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The principle involved in wedge film is interference.
resonanace...
Count Ferdinand von Zeppelin invented the first practical dirigibles in the late 1800's but he didn't fly the first ones till about 1910. There were previous balloons called dirigibles, but they did not have a frame.
Dirigibles is pronounced as "dir-i-juh-buhls" with the emphasis on the second syllable.
What are the two famous dirigibles
Dirigibles are lighter-than-air aircraft that can be maneuvered by their own power. There are different kinds of dirigibles, such as blimps and airships, but all are distinguished from other lighter-than-air craft, such as balloons, which do not have their own steering and power sources.
This is the Archimedes principle.
Dirigibles were not used in Ww2 London. Barrage balloons however were. See Related Links below.
electrostatic photocopiers
by satlite waves
solubility.
resonance