There is a popular notion that rods draw the lightning and increase the damage rather than otherwise. This is a mistake. Points will draw off electricity from a charged body silently. It would be possible to so protect a district of any size in such a way that thunder would never be heard within its boundaries if we should erect rods enough and run them high enough into the upper air. The points--if they were close enough together--would silently draw off the electricity from a cloud as fast as it formed, and thus effectually prevent any disruptive discharge from taking place. CHAPTER IX. ELECTRICAL MEASUREMENT. Having given a short account of some of the sources of electricity, let us now proceed to describe some of the practical uses to which it is put, and at the same time describe the operation of the appliances used. Before proceeding further, however, we ought to tell how electricity is measured. We have pounds for weight, feet and inches for lineal measure, and pints, quarts, gallons, pecks and bushels for liquid and dry measure, and we also have ohms, volts, amperes and ampere-hours for electricity. When a current of electricity flows through a conductor the conductor resists its flow more or less according to the quality and size of the conductor. Silver and copper are good conductors. Silver is better than copper. Calling silver 100, copper will be only 73. If we have a mile of silver wire and a mile of iron wire and want the iron wire to carry as much electricity as the silver and have the same battery for both, we will have to make the iron wire over seven times as large. That is, the area of a cross-section of the iron wire must be over seven times that of the silver wire. But if we want to keep both wires the same size and still force the same amount of current through each we must increase the pressure of the battery connected with the iron wire. We measure this pressure by a unit called the "volt," named for Volta, the inventor or discoverer of the voltaic battery. The volt is the unit of pressure or electromotive force. (In all these cases a "unit" is a certain amount or quantity--as of resistance, electromotive force, etc.--fixed upon as a standard for measuring other amounts of the same kind.)