Voltages during transient conditions in a grounded wire lying on the earth's surface due to current in a second grounded wire also on the earth's surface are formulated for types of transient currents ordinarily obtained in a.-c. and d.-c. circuits. The fundamental formula is for voltage due to a unit step current, that is, a current zero for time less than zero, and unity for time greater than zero: curves are given for the function determining this voltage for a wide range of values of its two parameters. The formulas for other types of currents are not well adapted for numerical computation, which should be more conveniently carried out by numerical integration using the above curves.