by Barry Parker
The French physicist Charles Coulomb began looking into the problem of the attraction and repulsion of electrified bodies in the early 1780s. He was particularly interested in the force between them. If they attracted or repulsed one another there had to be a force associated with the phenomena. He constructed a very sensitive device called a torsion balance that allowed him to measure the magnitude of the force, and he found that it was proportional to the inverse square of the distance between the two charges, and proportional to the product of the two charges. We now write this as F = q1q2/r2, where q1 and q2 are the magnitudes of the two charges and r is the distance between them.
The scene then switched to Italy, where the physician and physicist Luigi Galvani began to take an interest in the new field of “medical electricity” in about 1790. One day Galvani was skinning a frog on which he had been experimenting with static electricity. His assistant had touched a metal scalpel to a nerve on the frog's leg with a charged Leyden jar nearby. When the scalpel touched the nerve, the dead frog's leg jumped, as if alive. This observation surprised him, and he published it in 1791. He assumed that the jerking was caused by an electrical fluid in the nerves, and he called the phenomena “animal electricity.”9
Soon after the result was published, another physicist in Italy, Alessandro Volta, read about it and repeated the experiment. He noticed almost immediately that a frog was not needed; the only thing needed was two dissimilar metals and a moist conductor (they replaced the frog leg). And within a short time he went a step further, showing that a series of several bimetallic strips and moist conductors worked even better. Volta continued working on his new device, which he called a pile, using disks of silver and zinc on top of one another with cardboard disks soaked in salt water between them. With the new device, which we now know as a battery, the continuous flow of electrical current was created for the first time.
Once scientists had a “current” of electricity flowing in a wire conductor, many physicists began experimenting with it. Among them was the German physicist Georg Ohm. Ohm soon found that the current that flowed along a wire between two points depended on the “resistance” of that section of wire. His law is now referred to as Ohm's law. Current is now measured in terms of a unit called an ampere, and resistance is measured in units called ohms. Mathematically, his law can be stated as V = IR, where V is the voltage between the two points, I is the current, and R is the resistance.10
The voltaic pile of Volta.
But there was still a serious problem. Because electricity had so many properties that were similar to magnetism, it appeared that they had to be related, but no one could prove it. In 1813 the Danish physicist Hans Christian Oersted became interested in the problem, but after experimenting for several years he was unable to find a connection between the two. Then one day in 1820 he was giving a lecture; during the lecture he was turning an electrical current off and on. Nearby was a compass, and, to his surprise, he noticed that his actions were having an effect on the compass. He brought the compass up to the wire, holding the compass needle parallel to the wire. When he turned the current on, the needle moved to a perpendicular direction. As a result, he determined that an electrical current has a magnetic field associated with it. The magnetic field surrounded, or circled, the current-carrying wire, and the magnitude of the field weakened as the distance from the wire increased.11 Oersted published his results in July 1820, and they soon caused a sensation. There was now proof: electricity and magnetism were, indeed, related. In particular, an electric field would produce a magnetic field. It was also soon found that a moving magnet could produce electrical current. The interaction between the two fields is now referred to as electromagnetism.
Within a few weeks of the publication of Oersted's discovery, the French physicist Andre Ampere read about it. He verified Oersted's work and went on to conduct experiments on the fields around the wire. He showed that two parallel wires carrying electrical currents attracted or repelled each other, depending on whether the current flow was in the same direction or in opposite directions. Working out the details of the interaction, he showed that the forces between them obeyed an inverse square law. He then went on to develop the “right-hand rule” for current, which says that if you grasp a current-carrying wire with your thumb in the direction of the current and close your fingers, your fingers will point in the direction of the magnetic field. He was also the first to develop a solenoid—a coil of wire wound in a spiral that created a magnetic field down its center.
But perhaps the greatest shining light of the era was Michael Faraday, who was born in 1791. He was basically self-educated; at fourteen he was apprenticed to a local bookbinder, which brought him into contact with large numbers of books. He read as many of them as he could in his spare time, and he was particularly inspired by one that described the new phenomena of electricity. Later he attended lectures given by the eminent physicist Humphrey Davy.12
After reading about Volta's pile he constructed one for himself, and in 1821, after Oersted announced his discovery, Faraday built two devices that produce what he called “electromagnetic rotation.” They were simple versions of the electric motor. Then in 1830 he began asking himself if a magnetic field that was already in existence could produce an electrical current. To find out he wound a wire around an iron ring and attached the two ends to a battery, producing a solenoid, then he placed a switch in the circuit so that it could be turned on and off. On the opposite side of the ring he wound several loops of another wire and attached its ends to an instrument that measured current, called a galvanometer. Faraday then turned the switch off and on several times, expecting to see a current in the second wire. To his disappointment, however, there was only a tiny current that lasted for a fraction of a second. Experimenting further, he finally determined that it was not the existence of the magnetic lines that created the current but rather the motion of the magnetic field across the wire. He soon showed that if he merely pushed a magnet into a coil of wire, it would produce a current in the wire. We now refer to this as electromagnetic induction.
