A machine so efficient that it would free up people to do other things, kind of like the personal computer.

But the machine I'm going to tell you about did none of this. In fact, it accomplished just the opposite. In the late 1700s, just as America was getting on its feet as a republic under the new U.S Constitution, slavery was a tragic American fact of life.

George Washington and Thomas Jefferson both became President while owning slaves, knowing that this peculiar institution contradicted the ideals and principles for which they fought a revolution.

But both men believed that slavery was going to die out as the 19th century dawned, They were, of course, tragically mistaken.

The reason was an invention, a machine they probably told you about in elementary school:

Mr. Eli Whitney's cotton gin.

A Yale graduate, 28-year-old Whitney had come to South Carolina to work as a tutor in 1793. Supposedly he was told by some local planters about the difficulty of cleaning cotton.

Separating the seeds from the cotton lint was tedious and time consuming.

Working by hand, a slave could clean about a pound of cotton a day. But the Industrial Revolution was underway, and the demand was increasing.

Large mills in Great Britain and New England were hungry for cotton to mass produce cloth. As the story was told, Whitney had a "eureka moment" and invented the gin, short for engine. The truth is that the cotton gin already existed for centuries in small but inefficient forms.

In 1794, Whitney simply improved upon the existing gins and then patented his "invention": a small machine that employed a set of cones that could separate seeds from lint mechanically, as a crank was turned. With it, a single worker could eventually clean from 300 to one thousand pounds of cotton a day.

In 1790, about 3,000 bales of cotton were produced in America each year. A bale was equal to about 500 pounds. By 1801, with the spread of the cotton gin, cotton production grew to 100 thousand bales a year.

After the destructions of the War of 1812, production reached 400 thousand bales a year. As America was expanding through the land acquired in the Louisiana Purchase of 1803, yearly production exploded to four million bales. Cotton was king.

It exceeded the value of all other American products combined, about three fifths of America's economic output. But instead of reducing the need for labor, the cotton gin propelled it, as more slaves were needed to plant and harvest king cotton.

The cotton gin and the demand of Northern and English factories re-charted the course of American slavery. In 1790, America's first official census counted nearly 700 thousand slaves.

By 1810, two years after the slave trade was banned in America, the number had shot up to more than one million. During the next 50 years, that number exploded to nearly four million slaves in 1860, the eve of the Civil War.

As for Whitney, he suffered the fate of many an inventor. Despite his patent, other planters easily built copies of his machine, or made improvements of their own. You might say his design was pirated.

Whitney made very little money from the device that transformed America. But to the bigger picture, and the larger questions. What should we make of the cotton gin?

History has proven that inventions can be double-edged swords. They often carry unintended consequences. The factories of the Industrial Revolution spurred innovation and an economic boom in America. But they also depended on child labor, and led to tragedies like the Triangle Shirtwaist fire that killed more than 100 women in 1911.

Disposable diapers made life easy for parents, but they killed off diaper delivery services. And do we want landfills overwhelmed by dirty diapers?

And of course, Einstein's extraordinary equation opened a world of possibilities. But what if one of them is Hiroshima?