Heinrich Rudolph Hertz, a German physicist, discovered the existence of electromagnetic waves in 1887. This was a result of his expansion of James Clerk Maxwell's mathematical "Electromagnetic Theory of Light," published in 1873. The international unit of frequency, one cycle per second, is named in his honor.Continue Reading
Hertz engineered the oscillator used to prove Maxwell's theory. The oscillator – two brass knobs connected by induction coils – created tiny sparks that jumped between the knobs when it was turned on.
He designed a circular receiving wire, also with two knobs separated by a gap, and placed it away from his oscillator. Hertz powered the oscillator, and it generated a spark that traveled the distance to the receiver, thus proving the existence of electromagnetic waves.Learn more about Inventions
Barometric pressure was discovered in about 1644 when physicist and inventor Evangelista Torricelli invented the first mercury barometer. Torricelli was an assistant to Galileo Galilei who suggested that Torricelli try using mercury in his vacuum experiments. As Torricelli experimented, he realized the height of the mercury varied from day to day because of changes in atmospheric pressure, thus discovering the principle of the barometer.Full Answer >
The German physicist Julius Mayer first stated the law of conservation of energy in 1842. He discovered that a chemical reaction created heat and work, which then made more heat. The law of conservation of energy states that the amount of energy is constant, meaning it is not destroyed or created.Full Answer >
Scottish physicist and chemist Sir James Dewar invented the Dewar flask, better known as the thermos, in 1892. The thermos is a container that minimizes the change in temperature within the flask, thus allowing cold substances inside to remain cold and hot substances to stay hot.Full Answer >
Sir Joseph John Thomson, a British physicist, discovered the electron in 1897. In experiments studying electric discharge in cathode tubes, he noted a high value for the ratio of charge to mass. His observation led him to identify the first subatomic particle, the electron.Full Answer >