The Physics of War (20 page)

An early telegraph.

But there was still the problem of the message. It was necessary to translate the clicks developed by opening and closing the circuit. Samuel Morse (1791–1872) realized that the clicks could be arranged as a series of dots and dashes that could be sent over the wires, and he set up a code, now referred to as the Morse code. Each letter of the alphabet was coded into a brief series of dots and dashes (A, for example, was a dot and a dash, and B was a dash and three dots). And in 1844 wires were strung between Boston and Washington, DC, and a message was successfully sent between the cities. The message sent was “What hath God wrought,” from the Bible's Book of Numbers 23:23.

By the beginning of the Civil War, telegraphy was becoming an important mode of communication across America. The first transcontinental telegraphic system, which ran from California to Washington, was completed in October 1861, about the time that war broke out. And as we saw earlier, Lincoln made extensive use of it. Interestingly, there was not a telegraph in the White House itself, but there was one at the Department of War building, next door, and Lincoln spent many hours in the building. It's estimated that he sent over a thousand messages to his generals and other officers during the war.

THE DYNAMO (GENERATOR)

The Civil War was the first war in which electricity began to play a large role in many different ways. And its impact extended far beyond the telegraph. Initially, most electrical currents were produced by batteries, but batteries are limited in the amount of electrical power they can generate. And for factories and mills, considerable power was needed. The Civil War was, in fact, one of the first truly industrialized wars. Mass-produced weapons, ironclad steamships, large factories producing various goods for the war, railroads, and so on all played important roles. Electricity was central to many of them, and at this point, many of its properties and applications were still not well understood. Furthermore, a cheap source of electricity was still not known.

Nevertheless, the first step had already been taken. Faraday demonstrated electromagnetic induction in 1831 when he showed that a brief current would flow when he moved a magnet in a solenoid. The problem was that the current was too brief, and even if the magnet was moved back and forth, only a fluctuating current could be produced. Faraday decided to look into the possibility of producing a more useful current. To do this he set up a thin copper disk that could be turned on a shaft. The outer rim of this disk would pass between the poles of a strong magnet, and as the disk turned it cut through magnetic lines of force. As a result, a potential difference, or voltage difference, was set up on the disk. The voltage was highest near the rim of the disk, since that was where the disk moved the fastest. Faraday then set up two sliding contacts on the disk, with wires attached to them, one near the edge and one closer to the center. If a galvanometer was placed in the circuit, a current flowed through it, and as long as the disk moved, the current flowed continuously.
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But Faraday's disk created only a small voltage difference because it contained only a single current path through the magnet. Soon it was found that much higher voltages could be generated by winding multiple turns of wire into a coil. In 1832 a French instrument maker, Hippolyte Pixii, improved on Faraday's device. He used a permanent magnet that could be rotated by a crank. Placing the magnet so that its poles passed a piece of iron wrapped in insulated wire, Pixii found that the spinning magnet produce a pulse of current in the wire each time a north or south pole passed the coil. But the two poles induced currents in opposite directions. To overcome this, so that both currents were in the same direction, Pixii placed a split metal device, called a commutator, on this shaft (with springs attached to it) that pressed against it.

The result was generally continuous, but not the direct current that we know today. Within a few years, however, a smooth direct current was produced. This
was the first dynamo, or simple generator—in short, a device that generated an electrical current as a result of mechanical motion. It meant, however, that you had to have something to push the device around to create circular motion. The steam engine could be used for this, or water in the form of a waterfall, or just flowing water. Electricity, and therefore electrical currents, could therefore be produced if an appropriate outside source of mechanical power was available. The dynamo was the first device that allowed a large amount of electrical power to be generated, such as that needed for a factory.

THE GATLING GUN

Strangely, one of the best “super weapons” of the Civil War saw little action. The Gatling gun was designed by Dr. Richard Gatling in 1861 and patented in November 1862, but the army appeared to have little interest in it at first. Also strange is the fact that Gatling abhorred war and hoped that his weapon would overcome the need for large numbers of soldiers on the battlefield. Even more so, he hoped it would show how gruesome and terrible war could be, which might convince nations to think twice before they went to war.
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The Gatling gun used multiple rotating barrels to fire two hundred bullets per minute. The barrels, six in all, were mounted around a central shaft, and the entire assembly could be rotated with a hand crank. Each barrel fired a single shot as it rotated to a certain point. The shells consisted of steel cylinders containing black powder and a percussion cap. Compared to other attempts to increase firepower, the shells used in the Gatling gun were gravity fed into the breach from a hopper on the top of the gun. After each bullet was fired the empty cartridge was ejected and a new round was loaded. One of the major problems in earlier attempts at such a gun was overheating of the barrels. In this case the barrel was allowed to cool as it rotated; in addition, in the earliest models, fibrous matting that had been soaked with water was stuffed between the barrels.

Gatling demonstrated his new weapon to the Union army in December 1862, several months before the Battle of Gettysburg, but the army was slow to accept it, perhaps for the best, since it would soon have become a major killing weapon.