The right-handed rule for the direction of the magnetic field.
Faraday's induction coil.
In 1845 Faraday also discovered that certain materials exhibited a weak repulsion from a magnetic field. He called the phenomena diamagnetism. In addition, he showed that magnetism could affect a ray of light, demonstrating an apparent relationship between magnetism and light. Finally, in his later years, he proposed that the electromagnetic force actually extended into the empty space around a conductor in the form of “lines of flux.” We now refer to them as electric field lines.
Within a few years Faraday's work led to two very important inventions: the electrical generator and the transformer. The electrical generator could be used as a source of power for industry, and the transformer was soon being used extensively for changing or adjusting the voltage of a source.
HOW THIS AFFECTED WARFARE
Even though the above discoveries were some of the most important in the history of the world, it was several years before they were used in war. But when they were finally applied to the technology of the time, they created a revolution. Electrical generators and electrical motors were soon developed as a result of these discoveries, and they eventually played a large role in the development of weapons of war. Large electrical generators eventually replaced steam engines as the major source of power. Power plants sprang up across much of the civilized world, spurring production on many fronts. Weapons were soon produced at a tremendous rate.
But one of the major outcomes of the breakthroughs in electricity and magnetism was a sudden new interest in science and technology, with physics at the forefront. Most countries began to realize how important physics and other sciences were to warfare and the development of new weapons. Pure science had been frowned upon prior to this, but government officials increasingly began to realize the importance of pure science, and physics in particular, in relation to the t
echnology of military applications.
Faraday's lines of flux, or electrical field lines for a positive charge and a negative charge.
Many new universities sprang up in England, France, and Germany, and also in America. And a new emphasis on science and math, including physics ensued. Other countries, such as Japan and Russia, also soon came to the same conclusion.
The first “dynamo”—an electrical generator capable of producing power for industry—was built in 1832. Then came the electrical telegraph and fuel cells.
Historians refer to the American Civil War as the first truly modern war because it used so many new and greatly improved methods and weapons. Many important developments in physics and weaponry occurred just before and during the war. Although weapons had been produced in large numbers in Europe earlier, the first true mass production of some of the most deadly weapons that had ever been used in war occurred during these years. In addition, developments in physics and other sciences led to the wartime use of the electric telegraph, electric generators, surveillance balloons, better and larger ships, torpedoes, and significantly improved telescopes.
DEVELOPMENT OF THE PERCUSSION CAP
The flintlock was still being used by many at the beginning of the war. But a new invention that would supersede it had already been made. In 1800 Edward Howard, an English chemist, had discovered a highly explosive material called mercury fulminate. He hoped it might replace gunpowder, but to his disappointment, when he tried it in a musket, it blew the barrel apart. It was too explosive.1
Reverend Alexander John Forsyth of Scotland followed up on this discovery in 1807. Like Howard, he thought there was a definite need for a new gun explosive. But he was more concerned with the mechanism used to set off the charge, namely the spring-loaded flint. A spark was needed to trigger the primer, and things didn't work well during damp weather or rainy days. He decided to try mercury fulminate as a primer. It had a serious advantage: it didn't take a match to make it explode. In fact, it could easily be made to explode just by banging it with a small hammer. So he developed a spring-loaded device that would strike some mercury fulminate in a small paper cartridge. The cartridge was attached to a tube that led into the gun barrel. The flames from the explosion went down the tube and ignited the powder that propelled the bullet. He was pleased at how well it worked.
Forsyth and others continued to work on the new system over the next few years. First a paper cartridge was used with mercury fulminate sealed between paper sheets. By 1814, small iron caps were used to contain the fulminate, and later this was changed to copper. Eventually a copper or brass cartridge was used that contained both the bullet and the gunpowder.
The new percussion system had many advantages: weather was no longer a problem, and it was much faster and more convenient to load. We can, in fact, say that the percussion cap revolutionized muskets and pistols. Armories throughout the world soon began converting flintlocks to fulminate-fired weapons. And indeed this also happened in America, but not until the Civil War was well underway.2
A significant breakthrough had been made, but there were still problems. And one of the main ones was related to reloading the gun. Most muskets were single-barreled and had to be reloaded after each bullet was shot. A number of inventors tried to use side-by-side barrels, each with a bullet in it, but this didn't work well for warfare. Something better was needed. And one of the first to try to do something about it was Samuel Colt.
Colt's main concern early on was the pistol. How could it be made to shoot several bullets one after the other? He began by making a wooden model. His idea was to have a revolving cylinder with several chambers. Bullets could be placed in the chambers, with one of the bullets lining up with the barrel, and when the trigger was pulled the cylinder would revolve and another chamber, with another bullet ready to fire, would line up with the barrel. What he had was several bullets in a cylinder that rotated; his most famous gun had six bullets.3
Colt took his new invention to the army in the early 1840s, well before the Civil War, but the army had little interest in it. Despite the setback, he managed to scrape together enough money to set up a factory at Patterson, New Jersey. But at this stage his “six shooter” was still crude, and it wasn't too successful. He continued working on it, however, and gradually reduced the number of parts in it down to seven.
