Time dependencies of Bradford distributions are investigated for 19th-century mathematics and for 20th-century logic. To facilitate comparisons, for the representation of empirical Bradford distributions "Pareto's law" and Lorenz diagrams are used. It is shown that the character of a Bradford distribution (including the "core zone" and the "Groos droop") depends on the stage in the development of a scientific field and that it varies with the time-span considered.