As a means of developing mechanical power in small units, the electric motor has made possible its application in many household uses that were formerly performed entirely by manual labor. As a domestic utility electrical power is generated at a cost that is the least expensive of all its applications. As a means of lighting and heating electricity has had to compete with established methods and has won place because of the advantages it possesses over that of cost. In the development of domestic power it has practically no opponent. There is no other form of power that can be so successfully utilized in delivering mechanical work for the purposes required. A kilowatt of electric energy, for which 10 cents is a common price, will furnish a surprising amount of manual labor. Theoretically, 746 watts is equal to 1 horsepower. The commercial kilowatt is rated at an hour of time, and is, therefore, equal theoretically to 1 1/3 horsepower for one hour. While motors cannot be expected to transform all of this energy into actual work without loss, even at the low rate of efficiency attained by the small electric motor, they furnish power at a relatively small cost.

The first applications of electric power were those for sewing machines, fans, washing machines, etc. Its use has made possible the vacuum cleaner, automatic pumping, refrigeration, ventilation, and many other minor uses as the turning of icecream freezers, churning and rocking the cradle.

Electric motors are made in many sizes for power generation and in forms to suit any application. They are made to develop 1/30 horsepower and in other fractional sizes for both direct and alternating current.

In applying mechanical power to any particular purpose special appliances must be made to adopt electric motors to the required work. This is accomplished in all household requirements. The motors are made to run at a high rate of speed and must be reduced in motion by pulleys or gears to suit their condition of operation. As in the case of electric lamps they must be suited to the voltage and type of current of the circuit on which they are to be used.

Commercial electric circuits furnish electricity in two types, direct current, ordinarily termed D.C., and A.C. or alternating current. The terms direct and alternating current apply to the direction of the electric impulses which constitute the transmitted energy. In the electric dynamo, the generation of the current is due to impulses that are induced in the wires of the dynamo armature as they pass.through a magnetic field of great intensity. These electric impulses are directed by the manner in which the wires cut across the lines of force which make up the magnetic field. In the case of the direct current the impulses are always in the same direction through the circuit, while in the other they are induced alternately to and fro and so produce alternating current.

The term electric current is used only for convenience of expressing a directed form of energy. Since nothing really passes through the wires but a wave of energy, the effect is the same whether the electric impulses are in the same or in opposite directions. An incandescent lamp will work equally well on an A.C. or a D.C. circuit of the proper voltage; but in the case of motors the form of corstruction must be suited to the kind of current. Both A.C. and D.C. commercial circuits are in common use, the units of measurement are the same for each but in ordering a motor it is necessary to state the type of current and the voltage, in order that the dealer may supply the required machine. In the case of an alternating motor it is further necessary to state the number of cycles of changes of direction made per second in the A.C. circuit. All of this information maybe obtained by inquiring of a local electrician or of the power station from which the current is obtained.

There is still another item of information necessary to be supplied with an order for a motor, other than those of fractional horsepower. With motors of a horsepower or more it is necessary to state the number of phases included in the circuit. This information to be complete must state whether the motor is to operate on a single-phase, two-phase, or three-phase circuit. These terms apply to a condition made possible in A.C. generation that permits one, two, or three complete impulses to be developed in a circuit at the same time. These phases are transmitted by three wires, any two of which will form a circuit and give a supply of energy at the same voltage. Either one phase or all may be used at the same time and for this reason the phase of an A. C. motor should be given in an order. To make the information complete there should be included the number of cycles or complete electric impulses per second produced in the circuit. Suppose that a 1-horsepower motor is required to work on an A.C. circuit of 110 volts. Inquiry of the electric company reveals that the circuit is three-phase at 60 cycles per second. The dealer on receiving this information will be able to send a motor to suit your conditions. Most A.C. motors of 1 horsepower or less are of the single-phase variety. In the case of D.C. motors it is necessary only to state the voltage of the circuit to make the required information complete.