Experimental observations of the normal modes in a cylindrical plasma without external excitation is presented. The experimental results compare favorably with theory. Measurement of the high‐frequency electromagnetic field outside of the plasma and its spectrum lead to a method of measuring the electrostatic oscillations spectrum in a plasma without perturbing it in any way. Exact measurement of the emission profile at the plasma frequency can give information about the mean thermal speed of the electrons without any assumption about their distribution function.