politics, signifies a change in the constitution of a state; and is a word of different import from revolt, with which it is sometimes confounded. When a people withdraw their obedience from their governors for any particular reason, without overturning the government, or waging an offensive war against it, they are in a state of revolt; when they overturn the government and form a new one for themselves, they effect a revolution.

That which is termed the revolution in Britain is the change which, in 1688, took place in consequence of the forced abdication of King James II. when the Protestant succession was established, and the constitution restored to its primitive purity. Of this important transaction, which confirmed the rights and liberties of Britons, we have endeavoured to give an impartial account under another article (see BRITAIN, No. 281, &c.). Of the rise and progress of the American revolution, which is still fresh in the memory of some of our readers, a large detail is given under the article AMERICA. By the revolution which took place in Poland about the end of the 18th century, that kingdom was dismembered and seized by Austria, Prussia and Russia. For an account of this revolution, see POLAND; and for the history and progress of the French revolution, the most extraordinary of all, whether considered with regard to the events which accompanied, or the consequences which followed it, see FRANCE.

Geometry, the motion of rotation of a line about a fixed point or centre, or of any figure about a fixed axis, or upon any line or surface. Thus, the revolution of a given line about a fixed centre, generates a circle; and that of a right-angled triangle about one side, as an axis, generates a cone; and that of a semicircle, about its diameter, generates a sphere or globe, &c.

Astronomy, is the period of a star, planet, or comet, &c. or its course from any point of its orbit, till it return to the same again.