A discharge tube containing air at low pressure is excited by h.f. frequency oscillations from a modified Hartley circuit. It is observed that there is a critical frequency of exciting oscillations, namely 735 k.c.|sec. below which the colour of the discharge is pinkish red and above which the colour is orange yellow. The spectrum of the discharge in the visible region consists of the first positive and second positive bands of nitrogen. A study of some of these bands as regards their intensity variation depending upon the frequency of exciting oscillations is made. It is found that the first positive bands at 5371, 5406 and 5441 Å decrease in intensity as the frequency of exciting oscillations is reduced from 790 to 680 k.c.|sec. The second positive bands at 4355, 4417, 4490, 4649, 4724, 4815 and 4917 Å on the other hand, increase in intensity under the same conditions. The results are in harmony with the theoretical conceptions, regarding such phenomena and allow us to conclude that in the present experiments an energy of 15 e.v. is available for excitation when oscillations of frequency 735 k.c.|sec. are used.