At last Mejnour professed himself satisfied with the progress made by his pupil. “The hour now arrives,” he said, “when thou mayst pass the great but airy barrier,--when thou mayst gradually confront the terrible Dweller of the Threshold. Continue thy labours--continue to surpass thine impatience for results until thou canst fathom the causes. I leave thee for one month; if at the end of that period, when I return, the tasks set thee are completed, and thy mind prepared by contemplation and austere thought for the ordeal, I promise thee the ordeal shall commence. One caution alone I give thee: regard it as a peremptory command, enter not this chamber!” (They were then standing in the room where their experiments had been chiefly made, and in which Glyndon, on the night he had sought the solitude of the mystic, had nearly fallen a victim to his intrusion.) “Enter not this chamber till my return; or, above all, if by any search for materials necessary to thy toils thou shouldst venture hither, forbear to light the naphtha in those vessels, and to open the vases on yonder shelves. I leave the key of the room in thy keeping, in order to try thy abstinence and self-control. Young man, this very temptation is a part of thy trial.” With that, Mejnour placed the key in his hands; and at sunset he left the castle. For several days Glyndon continued immersed in employments which strained to the utmost all the faculties of his intellect. Even the most partial success depended so entirely on the abstraction of the mind, and the minuteness of its calculations, that there was scarcely room for any other thought than those absorbed in the occupation. And doubtless this perpetual strain of the faculties was the object of Mejnour in works that did not seem exactly pertinent to the purposes in view. As the study of the elementary mathematics, for example, is not so profitable in the solving of problems, useless in our after-callings, as it is serviceable in training the intellect to the comprehension and analysis of general truths.