Harvey was fourteen years younger than Galileo, who struck crippling blows at the Aristotelian physics, yet could not explain the common pump;[250] and Harvey's discovery of the circulation was made public thirteen years before the momentous work on the movement of liquids done by Torricelli, who was thirty years younger than Harvey.[250] Moreover, it was only a year before the publication of the Exercises to Riolanus in Harvey's old age that Blaise Pascal supplied the final proof that the mercurial column below the vacuum of Torricelli's barometer is really sustained by the pressure of the atmosphere.[250] It was not till one hundred years after the publication of Harvey's discovery that the Reverend Stephen Hales published the first comparative manometric measurements of the blood-pressure in the arteries and the veins of the same living animal, and stated in his preface that "the animal fluids move by Hydraulick and Hydrostatical Laws."[251] Now let us turn to some delineations of the movement of the blood made by Harvey himself. I have found no evidence that he knew the venous flow to be promoted by the aspiration of the chest; but he knew well the effect of the muscular movements of the body upon that flow. Of course he had a perfect grasp of the fundamental truth that the main cause of the venous return is the forcible emptying of the ventricles into the arteries. He says to Riolanus:-- "Among these things should be noted the force and violence and rapid vehemence which we perceive by touch and sight in the heart and greater arteries; and the systole and diastole of the pulse in the larger and warmer animals I do not affirm to be the same in all the vessels which contain blood, nor in all blood-containing animals; but to be such and so ample in all that as a result thereof a streaming and an accelerated course of the blood through the small arteries, the porosities of the parts, and the branches of all the veins are necessarily brought about; and as a result thereof a circulation....[252] In the case of the arteries, over and above the shock, pulse, or vibration of the blood (which is not equally perceptible in all), a continual flow and movement thence take place until the blood returns to the point whence it started first, namely, the right auricle."[253] [Illustration: The Title-page of William Harvey's _Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus_, Frankfort, 1628.] With the calm quantitative account which a reader of Hales' "Statical Essays" will find given by that clergyman of his epoch-making physical experiments upon the blood-pressure, it is interesting to compare the following vivid qualitative recital of inferences made from surgical observations by his great predecessor. Harvey says:--