VENTRILOQUISM.

This is an art by no means very difficult of acquirement, if the young reader will take the pains. It is produced by a reflection of sound within the mouth, the voice being brought to the lowest possible place in the larynx. When the art is acquired by practice, the voice may be made to appear as if coming from any part of a room, from up a chimney, or from the depths of a cellar. The celebrated Dr. Wolcott, better known as Peter Pindar, used to amuse his friends in a remarkable manner with this art. He would represent his landlady as demanding payment of her rent, and hold a colloquy with her, which would at last rise to terms of reproach and fury, and end by a noise as if the landlady had been kicked down stairs. The marvellous powers of Matthews, Le Lagg, Alexander, and, lastly, Mr. Love, are familiar to most persons. To learn the art, the young pract.i.tioner must have the power of enunciating well, and that without motion of the lips,--of disguising the voice, so as to imitate other sounds,--and of adapting the degree to the apparent source of the sound. By practice this art is attainable by any person whose organs of speech are completely and fully developed.

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AERONAUTICS.

BALLOONS.

The art of sailing or navigating a body through the air is called aeronautics. In remote ages, Icarus is said to have risen so high in the air that the sun melted his wings, and he fell into the aegean sea, and was drowned; and there is reason to believe, from some figures that have recently been discovered on Egyptian and a.s.syrian monuments, that the ancients possessed means of rising in the air with which we are not now acquainted.

The air-balloon, as now constructed, is a bag of silk of large dimensions, usually cut in gores, and is, when expanded by gas, of a pear-shape. It ascends in the atmosphere because its whole bulk is much lighter than the air would be in the s.p.a.ce it occupies. It is, in fact, a vessel filled with a fluid which will float on another fluid lighter than itself.

HOW TO MAKE AN AIR-BALLOON.

The best shape for an air-balloon, or rather a gas-balloon, is that of a pegtop. And in preparing the gores proceed as follows: Get some close texture silk, and cut it into a form resembling a narrow pear with a very thin stalk. Fourteen of these pieces will be found to be the best number; and, of course, the breadths of each piece must be measured accordingly. When sewing them together, it will be of advantage to coat the parts that overlap with a layer of varnish, as this will save much trouble afterwards, and hold the silk firmer in its place during the st.i.tching. The threads must be placed very regularly, or the balloon will be drawn out of shape, and it will be found useful if the gores are covered with an interior coating of varnish before they are finally sewn together. Take care not to have the varnish too thick. To the upper part of the balloon there should be a valve opening inwards, to which a string should be fastened, pa.s.sing through a hole made in a small piece of wood fixed in the lower part of the balloon, so that the aeronaut may open the valve when he wishes to descend; and this should be imitated on a small scale, so that the young aeronaut may be perfectly familiar with the construction of a balloon. The gores are to be covered with a varnish of India-rubber dissolved in a mixture of turpentine and naphtha. Over the whole of the upper part should be a net-work, which should come down to the middle with various cords, proceeding from it to the circ.u.mference of a circle about two feet below the balloon. The circle may be made of wood, or of several pieces of slender cane bound together. The meshes should be small at top, against which part of the balloon the inflammable air exerts the greatest force, and increase in size as they recede from the top.

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The car is made of wicker-work; it is usually covered with leather, and is well varnished or painted. It is suspended by ropes proceeding from the net which goes over the balloon. Balloons of this kind cannot be made smaller than six feet in diameter, of oiled silk, as the weight of the material is too great for the air to buoy it up. They may be made smaller of thin slips of bladder, or other membrane glued together, or of thin gutta-percha cloth, which is now extensively used for this purpose; with this they may be made a foot in diameter, and will rise beautifully.

HOW TO FILL A BALLOON.

Procure a large stone bottle which will hold a gallon of water, into this put a pound of iron filings, or granulated zinc, with two quarts of water, and add to this by degrees one pint of sulphuric acid. Then take a tube, either of gla.s.s or metal, and introduce one end of it through a cork, which place in the bottle, then put the other end into the neck of the balloon, and the gas will rise into the body of it. When quite full withdraw the tube, and tie the neck of the balloon with strong cord very tightly. If freed it will now rise in the air.

TO MAKE FIRE-BALLOONS.

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Cut the gores, according to the forms already given, from well-woven tissue paper, paste the gores nicely together, and look well over the surface of the paper for any small hole or slit, over which paste a piece of paper, and let it dry. Pa.s.s a wire round the neck of the balloon, and have two cross pieces at its diameter a little bent, so that a piece of soft cotton dipped in spirits of wine may be laid on them. When all is prepared let some one hold the balloon from its top by means of a stick, while you dip the cotton in spirits of wine till it is thoroughly saturated, place it under the balloon and set fire to it, but be very careful you do not set fire to the balloon. When the air is sufficiently heated within, the balloon will indicate a desire to rise, and when it pulls very hard, let it go, and it will ascend to a great height in the air, and at night present a very beautiful appearance.

