FROM THE HISTORY OF PHYSICS

ON THE SEVENTY-FIFTH ANNIVERSARY OF THE DEATH OF B. S. JACOBI (1874–1949)

T. P. Kravets

The author of these lines came into possession of a rather interesting brochure by B. S. Jacobi entitled “On the Use of the Natural Forces of Nature for Human Needs”*). It is the text of a lecture delivered by B. S. Jacobi in 1834, when he was still young, 33 years old, engaged in architecture and apparently had no intention of devoting himself to scientific and technical activity. The brochure is curious for the statements by B. S. Jacobi that concern questions of energy, its conservation and its use. It is also curious for characterizing the author himself.

Let us begin with the latter. He appears before us as an exceptionally educated man, an engineer with a broad outlook, abreast of the very latest scientific achievements. The fact alone is remarkable that he constantly speaks of work as a firmly established mechanical concept. Let us recall that at that time this concept was new in science.

He measures and expresses work in foot-pounds. True, he also mentions the metric (gravitational) system, its unit the “tonne-metre,” but this system finds no further application with him. Let us recall that subsequently B. S. Jacobi was an ardent defender of the metric system and one of the principal figures of the later international metric convention; as M. A. Shatelen convincingly showed at the last (Leningrad) session of the Academy of Sciences, the presently valid definition of the metre, as the length of a certain real standard and not “one forty-millionth part of the Paris meridian,” belongs precisely to B. S. Jacobi. Here, we repeat, the metric system is mentioned only in passing.

Among the names that Jacobi cites in the brochure of interest to us, we find Fr. Bernoulli (beginning of the 18th century), d’Alembert

*) The brochure was found by M. G. Novlyanskaya while working on the scholarly description of B. S. Jacobi’s archive, kept in the Archive of the USSR Academy of Sciences; M. I. Radovsky drew my attention to it.

(1717–1783), Watt (1736–1819), Prony (1755–1839), Navier (1785–1836), Poncelet (1788–1867), and others.

But the greatest interest of the brochure lies in Jacobi’s statements on the law of conservation of energy. The conservation of energy in the domain of pure mechanics is beyond doubt for him. He writes: “Here we must mention one misconception, which may be called very common and has often been the cause of many fruitless efforts: it is sometimes supposed that, by using levers, winches, pulleys, wheels, and the like, one can obtain more work than without any of these devices. However, ... it can be proved ... that under all conditions the product which we have called work remains unchanged. To the same category belongs the so-called perpetuum mobile, or a machine which is supposed to work without requiring the expenditure of force.”

Thus, it is clear to the young B. S. Jacobi that a purely mechanical perpetuum mobile is impossible. But how do matters stand with other sources of work, and above all—with heat?

Jacobi writes on this question: “Since heat is the animating principle of all nature, it is that motor which, more or less directly, excites the activity of all its forces. Expanding or compressing all bodies ... with irresistible force, it produces work equal to that produced by other mechanical devices”... And further: “It remains only for us to determine the magnitude of the purely mechanical work which, depending on circumstances, is reduced because of unproductive work, often by more than half.” And still further: “1 pound of water vapor at \(80^\circ R\) produces work equivalent to lifting about 70,000 pounds to a height of 1 foot.”

The number given by Jacobi may be inaccurate, but it is clear that he distinctly understands the following propositions: a) heat is a source of work; b) there exists a certain equivalent relation between the quantity of heat expended and the quantity of mechanical work created at its expense; c) the real ratio of the one to the other is still determined by “dependence on circumstances”—by the coefficient of useful action; d) one may try, from technical data, to calculate the above-mentioned coefficient of equivalence.

All these propositions, carried to their logical conclusion, constitute the first principle of thermodynamics. We see that B. S. Jacobi can, with full justification, be called one of the predecessors of the great discovery of the law of conservation of energy.

We would like especially to emphasize that the train of thought developed above is entirely natural for an engineer, for whom the question of the conversion of heat into work appears as a practical task of every day, and not as an abstract problem of a natural-philosophical character. And here we see how firmly he stands on his

on a production-and-technical basis, the engineer Jacobi, in comparison, for example, with W. Thomson. The latter, as his correspondence shows, experiences Joule’s discovery in the literal sense painfully. Indeed, according to his notions, heat is a substance, caloric. Lomonosov and Lavoisier had proved that substance is uncreatable and indestructible. What, then, can the equivalence of heat and work mean? The whole point is that W. Thomson, one of the greatest minds of his time, approached Joule’s experiments from the quiet of his physics study, whereas Jacobi did so from the workshop where the steam engine stood. Here is a brilliant example of how science is enriched by the demands of technology.

Thus, the young Jacobi, also on the question of heat as a source of energy, stands in the very foremost positions of physical thought.

How do matters stand with other physical forces?

Alas, here foresight deserts the engineer Jacobi, and in his brochure we read the following naïve lines: “A mechanical perpetuum mobile is impossible, since every moving force can give only an effect equal to itself; a physical one, of course, can be imagined, for it would need only a moving force which could, like Faraday’s magnetism, be excited by simple motion, and therefore would not need nourishment or would require very little of it, and in this, in essence, would lie the significance of the perpetuum mobile—an action which would cost nothing or almost nothing.”

The heat engine governs all the technology contemporary with him—and the engineer Jacobi clearly sees that a thermal perpetuum mobile is impossible; but the electric motor has not yet entered technology, and the same engineer Jacobi does not consider it possible to extend this principle to it without further discussion.

Let us recall that another Russian scientist, E. Kh. Lenz, a year before, in his classic work “On the Determination of the Direction of Galvanic Currents Excited by Electromagnetic Induction,” stated the law “of the correspondence of electromagnetic and magnetoelectric phenomena.” In it, in an unclearly expressed form, there is undoubtedly contained an assertion of an energetic character: if two currents attract one another, then the motion of one conductor with a current toward the other induces in this other a current by which the first is repelled. Lenz based many subsequent works (among them those carried out jointly with Jacobi) on this principle, which he had first formulated. Lenz anticipated the law of conservation of energy in application to electrical energy.

We see that Russian scientists were in the phalanx of the leading figures who prepared the discovery of the law of conservation of energy in its most general form.