Failure of memory takes place in a variety of ways. It is sometimes general, and extends to every subject; but it is frequently far more manifest on some subjects than on others. Salmuth mentions a case in which the affected person had forgotten to pronounce words, but could nevertheless write them. Mr. J. Hunter was suddenly attacked with a singular affection of this kind in December 1789, when on a visit at the house of a friend in town. "He did not know in what part of the house he was, not even the name of the street when told it, nor where his own house was: he had not a conception of any thing existing beyond the room he was in, and yet was perfectly conscious of the loss of memory. He was sensible of impressions of all kinds from the senses, and therefore looked out of the window, although rather dark, to see if he could be made sensible of the situation of the house. The loss of memory gradually went off, and in less than half an hour his memory was perfectly recovered." This might possibly be connected with a gouty habit to which Mr. Hunter was subject, though not at this time labouring under a paroxysm. The late Bishop of Landaff, Dr. Watson, gives a singular case of partial amnesia in his father, the result of an apoplectic attack. "I have heard him ask twenty times a-day," says Dr. Watson, "What is the name of the lad that is at college?" (my elder brother); and yet he was able to repeat, without a blunder, hundreds of lines out of classic authors. And hence, there is no reason for discrediting the story of a German statesman, a Mr. Von B. related in the seventh volume of the Psycological Magazine, who having called at a gentleman's house, the servants of which did not know him, was under the necessity of giving in his name; but unfortunately at that moment he had forgotten it, and excited no small laughter by turning round to a friend who accompanied him, and saying with great earnestness, "Pray tell me who I am, for I cannot recollect."
From severe suffering of the head in many fevers a great inroad is frequently made upon the memory, and it is long before the convalescent can rightly put together all the ideas of his past life. Such was one of the effects of the plague at Athens, as we learn from Thucydides; "and many, on recovery, still experienced such any extraordinary oblivion of all things that they knew neither themselves nor their friends." A few years ago a man with a brain-fever was taken into St. Thomas's Hospital, who as he grew better spoke to his attendants, but in a language they did not understand. A Welsh milk-woman going by accident into the ward, heard him, answered him and conversed with him. It was then found that the patient was by birth a Welshman, but had left his native land in his youth, forgotten his native dialect, and used English for the last thirty years. Yet, in consequence of this fever he had now forgotten the English tongue, and suddenly recovered the Welsh.
Boerhaave, however, gives a still more extraordinary instance of oblivion in the case of a Spanish tragic author who had composed many excellent pieces, but so completely lost his memory in consequence of an acute fever, that he forgot not only the languages he had formerly learnt, but even the alphabet; and was hence under the necessity of beginning to read again. His own poems and compositions were shown to him, but he could not he persuaded that they were his production. Afterwards, however, he began once more to compose verses; which had so striking a resemblance to his former writings that he at length became convinced of his being the author of them.—From the Doctor.
READING COINS IN THE DARK.
(From Sir David Brewster's Letters on Natural Magic.)
Among the numerous experiments with which science astonishes and sometimes even strikes terror into the ignorant, there is none more calculated to produce this effect than that of displaying to the eye in absolute darkness the legend or inscription upon a coin. To do this, take a silver coin, (I have always used an old one,) and after polishing the surface as much as possible, make the parts of it which are raised rough by the action of an acid, the parts not raised, or those which are to be rendered darkest, retaining their polish. If the coin thus prepared is placed upon a mass of red hot iron, and removed into a dark room, the inscription upon it will become less luminous than the rest, so that it may be distinctly read by the spectator. The mass of red hot iron should be concealed from the observer's eye, both for the purpose of rendering the eye fitter for observing the effect, and of removing all doubt that the inscription is really read in the dark, that is, without receiving any light, direct or reflected, from any other body. If, in place of polishing the depressed parts, and roughening its raised parts, we make the raised parts polished, and roughen the depressed parts, the inscription will now be less luminous than the depressed parts, and we shall still be able to read it, from its being as it were written in black letters on a white ground. The first time I made this experiment, without being aware of what would be the result, I used a French shilling of Louis XV. and I was not a little surprised to observe upon its surface in black letters the inscription BENEDICTUM SIT NOMEN DEI.
The most surprising form of this experiment is when we use a coin from which the inscription has been either wholly obliterated, or obliterated in such a degree as to be illegible. When such a coin is laid upon the red hot iron, the letters and figures become oxidated, and the film of oxide radiating more powerfully than the rest of the coin will be more luminous than the rest of the coin, and the illegible inscription may be now distinctly read to the great surprise of the observer, who had examined the blank surface of the coin previous to its being placed upon the hot iron.
In order to explain the cause of these remarkable effects, we must notice a method which has been long known, though never explained, of deciphering the inscriptions on worn out coins. This is done by merely placing the coin upon a hot iron: an oxidation takes place over the whole surface of the coin, the film of oxide changing its tint with the intensity or continuance of the heat. The parts, however, where the letters of the inscription had existed, oxidate at a different rate from the surrounding parts, so that these letters exhibit their shape, and become legible in consequence of the film of oxide which covers them having a different thickness, and therefore reflecting a different tint from that of the adjacent parts. The tints thus developed sometimes pass through many orders of brilliant colours, particularly pink and green, and settle in a bronze, and sometimes a black tint, resting upon the inscription alone. In some cases the tint left on the trace of the letters is so very faint that it can just be seen, and may be entirely removed by a slight rub of the finger.
When the experiment is often repeated with the same coin, and the oxidations successively removed after each experiment, the film of oxide continues to diminish, and at last ceases to make its appearance. It recovers the property however, in the course of time. When the coin is put upon the hot iron, and consequently when the oxidation is the greatest, a considerable smoke arises from the coin, and this diminishes like the film of oxide by frequent repetition. A coin which had ceased to emit this smoke, smoked slightly after having been exposed twelve hours to the air. I have found from numerous trials that it is always the raised parts of the coin, and in modern coins the elevated ledge round the inscription, that becomes first oxidated. In an English shilling of 1816 this ledge exhibited a brilliant yellow tint before it appeared on any other part of the coin.