TABLE OF CONTENTS Of the countless inventions which have been conceived by the mind of man, there are a few which can be classed as truly great. These are the ones which have had profound and far-reaching influences upon the ways of human life, influences that have continued and extended far beyond the original intent of the invention. The wheel is one of these great inventions; it removed the burdens from the backs of men and animals, but its principle appears just as surely in the mechanism of a modern jet engine as it did on an archaic oxcart. Another example is the steam engine; not only did it make muscle power obsolete as the prime mover of industry, but it laid the foundations of the science of thermodynamic engines for ages to come.
A third great invention in this category is the thermionic vacuum tube. Originally of importance because of its ability to detect and amplify electrical signals, this device heralded the beginning of the electronic era and opened the door to such marvels as world-wide communications, television, and the electronic computer.
About the year 1883, during the course of his development of the incandescent lamp, Thomas Edison discovered that, if a metal plate is placed near the filament inside a lamp bulb, current can be made to flow between the plate and the filament if the plate is made positive with respect to the filament, but not if it is negative. He had...
