A Catechism of Familiar Things. AnonymousЧитать онлайн книгу.
of rain frozen in their passage through cold air. Hail assumes various figures according to the degrees of heat or cold through which it passes, being sometimes round, flat, &c.
What is the Atmosphere?
The mass of aëriform fluid which encompasses the earth on all sides: it extends about fifty miles above its surface. Air is the elastic fluid of which it is composed.
Elastic, having the power of springing back, or recovering its former figure after the removal of any external pressure which has altered that figure. When the force which compresses the air is removed, it expands and resumes its former state.
What are the uses of air?
It is necessary to the well-being of man, since without it neither he nor any animal or vegetable could exist. If it were not for atmospheric air, we should be unable to converse with each other; we should know nothing of sound or smell; or of the pleasures which arise from the variegated prospects which surround us: it is to the presence of air and carbonic acid that water owes its agreeable taste. Boiling deprives it of the greater part of these, and renders it insipid.
Variegated, diversified, changed; adorned with different colors.
Insipid, tasteless.
What is Wind?
Air in motion with any degree of velocity.
What is Lightning?
The effect of electricity in the clouds. A flash of lightning is simply a stream of the electric fluid passing from the clouds to the earth, from the earth to the clouds, or from one cloud to another. Lightning usually strikes the highest and most pointed objects, as high hills, trees, spires, masts of ships, &c.
What is Thunder?
The report which accompanies the electrical union of the clouds: or the echoes of the report between them and the earth. Thunder is caused by a sudden discharge of electrical matter collected in the air, by which vibrations are produced, which give rise to the sound.
What is Electricity?
One of those agents passing through the earth and all substances, without giving any outward signs of its presence, when at rest; yet when active, often producing violent and destructive effects. It is supposed to be a highly elastic fluid, capable of moving through matter. Clouds owe their form and existence, probably, to it; and it passes through all substances, but more easily through metals, water, the human body, &c., which are called conductors, than through air, glass, and silk, which are called non-conductors. When bodies are not surrounded with non-conductors, the electricity escapes quickly into the earth.
To what part of bodies is Electricity confined?
To their surfaces, as the outside may be electric, and the inside in a state of neutrality. The heat produced by an electric shock is very powerful, but is only accompanied by light when the fluid is obstructed in its passage. The production and condensation of vapor is a great source of the atmospheric electricity.
Condensation, the act of making any body dense or compact; that is, of bringing its parts into closer union.
In what other sense is the term Electricity employed?
This term is also employed to designate that important branch of knowledge which relates to the properties shown by certain bodies when rubbed against, or otherwise brought in contact with, each other, to attract substances, and emit sparks of fire.
Designate, to point out by some particular token.
Emit, to send forth, to throw out.
Whence is the word derived?
From electron, the Greek word for amber, a yellow transparent substance, remarkable for its electrical power when rubbed: amber is of a resinous nature, and is collected from the sea-shore, or dug from the earth, in many parts of the world. It is employed in the manufacture of beads and other toys, on account of its transparency; is of some use in medicine, and in the making of varnishes.
Transparent, clear, capable of being seen through.
Resinous, containing resin, a gummy vegetable juice.
Name a few substances possessing this remarkable property.
Silks of all kinds; the hair and fur of animals, paper, sulphur, and some other minerals; most of the precious stones; the paste of which false gems are made; and many other substances used by us in the common affairs of life, are susceptible of electrical excitement; among domestic animals the cat furnishes a remarkable instance. When dry and warm, the back of almost any full-grown cat (the darker its color the better) can be excited by rubbing it with the hand in the direction of the hair, a process which is accompanied with a slight snapping noise, and in the dark by flashes of pale blue light. When a piece of glass is rubbed with silk, or a stick of red sealing-wax with woollen cloth, each substance acquires the property of attracting and repelling feathers, straws, threads of cotton, and other light substances; the substances just mentioned as highly electric are, however, merely specimens. All objects, without exception, most probably are capable of being electrically excited; but some require more complicated contrivances to produce it than others.
Electric, having the properties of electricity.
Susceptible, disposed to admit easily.
Repelling, the act of driving back.
Complicated, formed by the union of several parts in one.
Is there not a machine by which we are enabled to obtain large supplies of electric power at pleasure?
Yes; the electrical machine. It is made of different forms and sizes: for common purposes those of the simplest form are the best. A common form of the machine consists of a circular plate of glass, which can be turned about a horizontal axis by means of a suitable handle. This plate turns between two supports, and near its upper and lower edges are two pairs of cushions, usually made of leather, stuffed with horse-hair and coated with a mixture of zinc, tin, and mercury, called an amalgam. These cushions are the rubbers for producing friction, and are connected with the earth by means of a metal chain or rod. Two large hollow cylinders of brass with globular ends, each supported by two glass pillars, constitute the reservoir for receiving the electricity. They are called the prime conductors, and are supplied with U-shaped rods of metal, furnished with points along their sides, called combs, for the purpose of receiving the electricity from the glass plate, the arms of the U being held upon either side. The other ends of the conductors are connected by a rod from the middle of which projects another rod terminating in a knob, for delivering the spark.
On turning the plate, a faint snapping sound is heard, and when the room is darkened, a spark is seen to be thrown out from the knob projecting from the prime conductors.
Many curious and interesting experiments may be performed by means of the machine, illustrating the general properties of electricity. For instance: a person standing on an insulated bench, that is, a bench with glass legs, or having the legs resting on glass, and having one hand on the conductor, can send sparks, with the other hand, to everything and everybody about. This illustrates communication of electricity by contact. A wooden head, covered with long hairs, when placed on the conductor, illustrates electrical repulsion, by the hairs standing on end.
If the hand is held to the knob, sparks will pass from it in rapid succession, causing in the hand a sensation of pain. This is called an electric shock, and is caused by the electric fluid occasioning a sudden motion by the contraction of the muscles through which it passes. The force of the shock is in proportion to the power of the machine.
What are the Muscles?
Bundles