Power spectral analyses are presented of the voltage fluctuations in a transatlantic cable on two days of moderate geomagnetic activity and four days of magnetic quiet. The voltage fluctuations with periods from about twenty minutes to a day are predominantly of geomagnetically-induced origin, with similar peaks often found in the geomagnetic and voltge spectra. The voltage spectral power SV at a given frequency f can be expressed in terms of the horizontal field spectral power SH as &bgr;Shf&ggr;.