April 30 » J. J. Thomson of the Cavendish Laboratory announces his discovery of the electron as a subatomic particle, over 1,800 times smaller than a proton (in the atomic nucleus), at a lecture at the Royal Institution in London.
June 16 » A treaty annexing the Republic of Hawaii to the United States is signed; the Republic would not be dissolved until a year later.
June 22 » British colonial officers Charles Walter Rand and Lt. Charles Egerton Ayerst are assassinated in Pune, Maharashtra, India by the Chapekar brothers and Mahadeo Vinayak Ranade, who are later caught and hanged.
July 11 » Salomon August Andrée leaves Spitsbergen to attempt to reach the North Pole by balloon. He later crashes and dies.
August 10 » German chemist Felix Hoffmann discovers an improved way of synthesizing acetylsalicylic acid (aspirin).
December 9 » Activist Marguerite Durand founds the feminist daily newspaper La Fronde in Paris.
Day of marriage April 30, 1921
The temperature on April 30, 1921 was between 6.8 °C and 20.2 °C and averaged 13.7 °C. There was 12.0 hours of sunshine (81%). The average windspeed was 3 Bft (moderate breeze) and was prevailing from the northeast. Source: KNMI
In The Netherlands , there was from September 9, 1918 to September 18, 1922 the cabinet Ruys de Beerenbrouck I, with Jonkheer mr. Ch.J.M. Ruys de Beerenbrouck (RKSP) as prime minister.
February 21 » Constituent Assembly of the Democratic Republic of Georgia adopts the country's first constitution.
February 22 » After Russian forces under Baron Roman von Ungern-Sternberg drive the Chinese out, the Bogd Khan is reinstalled as the emperor of Mongolia.
March 1 » Following mass protests in Petrograd demanding greater freedom in the RSFSR, the Kronstadt rebellion began, with sailors and citizens taking up arms against the Bolsheviks.
July 11 » Former president of the United States William Howard Taft is sworn in as 10th chief justice of the U.S. Supreme Court, becoming the only person ever to hold both offices.
July 29 » Adolf Hitler becomes leader of the National Socialist German Workers Party.
October 29 » United States: Second trial of Sacco and Vanzetti in Boston, Massachusetts.
Day of death September 2, 1980
The temperature on September 2, 1980 was between 7.3 °C and 20.5 °C and averaged 14.1 °C. There was -0.1 mm of rain. There was 10.5 hours of sunshine (77%). The partly clouded was. The average windspeed was 1 Bft (weak wind) and was prevailing from the south-southeast. Source: KNMI
In The Netherlands , there was from Monday, December 19, 1977 to Friday, September 11, 1981 the cabinet Van Agt I, with Mr. A.A.M. van Agt (CDA/KVP) as prime minister.
February 17 » First winter ascent of Mount Everest by Krzysztof Wielicki and Leszek Cichy.
February 22 » Miracle on Ice: In Lake Placid, New York, the United States hockey team defeats the Soviet Union hockey team 4–3.
February 28 » Andalusia approves its statute of autonomy through a referendum.
May 18 » Mount St. Helens erupts in Washington, United States, killing 57 people and causing $3billion in damage.
July 5 » Swedish tennis player Björn Borg wins his fifth Wimbledon final and becomes the first male tennis player to win the championships five times in a row (1976–1980).
September 5 » The Gotthard Road Tunnel opens in Switzerland as the world's longest highway tunnel at 10.14 miles (16.32km) stretching from Göschenen to Airolo.
When copying data from this family tree, please include a reference to the origin: Hendrik Dreyer, "Dreyer Tree", database, Genealogy Online (https://www.genealogieonline.nl/dreyer-tree/I18762.php : accessed January 28, 2026), "Roelof Jacobus Coertze (1897-1980)".
Copy warning
Genealogical publications are copyright protected. Although data is often retrieved from public archives, the searching, interpreting, collecting, selecting and sorting of the data results in a unique product. Copyright protected work may not simply be copied or republished.
Please stick to the following rules
Request permission to copy data or at least inform the author, chances are that the author gives permission, often the contact also leads to more exchange of data.
Do not use this data until you have checked it, preferably at the source (the archives).
State from whom you have copied the data and ideally also his/her original source.