Gamma Rays Discovered - 1900
Paul Villard

First Transatlantic Wireless Message - 1901
Guglielmo Marconi sent the first wireless transmission from
England to Canada. The message was three dots Morse Code
representing the letter S.

Air Conditioner- 1902
Willis Carrier, a young engineer, created what he called
an Apparatus for Treating Air

First Man Made Fiber - 1902
William H. Walker, Arthur D. Little, and Harry S. Mork. The fabric
was originally called Viscose, but in 1924, the textile industry
changed its name to Rayon.

Electrocardiograph - 1903
Wilhelm Einthoven Dutch physiologist, refines A.D. Waller's
electrocardiogram, and devises an instrument to record the
heart's electrical impulses

Stainless Steel - 1904
Leon Guillet develops stainless steel but doesn't recognize
it's noncorrosive
 

Electric Plug Patented - 1904
Harvey Hubbell II

First Radio Program- 1906
Professor Reginald Fessenden broadcast a poetry reading, a
violin solo, and a speech from Brant Rock, Massachusetts, to
promote his new alternator-transmitter system.

Plastic - 1907
Leo Baekeland invented the first synthetic polymer the first 
artificial material made by linking small molecules together
to make large ones.

Geiger Counter - 1908
Hans Geiger and Ernest Rutherford invent the Geiger counter
for measuring radiation

Electric Washing Machine - 1908
The first electric-powered washing machine was introduced by
the Hurley Machine Company of Chicago, Illinois. Alva J. Fisher
was the inventor. The machine was a drum type with a
galvanized tub and an electric motor, for which a patent was
issued on Aug. 9, 1910

Pop Up Toaster - 1909
Charles Strite 

Cellophane - 1908
Jaques Edwin Brandenberger in Switzerland.