OCR Text |
Show Curve No. 3 ( o^= - 7.91 ( b), - 28.81 ( c) o C). Here ^_ was chosen so that with a non- melting surface and < ZL = 50 meal cm" 2 min" 1 deg" 1, - dM/ d£, = 0. Because the cross- over point to a non- melting surface lies above 0C.= 50 meal cm" min deg" 1, this curve does not appear in Fig. 7a. As shown in Figs. 7b and 7c, the minimum of - M(( T) is very broad, so that ablation can be described as accentuating surface irregularities only in a purely formal sense and the differentiation in surface form remains circumscribed. For Curve No. 4 (/^ = - 0.76 ( a), - 6.08 ( b), - 11.38 ( c) ° C), ^ w a s so chosen that - dM/ d& L = 0 at the inflection point, that is, at the cross- over point from a melting to non- melting surface. At still higher temperatures, therefore, - dM/ ddL can only be greater than zero for a non- melting surface. This is the case for Curve No. 5 ( n9 = 0.00 ( a, b, and c) ° C). For these, / T> = 0° C has been assumed for all three figures. Ablation which accentuates surface irregularities for a melting surface goes over at the inflection point to that which suppresses them for a non- melting surface. The same is shown by Curve No. 6 ( r$- = 3.76 ( b), 10.37 ( c) ° C), where /# L was so chosen that O i l the inflection point lies at 50 meal cm *• min" 1 deg_ i, and for Curve No. 7 (/$• = 5.67 ( b), 12.36 ( c) ° C) so that it lies at 100 meal cm" 2 min" deg" 1. Both curves are thus lacking in Fig. 7a. Curve No. 8 (/•$ = 0.86 ( a), 6.76 ( b), 12.66 ( c) ° C) corresponds to the limit of ablation which promotes irregularities on a melting surface. Here the equivalent temperature of air determined with rw is equal to that of saturated air at 0° C, or 13.5° C. For a melting surface, - M is independent of ( ZL , and rises for a non- melting surface only beyond the inflection point. At higher air temperature - M increases throughout its range. To serve as an example 24 |