PARACHUTES.

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These are easily made by cutting a piece of paper in a circular form, and placing threads round the edges, which may be made to converge to a point, at which a cork may be placed as a balance. They ascend by the air getting under them, and are frequently blown to a great distance.

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CHEMISTRY.

In the eleventh century, and during the reign of King Henry the First, surnamed Beauclerk, or the fine scholar, there appeared for the first time in certain books, professing to teach the art making of gold, the words chemistry, chemist, derived from the Greek ??e?a. Seven hundred years and more have pa.s.sed away, and that which was only the pursuit of a shadow called alchemy, has resulted in the acquisition of a great and n.o.ble science, now and again called chemistry. When we go to the French Exposition, we shall doubtless pa.s.s by much that is worthy of notice, and bring away with us only a general impression of the wonders it contains. So it is with the great edifice Chemistry; we may, in these brief pages, peep in at the open door, but should we desire to go beyond the threshold, there are numerous guides, such as Roscoe, Wilson, and Fownes, who will conduct us through the mazes of the interior, and explain in elementary language the beautiful processes which have become so useful to mankind.

Chemistry is one of the most comprehensive of all the sciences, and at the same time one which comes home to us in the most ordinary of our daily avocations. Most of the arts of life are indebted to it for their very existence, and nearly all have been, from time to time, improved by the application of its principles.

Chemistry is, in fact, the science which treats of the composition of all material bodies, and of the means of forming them into new combinations, and reducing them to their _ultimate elements_, as they are termed, that is, bodies which we are unable to split up, as it were, or separate into other bodies. To take a common substance as an ill.u.s.tration; water, by a great number of processes, can be separated into two other substances, called oxygen and hydrogen, in the proportion by weight of 8 parts of the first to 1 of the second; but no power that we at present possess can separate the oxygen and hydrogen into any other bodies; they are therefore called ultimate elements, or undecomposable bodies.

Again, sulphate of magnesia (common Epsom salts) can be very easily separated into two other substances,--sulphuric acid and magnesia; and in this instance, both these substances can again be sub-divided--the acid into sulphur and oxygen, and the magnesia into a metallic body called magnesium and oxygen; but sulphur, oxygen, and magnesium are incapable of further division, and are therefore called _ultimate elements_.

These ultimate elements amount to 64 in number, according to the present state of our knowledge, and may be arranged in various ways; the simplest plan, perhaps, is dividing them into Non-metallic and Metallic elements.

The Non-metallic elements are:--1. Oxygen. 2. Hydrogen. 3. Nitrogen. 4.

Chlorine. 5. Iodine. 6. Bromine. 7. Fluorine. 8. Carbon. 9. Sulphur. 10.

Selenium. 11. Tellurium. 12. Silicon. 13. Boron. 14. Phosphorus. The last-named element is the connecting link with the metals through a.r.s.enic, which phosphorus closely resembles in its chemical properties.

The Metallic elements may be sub-divided into the metals of the alkalies, the metals of the alkaline earths, the metals of the earths, and the other metals sometimes called metals proper.

1st. The metallic bases of the alkalies:--pota.s.sium, sodium, lithium, ammonium, caesium, rubidium.

2d. The metallic bases of the alkaline earths:--calcium, strontium, barium.

3d. The metallic bases of the earths:--aluminium, glucinum, zirconium, thorium, yttrium, erbium, cerium, lanthanum, didymium.

4th. The metals proper, the most important of which are:--platinum, gold, silver, mercury, copper, iron, tin, lead, nickel, zinc, bis.m.u.th, antimony, manganese, cobalt, a.r.s.enic.

Now, from these elementary bodies, united together in various proportions, is formed the infinite variety of substances around us, whether animal, vegetable, or mineral; in fact, a few only are generally employed;--in the case of animals and vegetables, oxygen, hydrogen, carbon, nitrogen, with occasionally some sulphur, calcium, phosphorus, and silicon, suffice for building up the beautiful forms of animated nature; while the fabric of our globe itself consists for the most part of the earths; silex, _i. e._ flint or crystal; lime, in the shape of chalk, marble, or limestone, such as our flagstones are composed of; slate and granite, which are compounds of aluminium, silica, and small quant.i.ties of oxide of iron, and sometimes a little potash, &c.; and through their ma.s.ses are projected irregular streams--veins as they are termed--of the metals, either in a pure state, as is the case sometimes with gold, silver, platinum, mercury, and perhaps one or two others; or combined with one of the non-metallic elements, or with one another.

