Ans. The ultimate nature of neither is known. There are, however, some differences. To sustain a current of electricity requires energy. To sustain magnetism requires no energy. A current of electricity is always accompanied by a magnetic field of peculiar form. Magnetism alone cannot produce electricity. Electricity can do work; but magnetism cannot in the same sense--and alike with electricity, neither can it exist without contact with matter. =Ques. How is energy transmitted from one part of a material substance to another?= Ans. Gradually and successively. It requires a medium and also time. =Ques. What is the principal use or function in mechanics of electricity?= Ans. It is purely that of transmission. It corresponds to ropes, shafts and fluids as a medium of conveying and translating power or work. =Ques. What is work?= Ans. Work is the overcoming of resistance through a certain distance. As a quantity of water moving from a higher to a lower level will do work, so also will a quantity of electricity falling through a difference of potential. =Ques. How is work measured?= Ans. In foot pounds. =Ques. What is a foot pound?= Ans. The amount of work done in raising a weight of one pound one foot or the equivalent, overcoming a pressure of one pound through a distance of one foot. =Ques. What is the electrical unit of work?= Ans. The _volt-coulomb_. A volt-coulomb of work is performed when one ampere of current flows for one second in a circuit whose resistance is one ohm, when the pressure is one volt. =The Ampere-Hour.=--A gallon of water may be drawn from a hydrant in a minute, or in an hour; it is still one gallon. So in electricity, a given amount of the current, say one _coulomb_, may be obtained in a second or in an hour. _The ampere is the unit rate of flow._ What is called the electric current is simply the relation of any quantity of electricity passed to the time it is passing; that is quantity in coulombs = current in amperes × time in seconds, or simply coulomb = ampere × second. Again: 10 coulombs = 2 amperes × 5 seconds = 10 amperes × 1 second = 1 ampere × 10 seconds, etc. One _ampere-hour_ is simply another way of saying 3,600 coulombs. Of course 3,600 coulombs of electricity may be obtained in any desired time. It all depends on the rate of flow or the current strength in amperes. For instance, 2 amperes in 1/2 hour, or 4 amperes in 1/4 hour will also give one ampere-hour of 3,600 coulombs. It is well to keep the distinction between coulombs and amperes in mind, as even in text books very lately published these units are confounded. To illustrate further the difference between coulombs and amperes, the following example is given. It is sometimes estimated that the quantity of electricity in a flash of lightning is 1/10 coulomb, and the duration of the discharge 1/20000 part of a second. What is the current in amperes? Now since