THERMO-ELECTRICITY is a term introduc ed a few years ago into natural philosophy, to sig nify the electrical current, excited in a circuit of conductors, when the equilibrium of its heat is dis turbed in such a manner as to cause therein a circu lation of caloric.
Thermoelectricity being a particular branch of Electromagnetism, which has been discovered since the publication of the volume of this work in which it ought to have been treated, it will be necessary to comprehend the whole doctrine of electromagne tism in the present article.
In the earliest period of the history of magnetism and electricity, the minds of philosophers were more struck by the resemblances of these two agen cies than by their disparities. The first philoso pher who undertook a regular series of compara tive experiments upon magnetism and electricity, was the celebrated Dr. William Gilbert, who first published his inquiries in the year 1600. He was aware of so many disparities between them, that he declared their resemblance to be merely acci dental. He had indeed strong reasons to think so at that time, for the magnetical polarity was well known to him, and principally by his own experi ments, but the discovery of the electrical polarity was reserved for a philosopher of the following century (du Fay). This discovery, and particu larly the fundamental law of electrical polarity, brought forward by Franklin, again countenanced the opinion of the resemblance of electrical and magnetical powers; and the sagacity of ..Epinus gave great credit to it. But immediately after this acknowledgment of their resemblance, another ex cellent philosopher, Van Swinden, was struck with the disparities which remained still unexplained, and his ingenious inquiries obtained much appro bation. The discoveries of Galvani and Volta, by which the electrical powers were exhibited in forms very different from those formerly known, gave the opinions upon this subject a new turn. The German philosopher, Joh. rm. Ritter, was thought during some time to have produced magnetical effects by the Voltaic pile, but his experiment having been repeated without success, the subject remained as it was. Thus the balance inclined alternately some
times to the one, and sometimes to the other side; hut at no time have either of these opinions met with ge neral reception. A certain turn of mind has here, as in most other controversial doctrines, exercised a considerable influence. One class of natural philoso phers have always a tendency to combine the pheno mena and to discover their analogies; another class, on the contrary, employ all their efforts in showing the disparities of things. Both tendencies are ne cessary for the perfection of science, the one for its progress, the other for its correctness. The phi losophers of the first of these classes are guided by the sense of unity throughout nature; the philoso phers of the second have their minds more direct ed towards the certainty of our knowledge. The one are absorbed in search of principles, and ne glect often the peculiarities, and not seldom the strictness of demonstrations; the other considers the science only as the investigation of facts, but in their laudable zeal they often lose sight of the har mony of the whole, which is the character of truth. Those who look for the stamp of divinity on every thing around them, consider the opposite pursuits as ignoble and even as irreligious; while those who are engaged in the search after truth, look upon the other as unphilosophical enthusiasts, and per haps as phantastical contemners of truth. Hap pily these two tendencies are in most natural phi losophers so well tempered with good sense, that their controversies seldom exhibit any of the exag gerations which have disgraced so many theologi cal and metaphysical controversies; but they always exercise their influence, which is generally a salu tary one, in forming an opposition of sentiment in the republic of letters by which stagnation is pre vented. This conflict of opinions keeps science alive, and promotes it by an oscillatory progress, though it seems to the common eye a mere fluctua tion, without any definite purpose.