“Very likely,” said the principal, “but you can read it after. Let me explain exactly what I want you to do. When you have heard the details you can decide better whether you want to go.”
Dr. Moorland had ceased pacing the room and settled deep in his comfortable study chair. With what seemed exasperating deliberateness to Jack, he removed his huge glasses and polished them thoroughly on his handkerchief before he was ready to talk. Then just as he was about to begin he seemed to remember something else of importance, for he began to search drawer after drawer of his desk until he finally brought to light a large yellow envelope bulging with what appeared to be blueprints. He tossed the package on the desk before him and once again resumed his comfortable attitude.
“Perhaps you never heard of my nephew, Harry Ryder. In fact, I am quite certain you haven’t, for he has never visited Drueryville since you’ve been at school. Harry Ryder is the chief engineer of the enormous hydro-electric power plant at Necaxa where light and power is supplied for Mexico City, the capital, one hundred and twenty-five miles away. He was appointed to that important position by President Madero a year ago, and he has done his best to keep Mexico City lighted in spite of all the trouble in that turbulent republic, and the recent change to the Huerta régime.
“Time and again rebels have tried to break down the four transmission lines that carry the current to the city but they have never yet been successful and I judge from Harry’s letters that he never intends they shall. But besides rebels, Harry has other important things to contend with. Up there in the mountains where the plant is located, thunderstorms are quite frequent and lightning is the troublesome element. Lightning is electricity in its most dangerous form, because of its very high voltage. Voltage, you know, is the pressure which causes it to travel. One of our scientists once tried to measure lightning and found that its voltage mounted well into the millions. This is tremendous force when you consider that the current used in lighting houses and stores is supplied at one hundred and ten volts.
“During thunderstorms the lightning plays about the transmission lines, often causing a great deal of trouble. If it should by any chance get into the station it would raise havoc with the generators and other machinery. To prevent this, lightning arresters have been constructed that will waylay the lightning, as it were, and send it into the ground before it reaches the vital machinery.”
Here Dr. Moorland paused and began to sketch rapidly on a piece of paper while Jack looked on, still very much mystified.
Dr. Moorland’s Sketch
“The usual transformer is arranged something like this. First a choke coil is put in the transmission line near the end. When the lightning strikes this coil it piles up and is forced back exactly like a flying wedge of football players that suddenly tries to break through an impregnable defense. The lightning that is thus forced back rushes into line ‘A,’ which is the point of least resistance, jumps the horn gap and plunges through the arrester tank and into the ground. When the excessive electricity has left the line and the flow is normal, the current is checked at the horn gap and arrested. This combination of gap and arrester does not permit current to flow into the ground during normal operation and does not actually become active until lightning gets into the line and there is danger of the plant being wrecked by an overload of electricity.”
“My, but that is interesting,” said Jack Straw as he fingered the master’s sketch. Indeed, he had been so carried away with the description of that interesting piece of engineering work that for the moment he had completely forgotten about Mexico. But Dr. Moorland revived his interest with his next sentence.