On the grain-size dependence of secondary creep In their recent paper Duval and Le Gac (1980) show that the permanent creep-rate of polycrystaJline ice does not increase with grain-size. We wish to agree with their conclusion by presenting data we have collected at higher strain-rates (5.5 X 10-4 S-I), on laboratory-grown, randomly oriented, polycrystalline ice tested at a constant strain-rate in compression. Figure I shows the maximum yield stress reached as a function of grain-size, for the,

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... lbeit narrow, range of grain-sizes from 0.8 to 1.8 mm diameter. No significant effect of grain-size is seen. We are extending the results to smaller grain-sizes, but are having difficulty in obtaining small-grain ice which is also air free . We cannot go to much larger grain-sizes because our sample diameter is fixed at 20 mm and our results (Fig. 2 ) show that the sample diameter should be approximately 12 times the grain d iameter for the maximum yield stress to be independent of grain-size. For this reason Duval and Le Gac should be cautious in interpreting their results from samples greater than 7 mm diameter when their sample size is 80 mm. The same comment applies to Baker's (1978) original work. 10 9f-•