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1904 (MCMIV)was a leap year starting on Friday of the Gregorian calendar and a leap year starting on Thursday of the Julian calendar, the 1904th year of the Common Era (CE) and Anno Domini (AD) designations, the 904th year of the 2nd millennium, the 4th year of the 20th century, and the 5th year of the 1900s decade. As of the start of 1904, the Gregorian calendar was 13 days ahead of the Julian calendar, which remained in localized use until 1923.
Port Arthur from Gold Hill
- October 1 – Phi Delta Epsilon, the international medical fraternity, is founded by Aaron Brown and 8 of his friends, at Cornell University Medical College.
- October 4 – Swedish IFK Göteborg is founded, becoming the 39th IFK-association.
- October 5 – Alpha Kappa Psi, a co-ed professional business fraternity, is founded on the campus of New York University.
- October 9 – German journalist Anna Rüling, in a speech to the Scientific-Humanitarian Committee in Berlin, makes the first known public statement of the socio-legal problems faced by lesbians.
- October 15 – Theta Tau, a professional engineering fraternity, is founded at the University of Minnesota in Minneapolis.
- October 19 – Polytechnic University of the Philippines is founded as Manila Business School, through the superintendence of American C.A. O'Reilley.
- October 21 – Russo-Japanese War – Dogger Bank incident: The Russian Baltic Fleet fires on British trawlers it mistakes for Japanese torpedo boats, in the North Sea.
- October 27 – The first underground line of the New York City Subway opens.
- October 28 – Panama and Uruguay establishes diplomatic links.
беларуская (тарашкевіца): 1904
srpskohrvatski / српскохрватски: 1904