Interrogating Nature — Henri Victor Regnault

Henri Victor Regnault approached scientific experimentation as the interrogation of Nature in pursuit of truth. If science can be described as the titration of observation with inspired insight, then Regnault was inclined to use the reagent of insight sparingly.

Regnault inherited an aptitude for math and science and manual skill from his father, who was an engineer in the army of Napoleon Bonaparte. Graduating from the Ecole Polytechnique in 1832, Regnault was on track to become a mining engineer. However, his talents soon brought him back to the chemistry laboratory, first as an assistant in Berthier’s laboratory at the Ecole de Mines and later as Gay-Lussac’s junior colleague on staff of the Ecole Polytechnique.

Regnault’s work in the new field of organic chemistry resulted in the discovery of vinyl chloride, a basic ingredient in making PVC plastic, but industrial application of this result was 50 years in the future. Regnault had more immediate effect with his exacting experiments to measure the thermodynamic properties of various substances, especially the properties of water vapor — steam.

In the mid-19th century, steam power was emerging as a driver of economic progress. Engineers needed information about the thermodynamic properties of steam — now known simply as the “Steam Tables” — to improve the performance of steam engines. Regnault succeeded, where Arago and Dulong had failed before him, in compiling tables of precise data on the thermodynamic properties of water vapor over a wide range of pressure and temperature. Regnault received generous funding from the government, which allowed him to develop new, highly precise instruments. With these Regnault was able to achieve a level of precision unobtainable by his colleagues, nearly 1 in 10,000.

Regnault was an adamant proponent for the value of clean and clear experimental design and precision in measurement. Colleagues who were more liberal with the use of insight accused Regnault of conducting “an unimaginative quest for unimpeachable numbers.” Regnault avoided the theorizing that many regard as truly the mark of the advance of science. But, his restraint had its advantages. Often enough, Regnault’s precise measurements exposed faults in theories based more on inspired insight and less on exacting data. No scientists likes having their ideas shown to be more fancy than fact.

Henri Victor Regnault is one of the 72 scientists and engineers named on the Eiffel Tower.