Attention is drawn to the application of Ohm's law to a portion of a direct-current series circuit containing both sources of emf and resistance elements. Circuits are presented wherein for a portion of the series circuit the difference in potential,V, and the current,I, satisfy separately the three following situations:—(1)V ≠ 0andI = 0, (2)V = 0andI = 0, (3)V = 0andI ≠ 0.