Thermionic Emission

Nicholas Callan invented the induction coil in Maynooth.

Geissler developed an efficient vacuum pump.

Thomson measured
q / m
for cathode rays.

Millikan measured the charge on an electron.

Perrin demonstated that electrons were negatively charged.

Edison discovered thermionic emission.

Stoney was the first to use the name electron for the fundamental unit of negative charge.

Nicholas Callan (1799 – 1864) was an Irish physicist, who invented the induction coil in 1836. Callan was a priest and was professor of natural philosophy at St Patrick's College, Maynooth, for nearly 40 years. His work on electromagnets led him to invent the induction coil, which enabled the production of a large spark of electricity from a low voltage battery. In 1853 he patented a rust-proofing treatment for cast iron.

William Crookes, (1832 1919) was an English scientist. Crookes discovered the element thallium. He also identified the first known sample of helium, in 1895. He invented the Crookes radiometer, which today is made and sold as a toy. He also developed the Crookes discharge tubes. These enabled him to investigate the conduction of electricity in low pressure gases. He discovered that as the pressure was lowered, that the negative electrode appeared to emit rays (the so-called cathode rays, now known as electrons). Thus he was a pioneer in the construction and use of vacuum tubes which ultimately enabled the development of television and many other inventions.

Heinrich Geissler ( 1814 - 1879) was a German physicist and a talented glassblower. Geissler is best remembered for the invention of an effective vacuum pump. By reducing the pressure of the gas in his sealed glass tubes and exciting the gas with an induction coil he observed remarkable optical effects. Geissler tubes can be regarded as the fore-runner of the fluorescent lamp. It was improved by Crookes and others.

J.J. Thomson ((1856 – 1940) born in Manchester. Became Cavendish Professor of Physics at Cambridge. Ernest Rutherford was a student under Thomson.. Thomson experimented with cathode ray tubes which led him to the discovery of the electron. He measured the charge-to-mass ratio of the cathode rays and found that it was over a thousand times higher than that of a proton, suggesting either that the particles were very light or very highly charged. J.J. Thomson won the Nobel in 1906 for his discovery of the electron. His son, George Paget Thomson, became a noted physicist in his own right, winning the Nobel Prize for his discovery of the wave-like properties of electrons. When J.J. Thomson died in 1940 he was buried in Westminster Abbey, close to Sir Isaac Newton.

Robert Millikan (1868 - 1953) was an American experimental physicist who won the Nobel Prize for Physics in 1923. Millikan performed his famous oil-drop experiment in 1909 in Chicago. His experiment measured the force on tiny charged droplets of oil suspended against gravity between two metal electrodes. Knowing the electric field, the charge on the droplet could be determined. Repeating the experiment for many droplets, Millikan showed that the results could be explained as integer multiples of a common value (-1.592×10 -19 coulomb), the charge on a single electron.

Jean Baptiste Perrin (1870 -- 1942) was born in France. From 1894 to 1897 he studied cathode rays and X-rays. In 1895, Jean Perrin showed that “cathode rays” had negative electric charge. He became a professor at the Sorbonne in Paris in 1910. Jean Perrin received the Nobel Prize in Physics in 1926 for his discovery of sedimentation equilibrium.

Thomas Edison (1847 – 1931) was an American inventor and businessman He pioneered the type of industrial research laboratory, that has become standard with large industries of all sorts. Edison is considered one of the most prolific inventors in history, holding more than a thousand patents in his name. Edison had very little formal education. One of his first jobs as a teenager was working as a telegraph operator. The invention which first made him famous was the phonograph in 1877. His first phonograph recorded on tinfoil cylinders that had low sound quality and limited replay opportunities. Edison did not invent the first electric light bulb, but instead invented the first commercially practical one. Edison made the first public demonstration of the incandescent light bulb on December 31, 1879, in Menlo Park. He said at the time that, "We will make electricity so cheap that only the rich will burn candles. During his work on the light bulb, Edison discovered thermionic emission.

George Stoney (1826 – 1911) was an Irish physicist, born in Birr, Co. Offaly and educated at Trinity College Dublin. He became Professor of Natural Philosophy at the University College Galway in 1852. Stoney made significant contributions to cosmic physics and to the theory of gases. In 1891, he proposed the term 'electron' to describe the fundamental unit of electrical charge, and his contributions to research in this area laid the foundations for the eventual discovery of the particle by J.J. Thomson. After cremation, his ashes were buried in Dundrum, County Dublin.