The periods, then, of real importance in the history of glass, either from the _cultur-historisch_ or from a purely artistic point of view, are separated by long intervals, during which little of interest was produced. The primitive glass of Egypt, the varied productions of the first centuries of the Roman Empire, the enamelled glass of the Saracens, and the Venetian glass of the Renaissance—this exhausts all that we find either of commanding historic interest or of superlative artistic merit. What follows—the German and the Netherlandish glass of the seventeenth and eighteenth centuries—is still of some importance under both these heads. I can hardly say so much of the English glass of the eighteenth century; but this glass must not be neglected—it is English, and it is highly prized by many enthusiastic collectors. It will be seen that there is a long gap between the first and second of our critical periods—between the beginning of the primitive Egyptian and the earliest Roman glass. This gap will be filled, in some measure, by some account of the rare surviving specimens of glass that can claim an Assyrian origin, of the glass pastes of the Mycenæan age, and of the few examples of glass that can be strictly classed as Greek of the classical age. So again of the second long hiatus—the interval of nearly a thousand years between the period of the Roman glass and that of the Saracens,—this may be partly filled by the few scanty pieces that have come down to us from Sassanian and Byzantine times. To this period belongs also the glass of the Germanic tribes of northern Europe, above all that of our Anglo-Saxon ancestors. Some notice must also be taken of a few districts situated on bypaths, of the glass from countries that lie away from the main centres of production—these latter centres, I may note, until comparatively recent times are mostly to be found in close connection with the basin of the Mediterranean. To these outlying districts we must finally turn to examine the glass of Persia, of India, and above all the glass of China. An interesting chapter, nay, a separate work, might be devoted to the classification and history of a class of objects of which the manufacture has been carried on continuously and with few changes from the time of the Middle Empire in Egypt—of beads, I mean, and other allied applications of glass, included in the French term _verroterie_. But, however great the claims to attention of such objects, their interest is rather archæological than artistic, and it will be sufficient to treat of them incidentally along with the, for us, more important class of ‘hollow ware’ produced with the aid of the glass-blower’s tube. PROPERTIES AND COMPOSITION OF GLASS