It formed part of Papin’s duty, in connection with his new office, to produce an experiment at each meeting of the Society. He was thus induced to prosecute the study of physical science; and in order to stimulate the interest of the members, he sought to introduce new subjects from time to time to their notice. One of the greatest novelties of his “entertainments” was the production of his well-known Digester, which excited a considerable degree of interest; and on one occasion a philosophical supper, cooked by the Digester, was served up to the Fellows, of which Evelyn gives an amusing account in his Diary. He was led to the invention of the Digester by certain experiments which he made for Boyle. He discovered that if the vapour of boiling water could be prevented escaping, the temperature of the water would be raised much above the boiling point; and it occurred to him to employ this increased heat in more effectually extracting nutritious matter from the bones of animals, until then thrown away as useless. The great strength required for his Digester, and the means he was obliged to adopt for the purpose of securely confining the cover, must have early shown him what a powerful agent he was experimenting on. To prevent the bursting of the vessel from the internal pressure, he was led to the invention of the safety-valve, which consisted of a small moveable plate, or cylinder, fitted into an opening in the cover of the boiler, and kept shut by a lever loaded with a weight, capable of sliding along it in the manner of a steel yard. The pressure of the weight upon the valve could thus be regulated at pleasure. When the pressure became so great as to endanger the safety of the boiler, the valve was forced up, and so permitted the steam to escape. Although Papin was thus the inventor of the safety-valve, it is a curious fact that he did not apply it to the steam-machine which he subsequently invented, but adopted another expedient.