For some time England had seemed to take little part in the progress of the fine arts in Europe, except commercially, or as the hostess of many famous artists, from Holbein to Van Dyck. There were a certain number of picture-dealers and print-sellers in London, but under Charles I. her only painters and engravers of merit were foreigners.[31] The famous portrait painter, Sir Peter Lely, whom the English are proud to own, was a German, as was Kneller, who inherited his reputation, and, as was Hollar, an engraver of unrivalled talent.[32] And while a few pupils of this last artist were doing their best to imitate his example, the taste for line engraving and etching, which processes were being slowly and painfully popularised by their efforts, was suddenly changed into a passion for another method, in which the principal success of the English school has since been won. Prince Rupert, so renowned for his courage and his romantic adventures, had the fortunate chance to introduce to London the process of engraving which is called mezzotint. In spite, however, of what has been alleged, the honour of the invention is not his. Ludwig von Siegen, a lieutenant-colonel in the service of the Landgrave of Hesse-Cassel, had certainly discovered mezzotint before the end of 1642, for in the course of that year he published a print in this style--the portrait of the Princess Amelia Elizabeth of Hesse--the very first ever given to the public. Von Siegen for awhile refused to divulge his secret. "There is not," he wrote to the Landgrave of Hesse concerning this same portrait, "a single engraver, nor a single artist, who knows how this work was done." And, indeed, no one succeeded in finding out, and it was only after a silence of twelve years that Von Siegen consented to reveal his mystery. Prince Rupert, then at Brussels, was the first initiated. He, in his turn, chose for confidant the painter Wallerant Vaillant, who apparently did not think himself bound to strict silence, for, soon afterwards, a number of Flemish engravers attempted the process. Once made public, no one troubled about the man who had invented it. He was, in fact, so quickly and completely forgotten, that even in 1656 Von Siegen was obliged to claim the title, which no one any longer dreamed of giving him, and to sign his works: "Von Siegen, the first and true inventor of this kind of engraving." It was still worse in London when the plates engraved by Prince Rupert were exhibited, and when the English artists had learnt how they could produce the like. They set themselves to work without looking out for any other models, and were much more taken up with their own results than the history of the discovery, the whole honour of which was attributed to Rupert, the man who in reality had only made it public. [Illustration: FIG. 81.--PRINCE RUPERT. Head of a Young Man (engraved in Mezzotint).]