The term " ampere-turn " is applied to winding dynamos and electrical instruments. The magnetising effort of a coil carrying a steady electric current depends on the product of the number of the complete turns or loops in the coil and the current in amperes, and the magnetic effect thus produced is measured in ampere-turns. Of course, the coil is supposed to be wound so that the magnetic effect of the turns is in one direction. Thus, if a coil of sixty complete turns carries a current of 5 amperes, the magnetic effect of the coil is 60 5 = 300 ampere-turns.