[en] Some properties of the density of vortex lines produced by helium II thermal counterflow in wide channels (approx. 1.0 cm) are studied. The homogeneity of the steady state vortex line density is determined from local measurements of second sound attenuation at nine positions along a 40 cm. channel. The vortex line density has a moderately steep gradient near the heater and is fairly uniform over the remainder of the channel. The second sound attenuation produced by thermal counterflow is compared with that produced by rotation of the cryostat. This allows determination of the absolute vortex line density produced by the counterflow. This measurement agrees well with existing work. Fluctuations in the vortex line density are studied by observing the attenuation of second sound waves and ion currents. The root mean square amplitude of the fluctuations is approximatley three percent of the total attenuation. The power spectral density of the fluctuations is approximately constant for frequencies below about 0.1 Hz. Above this frequency the power decreases as a low power of the inverse frequency, reaching the background noise level at approximately 10 Hz. The coherence between fluctuations measured simultaneously by ions and second sound was determined. The greatest coherence was found at low frequencies and low heater powers