Mersenne was a stimulating and indefatigable correspondent. His letters to Galileo, Jean Rey, Hobbes, Descartes, Gassendi, not to mention other scientists and philosophers, constitute an encyclopedia of the learning of the time. A mathematician and experimenter himself, he had a genius for eliciting discussion and research by means of adroit questions. Through him Descartes was drawn into debate with Hobbes, and with Gassendi, a champion of the experimental method. Through him the discoveries of Harvey, Galileo, and Torricelli, as well as of many others, became widely known. His letters, in the dearth of scientific associations and the absence of scientific periodicals, served as a general news agency among the learned of his time. It is not surprising that a coterie gathered about him at Paris. Hobbes spent months in daily intercourse with this group of scientists in the winter of 1636-37. Hartlib, though he scarcely takes rank with Mersenne as a scientist, was no less influential. Of a generous and philanthropic disposition, he repeatedly impoverished himself in the cause of human betterment. His chief reliance was on education and improved methods of husbandry, but he resembled Horace Greeley in his hospitality to any project for the public welfare. One of Hartlib's chief hopes for the regeneration of England, if not of the whole world, rested on the teachings of the educational reformer Comenius, a bishop of the Moravian Brethren. In 1637, Comenius having shown himself rather reluctant to put his most cherished plans before the public, his zealous disciple precipitated matters, and on his own responsibility, and unknown to Comenius, issued from his library at Oxford _Preludes to the Endeavors of Comenius_. Besides Hartlib's preface it contained a treatise by the great educator on a _Seminary of Christian Pansophy_, a method of imparting an encyclopedic knowledge of the sciences and arts. The two friends were followers of the Baconian philosophy. They were influenced, as many others of the time, by the _New Atlantis_, which went through ten editions between 1627 and 1670, and which outlined a plan for an endowed college with thirty-six Fellows divided into groups--what would be called to-day a university of research endowed by the State. It is not surprising to find Comenius (who in his student days had been under the influence of Alsted, author of an encyclopedia on Baconian lines) speaking in 1638 on the need of a collegiate society for carrying on the educational work that he himself had at heart.