A Catechism of Familiar Things Part 2

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-sh.o.r.e, 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 gla.s.s 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 gla.s.s, 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 cus.h.i.+ons, usually made of leather, stuffed with horse-hair and coated with a mixture of zinc, tin, and mercury, called an _amalgam_. These cus.h.i.+ons 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 bra.s.s with globular ends, each supported by two gla.s.s pillars, const.i.tute 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 gla.s.s 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 k.n.o.b, 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 k.n.o.b projecting from the _prime conductors_.

Many curious and interesting experiments may be performed by means of the machine, ill.u.s.trating the general properties of electricity. For instance: a person standing on an insulated bench, that is, a bench with gla.s.s legs, or having the legs resting on gla.s.s, and having one hand on the conductor, can send sparks, with the other hand, to everything and everybody about. This ill.u.s.trates communication of electricity by contact. A wooden head, covered with long hairs, when placed on the conductor, ill.u.s.trates electrical repulsion, by the hairs standing on end.

If the hand is held to the k.n.o.b, sparks will pa.s.s 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 pa.s.ses. The force of the shock is in proportion to the power of the machine.

What are the Muscles?

Bundles of thin fleshy fibres, or threads, fastened to the bones of animals, the contraction and expansion of which move the bones or perform the organic functions of life.

_Organic_, relating to organs or natural instruments by which some process is carried on.

_Functions_, employments or offices of any part of the body.

_Contraction_, drawing in or shortening.

_Expansion_, extending or spreading out.

What is Twilight?

The light from the first dawning of day to the rising of the sun; and again between its setting and the last remains of day. Without twilight, the sun's light would appear at its rising, and disappear at its setting, instantaneously; and we should experience a sudden transition from the brightest suns.h.i.+ne to the profoundest obscurity.

The duration of twilight is different in different climates; and in the same places it varies at different periods of the year.

_Instantaneously_, done in an instant, in a moment's time.

_Obscurity_, darkness, want of light.

How is it produced?

By the sun's refraction--that is, the variation of the rays of light from their direct course, occasioned by the difference of density in the atmosphere.

_Variation_, change.

_Density_, closeness of parts, compactness.

What is the poetical name for the morning Twilight?

Aurora, the G.o.ddess of the morning, and harbinger of the rising sun: whom poets and artists represent as drawn by white horses in a rose-colored chariot, unfolding with her rosy fingers the portals of the East, pouring reviving dew upon the earth, and re-animating plants and flowers.

_Harbinger_, a forerunner.

_Portals_, gates, doors of entrance.

_Reanimating_, invigorating with new life.

What remarkable phenomenon is afforded to the inhabitants of the polar regions?

The Aurora Borealis, or Northern Lights, a luminous appearance in the northern parts of the heavens, seen mostly during winter, or in frosty weather, and clear evenings; it a.s.sumes a variety of forms and hues, especially in the polar regions, where it appears in its perfection, and proves a great solace to the inhabitants amidst the gloom of their long winter's night, which lasts from one to six months, while the summer's day which succeeds it lasts in like manner for the same period of time.

Of what nature is the Aurora Borealis?

It is decidedly an electrical phenomenon which takes place in the higher regions of the atmosphere. It is somehow connected with the magnetic poles of the earth; and generally appears in form of a luminous arch, from east to west, but never from north to south.

_Phenomenon_, an extraordinary appearance. The word is from a Greek one, signifying, to show or appear.

_Magnetic_, belonging to the magnet, or loadstone.

_Luminous_, bright, s.h.i.+ning.

In what country is it seen constantly from October to Christmas?

In Siberia, where it is remarkably bright. On the western coast of Hudson's Bay, the sun no sooner disappears, than the Aurora Borealis diffuses a thousand different lights and colors with such dazzling beauty, that even the full moon cannot eclipse it.