[Illustration: FIG. 133.--A rule for direction of induced current which, in some cases, is more conveniently applied than Fleming’s rule: Hold the thumb, forefinger and remaining fingers of the right hand at right angles to each other; place the hand in such position that the forefinger points in the direction of motion of the conductor, the three fingers in the direction of the lines of force, then will the thumb point in the direction of the induced current.] 8. _Lenz’s law. The direction of the induced current is always such that its magnetic field opposes the motion which produces it._ This is illustrated in figs. 130 and 131. =Rules for Direction of Induced Current.=--There are a number of rules to quickly determine the direction of an induced current, when the direction of the lines of force, and motion of the conductor are known. The first rule here given was devised by Fleming and is very useful. It is sometimes called the “dynamo rule.” =Fleming’s Rule.=--_If the forefinger of the right hand be pointed in the direction of the magnetic lines, and the thumb (at right angles to the forefinger) be turned in the direction of the motion of the conductor, then will the middle finger, bent at right angles to both thumb and forefinger, show the direction of the induced current._ The application of this rule is shown in fig. 132. Here the right hand is so placed at the north pole of a magnet, that the forefinger points in the direction of the magnetic lines; the thumb in the direction of motion of the conductor; the middle finger pointed at right angles to the thumb and forefinger indicates the direction of the current induced in the conductor. [Illustration: FIG. 134.--The palm rule for direction of induced current: If the palm of the right hand be held against the direction of the lines of force, the thumb in the direction of the motion, then the fingers will point in the direction of the induced current.] =Ampere’s Rule.=--_If a man could swim in a conductor with the current, then the north seeking_ (+) _pole of a magnetic needle placed directly ahead of him, will be deflected to the left, while the south seeking_ (-) _pole will be urged to the right._ For certain particular cases in which a fixed magnet pole acts on a movable circuit, the following converse to Ampere’s rule will be found useful: If a man swim in the wire with the current, and turn so as to look along the direction of the lines of force of the pole (that is, as the lines of force run, _from_ the pole if it be north seeking, _toward_ the pole if it be south seeking), then he and the conducting wire with him will be urged _toward his left_. =The palm rule.=--_If the palm of the right hand be held facing or against the lines of force, and the thumb in the direction of the motion, then will the fingers point in the direction of the induced current._