If the collector asks me, as a critic, for my opinion of the Velasquez he is about to buy, I will tell him honestly what I think of it, as a work of art. I will tell him whether it moves me much or little, and I will try to point out those qualities and relations of line and colour in which it seems to me to excel or fall short. I will try to account for the degree of my aesthetic emotion. That, I conceive, is the function of the critic. But all conjectures as to the authenticity of a work based on its formal significance, or even on its technical perfection, are extremely hazardous. It is always possible that someone else was the master's match as artist and craftsman, and of that someone's work there may be an overwhelming supply. The critic may sell the collector a common pup instead of the one uncatalogued specimen of Pseudo-kuniskos; and therefore the wary collector sends for someone who can furnish him with the sort of evidence of the authenticity of his picture that would satisfy a special juryman and confound a purchasing dealer. At artistic evidence he laughs noisily in half-crown periodicals and five-guinea tomes. Documentary evidence is what he prefers; but, failing that, he will put up with a cunning concoction of dates and watermarks, cabalistic signatures, craquelure, patina, chemical properties of paint and medium, paper and canvas, all sorts of collateral evidence, historical and biographical, and racy tricks of brush or pen. It is to adduce and discuss this sort of evidence that the Collector calls in the Expert. Anyone whom chance or misfortune has led into the haunts of collectors and experts will admit that I have not exaggerated the horror of the diseases that we have inherited from the Classical Renaissance. He will have heard the value of a picture made to depend on the interpretation of a letter. He will have heard the picture discussed from every point of view except that of one who feels its significance. By whom was it made? For whom was it made? When was it made? Where was it made? Is it all the work of one hand? Who paid for it? How much did he pay? Through what collections has it passed? What are the names of the figures portrayed? What are their histories? What the style and cut of their coats, breeches, and beards? How much will it fetch at Christie's? All these are questions to moot; and mooted they will be, by the hour. But in expert conclaves who has ever heard more than a perfunctory and silly comment on the aesthetic qualities of a masterpiece?