HOBBES, THOMAS (b. Malmesbury, England, 5 April 1588; d. Hardwick, Derbyshire, England, 4 December 1679), political philosophy, moral philosophy, geometry, optics.

    menial, he was able with the passage of time to mingle with his master's guests on terms of some intimacy. In this way he came to know Ben Jonson, Lord Falkland, Sir Robert Ayton, Lord Herbert of Cherbury, and, some time later, the poet Edmund Waller, who became a particular friend. Moreover, in Chatsworth and Hardwick Hall, the great houses of the Cavendish family, Hobbes had at his disposal an excellent library in which, he said, he found the university he had missed at Oxford.

To a second branch of the Cavendish family residing at Welbeck Abbey, Hobbes owed the awakening of his interest in natural science. Sir Charles Cavendish was a skilled mathematician; and his more famous brother William, duke of Newcastle, was a scientific amateur who maintained a private laboratory and whose scientific speculations issued in such odd conclusions as that the sun is “nothing else but a very solid body of salt and sulphur, inflamed by its own motion upon its own axis.”3 Both men accepted Hobbes as a friend; and Newcastle, who had a passion for horses as well as a curiosity about optics and geometry, persuaded Hobbes to combine these interests in a curious treatise entitled “Considerations Touching the Facility or Difficulty of the Motions of a Horse on Straight Lines, or Circular,” a work printed from manuscript in 1903 and described by its editor as “an irrelevant superfluity of reasoning” such as was produced by “the tailor in Gulliver's Travels who measures his men with the help of a sextant and other mathematical instruments.”4 It was on Newcastle's behalf that Hobbes searched the London bookshops in vain for a copy of Galileo's Dialogues.

In 1610 Hobbes set out on a grand tour of the Continent with his pupil. It was the year of the assassination of Henry IV of France, an event which impressed itself on Hobbes's mind as an extreme example of the chaos that follows from the abolition of sovereignty. On this first tour, through France, Germany, and Italy, Hobbes perfected his knowledge of foreign tongues and resolved, on his return, to become a scholar. In the library at Chatsworth he immersed himself in classical studies and in 1628-1629 published a brilliant translation of Thucydides' Peloponnesian War.

For a brief period before the Thucydides was published, Hobbes served as secretary to Francis Bacon, to whom he had been introduced by the younger Cavendish, one of Bacon's friends. Bacon had by this time been deposed as lord chancellor and was living in retirement at Gorhambury, where Hobbes accompanied him on his “delicious walkes” and where he acted as amanuensis and editorial assistant in the Latin translation of several of Bacon's Essaies. The connection between these two personalities is inherently interesting, but it should not be read as evidence of a Baconian influence on Hobbes's thought. Although they held some points in common, the two philosophers had worked out their ideas independently and essentially along different lines.

In June of 1628 Hobbes's master and friend, the second earl of Devonshire, died. Hobbes accepted a new appointment as tutor and cicerone to the son of Sir Gervase Clinton of Nottinghamshire, with whom he embarked, in 1629, on a second tour of Europe, to Paris, Orléans, Geneva, and Venice. It was in a library in Geneva that he first read Euclid; he was ever afterward enamored of geometry.5 In particular, as Aubrey reports, he was attracted to the propositional character of geometry; it was a form of reasoning that fit in well with the conception of “truth” he was later to develop: that “truth” is the product of an analytical process in which definitions are placed in their proper order.

By November of 1630 Hobbes was recalled to the Cavendish family to serve as tutor in Latin and rhetoric to the next earl of Devonshire. With this young man, Hobbes, now in his forties, made his third grand tour of the Continent, the one which had the most important consequences for the development of his interest in natural science. That interest had not previously been dormant, since as Hobbes himself tells us, he had formulated a theory of light and sound as early as 1630;6 a short manuscript tract giving a theory of sense and appetite is assigned by Dr. Frithiof Brandt to 1630. But on the third journey—to France and Italy—Hobbes made personal contact with scientific minds. In Arcetri, near Florence, he visited Galileo, whom he ever afterward held in veneration as “the first that opened to us the gate of natural philosophy universal”; and in Paris he met Marin Mersenne, the Franciscan monk in whose cell informal scientific meetings, attended by some of the best scientists of the age, took place. He also met Gassendi and Roberval; he read Descartes; and everywhere he went, he meditated on the problems of motion, which he conceived to be the principle by which a wholly material universe is to be understood.

Hobbes's deepest scientific interest was in optics. Probably this interest was awakened in him by his contact with the Cavendish circle, especially with Charles Cavendish, Walter Warner, and John Pell. A large part of the short tract of 1630 on sensation and appetite was devoted to optics; in that early work Hobbes adopted an emission or “corpuscular” theory of light, according to which there is a movement of particles of matter from the luminous source to the