Al-Qaeda's main targets on September 11, 2001 were the two World Trade Center towers in New York City and the Pentagon in Arlington. A fourth flight (United Airlines Flight 93) crashed in Pennsylvania after passengers stormed the hijacked cockpit. It is believed that this flight was intended to crash into the White House in Washington, DC.
In the 1700s, James Watt caused a revolution in transportation<em> by improving steam engine technology.</em>
He was a Scottish inventor and mechanical engineer. He made improvements on Thomas Newcomen's steam engine that was patented in 1698 and widely in use at the time of Watt's birth ( 1736).
It all started when Watt was given a model Newcomen engine to repair. He realized it was very inefficient and he began to find ways to improve its performance. He designed a separating condensing chamber for the engine to avoid huge losses of steam. He patented his improvements in 1769.
A unit of measurement of electrical and mechanical power -<em> the watt</em> - is named in his honor.
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The Nazis began experimenting with poison gas for the purpose of mass murder in late 1939 with the killing of patients with mental and physical disabilities in the Euthanasia Program.
Grandfather clauses were designed to prevent poor and illiterate African Americans from voting.
This term was coined in the 19th century when new rules for literacy tests, poll taxes and requirements for voting were established.
Some white people who did not fulfill the requirements were still allowed to vote because their ancestors ( grandfathers ) had the right to vote. This was a way to make voting possible for white Americans, and to make voting almost impossible for black people.
Today, this term applies to a provision in which an old rule continues to apply to some existing situation while a new rule will apply to future cases.
