"The strength of the presumption against retrospectivity in any particular case, and accordingly the ease or difficulty with which it may be overcome, must, I would think, depend on the nature and degree of the injustice which would result from giving a statute a retrospective operation. Where a palpable injustice would result, the presumption should be given its fullest weight. In such a case it is but common sense to require the clearest indication of legislative intention that such an unjust result was intended. On the other hand, where to give retrospective operation to a statute might be considered to work some injustice to one party, but is clearly required to rectify a manifest injustice to others, there would, on principle, seem little reason for giving much weight to the presumption. In such a case, where the Legislature has used language which is apt to give to its statute retrospective operation, it would appear to be a matter of conjecture to presume that it preferred the interests of the one to the others."