Soon after we reached the Bel Alp, on the occasion just referred to, the front of the torrent appeared at the opposite side of the valley carrying everything movable before it, and immediately afterwards swept through the hollow that we had traversed a little earlier in the day. When at the end of the glacier I was struck by the force and volume of the Massa, and the grandeur of its vault, but I could not then account for the huge blocks of ice which it incessantly carried down. Doubtless the eruption above had been partial before the grand rush set in. The Rhone was considerably swollen, crops were damaged or ruined, and the driver of the diligence was sorely perplexed to find himself in three feet of water, without any apparent reason, on the public highway. Two or three days subsequently I learned at the Æggischhorn that an engineer had been sent up to report on the possibility of opening a channel, so as to prevent any future accumulation of water in the Märgelin See. If this be done a useful end will be gained, by the abolition, however, of one of the most beautiful objects in Switzerland. J. Tyndall. _September, 1872._ PREFACE TO THE FOURTH EDITION. At a meeting of the Managers of the Royal Institution held on December 12, 1825, "the Committee appointed to consider what lectures should be delivered in the Institution in the next session," reported "that they had consulted Mr. Faraday on the subject of engaging him to take a part in the juvenile lectures proposed to be given during the Christmas and Easter recesses, and they found his avocations were such that it would be exceedingly inconvenient for him to engage in such lectures." At a general monthly meeting of the members of the Royal Institution, held on December 4, 1826, the Managers reported "that they had engaged Mr. Wallis to deliver a course of lectures on Astronomy, adapted to a juvenile auditory, during the Christmas vacation." In a report dated April 16, 1827, the Board of Visitors express "their satisfaction at finding that the plan of juvenile courses of lectures had been resorted to. They feel sure that the influence of the Institution cannot be extended too far, and that the system of instructing the younger portion of the community is one of the most effective means which the Institution possesses for the diffusion of science." Faraday's holding aloof was but temporary, for at Christmas 1827 we find him giving a "Course of Six Elementary Lectures on Chemistry, adapted to a Juvenile Auditory."[A] [A] There is no record to show that Mr. Wallis gave the Astronomical lectures referred to, and our librarian believes that the _Christmas_ courses were opened by Faraday. The Easter lectures were soon abandoned; but from the date here referred to to the present time the Christmas lectures have been a marked feature of the Royal Institution.