The French Connection: Giffard's Injector and the Nature of Heat

Abstract

In 1858 a Parisian inventor, Henri Giffard, patented the injector, a device to feed water into steam boilers. In 1908 Henri Poincare, in his Thermodynamique, presented an original theoretical analysis of the injector.1 That a scientist of Poincare's stature would take interest in a steam-engine apparatus that had been introduced fifty years earlier may seem surprising. However, Poincare was only one of a large number of scientists and engineers intrigued by the device. For it was observed from the very outset that the operation of the injector was paradoxical. As one engineer commented: Seldom has an invention caused so much astonishment and wild speculation among mechanics, and even among scientists, as the injector did.... It was regarded as a case of perpetual motion-the means of doing work without power, or, as the Americans expressed it, by the same means a man could raise himself by pulling on his bootstraps.2 The purpose of Poincare's analysis was to show that the paradox of the injector could be explained on the basis of the laws of thermodynamics. At the very least, an explanation of its operation required an understanding of the interconvertibility of heat and mechanical work (a corollary of the first law of thermodynamics). The foundations for the first law were established before 1850, primarily by Joule and Helmholtz. Between 1843 and 1849 Joule published the results of a series of experiments which culminated in a very precise