I should have let this bit of persiflage go unanswered, assuming it to be one of those witty sallies for which the princes of science are so justly famed and to which they often treat us even when they are not in the presence of works of art, had not the professor followed up his clue with the utmost gravity, assuring me at last that no picture in the gallery was beyond the reach of optical diagnostic.  Still suspicious of his good faith, I suggested, tentatively, that perhaps the discrepancies between the normal man’s vision and the pictures on the wall were the result of intentional distortion on the part of the artists.  At this the professor became passionately serious—­“Do you mean to tell me,” he bawled, “that there has ever been a painter who did not try to make his objects as lifelike as possible?  Dismiss such silly nonsense from your head.”  It is the old story:  “Clear your mind of cant,” that is to say, of anything which appears improbable or unpalatable to Dr. Johnson.

The religious, on the other hand, are apt to be a little prejudiced against common-sense; and, for my own part, I confess that I am often tempted to think that a common-sense view is necessarily a wrong one.  It was common-sense to see that the world must be flat and that the sun must go round it; only when those fantastical people made themselves heard who thought that the solar system could not be quite so simple an affair as common-sense knew it must be were these opinions knocked on the head.  Dr. Johnson, the great exemplar of British common-sense, observing in autumn the gathered swallows skimming over pools and rivers, pronounced it certain that these birds sleep all the winter—­“A number of them conglobulate together, by flying round and round, and then all in a heap throw themselves under water, and lie in the bed of a river”:  how sensibly, too, did he dispose of Berkeley’s Idealism—­“striking his foot with mighty force against a large stone”—­“I refute it thus.”  Seriously, is the common-sense view ever the right one?

Lately, the men of sense and science have secured allies who have brought to their cause what most it lacked, a little fundamental thought.  Those able and honest people, the Cambridge rationalists, headed by Mr. G.E.  Moore, to whose Principia Ethica I owe so much, are, of course, profoundly religious and live by a passionate faith in the absolute value of certain states of mind; also they have fallen in love with the conclusions and methods of science.  Being extremely intelligent, they perceive, however, that empirical arguments can avail nothing for or against a metaphysical theory, and that ultimately all the conclusions of science are based on a logic that precedes experience.  Also they perceive that emotions are just as real as sensations.  They find themselves confronted, therefore, by this difficulty; if someone steps forward to say that he has a direct, disinterested, a priori, conviction of the goodness of his emotions towards the Mass,