Pascal thought that this pressure would be less at a high altitude. His supposition was tested on a church steeple at Paris, and, later, on the Puy de Dôme, a mountain in Auvergne. In the latter case a difference of three inches in the column of mercury was shown at the summit and base of the ascent. Later Pascal experimented with the siphon and succeeded in explaining it on the principle of atmospheric pressure. Torricelli in the space at the top of his barometer (pressure-gauge) had produced what is called a Torricellian vacuum. Otto von Guericke, a burgomaster of Magdeburg, who had traveled in France and Italy, succeeded in constructing an air-pump by means of which air might be exhausted from a vessel. Some of his results became widely known in 1657, though his works were not published till 1673. Robert Boyle (1626-1691), born at Castle Lismore in Ireland, was the seventh son and fourteenth child of the distinguished first Earl of Cork. He was early acquainted with these various experiments in reference to the air, as well as with Descartes' theory that air is nothing but a congeries or heap of small, and, for the most part, flexible particles. In 1659 he wrote his _New Experiments Physico-Mechanical touching the Spring of the Air_. Instead of _spring_, he at times used the word _elater_ (ἐλατὴρ). In this treatise he describes experiments with the improved air-pump constructed at his suggestion by his assistant, Robert Hooke. One of Boyle's critics, a professor at Louvain, while admitting that air had weight and elasticity, denied that these were sufficient to account for the results ascribed to them. Boyle thereupon published a _Defence of the Doctrine touching the Spring and Weight of the Air_. He felt able to prove that the elasticity of the air could under circumstances do far more than sustain twenty-nine or thirty inches of mercury. In support of his view he cited a recent experiment.