Remembering the Irish man who invented a method of taking color photos. 

John Joly, an Irish physicist and inventor working at Trinity College, invented dozens of innovative products, including a system of color photography based on taking and viewing photographs on plates with many narrow lines in three different colors: red, green, and blue.

The Joly Color Screen used a glass photographic plate as a filter to produce a limited-color transparency that could be viewed by transmitted life in a viewing screen. 

The color screen was sold commercially from 1895 and remained on the markets for several years. However, it was expensive and images rarely had a natural color and the screen was eventually phased out as newer models and techniques became available. 

Born in Co Offaly in 1857, Joly lived a colorful life full of invention and innovation. 

He graduated from Trinity College as an engineer in 1882 and became an assistant professor in civil engineering shortly afterward.

He was appointed professor of geology in 1897 and went on to write a staggering 270 papers and several books in addition to his several inventions. 

Most notable among Joly's inventions was arguably his development of radiotherapy to treat cancer patients. 

Joly developed a method of extracting radium and using it to treat cancer patients, a method later adopted in hospitals around the world.

Joly, along with his colleague Henry Dixon also put forward the cohesion-tension theory to explain how water moves upwards in plants in 1894. To this day, the theory is the most widely accepted explanation for how water moves through a plant's system. 

He also discussed theories of using radium in the earth's crust and sodium in the earth's seas to measure the earth's age.

Although the sodium method was later proven incorrect, it did radically alter the results of other methods at the time which previously estimated that the earth was about 20 million years old. Joly's estimation placed the earth at about 100 million years old.  

One of the most brilliant Irish scientists of his generation, John died in December 1933 and is buried in Mount Jerome Cemetary on the south side of Dublin. 

A crater on Mars was named after him 40 years after his death. 

*Originally published in June 2021. Updated in July 2024.