The Hydrodynamica and the Hydraulica

This chapter is dedicated to two men, two works and a plagiarism. On the face of it, the plagiarism should come as no surprise, as the history of science is replete with similar conflicts from time to time. The unusual thing here is the special relation that existed between these two men: the father and son, and the father plagiarised the son. They are Daniel and Johann Bernoulli, members of an outstanding family of mathematicians.1 Both are actors known to us, as they have previously appeared in these pages, and they will continue to show up after this chapter that discusses their principal works. These works are the Hydrodynamica, sive de viribus et motibus fluidorum comentarii (Hydrodynamics or Commentaries on Forces and Motions of Fluids) and the Hydraulica, equally valuable and famous milestones along the road of the science of fluids.

But the conflict does not alter the outcome of the science, for each of them represents a particular way of approaching science: that of the mathematician and that of the physicist, or in eighteenth-century terminology, the way of the geometer and the way of the natural philosopher. Johann comes in the first category, as do d’Alembert and Euler. Daniel comes under the other, along with Galileo and Newton. The tension between these points of view is a constant in science, and perhaps they are two intrinsic poles of science, a fact illustrated by Daniel’s own thoughts expressed at the beginning of Hydrodynamica:

How little hope there is that at sometime the Laws of motions for fluids will be reduced to the rules of pure Geometry without any physical hypothesis. … The principles of the Theory are physical, and are to be accepted, not without generosity, as approximately true. But, after the principles have been accepted, all will be Geometry: they will be interconnected by the necessary links, without being subjected to any restrictions whatsoever