Fortunately, however, the time for such ignorant and sordid exploitation of the treasures of the past was not to last for long; though it lasted far too long for the welfare of Egyptology. By 1822, Jean François Champollion, working on the material supplied by the Rosetta Stone and the Philæ Obelisk, and aided to some extent in his brilliant achievement by the previous labours of Akerblad and Young, gave to the world the key to the hieroglyphic inscriptions, so that the Egyptian monuments were no longer dumb. In 1828 came the second great general survey of the monuments under Rosellini and Champollion. It was now possible to read some, at least, of the inscriptions, and therefore to reach some approach to order in the classification of the monuments dealt with. The work suffered an irreparable loss by the early death of Champollion; but the results of the expedition, presented in the ten volumes of the _Monumenti storichi dell’ Egitto e della Nubia_ constituted a great enlargement of real knowledge as opposed to the conjectures which had previously held the field. For a time after the Rosellini Expedition, the field was left to individual workers, of whom the most notable were two Englishmen, F. E. Perring and Colonel Howard Vyse, whose careful measurements of the pyramids, especially the great group of Gizeh, laid the foundation for all subsequent study of these wonderful structures. The work of Perring and Vyse was done in 1837, and three years later came the important Prussian Expedition directed by Karl Richard Lepsius, whose name must always stand among the foremost on the roll of Egyptology. Lepsius began with the Pyramid field at Memphis, where his theorising on the method of erection of the pyramids, though perhaps the part of his work by which he is most generally known, was of less importance than his investigation of the Old Kingdom tombs of the nobles in the necropolis, with its revelation of the life and culture of the Egypt of 3000 B.C. Thence the mission worked southwards, visiting the Fayum, and carrying out investigations as to the whereabouts of Lake Moeris and the Labyrinth.