On this day, July 31 …
1991: President George H.W. Bush and Soviet President Mikhail S. Gorbachev sign the Strategic Arms Reduction Treaty in Moscow.
Also on this day:
- 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.
- 2002: A bomb explodes inside a cafeteria at the Hebrew University of Jerusalem, killing nine people, including five Americans.
- 2008: Scientists report the Phoenix spacecraft has confirmed the presence of frozen water in Martian soil
- 2009: Three American tourists are arrested by Iran on suspicion of espionage while hiking along the Iraq-Iran border. (Shane Bauer and Josh Fattal would be sentenced to eight years after being convicted on spy-related charges, but released after more than two years; Sarah Shourd would be released on health grounds after 14 months.)