Refrigerant gas

The invention: A safe refrigerant gas for domestic refrigerators,
dichlorodifluoromethane helped promote a rapid growth in the
acceptance of electrical refrigerators in homes.
The people behind the invention:
Thomas Midgley, Jr. (1889-1944), an American engineer and
chemist
Charles F. Kettering (1876-1958), an American engineer and
inventor who was the head of research for General Motors
Albert Henne (1901-1967), an American chemist who was
Midgley’s chief assistant
Frédéric Swarts (1866-1940), a Belgian chemist
Toxic Gases
Refrigerators, freezers, and air conditioners have had a major impact
on the way people live and work in the twentieth century.With
them, people can live more comfortably in hot and humid areas,
and a great variety of perishable foods can be transported and
stored for extended periods. As recently as the early nineteenth century,
the foods most regularly available to Americans were bread
and salted meats. Items now considered essential to a balanced diet,
such as vegetables, fruits, and dairy products, were produced and
consumed only in small amounts.

Radio interferometer

The invention: An astronomical instrument that combines multiple
radio telescopes into a single system that makes possible the
exploration of distant space.
The people behind the invention:
Sir Martin Ryle (1918-1984), an English astronomer
Karl Jansky (1905-1950), an American radio engineer
Hendrik Christoffel van de Hulst (1918- ), a Dutch radio
astronomer
Harold Irving Ewan (1922- ), an American astrophysicist
Edward Mills Purcell (1912-1997), an American physicist
Seeing with Radio
Since the early 1600’s, astronomers have relied on optical telescopes
for viewing stellar objects. Optical telescopes detect the
visible light from stars, galaxies, quasars, and other astronomical
objects. Throughout the late twentieth century, astronomers developed
more powerful optical telescopes for peering deeper into the
cosmos and viewing objects located hundreds of millions of lightyears
away from the earth.

Radio crystal sets

The invention: The first primitive radio receivers, crystal sets led
to the development of the modern radio.
The people behind the invention:
H. H. Dunwoody (1842-1933), an American inventor
Sir John A. Fleming (1849-1945), a British scientist-inventor
Heinrich Rudolph Hertz (1857-1894), a German physicist
Guglielmo Marconi (1874-1937), an Italian engineer-inventor
James Clerk Maxwell (1831-1879), a Scottish physicist
Greenleaf W. Pickard (1877-1956), an American inventor
From Morse Code to Music
In the 1860’s, James Clerk Maxwell demonstrated that electricity
and light had electromagnetic and wave properties. The conceptualization
of electromagnetic waves led Maxwell to propose that
such waves, made by an electrical discharge, would eventually be
sent long distances through space and used for communication
purposes. Then, near the end of the nineteenth century, the technology
that produced and transmitted the needed Hertzian (or radio)
waves was devised by Heinrich Rudolph Hertz, Guglielmo Marconi
(inventor of the wireless telegraph), and many others. The resultant
radio broadcasts, however, were limited to the dots and
dashes of the Morse code.