Of such paramount importance is a retentive memory considered, that the improvement of the faculty by constant exercise is the first object in education, and artificial aids for its advantage have been invented. So essential did the ancients regard its vigor for any work of imagination, that "they described the muses as the daughters of memory." Though a retentive memory may be found where there is no genius, yet genius, though sometimes, is rarely deficient in this most valuable gift. There are so many examples of its great power in men of transcendent abilities, that every one can name a host. Some of these examples would appear incredible, had they not been given on unquestionable authority. Themistocles, we are told, could call by their names every citizen of Athens, though they amounted to twenty thousand. Cyrus knew the name of every soldier in his army. Hortentius, after attending a public sale for the day, gave an account in the evening of every article which had been sold, the prices, and the names of the purchasers. On comparing it with that taken at the sale by the notary, it was found to agree as exactly with it as if it had been a copy. "Memory Corner Thompson," so called from the extraordinary power which he possessed, drew, in the space of twenty-two hours, a correct plan of the parish of St. James's, Westminster, with parts of the parishes of St. Marylebone, St. Ann, and St. Martin. In this were included all the squares, streets, courts, lanes, alleys, markets, and all other entries; every church, chapel, and public building; all stables and yards; all the public-houses and corners of streets, with every pump, post, tree, house, bow-window; all the minutiæ about St. James's Palace; this he did in the presence of two gentlemen, without any plan or notes of reference, but solely from his memory. He afterward completed the plans of other parishes. A house being named in any public street, he could tell the trade of the shop, either on the right or left hand. He could from memory furnish an inventory of every thing contained in any house where he was intimate, from the garret to the cellar.