One of my cousins who had a good deal of free time to dispose of, spent it for several months, with the assistance of his comrade, in counting the number of horses that passed daily, in the course of two hours, by a café they frequented. The conscientious and controlled count indicated that every day there came one bay horse to every four. If then, on any given day, an incommensurably large number of brown, black, and tawny horses came in the course of the first hour, the counters were forced to infer that in the next 60 minutes horses of a different color must come and that a greater number of bays must appear in order to restore the disturbed equilibrium. Such an inference is not contradictory to the Humian proposition. At the end of a series of examinations the counters were compelled to say, “Through so many days we have counted one bay to every four horses; we must therefore suppose that a similar relationship will be maintained the next day.” So, the lawyer, too, must suppose, although we lawyers have nothing to do with figures, that he knows nothing a priori, and must construct his inferences entirely from experience. And hence we must agree that our premises for such inferences are uncertain, and often subject to revision, and often likely, in their application to new facts, to lead to serious mistakes, particularly if the number of experiences from which the next moment is deduced, are too few; or if an unknown, but very important condition is omitted. These facts must carefully be kept in mind with reference to the testimony of experts. Without showing ourselves suspicious, or desirous of confusing the professional in his own work, we must consider that the progress of knowledge consists in the collection of instances, and anything that might have been normal in 100 cases, need not in any sense be so when 1000 cases are in question. Yesterday the norm may have been subject to no exception; to-day exceptions are noted; and to-morrow the exception has become the rule.