9
it was the sole efficient cause of the motion thus engendered (indeed, he uses the phrase, “solum a corde”); that the lungs, although an air-pump of no inconsiderable power, both for compression and rarefaction, had nothing whatever to with this; that the valves of the heart acted equally as machines to make good the dynamical advantage thus obtained, and that the quantity of fluid thus raised was incomparably greater than had been before supposed. The conception is as distinctly mechanical as that of the steam engine, or of the mechanical equivalent of heat which were to arise in later centuries. Even of this last great generalisation in mechanics, he had no indistinct glimpse, for in the thirteenth page of the MS. he compares heat to a hammer. “ Calor ut malleus instrumenturn instrumentorum.” With the working out of this complex but perfectly precise problem in hydrodynamics, came accuracy and certainty in place of theory and conjecture. “Flux and reflux” had had their day, and no more need be said of that unlucky Euripus which is fabled to have driven a great natural philosopher, Aristotle, to suicide,
