Tag Archives: physics

“Repair this model, if you please.” These words were spoken to James Watt, an instrument maker at the University of Glasgow, Scotland, in 1764. The model showed how a steam engine worked, but what a steam engine! The original engine of which this miniature working model was a copy, was heavy and clumsy. Worse than that, it was extremely wasteful of the steam that ran it and therefore of the coal that was burned to generate the steam. Such steam engines, built by an English blacksmith named Newcomen, had been used for 40 years, but only in mines to pump out water. Wasteful or not, one steam pump, night and day, did the work of 50 men. Watt had an orderly mind. Moreover, he was a Scotsman, with a Scotsman’s traditional dislike of waste. Any machine that wasted most of the fuel that made it go was something to be improved, not merely repaired. Watt worked on the model and found out what the matter was. The steam was turned back into water (condensed) in the same part of the engine where it pushed against the piston, that is, in the cylinder. Only hot cylinders worked well, yet condensing steam in the cylinder cooled it off. Then why not condense the steam somewhere else? That is what Watt did. He worked for years planning a new model with a separate cooling chamber for the steam. Now, with the same amount of fuel, the engine did two or three times as much work as before and why not let steam, like flowing water, turn Wheels? Watt hitched up the steam engine in such a way that it could turn wheels and run machinery. He also built a governor to keep engines going at the same rate of speed. These inventions, in turn, …

In the first years of Spartan peace, Greece was filled with wandering soldiers. Their little cities needed them no more. The new governments, which Spartans appointed, looked on them as men who might make trouble and were quick to get rid of them. Homeless and with no way to earn a living, the old campaigners roamed from place to place. They became soldiers of fortune, men who fought for any general or city that offered pay and three meals a day. In 401 B. C., ten thousand of them hired themselves out to Cyrus, a prince of Persia, who hoped to steal his brother’s throne. The Army of Ten Thousand was an odd lot. There were officers and men from a dozen or more Greek states, soldiers who had fought with and against each other during the thirty years of war that had torn Greece apart. Yet, under a foreign commander, they worked well together. They made a strong force which no Asian army could begin to match. Cyrus led them far into Persia and wherever they went they were victorious. Then Cyrus was killed in battle and the Greek officers were tricked and treacherously murdered. The great army suddenly found itself stranded, with neither money nor leaders. The men were not even sure where they were, except that it was hundreds of miles from the coast of Greece. Election of Xenophon The Persian king waited for them to lose heart and surrender, as any Asian army did when it had no officers to give it orders. The Army of Ten Thousand was Greek. After a day of confusion, the soldiers called an Assembly and elected a new general, Xenophon, a young Athenian who had been the assistant of one of the dead officers. For four months he led them …