content of the writings. This restriction, it should be borne in mind, was much more considerable in Petty's day than it would be in our own, because the masses of raw material for statistical treatment which now lie open upon every hand were at that time almost altogether wanting. Petty's predilection for a statistical method is due, I fancy, to the influence of Bacon, which was predominant among his scientific associates in the inchoate Royal Society. Like all Baconians, he believed in the usefulness of observations, and, by implication, in the uniformity of nature, and looked forward with confidence to the time when a precise knowledge of the external world should lay firm foundations for invention, and thus introduce the rule of man. Accordingly, he was unwearying in suggesting accurate physical and chemical experiments, many of which he himself assayed to perform. When, in a session of the Royal Society, some one chanced to use the words "considerably bigger," he characteristically requested that thenceforward "no word might be used but what marks either number, weight, or measure."
In the field of his particular interests he sought the same quantitative precision which, as a true Baconian, he demanded of his scientific colleagues. He had a clear notion both of the end at which he aimed and of the means by which it must be achieved. "The Method I take," he says, "is not very usual; for, instead of using only comparative and superlative Words, and intellectual Arguments, I have taken the course (as a Specimen of the Political Arithmetick I have long aimed at) to express myself in Terms of Number, Weight, or Measure; to use only Arguments of Sense, and to consider only such Causes, as have visible Foundations in Nature; leaving those that depend upon the mutable Minds, Opinions, Appetites and Passions of particular Men, to the Consideration of others: Really professing myself as unable to speak satisfactorily upon those Grounds (if they may be
