October 9 – The Cook Islands become a territory of the United Kingdom. October 19 – Max Planck first states Planck's law of black-body radiation to a meeting of the German Physical Society in Berlin, marking the birth of modern quantum mechanics. He restates it on December 14. October 24 – The United Kingdom concludes voting in the 1900 United Kingdom general election Marquess of Salisbury wins re-election October 25 – The United Kingdom annexes the Transvaal.
october 9 – the cook islands become a territory of the united kingdom october 19 – max planck first states planck's law of black-body radiation to a meeting of the german physical society in berlin marking the birth of modern quantum mechanics he restates it on december 14 october 24 – the united kingdom concludes voting in the 1900 united kingdom general election marquess of salisbury wins re-election october 25 – the united kingdom annexes the transvaal