This Day in History - July 31

1790 - President Washington signs the first U.S. patent, issued to Samuel Hopkins for a process of making potash, an ingredient used in fertilizer.
1961 - IBM introduces its first Selectric typewriter with its distinctive "typeball."
1964 - The unmanned American space probe Ranger 7 reaches the moon, transmitting photos back to Earth before impacting the lunar surface.
1970 - "The Huntley-Brinkley Report" comes to an end after nearly 14 years as co-anchor Chet Huntley signs off for the last time; the broadcast is renamed "NBC Nightly News."
1971 - Apollo 15 crew members David Scott and James Irwin become the first astronauts to use a lunar rover on the surface of the moon.
1972 - Democratic vice presidential candidate Thomas Eagleton withdraws from the ticket with George McGovern following disclosures that Eagleton had once undergone psychiatric treatment.
1991 - President George H.W. Bush and Soviet President Mikhail S. Gorbachev sign the Strategic Arms Reduction Treaty in Moscow.
2008 - Scientists report the Phoenix spacecraft has confirmed the presence of frozen water in Martian soil