Ques. What will be the result if the connections of some of the field coils of a dynamo be reversed? Ans. If one-half the number of coils oppose the other half, the field magnetism will be neutralized and the machine will not build up at all; but if one of the coils be opposed to the others, the machine might build up, but the generated voltage will be low, and there will be considerable sparking at some of the brushes. Ques. How may it be ascertained which coil is reversed? Ans. In all dynamos there should be an equal number of positive and negative poles, and in almost all of them the poles should be alternately positive and negative. Therefore, if a pocket compass be brought near the pole pieces, and it show that there are more poles of one kind than the other, the indication is that one or more of the coils are reversed, and the improper sequence of alternation will determine which one is wrongly connected. Ques. When a dynamo loses its residual magnetism, how can it be made to build up? Ans. By temporarily magnetizing the field. To do this a current is passed through it from another dynamo, or from the cells of a small primary battery. Usually, this will set up sufficient initial magnetism to allow the machine to build up. The battery circuit should be broken before the machine has built up to full voltage. Ques. What should be done if a dynamo become reversed by a reversal of its field magnetism due to lightning, short circuit, or otherwise? Ans. The residual magnetism should be reversed by a current from another dynamo, or from a battery; but if this be not convenient, the connections between the machine and the line should be crossed so that the original positive terminal of the dynamo will be connected to the negative terminal of the line, and vice versa.