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tokens: 54 value measured for our sample. Fig. 8 shows the distribution of D 34 and D 54 for our program stars. Figure 8. D 34 and D 54 distribution for our program stars. Among 105 stars for which we estimated D 34 values, 19 (≈20 per cent) show D 34 ≥ 2.7. However, D 54 for our stars mostly range between 0.2 and 1.5 (≈70 per cent). Only 19 stars exhibit D 34 1.0, whereas D 54 > 1.5 in 27 cases. Comparing with literature, we find that Dachs et al. ( 1990 ) reported D 34 to lie within 1.2–3.2 for their sample of 26 southern early-type Be stars. However, D 54 for their case range within 0.4–1.0, clustering near 0.7. On the contrary, Slettebak et al. ( 1992 ) obtained D 34 for 41 CBe stars to range between 2.05 and 5.7, while D 54 being always less than 1.0. Both the previous authors also noticed that on an average, weak H α emission (H α EW −25 Å) is usually characterized by flat Balmer decrements ( D 34 2.0, D 54 > 0.6). Our study could not confirm any such trend that is evident from Table 4 . Our result for D 34 fairly agrees with Slettebak et al. ( 1992 ) and Dachs et al. ( 1990 ), although the range of our D 34 is larger. This is possibly due to the larger number of stars for our sample. We found that 19 of our program stars show D 34 ≥ 2.7, implying that the disc for these stars are optically thick in nature. But our result does not match for D 54 . The different range of D 34 and D 54 values obtained in our study might be due to the fact that we considered A V values for calculating the Balmer decrements in our case. This may not have been done by previous authors. Moreover, we estimated D 34 for all 20 weak emitters also that show H α EW −5 Å. 3.4.2 Epoch-wise variation of <italic>D</italic><sub>34</sub> Apart from looking into the H α line, the transient nature of CBe star discs can be identified by studying the epoch-wise variation of estimated D 34 values of those stars where repeated observations are done. For our program stars where previous estimations of D 34 are available (at least two), we compared our estimated D 34 values to those obtained by other authors. We found that only 10 of our program stars have at least two sets of observations for D 34 including our estimations. Only one among them (HR 2142) has three observations for D 34 . Fig. 9 demonstrates the variation of D 34 as observed by us and previous authors. It is seen that our value of D 34 is lower than that of previous authors (e.g. Dachs et al. 1990 , Briot 1971 , Rojas Herman 1958 , Burbidge Burbidge 1953 , and Karpov 1934 ) in every case. Figure 9. Variation of D 34 in 10 of our program stars as observed by us and previous authors. The black line indicates the cut-off value 2.7, adopted from Hummer Storey ( 1987 ), which is assumed to distinguish between an optically thin and thick region that prevails in case B condition defined by Baker Menzel ( 1938 ) and later by Brocklehurst ( 1971 ). The epoch-wise variation study of D 34 for 10 of our program stars certainly imply