In this paper, using the intensity ratio between two spectral lines arising from the common lower level, we determine the optical depth of the solar atmosphere of CIV emission lines. The optical depth at the line center of the (1/2-3/2) component is calculated to be 0.05 at the center of the solar disc. By introducing a measured abundance of carbon and the results of ionization balance calculations, we estimate the line-of-sight physical thickness of the regions emitting CIV lines as Heff = 27 km, and we estimate the population density of the lower level to be 1.8 × 106 cm-3 .
