  For those inclined to judge theories by the extent to which they fruitfully guide experiment and lead to the discovery of experimental laws, we get a more qualified appraisal. For two decades or more the mature kinetic theory proved to be a fruitful guide as far as the explanation and prediction of experimental laws is concerned. But, in the view of a number of scientists involved at the time, the kinetic theory had ceased to bear fruit for the remainder of the century, as Clarke (1976, 88–9) has stressed.