic bodies tend from stronger to weaker. He then says we must consider the magnetic character and relation of space free from any material substance. “Mere space cannot act as matter acts, even though the utmost latitude be allowed to the hypothesis of an ether.” He then proceeds as follows:—
MORE NEW WORDS.
Now that the true zero is obtained, and the great variety of material substances satisfactorily divided into two general classes, it appears to me that we want another name for the magnetic class, that we may avoid confusion. The word magnetic ought to be general, and include all the phenomena and effects produced by that power. But then a word for the subdivision opposed to the diamagnetic class is necessary. As the language of this branch of science may soon require general and careful changes, I, assisted by a kind friend, have thought that a word—not selected with particular care—might be provisionally useful; and as the magnetism of iron, nickel, and cobalt when in the magnetic field is like that of the earth as a whole, so that when rendered active they place themselves parallel to its axes or lines of magnetic force, I have supposed that they and their similars (including oxygen now) might be called paramagnetic bodies, giving the following division:—
{ paramagnetic
Magnetic {
{ diamagnetic.
The “kind friend” alluded to was Whewell, as the following letter shows:—
[Rev. W. Whewell to M. Faraday.]
July, 1850.