‘Videas tamen utrum loquar in ænigmate vel secundum veritatem.’ And, further (which we translate): ‘He that would see these things shall have the key that openeth and no man shutteth, and when he shall shut no man is able to open again.’ ‘But the secret—the secret!’ cried Hubert, impatiently, ‘let me know what “these things” are!’ He hastily turned the leaf back and read again. The passage was that one in the ‘_Epistola de Secretis_’ which spoke of the artificial thunder and lightning, and beneath it was the full and precise recipe for its composition. This at once explained the strange noises and the flashes of light which he had so anxiously noticed. Surprising and gratifying as this discovery might be, there was, Hubert thought, something beyond. Roger Bacon, he reasoned, was not one to practise an experiment like this for mere amusement. It was, he felt certain, a new form of invocation, more potent, doubtless, over the beings of another world, than any charm yet recorded. Be it as it might, he would try whether, from the materials around him, it were not in his power to produce the same result. ‘Here are all the necessary ingredients,’ he exclaimed; ‘this yellowish powder is the well known sulphur, in which I daily bathe the argent-vive; this bitter, glistening substance is the salt of the rock, the _salis petræ_; and this black calcination, the third agent—But the proportions are given, and here stands a glass cucurbit in which they should be mingled. It is of the form my master mostly uses—round, with a small neck and a narrow mouth, to be luted closely, without doubt. He has often told me that the sole regenerating power of the universe is heat; yonder furnace shall supply it, and then Hubert de Dreux is his master’s equal!’ * * * * * The short November day was drawing to a close, when, after carefully tending the wounded sheriff, and leaving such instructions with the Abingdon leech as he judged sufficient for his patient’s well-doing, Roger Bacon again mounted his palfrey, and turned its head in the direction of Oxford. He was unwilling to be a loiterer after dark, and his beast was equally desirous to be once more comfortably housed, so that his homeward journey was accomplished even more rapidly than his morning excursion; and barely an hour had elapsed when the Friar drew the rein at the foot of the last gentle eminence, close to which lay the walls of the cloistered city. To give the animal breathing-space, he rode quietly up the ascent, and then paused for a few moments before he proceeded, his mind intent on subjects foreign to the speculations of all his daily associations.