ment in navigation and land carriage his own time and money were devoted toward the close of his life.
Petty's obligations to the Baconian method are apparent, but they are not so noticeable as his obligations to Hobbes. It is true that Bacon's name is mentioned, and it is also true that no reference is ever made to Hobbes. But it is certain that Hobbes exerted a much greater influence than Bacon over him. In Petty's biography we have seen his early association with Hobbes. This association did not end with Petty's residence in Paris; their friendship remained unbroken. In the contemporary life of Hobbes by Aubrey, in the list of Hobbes' most intimate friends, Petty's name is found. Although Petty depreciated reading, and had rather a contempt for book learning, we know that he was acquainted with Hobbes' works. In a (MS) list of books drawn up by Petty for his son's use, the "De Cive" of Hobbes is the only English book mentioned. Petty's predilection for mathematics is an evidence of the intellectual kinship between Hobbes and himself. Petty follows Hobbes in assigning to mathematical proof the highest place. In the preface to his last "Essay on Political Arithmetick," he says "observations expressed by number, weight and measure" are the data he uses. And, again, "I have taken the course… to express myself in terms of number, weight or measure, to use only arguments of sense" (207). Mathematical proof has the greatest certainty, and as the great aim of investigation is to reach certainty, mathematical reasoning is to be extended as far as possible. We have seen the good results of this principle when Petty took in hand the Bills of Mortality and made them the
