During the course of the last century it has grown increasingly clear that not all the issues with which an experimental science can be faced are experimental issues. If there were no other ground for this belief, history itself would force upon us some such conviction. For there are differences of opinion dividing men today that have divided men from the earliest times recorded, and in every one of the ages in between the self-same issue will have involved in dissension, not an occasional disputant here and there, but all the best thinkers in all the known sciences of their day. Yet at no time has either party to such strifes been in possession of facts ignored by the other; for had this been the case, the ignorant party must ere now have been driven from the field by force of the facts it ignored. It is fair to suppose that an issue which has come no nearer to solution as century after century added its contribution to the store of human knowledge, cannot depend for its decision on any information to be looked for from the centuries to come.