What is electricity? When the question is asked the answer is sometimes given that "no one knows". This is far from being correct. Science knows a great deal about electricity. It is possible to explain its behavior under numerous and varied conditions, to design electrical equipment like motors, generators, and transformers with great precision and efficiency, and to even say of what electricity is composed. The student should be able to make diagrams illustrating the electric field and the lines of force in the neighborhoods of charged bodies, define capacity, name the essential elements of an electrical condenser, and its general purpose. These magnetic lines of force do not really exist; but they are useful for describing the different magnetic phenomena