"Electricity has shown itself capable of infinite service, and its field is daily widening. It can bear thought on its rhythmic wings around the globe; carry the human voice hundreds of miles; deliver messages on board moving trains; flash into dazzling splendors along city thoroughfares; light the abyss of the ocean; operate countless automatic devices; warm us when cold; fan us when heated, and treasure up and repeat all sounds and harmonies. At the summons of inventive genius it has outwrought the dreams of magic."

ELECTRICITY.

While the nature and source of electricity still remains a mystery, and a constant challenge to the philosopher and engineer, many things about it have become positively known-thus-it is positively assured that electricity never manifests itself except when there is some mechanical disturbance in ordinary matter, and every exhibition of electricity in any of its multitudinous ways may always be traced back to a mass of matter.

Electricity, it is also conceded, is without weight, and, while electricity is without doubt, one and the same, it is for convenience sometimes classified according to its motion, as

1. Static Electricity, or electricity at rest. 2. Current Electricity, or electricity in motion. 3. Magnetism, or electricity in rotation.

4. Electricity in vibration (Radiation).

NOTE.-ELECTRICITY is a name derived from the Greek word ELECTRON-amber. It was discovered more than 2,000 years ago that amber when rubbed possessed the curious property of attracting light bodies. It was discovered afterwards that this property could be produced in jet by friction, and in A. D. 1600 or thereabouts, that glass, sealing-wax etc., were also affected by rubbing, producing electricity.

Other useful divisions are into

1. Positive and

And into

2. Negative Electricity.

1. Static, as the opposite of

2. Dynamic Electricity.

There are still other definitions or divisions which are in every-day use, such as "Frictional electricity," "Atmospheric electricity," "resinous electricity," "vitreous electricity." "photo-electricity," etc., etc.

While it is almost certain that, broadly, magnetism and electricity are one, in practice it is a necessity to use these divisions to explain the various conditions and uses to which they are put and in which they exist.

USEFUL DEFINITIONS RELATING TO ELECTRICITY.

Static Electricity. This is a term employed to define electricity produced by friction. It is properly employed in the sense of a static charge which shows itself by the attraction or repulsion between charged bodies. When static electricity is discharged, it causes more or less of a current, which shows itself by the passage of sparks or a brush discharge; by a peculiar prickling sensation; by a peculiar smell due to its chemical effects; by heating the air or other substances in its path; and sometimes in other ways.

NOTE.-Statics is that branch of mechanics which treats of the forces that keep bodies at rest or in equilibrium. Dyuamics treats of bodies in motion. Hence static-electricity is electricity at rest. The earth's great store of electricity is at rest or in equilibrium.

That branch of the science which treats of the laws of electricity resid ing on the surface of bodies, as a charge, is termed electro-statics.

Current electricity. This may be defined as the quantity of electricity which passes through a conductor in a given time-or, electricity in the act of being discharged, or electricity in motion.

An electric current manifests itself by heating the wire or conductor, by causing a magnetic field around the conductor and by causing chemical changes in a liquid through which it may pass.

Radiated electricity is electricity in vibration. Where the current oscillates or vibrates back and forth with extreme rapidity, it takes the form of waves which are similar to waves of light.

Positive electricity. This term expresses the condition of the point of an electrified body having the higher energy from which it flows to a lower level. The sign which denotes this phase of electric excitement is +; all electricity is either positive or,, negative.

Negative electricity. This is the reverse condition to the above and is expressed by the sign or symbol - These two

terms are used in the same sense as hot and cold.

In 1749, Benjamin Franklin observing lightning to possess almost all the properties observable in electric sparks, suggested that the electric action of points, which was discovered by him, might be tried on thunderclouds, and so draw from them a charge of electricity. He proposed, therefore, to fix a pointed iron rod to a high tower, but shortly after succeeded in another way. He sent up a kite during the passing of a storm, and found the wetted string to conduct electricity to the earth, and to yield abundance of sparks. These he drew from a key tied to the string, a silk ribbon being interposed between his hand and the key for safety. Leyden jars could be charged, and all other electrical effects produced, by the sparks furnished from the clouds. The proof of the identity was complete. The kite experiment was repeated by Romas, who drew from a metallic string sparks 9 feet long. In 1753, Richmann, of St. Petersburg, who was experimenting with a similar apparatus, was struck by a sudden discharge and killed

Atmospheric electricity is the free electricity of the air which is almost always present in the atmosphere. Its exact cause is unknown.

The phenomena of atmospheric electricity are of two kinds; there are the well-known manifestations of thunderstorms; and there are the phenomena of continual slight electrification in the air, best observed when the weather is fine; the Aurora constitute a third branch of the subject.

Dynamic electricity. This term is used to define current electricity to distinguish it from static electricity. This is the electricity produced by the Dynamo.

Frictional electricity is that produced by the friction of one substance against another.

Resinous electricity. This is a term formerly used, in place of negative electricity. The phrase originated in the well known fact that a certain (negative) kind of electricity was produced by rubbing rosin.

Vitreous electricity is a term, formerly used, to describe that kind of electricity (positive) produced by rubbing glass. Magneto-electricity is electricity in the form of currents flowing along wires; it is electricity derived from the motion of magnets-hence the name.

Voltaic electricity. This is electricity produced by the action of the voltaic cell or battery.

Electricity itself is the same thing, or phase of energy by whatever source it is produced and the foregoing definitions are only given as a matter of convenience to aid in its daily application to the service of man.