The kind of experimenting you will do will, of course, depend altogether on the nature of the invention on which you are working.

But, as good fortune would have it if you are not mechanically inclined you are not apt to hit upon a mechanical invention. And if you know nothing of electricity, you are not likely to think out an improved electrical device.

But this much is certain if you are going to experiment the right way you must know something about the right way to experiment. No one should expect to work out to a successful conclusion a new machine or apply a new improvement to an old machine if he knows nothing of the first principles of mechanics or about mechanical movements, and by rights he ought to have some knowledge of machine design.

And the above statement is just as true of electrical inventions. A worker who does not know the difference between a binding post and an alternating current need not expect to progress very far with an invention of, say, an electric block signal system—unless he calls in an expert to help him; but what he should do is to study the principles of electricity and magnetism, learn the various currents that can be used and what apparatus and instruments are needed for utilizing these currents.

The same thing applies to inventions in chemistry in that to work intelligently you must know about the properties of substances, chemical change and acids, bases and salts. And with electro-chemistry both a knowledge of chemistry and electricity are needed.

It is easy to see that it would not be possible in the limited space I have here to say more than a word or two about the subjects of mechanics, electricity, chemistry and electro-chemistry when each requires a whole chapter to explain it even in a rough way and a whole book to explain it thoroughly. But there are a few things I can tell you about them that will put you on the right track and then I shall give you the names of some books that will be of great service to you when you are in need of them, and with your help we’ll make a real inventor of you.

How to Experiment with Machines.—Any one who possesses the slightest bent for mechanics can work out improvements on devices like egg-beaters and monkey-wrenches and feel their way as they go along.

But when it comes to designing and building real machines where numerous levers, gears, and springs are combined to make a working unit you should by all means read up on the subjects of work, energy and power, learn about the six mechanical powers—and the action of machines in general. The following definitions will give you an idea about all of them.

Work, Energy and Power.—A wheel will not turn of its own accord but if it is moved round by some force applied to it such as the hand, a coiled spring or a motor, work is done. In fact whenever a thing is made to change its position work is done.

The power to do work is caused by energy; energy is developed when some force is applied and can be stored up in bodies as when a ball is thrown. When the energy stops acting, or is used up, there can no longer be any work done. Energy can be transferred from one body to another, as from a clock-spring to a wheel, or from one wheel to another wheel; and energy can be transformed, as the chemical energy of a battery into the rotary energy of a motor or from steam into mechanical motion.

The unit of work is the foot-pound and this is the work done to raise one pound one foot high. The rate of doing work is the horse power and a horse power is equal to lifting 550 foot-pounds in a second, or 33,000 foot-pounds in a minute.

Energy may be either potential or kinetic; potential energy means energy that is stored up and with nothing to act on, and for this reason it is called energy of position. The electric charge of a Leyden jar is potential energy but the moment it is released it makes a spark and becomes kinetic energy or energy of motion. Potential energy can be changed into kinetic energy and kinetic energy back again into potential energy with amazing freedom. Energy has a definite relation to velocity which means that when the speed of a moving body is increased its power to do work is also increased.

Like matter, energy cannot be destroyed, and so all of it taken together is called a constant quantity. When the energy stored up in a spring, or a battery, has been used the energy is not destroyed, though it may be very hard to find out where it has gone, but you may know that it has vanished in heat and in other forms of energy.

Work Against Friction.—The chief resistance which machines have to overcome is caused by friction. Since there is no such thing as a perfectly smooth surface friction is always present in machines and much energy must be spent in overcoming it. The energy wasted by friction is not destroyed but is transformed into another kind of energy and that is heat. When a marble is rolled over the surface of a table there is less friction between the two than when the marble slides across the table. Hence with ball bearings there is less friction than with cone bearings. (See Appendix I.)

Forms of Energy.—There are nine forms of energy that you can make use of in your experiments and in your inventions, and these are:

Machines and the Principles of Machinery.—A machine is a contrivance of mechanical parts by which energy is transferred from one part to another. Beside the amount of energy required for doing useful work there must be an extra amount for overcoming the friction. Remember that no machine can either create energy or increase it, and, as you have seen, every machine wastes some energy in friction; this being true it must be clear then that it is impossible to make a machine which when once set in motion would continue to run forever, or at least until its parts were worn out. So don’t waste your energy in trying to invent a perpetual motion machine.

The Uses of Machines.—These are many and varied from a commercial point of view in that they are designed to do better, faster or cheaper work and sometimes all of these good qualities are found in a single machine.

From a mechanical point of view, though, a machine is used to

(1) Change one form of energy into another form, as steam into electricity.

(2) To make a slow moving, but powerful force produce a high speed or velocity, as in a sewing machine.

(3) To change a small, fast moving force into a powerful force, as in the action of a crowbar.

(4) To change the direction of a force so that the power can be applied where and when it is needed, and

(5) To make use of whatever force is at hand as the strength of animals, wind, water, steam, gas and electricity.

The Six Mechanical Powers.—As a matter of fact there are really only two of these, namely the lever and the inclined plane, the other four, that is the wheel and axle, the pulley, the wedge and the screw being simply modified forms of the first two.

The lever is a rigid bar resting on, and which can be moved about a fixed point, called the fulcrum. There are three classes of levers and these are:

(1) Where the fulcrum is placed between the load and the power which moves it, as shown at A, Fig. 37; a pair of shears, pliers, a balance and a crowbar are levers of the first-class, see B, Fig, 37.

