The relative intensities of the emission lines in the triplet system of neutral helium are determined as a function of the optical depth of an atmosphere in X 3889. The atmosphere considered is one of low density, comparable to nebulae, so as to minimize the importance of effects due to electron collisions. The range of optical depth considered is limited so that only lines originating from the metastable level show effects of optical depth. This limits us to r(1083Q < 10 , since above this value the population of the 23P level becomes large enough that one cannot ignore the optical depth in lines arising from that level. A comparison with the helium observations of five well-known nebulae indicates positively the effects of optical depth in at least three and probably four of these nebula.