THE WAR AT SEA

While war raged on land, war was also taking place on the high seas and in the bays along the Gulf of Mexico, and even up the larger rivers such as the Mississippi. Soon after the war began, Lincoln ordered a blockade of the seaports in the South, and it was, indeed, a smart move. The South had limited resources and had hoped to get support, or at least supplies, from Europe, and with the blockade on, they didn't get much of either. The blockade was particularly effective because the navy, as limited as it was at the time, remained loyal to the Union. At the time, in fact, it had only wooden ships, which would soon become so vulnerable to gunfire that they were of little use, unless guarded by an “ironclad.”

As guns got bigger and bigger, it soon became obvious that wooden ships were sitting ducks. Something would have to be done. Iron or steel plating was placed over the wood at first, but it soon became apparent that it would be better to make the entire hull out of metal. Such ships became known as ironclads.

Early on most ships were propelled by a giant paddlewheel, which in turn was powered by a steam engine. But paddle wheelers were large, cumbersome, inefficient, and vulnerable. One well-directed artillery shell and the ship would be out of commission. Engineers were therefore looking for something better for propulsion, and the obvious thing was some sort of “screw” device. Centuries earlier Archimedes had used a screw-like propeller for lifting water for irrigation, and the Egyptians had used a similar devise for years to irrigate their lands. Furthermore, Leonardo da Vinci had used the same principle in his design for a simple helicopter. It was obvious it could move water and exert a force against water. One of the first to propose that such a device could be used to propel a boat was James Watt, but strangely there's little evidence that he suggested using it with his steam engine.

The first “screw” propellers were, indeed, in the form of a long screw. But in 1835 Francis Smith made an important discovery. He was experimenting with long-screw propellers when a large section of the screw broke off. To his surprise, the remaining piece of the propeller seemed to work even better than the long screw. This was the beginning of the shorter, modern propeller that we know today. The man who perfected the design was the engineer John Ericsson of Sweden. By 1836 he had added larger blades and made it much more efficient. He worked in England for a while but came to the United States a few years before the Civil War, and his talent soon came to the attention of the naval officer Captain Robert Stockton. Stockton was ambitious and was determined to modernize the navy with armored steamships and much larger guns. With the
help of Ericsson, he designed and built one of the most formidable warships of the day, naming it the
Princeton
, after his hometown. Its guns were in turrets, the two largest of which had twelve-inch barrels that fired 212-pound cannonballs. In addition it had twelve forty-two-pound guns, and it was powered by Ericsson's new propeller.
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In 1844 it was paraded out before President Tyler and a large audience in Washington, DC. Stockton, eager to show off its guns, ordered a demonstration. As the third shot was fired, the large gun exploded, spraying the attending crowd with fragments of iron. The secretary of state, the secretary of the navy, and several other officials were killed. It was a tremendous blow to both Stockton and Ericsson, who had helped in the design.

When the Civil War broke out, however, Eriksson was employed by the Union to design a new and even better warship. When completed, it was called the USS
Monitor
. It was heavily armored in iron and was 179 feet long and powered with a steam engine that drove a nine-foot propeller. It looked rather strange in that its deck was only eighteen inches above the water, but this made it an extremely poor target for enemy ships.

In the meantime the Confederate navy had also built an ironclad, which they named the CSS
Virginia
; it was the pride of the South. In March 1822, the two ships met at Hampton Roads, Virginia. The
Virginia
attacked the Union blockade squadron at Hampton Roads and destroyed two small frigates. Early in the battle the large frigate
Minnesota
had run aground while attempting to engage the
Virginia
. But it got dark before the
Virginia
could finish off the
Minnesota
, so early the next morning it returned, but in the meantime the Union navy had brought the
Monitor
in, and it was waiting for the
Virginia
. The two ironclads blasted at one another with their guns but did little damage, then the
Virginia
tried to ram the
Monitor
, but this also did little damage. The two ships continued to battle for hours, but in the end it was a draw. However, the
Monitor
had stopped the
Virginia
from destroying the
Minnesota
and several other ships.

Pleased with the performance of the
Monitor
, the Union soon built an entire fleet of ships modeled on it. They also built a fleet of smaller ironclads referred to as the “City” class, which were used in the west—the bays of the Gulf of Mexico and the larger rivers such as the Mississippi.

The Confederate navy also built several smaller ships, but it was soon obvious that they could not keep up with the Union navy, and they could do little on top of the water to stop the blockade.

PHYSICS OF THE PROPELLER

Propellers of the time had two or more blades that were attached to a rotating shaft. As the propeller turned, it transmitted power to the boat by converting rotational motion into forward thrust. Basically, a pressure difference was produced on opposite sides of the blade, with the pressure on the rear surface greater than that on the front, and this differential forced the ship forward. In effect, the blades imparted momentum to the water, which created a force on the ship.

Propellers can turn clockwise or counterclockwise, according to the design of the blades. The force on the blade depends on its area (A), the fluid density (
), the velocity (v), and the angle of the blade to the fluid flow (α).

One way to look at the propeller is to compare it to a screw. You know that to screw it into a wall, you apply torque to the head of the screw. The helical thread of the screw converts this torque into a “pushing” force that drives the screw into the wall.

Basically, a propeller is a machine that moves the ship through the water as it is turned. Machines, as we saw earlier, are devices that multiply or transform forces. So a propeller is a machine that moves the ship forward by pushing water backward, where the force on the backward-moving water is equal to the force on the forward-moving ship, according to Newton's third law. Also, since the force is a result of a change in motion, a propeller gives a ship forward momentum by giving the water backward momentum.