STODOLA, AUREL BOLESLAV

(b. Liptovský Mikuláš, Hungary [now Czechoslovakia], 10 May 1859; d. Zurich, Switzerland, 25 December 1942)

Mechanical engineering.

Stodola was born in a small Slovakian town at the foot of the High Tatra mountains, the second son of a leather manufacturer, Andreas Stodola, and his wife, Anna Kovač. After attending secondary school, he studied at the Budapest Technical University (1876 – 1877), the University of Zurich (1877 – 1878), and the Eidgenössische Technische Hochschule (1878 – 1880), from which he graduated as a mechanical engineer. He completed his theoretical and practical education informally: he spent two years as a volunteer in the machine factory of the Hungarian State Railways, studied in Berlin (1883) and Paris (1884), and worked in his father’s factory and in a machine shop in Brno. In his first permanent position (1886 – 1892), as chief engineer with Ruston & Co. in Prague, Stodola was responsible for the design of a great variety of steam engines. In 1892 the Eidgenössische Technische Hochschule of Zurich, where his exceptional performance as a student was still remembered, appointed him to its newly founded chair for thermal machinery. Stodola held this position until his retirement in 1929, after which he remained in Zurich. He was married to Darina Palka in 1887; they had two daughters.

During his lifetime Stodola’s reputation was very great. In the technical sense his role is best described by saying that during the decades of the main growth of the steam turbine, he was the leading authority on that machine. He also had remarkable personal charm. The importance of his accomplishments, the broad range of his learning, his friendly but aristocratic personality, and his ascetic appearance made him seem the embodiment of the central European ideal of a professor; the loyalty of his friends (among them Einstein) and disciples was extraordinary; and the eulogistic writing devoted to him is not only remarkable in quantity but also uncommonly persuasive.

In Stodola’s academic career teaching, industrial consultation, engineering design, and scientific research were intimately blended; perhaps most important was his scientific work, which was characterized by a combination of high mathematical competence with an explicit devotion to practical utility.

Stodola’s first publications dealt with the theory of automatic control. He derived the differential equations for the speed-regulating systems of hydroelectric power plants, analyzing them with respect to dynamic stability and checking his results at the power plant itself. In this work he enlisted the help of a colleague, Adolf Hurwitz, who was led through it to the discovery (1895) of the stability criterion named after him.

At the turn of the century Stodola’s attention shifted to the steam turbine, which, after its invention in the 1880’s, was gradually coming into industrial use and was soon to displace the reciprocating steam engine. It became the subject of his lifework. A lecture given in 1902 before the Society of German Engineers became the book Die Dampfturbinen und die Aussichten der Wärmekraftmaschinen (1903), which in later editions, entitled Dampf-und Gasturbinen, developed into an authoritative work that holds a unique place in the literature of engineering. Although Stodola also published many articles, most results of his researches were incorporated directly into the various editions of this book.

Perhaps the book’s most important innovation concerned the basic thermodynamic treatment of the flow of steam through the turbine. It had become clear that it was impractical to describe the properties of steam, which changed with temperature and pressure, in terms of mathematical formulas; instead these data, which were determined empirically, were presented in graphic charts and printed tables. Recognizing the superiority of entropy charts, which were easy to manipulate and at the same time facilitated the comparison of actual and ideal processes, Stodola was the first to base the analysis of heat engines upon these charts. After having first used the older temperature-entropy charts, he soon turned to the more convenient enthalpy-entropy charts proposed by Richard Mollier (1904). Shortly thereafter this approach was adopted universally.

Stodola also did pioneer work in the flow of steam through Laval nozzles. The possibility of supersonic flow in divergent nozzles was then still a matter of controversy. In careful experiments Stodola studied the conditions under which supersonic flow does occur and obtained results that for the first time could be reconciled with theoretical predictions. Through this line of inquiry he also became one of the first to investigate shock waves.

Although thermodynamics and fluid mechanics and their applications were Stodola’s true domain, he also did original work in pure mechanics. He investigated, for example, the strength of disks rotating at high speed and problems of vibration and critical speed.

Stodola’s innumerable more technical contributions to steam turbine design are reflected in the fact that the Swiss steam turbine manufacturers, who retained him as a consultant and employed his students, became international leaders in this field. They were also among the pioneers of the gas turbine, a machine in which Stodola had been interested since the beginning of his career, when its prospects had seemed dim indeed.

Stodola had a strong sense of social responsibility. During World War I he worked on the problem, totally unrelated to his basic interests, of improving artificial limbs. Social responsibility is also shown in a later philosophical and reflective work, Gedanken zu einer Weltanschauung vom Standpunkt des Ingenieurs (1931), which went through several editions.

BIBLIOGRAPHY

I. Original Works. Stodola’s publications are listed in Poggendorff, VI, 2551, and VIIa, pt. 4, 550; in his Festschrift (see below), xxi-xxiii; and in Schweizerische Bauzeitung, 121 (1943), 77–78. His major book is Die Dampfturbinen und die Aussichten der Wärmekraftmaschinen (Berlin, 1903), 5th ed. retitled Dampf-und Gasturbinen (Berlin, 1922; 6th ed., 1925); 1st ed. translated by Louis C. Lowenstein as Steam Turbines, With an Appendix on Gas Turbines, and the Future of Heat Engines (New York, 1905; 2nd ed., 1906), and the 5th ed. by Lowenstein as Steam and Gas Turbines (New York, 1927) and by E. Hahn as Turbines à vapeur et à gaz, 2 vols. (Paris, 1925). Other books are Gedanken zu einer Weltanschauung vom Standpunkt des Ingenieurs (Berlin, 1931); and Geheimnisvolle Natur: Weltanschauliche Betrachtungen (Zurich, 1937).

II. Secondary Literature. The most useful biographical treatments of Stodola are the following, listed chronologically: W. G. Noack, “Prof. Dr. Aurel Stodola,” in E. Honegger, ed., Festschrift Prof. Dr. A. Stodola zum 70. Geburtstag (Zurich–Leipzig, 1929), ix-xx: G. Eichelberg, “Aurel Stodola,” in Schweizerische Bauzeitung, 121 (1943), 73–74: H. Quiby, “Aurel Stodola, sein wissenschaftliches Werk,” ibid., 74–77: E. Sörensen. “Aurel Stodola,” in Zeitschrift des Vereins deutscher Ingenieure, 87 (1943), 169–170; Anton Turecký, ed.,Aurel Stodola 1859–1942, pamiatke storočnice narodenia (Bratislava, 1959); C. Keller, “Zum 100. Geburtstag von Aurel Stodola am 10. Mai 1959,” in Zeitschrift des Vereins deutscher Ingenieure, 101 (1959), 558–560; and A. Sonntag, “Aurel Stodola 1859/1942,” in Brennstoff-Wärme-Kraft, 11 (1959), 211–212.

Otto Mayr