As regards direct assistance in the production of this book, I hope that definite acknowledgements will be found in their place. But I must thank the authorities of the various museums, especially of the Museum of the Louvre, the British Museum, the Royal Museum of Copenhagen, and the Museo Kircheriano at Rome, for much generous aid in the prosecution of my enquiries. Beyond all, however, in this way, my heartiest thanks are due to the Syndics of the Cambridge University Press, who have generously undertaken the whole cost and responsibility of publishing the book. Mrs Lucy M. Mitchell has kindly consented to allow me the use of some wood-cuts illustrating her articles in the Century Magazine. I must also thank Dr Henry jackson, Fellow and Praelector of Trinity College, Cambridge, for looking over the proof-sheets of the first two essays and for making useful suggestions.