Equatorial cold plasma density profiles determined from VLF whistlers propagating in magnetospheric ducts are compared with densities computed from the observations of ULF hydromagnetic waves (geomagnetic pulsations). The densities obtained by the ULF technique are based on the identification of resonant geomagnetic field lines, assumed to be driven by a monochromatic source. The ULF results thus obtained agree well with the whistler results throughout the period, June 17--20, 1973, when simultaneous data comparisons could be made. The ULF observations show that at mid-latitudes, shorter-period resonances can be supported in the plasma trough region, while those of longer period can occur inside the plasmasphere.