Late calculations have determined the composition of the earth's solid crust in 100 parts by weight to be

Oxygen 440 to 487 Silicon 228 362 Aluminium 99 61 Iron 99 24 Calcium 66 09 Magnesium 27 01 Sodium 24 25 Pota.s.sium 17 31 ----- ----- 100 100 ===== =====

All these combinations are effected by certain powers, termed _forces_; those which cause the union of the elements are called the forces of attraction; those causing their separation, the forces of repulsion.

The force of attraction when exerted between ma.s.ses of matter, is termed gravitation; when it unites particles of matter of a similar kind and produces ma.s.ses, it is called the attraction of cohesion; when the particles united are of a dissimilar character, it is then termed chemical or elective affinity. For example, the crystals of Epsom salts are formed from minute particles of the salt, united into a larger or smaller ma.s.s by the attraction of cohesion, while the _elements_ of which each particle consists, namely, the sulphur, oxygen, and magnesium, are united by the attraction of chemical affinity.

Cohesion thus unites particles of a similar kind; chemical affinity, of a dissimilar nature. It is to cohesion that the existence of _ma.s.ses_ of matter is owing, and its power increases as the squares of the distances diminish, in an inverse ratio to the squares of the distances of the particles on which it acts.

The power exerted by cohesion may be exhibited in various ways. This is one: Procure two discs of gla.s.s about three inches in diameter, their surfaces being ground extremely smooth; fix each into a square piece of wood, taking care that they are placed accurately in the centre; then put them together, by sliding their edges very carefully over each other, so as to avoid any air getting between them, and you will find a great force necessary to separate them. A hook should be fixed into the centre of each piece of wood, so that they may be suspended, and a weight hung to the lower one. It is almost impossible for any one to separate them by merely pulling them with both hands; a weight of many pounds is required for that purpose. In like manner two freshly-cut surfaces of caoutchouc will, on being squeezed together, cohere so perfectly, that it is difficult to tear them asunder, and it is in this way that tubes of caoutchouc may be rapidly prepared for experiments, where little or no pressure is exerted.

Chemical affinity is sometimes called _elective_, or the effect of _choice_, as if one substance exerted a kind of _preference_ for another, and chose to be united to it rather than to that with which it was previously combined; thus, if you pour some vinegar, which is a weak acetic acid, upon some pearlash (a combination of potash and carbonic acid), or some carbonate of soda (a combination of the same acid with soda), a violent effervescence will take place, occasioned by the escape of the carbonic acid, displaced in consequence of the potash or soda preferring the acetic acid, and forming a compound called an acetate.

Then, if some sulphuric acid be poured on this new compound, the acetic acid will in its turn be displaced by the greater attachment of either of the bases, as they are termed, for the sulphuric acid. Again, if into a solution of blue vitriol (a combination of sulphuric acid with oxide of copper) the bright blade of a knife be introduced, the knife will speedily be covered with a coat of copper, deposited in consequence of the acid _preferring_ the iron, of which the knife is made, a quant.i.ty of it being dissolved in exact proportion to the quant.i.ty of copper deposited.

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It is on the same principle that a very beautiful preparation, called a silver-tree, or a lead-tree, may be formed thus:--Fill a wide bottle, capable of holding from half a pint to a pint, with a tolerably strong solution of nitrate of silver (lunar caustic), or acetate of lead, in pure distilled water; then attach a small piece of zinc by a string to the cork or stopper of the bottle, so that the zinc shall hang about the middle of the bottle, and set it by where it may be quite undisturbed; in a short time, brilliant plates of silver or lead, as the case may be, will be seen to collect around the piece of zinc, a.s.suming more or less of the crystalline form. This at first is a case of elective affinity; the acid with which the silver or lead was united _prefers_ the zinc to either of those metals and in consequence discards them in order to attach the zinc to itself, subsequently a voltaic current is set up between the two metals, and the process will continue until almost the whole of the zinc is taken up, or nearly the whole of the silver or lead deposited.

Again, many animal and vegetable substances consist for the most part of carbon or charcoal, united with oxygen and hydrogen in the proportion which forms water. Now oil of vitriol (strong sulphuric acid) has so powerful an affinity, or so great a _thirst_ for water, that it will abstract it from almost any body in which it exists; if you then pour some of this acid on a lump of sugar, or place a chip of wood in it, the sugar or wood will speedily become quite black, or be _charred_, as it is called, in consequence of the oxygen and hydrogen being removed by the sulphuric acid, and only the carbon, or charcoal, left.