Couple

(kup'l.) [L. copula, a link.] (Statics.) Two equal parallel forces acting on a body in opposite directions form what is known as a C. It is evident that such a combination can only cause the body to rotate. A railway turn-table supplies an illustration. If equal forces be applied at each extremity of the same diameter in opposite directions, the turn-table is caused to rotate about its centre, together with the engine or carriage placed upon it; and it is obvious that in such a case no motion of translation could take place if the turn-table were free to move. The perpendicular distance between the directions of the forces is called the arm of the C.; and the perpendicular to the plane of the C. at the middle point of the arm is termed the axis of the C.(Elect.) When a plate of zinc and a plate of copper are partially immersed in dilute sulphuric acid, a disturbance of the electrical equilibrium ensues,for, by means of delicate electroscopic arrangements, it may be shown C Z that the zinc plate po e es a feeble charge of negative, and the copper plate a feeble charge of positive, electricity. At the same time there is a slight disengagement of hydrogen from the surface of the zinc. If now the plates be placed in direct contact, or, moro conveniently, be con-Fig. 218. VOLTAIC COUPLE. nected by means of a metallic wire, the chemical action increases, but the hydrogen is now disengaged from the surface of the copper (Fig. 218); and if the connecting wire be examined it will be found to po e many remarkable thermal, magnetic, and other properties described in other articles. This arrangement, consisting of two metals in metallic contact, and a conducting liquid in which they are placed, constitutes a simple voltaic element or couple. So long as the metals are not in contact, the C. is said to be open, and when connected it is closed. Couplet, (kup'lit.) (Lit.) A division of a poem, containing 2 verses or 2 lines. [s. 238] IMG:p0267_0.jpg:Gravür