If, by the public economy of a nation, we understand economic legislation and the governmental guidance or direction of the economy of private persons,(138) the science of public economy becomes, so far as its form is concerned, a branch of political science, while as to its matter, its subject is almost coincident with that of Political Economy. Hence it is, that so many writers use the terms public economy, or the economy of the state (_Staatswirthschaft_), and National Economy (_Volkswirthschaft_), as synonymous.(139) The hypothesis, in accordance with which, this science should discard all consideration of the state, or should refuse to presuppose its formation,(140) would lead us into an ideal region, difficult to define, probably entirely impossible, and inaccessible to experience. Just as clear, is the close connection between politics and Political Economy, in the case of the science of finance, or of the science of governmental house-keeping, otherwise the administration of public affairs. The latter, evidently, so far as its end is concerned, belongs to politics, but so far as the means to that end are concerned, to National Economy. As the physiologist cannot understand the action of the human body, without understanding that of the head; so we would not be able to grasp the organic whole of national economy, if we were to leave the state, the greatest economy of all, the one which uninterruptedly and irresistibly acts on all others, out of consideration.(141) By the term _police_, we mean the state power whose office it is, without mediation, to prevent all disturbances of external order among the people.(142) It may extend its action into all the domains of national life mentioned above, whenever external order is there threatened, or calls for protection; but its action is important especially in the domains of law and economy. The science of the _police power_, therefore, of all those doctrines resulting from investigation into national life, takes up only one phase of each of them; and the phases of doctrine thus taken up, it combines into a whole, for practical ends. Its relation to those sciences is like that of surgery to the medical sciences, or like the science of legal procedure to the science of law. Section XVIII. Sciences Relating To National Life.—Statistics.