The documents given below show the machinery in operation. Instances are given of the different tenures[45] (Nos. 1 to 6), while the uncertainty prevailing in the twelfth century as to the incidents due from land held by serjeanty is illustrated in No. 5. The gradual substitution of a money economy for a feudal economy, which finds expression in scutage (No. 17) and otherwise (No. 18), encouraged an elasticity of tenure which made a change from serjeanty to knight service (No. 7) and from personal service to a rent (No. 8) convenient equally to lord and tenant. The degree to which subinfeudation had commonly proceeded in the thirteenth century is shown in No. 9, and the burden of the feudal incidents is exemplified in Nos. 10 to 15. The ordinary revenues of the Crown from feudal incidents and aids, rents, the profits of justice, and escheats, were never sufficient to meet emergencies, just as the feudal army was inadequate for a protracted campaign, and hence the Crown was forced to resort on the one hand to a universal land-tax (No. 16) or a limited exaction from the crown demesnes (No. 19), and on the other to a tax on the feudal unit, the knight's fee (No. 17); the provisions for the collection of a carucage illustrate the royal determination to exact the uttermost farthing, while the assessment of a scutage was conducted on the modern principle of extracting the money first and settling the liability afterwards. No. 20 is a rare surviving instance of an original writ _Precipe_ issued before _Magna Carta_, and shows precisely the method of the royal procedure in attracting legal causes to the King's jurisdiction out of the hands of the lord. The section concludes with the important articles of enquiry initiated by Edward I., which led to the compilation of the Hundred Rolls and the proceedings _quo warranto_, and also set out in detail the King's conception of his sovereignty and of the royal origin of all feudal franchises and liberties (No. 21); while the last document (No. 22) furnishes a curious instance of one of the minor royal rights. AUTHORITIES The principal modern writers dealing with the subject of this section are:--Pollock & Maitland, _History of English Law_; Maitland, _Lectures on Constitutional History_; Stubbs, _Constitutional History_; Hazlitt, _Tenures of land and customs of manors_; Round, _Feudal England_; Round, _The King's Serjeants and Officers of State_; Baldwin, _Scutage and Knight Service in England_; McKechnie, _Magna Carta_; Freeman, _Norman Conquest_; Hatschek, _Englische Verfassungsgeschichte_; Digby, _History of the Law of Real Property_.