Even Priestley’s master-mind was sometimes sleeping thus, being subject (to quote his own words) “to humbling _failures of recollection_;” so that he lost all ideas of things and persons, and had so forgotten his own writings, that, on the perusal of a work, he sat himself to make experiments on points which _he had already illustrated_, but on which his mind was then a “_tabula rasa_.” Above all, the superlative memory of Sir Walter lay in a deep sleep, after a severe indisposition. It is recorded by Ballantyne, that when “the Bride of Lammermoor, in its printed form, was submitted to his perusal, he did not recognize, _as his own_, one single incident, character, or conversation it contained; yet the original tradition was perfect in his mind. When Mrs. Arkwright, too, sung some verses _of his_, one evening, at Lord Francis Egerton’s, the same oblivion was o’er his mind, and he whispered to Lockhart, ‘Capital words;—whose are they? Byron’s, I suppose; but _I don’t remember them_.’” My friend, Dr. Copland, informed me (in May, 1839) of a lady of fifteen, Miss D——, who, in consequence of extreme exhaustion from disorder, forgot all her accomplishments, and had to begin her education afresh. The Countess of Laval had, in her childhood, been taught the Armorican of Lower Brittany (which is a dialect of the Welch), but had, as she believed, forgotten it. On attaining the adult period, this lady had an acute fever, and, during her delirium, she ceased to speak in her native language, and chattered fluently in the bastard Welch. A foreign gentleman, as we were told by Mr. Abernethy, after an accident on the head, spoke French only, and quite forgot the English, which he had before this spoken very fluently. A Welch patient, in St. Thomas’s Hospital, some years since, having received an injury, began to speak in Welch, and ever after continued to do so, although before his accident he constantly conversed in English. On the contrary, we learn, from Dr. Pritchard, of a lady who, after a fit of apoplexy, forgot her _original_ language (the English), and spoke only in French, so that her nurses and servants conversed with her only by interpreters. There may be a _partial_ derangement of memory, _one set of impressions_ only being erased. A friend of Dr. Beattie, in consequence of a blow on the head, lost only his attainments in _Greek_; and Professor Scarpa (whose _corpus striatum_ was disorganised) lost only the memory of proper names. You may now comprehend how instantaneously material impressions derange and destroy memory, and its converse, the production of memory _by_ material impressions, will be far less mysterious to you.