Franz Ulrich Theodosius Aepinus¹ was born in Rostock, the chief town of the north German Duchy of Mecklenburg, on 13 December 1724, the second son and fifth and last child of Franz Albert Aepinus, the highly esteemed professor of theology in the local university.

In days gone by, Rostock had been an exceedingly prosperous trading center, enjoying all the advantages that a fine harbor and membership of the powerful Baltic trading alliance, the Hanseatic League, could bring. By the eighteenth century, however, and the years of Aepinus’s childhood, both its population and its economic power had been considerably reduced. The...

The eighteenth century was the golden age of electrical investigation. Restricted to a single obscure and little-known phenomenon at the beginning of the century, by the end electricity had become a major field of scientific endeavor, with ramifications spreading into a number of other disciplines. The basic laws had been established, so far as the phenomena of static electricity were concerned, and a well-articulated general theory had come to be almost universally accepted.

Aepinus played a central role in the development of this theory. When he took up the study of electricity, the principal phenomena had already been identified, and...

Although Aepinus’sEssayof 1759 is one of the most important eighteenth-century works dealing with electricity, Aepinus himself regarded its contributions to electrical science as peripheral to its contributions to the study of magnetism. At the very beginning of his book, in the dedication to Count Kiril Razumovskii, the president of the St. Petersburg Academy of Sciences, he states that the investigation of magnetism is the chief task he has set himself in what is to follow, and similar statements appear in the body of the work. This attitude had a considerable effect on the scope of Aepinus’s undertaking. His...

Eighteenth-century physics faced no more baffling task than to explain satisfactorily the mysterious powers associated with the magnet, or lodestone. Almost to a man, those writing on the subject began by bemoaning the complexity and seeming capriciousness of the phenomena at hand. When it came to accounting for these, they found it exceedingly difficult to agree among themselves on more than a few fundamentals. Indeed, so far as the theory of magnetism was concerned, the situation grew worse, if anything, as the century progressed. The general agreement on fundamentals that had existed at the outset gradually eroded as the years...

When, in June 1759, Aepinus sought approval from his colleagues in the St. Petersburg Academy of Sciences for the printing of his greatEssay on the Theory of Electricity and Magnetism,he also sought and obtained their permission to have the work published in the form of a supplement to the Academy’sCommentariifor that year.¹ As a consequence, the book is so described on its title page. Aepinus’s intention was not simply to insure that the printing costs were met out of the Academy’s purse rather than his own. He was also concerned about the remoteness of St. Petersburg...

1) After the discovery of the marvelous phenomena and laws of electricity, a force almost unknown to the ancients, some physicists soon began to contemplate a comparison between this newly discovered force and the magnetic force, which is equally marvelous but already known in ancient times. For at first sight they were presented, though obscurely, with an analogy between the phenomena depending on the two forces, and this stimulated those who were well aware of the extent nature loves to act according to analogical laws to work on this point. In this task, as in other matters, the most worthy...

1) The scholar who knowsFranklin’svery elegant theory of elec tricity, which agrees astonishingly with the phenomena, will recognize that it can be reduced to these few universal propositions.

α) There is a certain most subtle, truly elastic fluid producing all electrical phenomena, called electric on account of them, whose parts sensibly repel each other mutually even over rather large distances.

β) The particles of this fluid are attracted by the matter from which all bodies known to this time are made.

γ) There is a remarkable diversity in the way in which other bodies act on the particles...

107A)⁵⁵ The attraction of two bodies close to one another, both abounding beyond the natural quantity (by quantities α and δ) with a fluid endowed with the properties we have ascribed to the magnetic and electric fluids, has been found above, §34, to be generally=αδr

Since this formula embraces all the cases which can occur (§35), and since it disappears whether δ, or α, or both of these quantities, is made = o, what we have demonstrated above (§ 32) is obvious here: these two bodies not only plainly do not act on one another if both are constituted in...

194) It is abundantly established through experience that electrical and magnetic bodies can communicate their force to other bodies; in fact, in the magnetic case, I shall show later that all known methods of making a body magnetic can be reduced solely to communication, in such a way that unless there were some bodies endowed with magnetism of their own nature and without the help of art, it would be completely beyond our power to make any body magnetic. And so among the doctrines most worthy of examination must be those concerning the communication of the forces whose theory we...

274)¹²⁵ Since I shall be using the terms vortex or electric atmosphere or magnetic atmosphere in what follows, it is advisable for me to declare at the very start the sense in which I employ these words, so that my readers may not attribute to them a significance foreign to my meaning. It is manifest from the preceding explanations of magnetic and electric phenomena that I never consider magnetic or electric matter as clinging outside the body or ambient to it, so it is clear that I am not using the words vortex or atmosphere in their proper sense. Whenever...