Sir Thomas Ranken Lyle FRS[1] (26 August 1860 – 31 March 1944)[2][3] was an Irish-Australian mathematical physicist, radiologist, educator, and rugby player.

[5] He was educated at Trinity College, Dublin, graduating in 1883 with full honours and student medals for his work in mathematics and physics.

In 1892 Lyle married Frances Isobel Clare Millear, the daughter of a prominent Western District grazier, and the two set up home in a professorial house provided by the university.

[5] In February 1896, news reached the scientific community in Australia of Wilhelm Röntgen's discovery of a new type of electromagnetic radiation.

[2] Lyle is credited with taking and publishing one of the first X-ray photos in Australia, independently of contemporary fellow pioneers Father Joseph Patrick Slattery and Walter Drowley Filmer, namely a picture of the foot of a Professor Masson,[5] which was reproduced in newspapers the next day.

[1][3] In 1914, with Ranken family inheritances, his wife's money, and wise financial investments, he was able to announce his retirement from the university.

"His outstanding contribution to the nation's scientific life was recognized by the ANRC when in 1931 it created the Thomas Ranken Lyle medal for distinguished Australian research in mathematics and physics.

Lyle appeared on a 45-cent stamp, along with fellow pioneers of X-ray research Father Joseph Patrick Slattery and Walter Drowley Filmer.

He was impressive enough at university level to bring himself to the notice of the Irish selectors, and was capped for his first international match in the 1885 Home Nations Championship.

Despite a poor record the previous season, Lyle was reselected for the 1886 tournament, playing in a single game, a one-try loss to England.