Electrostatic wave propagation transverse to a magnetic field B is analyzed in the range of the ion cyclotron frequency in a toroidal device. The electrostatic ion cyclotron waves are excited by means of an electromagnetic signal injected through an antenna system located in the centre of the plasma. For the first time the backward mode is detected in hydrogen and deuterium plasmas. A comparison between the theoretical dispersion relation and the experimental results permits an indirect accurate estimate of the ion temperature, typically in the range 0.05-0.3 eV.