The pretended secret of the Alchemists was the transmutation of the baser metals into gold, which they occasionally exhibited to keep the dupes who supplied them with money in good spirits. This they performed in various ways. Sometimes they made use of crucibles with a false bottom. At the real bottom, they put a quantity of gold or silver. This was covered by a portion of powdered crucible mixed with gum or wax, and hardened. The material being put into a crucible and the heat applied, the false bottom disappeared; and at the end of the process, the gold or silver was found at the bottom of the crucible. Sometimes, they made a hole in a piece of charcoal, filled it with oxide of gold or silver, and stopped up the hole with a little wax; or they soaked the charcoal in solutions of these metals; or they stirred the mixture in the crucible with hollow rods, containing oxide of gold or silver within, and the end closed with wax. By these means, the gold or silver wanted was introduced during the operation, and considered as a product. Sometimes the cunning wights used solutions of silver in nitric acid, or of gold in aqua-regia, or an amalgam of gold or silver, which being adroitly introduced, furnished the requisite quantity of metal. A common exhibition was to dip nails into a liquid, and take them out, half converted into gold. The nails were one-half gold and the other half iron, neatly soldered together, and the gold was covered with something to conceal the colour, which the liquid was capable of removing. ------------------ INVENTION OF THE HAND GEAR. It has been said that we are indebted for the important invention in the steam-engine, termed hand gear, by which its valves or cocks are worked by the machine itself, to an idle boy named Humphrey Potter, who, being employed to stop and open a valve, saw that he could save himself the trouble of attending and watching it, by fixing a plug upon a part of the machine which came to the place at the proper times, in consequence of the general movement. If this anecdote be true, what does it prove? That Humphrey Potter might be very idle, but that he was, at the same time, very ingenious. It was a contrivance, not the result of accident, but of acute observation and successful experiment.--_Dr. Paris._ ------------------ POKER ACROSS THE FIRE. Boswell and Johnson held a conversation upon this experiment as follows:--_Boswell._ "Why, sir, do people play this trick, which I observe now when I look at your grate, putting the shovel against it to make the fire burn?"--_Johnson._ "They play the trick, but it does not make the fire burn. _There_ is a better (setting the poker perpendicularly up at right angles with the grate.) In days of superstition, they thought, as it made a cross with the bars, it would drive away the witch."