British prisoners of war. Siege of Spin Boldak (Third Anglo-Afghan War). This is the last time the British Army uses an escalade. May 29 Eddington experiment: Einstein's theory of general relativity is tested by Arthur Eddington's observation of the "bending of light" during a total solar eclipse in Príncipe, and by Andrew Crommelin in Sobral, Ceará, Brazil (confirmed November 19). The Republic of Prekmurje formally declares independence from Hungary. May 30 – By agreement with the United Kingdom, later confirmed by the League of Nations, Belgium is given the mandate over part of German East Africa (Ruanda-Urundi). June June – Earl W. Bascom, rodeo cowboy and artist, along with his father John W. Bascom at Lethbridge, Alberta, Canada, designs and makes rodeo's first reverse-opening side-delivery bucking chute, which becomes the world standard. June 2 – 1919 United States anarchist bombings: Eight mail bombs are sent to prominent figures. June 4 – Women's rights: The United States Congress approves the 19th Amendment to the United States Constitution, which would guarantee suffrage to women, and sends it to the states for ratification. June 5 – Estonian and Latvian Wars of Independence: The advancing pro-German Baltische Landeswehr initiates war against Estonia in Northern Latvia. June 6 – The Hungarian Red Army attacks the Republic of Prekmurje. June 7 Sette Giugno on Malta: British troops fire on a mob protesting against the colonial government, killing four. Russian Civil War: Counteroffensive of Eastern Front: The Red army captures the city of Birsk from the White forces. June 9 – Russian Civil War: Counteroffensive of Eastern Front: The Red army recaptures the city of Ufa June 14–15 – A Vickers Vimy piloted by British aviator John Alcock, with navigator Arthur Whitten Brown, makes the first nonstop transatlantic flight, from St. John's, Newfoundland, to Clifden, Connemara, Ireland. June 15 – Pancho Villa attacks Ciudad Juárez, Mexico. When the bullets begin to fly to the American side of the border, two units of the United States 7th Cavalry Regiment cross the border, to push Villa's forces from American territory. June 17 – Epsom Riot by Canadian troops: English Police Sergeant Thomas Green is killed. June 18 – The second most popular football club in Costa Rica, Liga Deportiva Alajuelense, is founded. July 1 – Russian Civil War: Perm Operation (1918–19) begins on the Siberian Front: The 2nd and 3rd armies of Soviet Russia recapture the city of Perm.