It will be interesting to quote for the information of such men, the opinion of the greatest of medieval scientists with regard to the reason why men do not obtain real knowledge more rapidly than would seem ought to be the case, from the amount of work which they have devoted to obtaining it. Roger Bacon, summing up for Pope Clement the body of doctrine that he was teaching at the University of Oxford in the Thirteenth Century, starts out with the principle that there are four grounds of human ignorance. "These are first, trust in inadequate authority; second, the force of custom which leads men to accept too unquestioningly what has been accepted before their time; third, the placing of confidence in the opinion of the inexperienced; and fourth, the hiding of one's own ignorance with the parade of a superficial wisdom." Surely no one will ever be able to improve on these four grounds for human ignorance, and they continue to be as {42} important in the twentieth century as they were in the Thirteenth. They could only have emanated from an eminently practical mind, accustomed to test by observation and by careful searching of authorities, every proposition that came to him. Professor Henry Morley, Professor of English Literature at University College, London, says of these grounds for ignorance of Roger Bacon, in his English Writers, Volume III, page 321: "No part of that ground has yet been cut away from beneath the feet of students, although six centuries ago the Oxford friar clearly pointed out its character. We still make sheep walks of second, third, and fourth and fiftieth-hand references to authority; still we are the slaves of habit; still we are found following too frequently the untaught crowd; still we flinch from the righteous and wholesome phrase, 'I do not know'; and acquiesce actively in the opinion of others that we know what we appear to know. Substitute honest research, original and independent thought, strict truth in the comparison of only what we really know with what is really known by others, and the strong redoubt of ignorance has fallen."