Sir Oliver Lodge, the Physicist Who Refined the Coherer and the Radio

Sir Oliver Lodge (knighted in 1902) was a British physicist born in 1851 credited with improving the early radio-wave detector model known as the coherer. The first model of the coherer was invented by his French colleague Édouard Branly, but Lodge improved it by adding a trembler to the basic glass container design. He also included a paper transcription of the detected radio signals. 

 

A portrait of Sir Oliver Joseph Lodge. Image used courtesy of the Library of Congress

 

Lodge challenged Einstein’s theory of relativity by proposing his own electrical theory of matter (the non-relativity theory), in which he discussed mass and velocity. He had a knack for explaining advanced physics in plain English and lived a long, scientifically abundant life until the age of 89.

 

A Contemporary With Great Engineers

Lodge’s discovered his gift for scientific subjects at 16 after he enrolled at the Royal College of Science in London. At the University College of London, he studied advanced maths, where he got his doctoral degree. His later academic career included a professorship at the University College Liverpool and a principal’s position at Birmingham University. 

Sir Oliver Lodge’s educational and career path crossed that of many renowned physicists. John Tyndall, a chief investigator of the natural greenhouse effect, was one of his early lecturers. James Clerk Maxwell, the father of the theory of electromagnetism, and Henrich Hertz, the practical demonstrator of Maxwell’s theory and the bearer of modern radiofrequency, were perhaps the most famous two.

Lodge also had a scientific rivalry with Guglielmo Marconi on the subject of wireless telegraphy and coherer improvements. Sir Lodge conducted experimental physics and openly theorized, while Marconi commercialized telegraphy and was well-versed in keeping his experimental work from prying eyes. 

 

Marconi reading a message from his wireless telegraph. Image used courtesy of Early Radio History

 

Two years before Marconi’s first radio broadcast took place in 1896, Oliver Lodge demonstrated the broadcasting at Oxford University. Lodge patented the moving-coil loudspeaker (used in all sound devices for turning radio waves into audio sound) and the variable tuner, a type of tuning capacitor. Marconi Company bought several of the radio patents Lodge developed in partnership with Alexander Muirhead and developed the ideas further. 

The phenomenon of simultaneous discoveries is not unusual in science. Even if Sir Oliver Lodge and Guglielmo Marconi didn’t start with the same premises and methods, their coinciding theoretical and experimental work on electromagnetic waves set the scene for today’s wireless telecommunications.

 

Lodge's Studies on Electromagnetic Waves

Lodge successfully generated radio waves from circuitry and presented his paper on electromagnetic waves along wires titled "On the Theory of Lightning Conductors" in 1888. This study added to Hertz’s work of electromagnetic wave transmission through space.  

Lodge's main line of work on electromagnetic waves came out of his experiments and lectures on lightning, in which he tried to explore why lightning rods didn’t always work as suggested—sometimes traveling alternate paths through structures instead of being conducted by cables. 

In an experiment with Leyden jars acting as a type of resonant (tuning) circuit, Lodge simulated lightning using long lengths of copper wires. He discovered that the charge would jump a spark gap, effectively taking a shorter high-resistance route, instead of traveling through a loop of copper wire—the longer, lower-resistance route. 

 

A modern demonstration of an LC circuit as used in Lodge’s experiment, consisting of a Leyden jar transmitter and receiver and a signaling neon bulb. Image courtesy of National Mag Lab

 

This concept helped Lodge devise the ideas of electrical resonance and the inductance effect, which was later endorsed by Lord Kelvin and publicly recognized. The electric spark plug used in internal combustion engines in automotive engineering known as the Lodge Igniter is another one of his inventions that has lasted through time. 

 

Perfecting the Coherer

Although the coherer was short-lived—it lost its utility in 1907 when the cat's whisker diode rectifier replaced it—it garnered interest from many well-known physicists. Branly, Marconi, and Lodge all worked on enhancing the coherer's performance during their lifetimes. 

 

Lodge-type coherer receiver created in Russia in 1895. Image used courtesy of the Science Museum Group

 

The coherer consisted of a glass tube with two iron filings positioned between two electrodes. These electrodes would clump together when triggered by radio waves. The trembler, which Oliver Lodge added to the basic coherer model, was used as an on-and-off controller of the spark gap, resetting the device by dislodging the clumped filings.  

The device was named the “coherer” to describe the behavior of the metal particles under electrical charge from the antenna; the electrical charge caused the particles to stick together or cohere and make the device conductive. The impulses from the coherer were recorded by a galvanometer that would return a visual signal about receiving an impulse. The iron filings were then separated manually by a vibrating bell every time a transmission was received.      

Although Sir Lodge is recognized as one of the key contributors to wireless telegraphy, he himself admitted that he couldn’t see the immense potential of wireless compared to wired communication at that time. However, his bountiful research and the 1898 patent for space-transmitted signals encouraged others to innovate wireless telecommunications as we experience it today.