Kitabı oku: «The Mirror of Literature, Amusement, and Instruction. Volume 20, No. 567, September 22, 1832», sayfa 5

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.

If we use an uniform and homogeneous disc of silver that has never been hammered or compressed, its surface will oxidate equally, provided all its parts are equally heated. In the process of converting this disc into a coin, the sunk parts have obviously been most compressed by the prominent parts of the die, and the elevated parts least compressed, the metal being in the latter left as it were in its natural state. The raised letters and figures on a coin have therefore less density than the other parts, and these parts oxiditate sooner or at a lower temperature. When the letters of the legend are worn off by friction, the parts immediately below them have also less density than the surrounding metal, and the site as it were of the letters therefore receive from heat a degree of oxidation, and a colour different from that of the surrounding surface. Hence we obtain an explanation of the revival of the invisible letters by oxidation.

THE GATHERER

Locomotive Engines have been established on the rail-roads near Philadelphia. The distance of 16-1/2 miles was performed by one of them going in an hour and thirteen minutes, returning (laden both ways) in an hour and eight minutes. The last mile was done in three minutes.

Blacking.—Shoes, among the classical ancients, were cleaned by a sponge; in the middle ages, by washing. Oil, soap, and grease were the substitutes for blacking, which was at first made with soot, but shone with a gloss.

Cool Tankard.—The custom of the Lord Mayor drinking a "cool tankard" with the governor of Newgate, on his Lordship's way to proclaim Bartholomew Fair, is better known to our readers than the precise contents of the said tankard. In olden times the "cool tankard" was, or nearly coincided with, the wine mixed with Burrage, (so the translators call the herb) of Plutarch, and the Herbosum Vinum of Du Cange. In all probability, the "cool tankard" of our times implies a well-appointed dejeuné à la fourchette.

Hanging—though as a punishment for thieves, ascribed to the reign of Henry I., occurs in a charter of Edgar. In hanging for public spectacle, an iron hoop with a strong chain was put round the body; but the chain was longer than the halter, so that when the latter was cut, the hoop slipped to the armpits, and left them suspended. When criminals escaped, an image of them was often hung up for several days; whence our hanging in effigy.

Elections.—Bribery, treating, canvassing, processions of voters at the heels of the candidate, dancing attendance after the great, forming factions, and other electioneering arts, occur in the classic ages. Among us, the candidates were not always present at the day of election, and under-sheriffs observe, that they mean to return according to the number of votes, provided the sheriff does not direct otherwise. Lord Chancellor Jefferies went to Arundel on purpose to overawe the electors. The seats were as much sought formerly as now. The members received wages as low as Elizabeth's reign.

Lucretius.—A summary of that part of the system of Lucretius, in which he describes man emerging from barbarity, acquiring the use of language, and the knowledge of various useful and polite arts, is comprised in a few lines of a satire of Horace, lib. i. sat. iii. v. 97. It has been ingeniously paraphrased by Dr. Beattie:

 
"When men out of the earth of old,
A dumb and beastly vermin crawled,
For acorns first and holes of shelter,
They tooth and nail and helter-skelter,
Fought fist to fist; then with a club,
Each learned his brother brute to drub;
Till more experienced grown, these cattle
Forged fit accoutrements for battle.
At last (Lucretius says, and Creech)
They set their wits to work on speech;
And that their thoughts might all have marks
To make them known, these learned clerks
Left off the trade of cracking crowns,
And manufactured verbs and nouns."
 

H.H.

Every trade has its technicalities. The other day we overheard a lamplighter complain of a cunning fellow workman who tried to get all the straightforward work himself, and to leave the turnings to others.

A Physician's Advice to his Student

 
"Dum aeger ait—Ah! ah!
Tu dicito—Du! du!"
 

A free translation is requested.

H.H.

Printed and published by J. LIMBIRD, 143, Strand, (near Somerset House,) London; sold by ERNEST FLEISCHER, 626, New Market, Leipsic; G.G. BENNIS, 55, Rue Neuve, St. Augustin, Paris; and by all Newsmen and Booksellers.

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