Finally, the gun began attracting the attention of others—particularly the Texas Rangers. Colt's invention was an ideal weapon for someone on a horse. In 1847 Colt set up another plant for his new, improved handgun at Hartford, Connecticut. It was a .31-caliber weapon that was relatively light compared to other pistols. Soon the new revolvers were being mass-produced. Using systems developed during the Industrial Revolution, he standardized all the parts within the gun so that the parts from one gun would fit all guns, and over the years he produced 325,000 of them.
But the army, even later in the Civil War, was slow to take up his gun.
THE MINIÉ BALL
The percussion cap was a dramatic step forward, but within a short time after its development an even greater invention made the musket into a much more deadly weapon with greater range and accuracy, and it doomed the smoothbore musket forever.
The new development began in 1823 in India when a British officer, Captain John Norton, noticed something strange. The Indian natives used a tube for projecting darts at their enemies, and when they got ready to fire, they began by blowing into the barrel. He discovered that they were doing this to create a foam that would fill the barrel and effectively seal it, so that when the dart was shot, the force on it would be much greater.
In 1836 a London gunsmith improved on Norton's idea by inserting a wooden plug in the base of the bullet so it would expand when shot. This helped, but the real advance came when a French army captain, Claude Minié, improved the design using a hollow cylindrical base. The bullet was now cone-shaped, similar to our modern bullets. So, even though it was called a Minié ball, it was not shaped like a ball. At first the Minié ball had a round cup in the base, and when the powder exploded the cup forced the lead outward to fill the barrel. What was particularly important about this was that the bullet was now fitting snugly into any rifled grooves that were in the barrel.4
Spiraling rifled grooves had been used for years, but for a snug fit, which was required, the bullet had to be slightly larger than the interior of the barrel, and it had to be pounded down to a position just above the powder, and this was a slow process. The Minié ball, on the other hand, could just be dropped into the barrel, and this was much faster. And as the Minié bullet caught the grooves as it exited it was forced into a spin, and as a result, it left the barrel with a very high spin rate.
To see why a spinning bullet was so revolutionary, we have to look at the physics of a spinning object. When an object of any type rotates, it rotates around an axis, and this axis of rotation acquires a special status. In the case of a bullet in flight (shot from a rifle) there are two motions we have to consider: its translational motion (that gives it its trajectory) and its rotational motion. It has both at the same time, in the same way a curving baseball does. A pitcher purposely gives a baseball a spin to curve its path so that it is more difficult for a batter to hit.
How do we deal with a spinning object? First of all, it's easy to see that it spins about an imaginary line called its rotational axis, and we refer to its spin rate as its angular speed (or angular velocity, for a particular direction). Speed of rotation is usually measured as so many revolutions per minute (rpm). Scientists also use another unit, which is particularly convenient in physics. To define it we first have to define what is called the radian; it is 360°/2π, which is approximately 57°. The unit, radians per second, is commonly used in physics.
So what does it take to set an object in rotational motion—in other words, to make it spin? It obviously takes a force. This takes us back to the concept of inertia. Remember that according to Newton's first law, an object in motion remain
s in uniform motion with a constant speed in a straight line unless acted upon by a force. In short, a body in motion has inertia, and it takes a force to overcome this inertia. Inertia is therefore a kind of “unwillingness” to change. In the same way, a spinning body has rotational inertia, and it prefers to maintain this inertia. In effect, it takes a force to change it. In the case above, however, we are dealing with a rotational motion, so the force is a rotational force, and we refer this force as torque. (You apply torque every time you turn a doorknob or open a jar.)
If we look at a spinning disk, however, it's easy to see that the “linear speed” (e.g., feet per second) across the disk varies. The speed at a point near the edge is obviously greater than the speed at a point near the center. This means that for a spinning object the speed at various points throughout the object increases as the distance from the spin axis increases. Because of this, ordinary (or linear) force f, and rotational force, or torque, which we denote by τ, are related. This can be expressed as τ = f × r.
Getting back to rotational inertia, it's easy to show that a spinning object prefers to maintain a spin in a particular direction. Assume you have a bicycle wheel with a handle on its axis so that you can hold on to it with your hands. If you set the wheel spinning, then try to twist it, you will find that it's very difficult to turn. In short, the wheel wants to keep spinning in the same direction. This means that a bullet spinning around an axis along its elongated shape, and traveling in a certain direction, prefers to maintain this direction. Spin therefore “stabilizes” a bullet in flight. As it turns out, it also decreases the effect the air around it has on it (i.e., air resistance). Because of this, the Minié ball was much more accurate and had a greater range.