also known as SEGUN AÎNÉ
(b. Annonay, Frances, 20 Aril 1786; d. Annonay, 24 February 1875)
The eldest son of a small but prosperous manufacturer in the Ardèche, Seguin completed his formal education at an undistinguished Parisian boarding school. From his arrival in Paris in 1799 his interest in science and engineering was stimulated and decisively shaped through his informal contact with his granduncle Joseph Montgolfier, the famous balloonist. Closely related by birth and later by marriage to the Montgolfier family, Seguin always regarded himself as Montgolfier’s leading disciple. From Montgolfier Seguin acquired several scientific community, notably an emphasis on vis viva (mv[sup(2)]) as the quantity that is convered not only in heat engines and machines bu t also in the universe. Seguin also credited Montgolfier with rejecting the caloric theory of heat and suggesting, instead, that heat and motion, both manifestations of unknown an but common cause, were interconvertible. Montgolfier died in 1810. and shortly thereafter Seguin returned to Annonay.
Over the next two decades Seguin, aided by his younger brothers, executed a series of successful and innovative engineering projects. In 1825, at Tournon on the Rhone, he erected the first successfully suspension bridge in France to use cables of iron wire. After a brief attempt to establish regular steamboat service on the Rhone, the Seguin brothers organized the company that built France’s first modern railroad, a line between Saint-Étienne and Lyone completed in 1832.Finding the Stephenson locomotive unable to generate enough dream for high-speed operation, in 1827 Seguin invented the multitubular, or fire tube, boiler, After working briefly on the Left Bank railroad between Paris and Versailles, Seguin retired from active engineering and moved to Fontenay in 1838. Marked both by numerous technical innovations and by shrewd economic planning, his engineering projects provide one of the earliest examples in France of large-scale civil engineering undertaken and financed by private companies. For these engineering achievements Seguin was elected a correspondent of the Académie des Sciences in 1845.
Except for some contact with J. B. Biot, who had invested heavily in the engineering enterprises, Seguin always remained on the periphery of professional French science. Through numerous visits to England, however, he became acquainted with several prominent British scientists, notably John Ferschel, Michael Haraday, and Humphry Davy. Two letters from Seguin to Herschel and to Brewster were published in Edinburgh journals in 1824 and 1825. These contain his first statements, perhaps derived from Montgolfier, of an extreme form of Newtonianism in which all physical forces are to be explained as the result of the inverse-square law of attraction between molecules. Matter, Seguin argued, consists of small, dense molecules in constant motion in miniature solar systems. Magnetic, electrical, and thermal phenomena are the result of particular velocities and orbits. Faster molecules escape from orbit along tangential paths, producing light and radiant heat. Explicitly identifying heat as molecule velocity, Seguin added that when molecules transmit their velocity to external objects, a conversion of heat into mechanical effect occurs. The qualitative, synthetic style of Seguin’s papers and his conceptions of heat and light were in sharp contrast with the mathematical caloric and wave theories then dominant in France. In spite of a close similarity to contemporary British science, the papers apparently had no influence.
In 1839 Seguin returned to the problem of heat in his most important publication, De l’influence des chemins de fer, a handbook for the design and construction of railroads. In the chapter on steam locomotive performance, he first rejected the caloric theory because its major premise, the existence of heat as a fluid conserved in all processes, would allow the reuse of heat in an engine and thus would imply perpetual motion. “It appears more natural to me to suppose that a certain quantity of heat disappears in the very act of the production of force or mechanical power, and conversely: and that the two phenomena are linked together by conditions that assign to them invariable relationships” (p. 382). This assumption was the basis for his later claim to priority over Joule and Mayer for the statement of the convertibility and conservation of heat and work.