(2) Where the load is applied between the power and the fulcrum, as shown at A, Fig. 38; a lemon squeezer and wire splicing clamps are examples of this class; see B, Fig. 38, and

(3) Where the power is applied between the load and the fulcrum as shown at A, Fig. 39; the foot treadle of a jig saw and sugar tongs are levers of this class. See B, Fig. 39. Then there is the bent lever, as shown in Fig. 40, where the power and load do not act parallel with each other, and the compound lever which takes the place of a single long lever as shown in Fig. 41, and which is used in large platform-scales.

The wheel and axle is really a form of lever and fulcrum. The axle provides a continuous fulcrum as shown in Fig. 42. Trains of wheel work, such as are used in clocks and other mechanical devices, are used to change a slow moving powerful force into a high speed, or velocity, or the other way about. Fig. 43 shows a train of wheel work.

The pulley is a wheel with a cord, rope or belt running round it as shown in Fig. 44. It is used to transmit power and also to change the direction of it. A pulley can be either fixed or movable. A compound pulley makes it possible to raise a heavy weight with a very small force, not by increasing the energy, but by transposing velocity into power.

The inclined plane is any hard smooth surface set at a slant to the force to be overcome. A barrel can be rolled up an inclined plane against the force of gravity, as shown in Fig. 45, while it could not be lifted straight up to the same height.

The wedge is simply an inclined plane on a small scale. It is useful where a great force must be exerted through a small distance, as in splitting a stick of wood, as shown in Fig. 46.

A screw is also a modified form of an inclined plane. By means of a screw great pressures can be exerted in a small space and here again a powerful force is had with a corresponding loss of velocity. It is shown in Fig. 47.

Compound Machines.—Any of the above six simple machines can be combined with any or all of the others and every machine that has ever been invented for any purpose is made up of a combination of these six mechanical powers.

Since the beginning of invention there has been made by combining these six mechanical powers in different ways, a large number of simple machines called mechanical movements; and there has not been a single new mechanical movement invented in many years.

Hence when you begin to work on your machine don’t waste time and energy trying to devise the mechanical movement you need, or what is still more foolish attempting to invent a new mechanical movement but look at the pictures in Fig. 48 which gives over 60 of the most useful mechanical movements. If you cannot find one among them that will do the work then look for it in Gardner D. Hiscock’s book of Mechanical Movements which gives them all.

Books.—And it would be a good idea for you to read one of the following books which you can, most likely, get at any library:

• Elementary Physics: Elroy M. Avery.
• Elements of Physics: Edwin J. Houston.
• Elements of Physics: George H. Hoadley.
• College Physics: A. L. Kimball.

The first-named books go deeply enough into the subject of physics for all ordinary purposes while the last named is very thorough and has a lot of math in it; and all of them treat of liquids, air, electricity and magnetism, sound, heat and light. In whatever field you are working a general knowledge of physics will give you the key to a new and a mighty interesting world.

With the first principles of mechanics well in mind and the mechanical movements I have given, you can go on with your experiments in a safe and sensible way.

How to Experiment with Electricity.—Electricity is very much like mechanics in that any one can put up an electric bell or screw in a plug-fuse but to experiment and build an apparatus in which electricity and magnetism are the powers used you must know how electricity is generated, how magnetism is produced, the different forms of electricity that are available and finally the kinds of apparatus best suited for the work that is required of them.

Forms of Electricity.—Though there is only one kind of electricity it can be divided into four classes, or forms, and these are:

(1) Electricity at rest, or static electricity, that is electricity stored up but not active as in a charged Leyden jar.

(2) Electricity in locomotion, or current electricity, in which electricity flows along wires, through solutions and other conductors when it is able to do work.

(3) Electricity in rotation, or magnetism in which electric whirls produce attraction and repulsion, and:

(4) Electricity in vibration, or radiation in which electric charges moving to and fro millions of times a second set up waves in the ether which our eyes can see and which we call light. Then there are waves much too short for the eye to see and these are called ultra-violet waves; there are waves too long for the eye to see and these are the infra-red waves which we can feel for they are heat waves, and finally there are very long waves set up in the ether by surging high frequency currents in wires and these are called electric or wireless waves.[2]

Static Electricity.—You can think of electricity as being a fluid, like water, for it has both quantity and pressure, and in many ways it acts like a fluid.

If you filled a tank, raised above the ground, with water, the latter would be at rest, but it would be under pressure too and the moment a hole was bored in any part of the tank below the level of the water it would squirt out; in other words the potential water would be changed into kinetic water or water in locomotion. If, now, you charge a Leyden jar, or a condenser, with electricity it will be at rest until you bring the alternate coatings of tin-foil closely together when a spark will result and a current will flow.

Static electricity is generated by friction and by induction, but the electricity so produced is very small in quantity and very high in pressure. A Leyden jar, or other condenser can be charged, though, with a low pressure current of electricity, as in a spark coil.

Current Electricity.—Whenever electricity flows in a wire, or other conductor, it acts like water flowing through a pipe and it is then called current electricity. The two most common ways to generate a current of electricity is by means of a chemical battery and by a dynamo electric machine.

A current of electricity may have a small current strength, as its quantity is called, and a high voltage, as its pressure is called, like the discharge of a Leyden jar, or it may have a large current strength and a low voltage, as a current generated by a battery.

A direct current, see Fig. 49, is a current which flows steadily in one direction and this can be generated by a battery or a dynamo. An interrupted current, see Fig. 50, is a current that is made and broken a number of times a minute and this is usually done by a vibrator, or interruptor as it is often called. A pulsating current, see Fig. 51, is one whose current strength is varied. One way to produce a pulsating current is to talk into a telephone transmitter which is connected with a battery.