For although it is certainly true that quantitative measurements are of great importance, it is a grave error to suppose that the whole of experimental physics can be brought under this heading. We can start measuring only when we know what to measure: qualitative observation has to precede quantitative measurement, and by making experimental arrangements for quantitative measurements we may even eliminate the possibility of new phenomena appearing.
in his memoirs, as quoted by Jean Matricon, G. Waysand, Charles Glashausser (2003). The cold wars: a history of superconductivity. Rutgers University Press. p. 18. ISBN 0813532957.