As each of these candles was one foot long, and burned three inches in an hour, it follows that it would last four hours; when this time was expired, the attendant who had the apparatus in charge lighted another. There were, of course, six required for the whole twenty-four hours. The system worked very well, though there was one difficulty that occasioned some trouble in the outset, which, however, was not much to be regretted after all, since the remedying of it awakened the royal ingenuity anew, and led, in the end, to adding to Alfred's other glories the honor of being the inventor of _lanterns_! The difficulty was, that the wind, which came in very freely in those days, even in royal residences, through the open windows, blew the flames of these horological candles about, so as to interfere quite seriously with the regularity of their burning. There was no glass for windows in those days, or, at least, very little. It had been introduced, it is said, in one instance, and that was in a monastery in the north of England. The abbot, whose name was Benedict, brought over some workmen from the Continent, where the art of making glass windows had been invented, and caused them to glaze some windows in his monastery. It was many years after this before glass came into general use even in churches, and palaces, and other costly buildings of that kind. In the mean time, windows were mere openings in stone walls, which could be closed only by shutters; and inasmuch as when closed they excluded the light as well as the air, they could ordinarily be shut only on one side of the apartment at a time--the side most exposed to the winds and storms. Alfred accordingly found that the flame of his candles was blown by the wind, which made the wax burn irregularly; and, to remedy the evil, he contrived the plan of protecting them by thin plates of horn. Horn, when softened by hot water, can easily be cut and fashioned into any shape, and, when very thin, is almost transparent. Alfred had these thin plates of horn prepared, and set into the sides of a box made open to receive them, thus forming a rude sort of lantern, within which the time-keeping candles could burn in peace. Mankind have consequently given to King Alfred the credit of having invented lanterns.