*102. Princes of the Blood and Hereditary Peers.*--In respect to its fundamental constitution the House of Lords has undergone but slight modification during the many centuries of its existence. In respect, however, to the composition and size of the body changes have been numerous and important. There are in the chamber to-day at least six distinct groups of members, sitting by various rights and possessing a status which is by no means identical. The first comprises (p. 098) princes of the royal blood who are of age. The number of these is variable, but of course never large. They take precedence of the other nobility, but in point of fact seldom participate in the proceedings of the Chamber. The second group is the most important of all. It comprises the peers with hereditary seats and is itself divided properly into three groups: the peers of England created before the union with Scotland in 1707, the peers of Great Britain created between the date mentioned and the union with Ireland in 1801, and the peers of the United Kingdom created since that date. Technically, peers are created by the crown; but in practice their creation is controlled largely by the premier; and the act may be performed for the purpose of honoring men of distinction in law, letters, science, or business, or for the more practical purpose of altering the political complexion of the upper chamber.[139] The power to create peerages is unlimited[140] and, this being the only means by which the membership of the body can be increased at discretion, the power is one which is not infrequently exercised. Originally the right to sit as a peer was conferred simply by an individual writ of summons, or by the fact that such a writ had been issued to one's ancestor, but this method has long since been replaced by a formal grant of letters patent, accompanied by bestowal of the requisite writ. With exceptions to be noted, peerages are hereditary, and the heir assumes his parliamentary seat at the age of twenty-one. Peers are of five ranks--dukes, marquises, earls, viscounts, and barons. The complicated rules governing the precedence of these classes are of large social, but of minor political, interest.