PREFACE ix those pictures which are now lost and are known only from books, that is to say, in most cases from the catalogues of exhibitions and sales by auction. In such cases, as is well known, the rule is that the pictures are catalogued under the names given them by their owners. The ascriptions to great masters for the most part merely represent the owner's personal opinion, and are therefore untrustworthy. But there are degrees in this untrustworthiness. The more famous a collection has been in its time, the greater is the probability that the pictures which gained it fame were genuine. The higher the price which pictures fetched in a public auction, the more probable is it that they were of high artistic quality. Again, the shorter the time elapsing between an auction and the death of an artist, the more likely is it that a vendor would be careful not to offer the public forged pictures as genuine works of that artist. Still in all these cases we are dealing only with probabilities ; certainty as to its character is to be attained in very few instances when a work of art has been lost. The question now arises, how such pictures, known only from notices in books, are to be treated. To reject them all would be absurd, for it is safe to assume that, of the pictures mentioned only in sale-catalogues and now lost, a considerable percentage were genuine. Again, it would be difficult to separate those works that were probably genuine from those that were probably not, whether one judged from the importance of the collection, the price attained, or the date of the auction, or from all these considerations taken together. Wrongly named pictures have been included in great collections and have fetched high prices, while genuine pictures by masters have been misjudged and sold for trivial sums. Under these circumstances the compiler has thought it better to give too much rather than too little, and, at least in the case of important painters, has noticed all the pictures to be found in the sale-catalogues examined. The titles of these are printed in ordinary lower-case type. They are thus dis- tinguished from the pictures personally inspected by the compiler or known to him from trustworthy reports or reproductions, the titles of which are printed in capitals. It follows that the mention of the lost pictures in the Catalogue is no guarantee of their authenticity. They must include pictures of varying merit,
