The student is requested, in perusing the work, to pass by no remark until its meaning is thoroughly comprehended. Also, excepting the fundamental 2 3 first principle of paragraph 8, on which the whole fabric is based, he is requested to take no single calculation for granted, but to verify each and all for himself. It will perhaps be found an advantage to read first the Summary in part VI., and refer back to the different paragraphs as marked therein. A learned friend and great traveller, who it was hoped would have furnished an Introduction on the history of Byzantine art in its various branches, has, through ill-health and multiplicity of engagements, been obliged to decline the task. This is a cause of regret to the writer, with which his readers would fully sympathise could they guage the extent of the loss sustained.