[Sidenote: Committees of Correspondence (1772-75).] Nine years elapsed without another congress. Meanwhile the political excitement, with occasional lulls, went on increasing, and some sort of cooperation between the colonial governments became habitual. In 1768, after parliament had passed the Townshend revenue acts, there was no congress, but Massachusetts sent a circular letter to the other colonies, inviting them to cooperate in measures of resistance, and the other colonies responded favourably. In 1772, as we have seen, committees of correspondence between the towns of Massachusetts acted as a sort of provisional government for the commonwealth. In 1773 Dabney Carr, of Virginia, enlarged upon this idea, and committees of correspondence were forthwith instituted between the several colonies. Thus the habit of acting in concert began to be formed. In 1774, after parliament had passed an act overthrowing the government of Massachusetts, along with other offensive measures, a congress assembled in September at Philadelphia, the city most centrally situated as well as the largest. If the remonstrances adopted at this congress had been heeded by the British government, and peace had followed, this congress would probably have been as temporary an affair as its predecessors; people would probably have waited until overtaken by some other emergency. But inasmuch as war followed, the congress assembled again in May, 1775, and thereafter became practically a permanent institution until it died of old age with the year 1788. [Sidenote: Continental Congress (1774-1789).] This congress was called "continental" to distinguish it from the "provincial congresses" held in several of the colonies at about the same time. The thirteen colonies were indeed but a narrow strip on the edge of a vast and in large part unexplored continent, but the word "continental" was convenient for distinguishing between the whole confederacy and its several members.