To determine the numerical relationship, Seguin imagined a unit weight of steam generated under pressure in a cylinder and allowed to expand adiabatically until its temperature fell twenty degrees Centigrade. Assuming that steam is a perfect gas that remains saturated during expansion, he used standard engineering formulas and steam tables to calculated the word performed against the piston. The results, given in a table for different twenty-degree intervals, showed a steady decrease in the amount of work produced as the intervals were located higher on the temperature scale, a result indicating either that the conversion of heat into work did not follow an invariable law or, as Seguin chose to conclude, that the heat loss of twenty degrees as measured on a thermometer was not a true measure of the heat lost by the steam. Unable to specify the relation between temperature loss and total loss of heat content, he made no attempt to define a unit of heat or to state its mechanical equivalent.
Joule’s determination of the mechanical equivalent was published in France in 1847, and one month later Seguin responded with a note to the Academy supporting Joule’s conclusions. Seguin called attention to his 1839 work as an earlier attempt to find the numerical equivalent and demonstrated that the average of his tabular results, converted to Joule’s units, gave a value very close to the figure Joule had obtained by completely different methods. Conversely, Seguin regarded Joule’s experiments as a confirmation of his own more general theory outlined in 1824, and his paper concluded with an announcement of his intention to explain the identity of heat and work through an extension of the law of universal attraction.
In the later priority controversy surrounding the principle of energy conservation, it became clear that Mayer, Joule, and Helmholtz had worked independently of Seguin and that, despite Seguin’s repeated claims, only in retrospect could his 1839 suggestions be clearly interpreted as a mechanical equivalent of heat. Although Seguin’s theory of forces implied a conservation of energy, he focused his attention on the motion of molecules and made no attempt to define a concept of energy or to state its conservation.
From 1848 until his death Seguin conducted a broad campaign to win acceptance for his program of reducing all physical forces to the single Newtonian law of molecular attraction. In 1853 he bought a bankrupt journal and began publishing a weekly scientific magazine, Cosmos, Under the editorship of the abbé Francois Moigno the journal served as an important vehicle for the popularization of science and as a forum for Seguin’s theories. In 1856 Seguin commissioned a French translation of William Grove’s Correlation of Physical Forces and added notes and commentary. Throughout Seguin’s prolific publications the earlier themes of 1824 were repeated and elaborated. The only major addition was a strong emphasis, adopted from Biot, on crystal structure and polarized light. Seguin developed gravitational models for the structure of matter and presented particle theories for heat, light, electricity, and magnetism. These theories, together with his attacks on the ether hypothesis and on the reduction of physics to analytical mathematics, were completely contrary to contemporary scientific opinion and had no apparent subsequent influence.
I. Original Works. Seguin’s thirty-six journal articles are listed in the Royal Society Catalogue of Scientific Papers, V and VIII. The most important are “Letter to Sir. J. Herschel: Observations on the Effects of Heat and of Motion,” in Edinburgh Philosophical Journal, 10 (1824), 280–283; “Letter to Dr. Brewster on the Effects of Heat and Motion,” in Edinburgh Journal of Science, 3 (1825), 276–281; and “Note à l’appui de l’opinion émise par M. Joule, sur l’identitè du movement et du calorique,” in Comptes rendus ... de l’Académie des sciences, 25 (1847), 420–422. Seguin published nearly thirty books, many of them reprints of earlier journal articles. Of special interest are Des ponts en fil de fer (Paris, 1824; 2nd ed.,1826); De l’influence des chemins de fer et de l’art de les tracer et de les construie (Paris, 1839; repr, 1887); and Mémoire sur les causes et sur les effects de la chaleur, de la lumiée et de l’electricité (Pairs, 1865).
II. Secondary Literature. The only biography, P. E. Marchal and Laurent Seguin, Marc Seguin 1786–1875; La naissance du premier chemin de fer francais (Lyons, 1957), is useful, but uncirtical. Seguin is discussed in the context of the several men who approached energy conservation by various routes in T.S. Kubnm “Energy Conservation as an Example of Simultaneous Discovery,” in Marshall Clagett, ed., Critical Problems in the History of Science (Madison, Wis., 1959), 321–356.
James F. Challey.