‘Theophilus, an humble priest, servant of the servants of God, addresses his words to all who desire by the practical work of their hands and by the pleasing meditation of what is new, to put aside and trample under foot all sloth of mind and wandering of spirit....’ In this book they will find ‘all that Greece possesses in the way of divers colours and mixtures, all that Tuscany knows of the working of enamels [_electrorum operositate_] or of niello [_nigellum_], all that Arabia has to show of works ductile, fusible, or chased, all the many vases and sculptured gems and ivory that Italy adorns with gold, all that France prizes in costly variety of windows, all that in gold, silver, copper and iron or in subtle working of wood and stone is extolled by inventive [_sollers_] Germany.’ We are here in a healthy northern atmosphere, far removed from the shuffling statements and ambiguous formulas of the oriental alchemists.[88] The second book of the _Schedula_ is concerned exclusively with glass, but most of the thirty-one sections deal with the preparation of stained glass for windows. In a curious passage to be found in the prologue of this book, Theophilus tells us that he has ‘approached the atrium of the Holy Wisdom [_Agiæ Sophiæ_] and beheld the _cellula_ adorned with every variety of divers colours, showing the nature and use of each.’[89] The first chapter treats of the construction of the glass furnace, and enters at once into practical details. A German writer (A. Friedrich, _Alt-Deutsche Gläser_) has illustrated the furnaces of Theophilus by means of a diagram, and attempts to show how they differ from those described by the pseudo-Heraclius. All we can say is, that while the furnace of the later writer consisted distinctly of three parts—the main furnace with the glass pots in the centre, the fritting oven on one side, and the annealing oven on the other—in the earlier type of Theophilus there is no separate building for the fritting, which, it would seem, was done on the roof of the main furnace. In both cases the ovens form a compact group, heated by one fire. In the earlier furnace there were as many as eight pots, with corresponding openings, but these pots were probably much smaller than those of the thirteenth-century oven.