James Croll
Who was he?
James Croll was a 19th century Scottish
scientist who developed a theory of climate change based on changes
in the Earth's orbit. He was born in 1821 on the farm of Little Whitefield, near
Wolfhill in Perthshire. He was largely self-educated, teaching
himself physics and astronomy. At 16 he became an apprentice
wheelwright at Collace near Wolfhill, and then because of health
problems a tea merchant in Elgin, Moray. In the 1850s he managed a
temperance hotel in Blairgowrie, and was then an insurance agent in
Glasgow, Edinburgh and Leicester.
In 1859 he became a caretaker in the museum at the Andersonian
College and Museum, Glasgow, so as to have access to books to allow
him to develop his ideas. From 1864, Croll corresponded with Sir
Charles Lyell, on links between ice ages and variations in the
Earth's orbit. This led to a position in the Edinburgh office of
the Geological Survey of Scotland, as keeper of maps and
correspondence, where the director, Sir Archibald Geikie,
encouraged his research.
What was his theory?
During Croll's lifetime the
Great Ice Age had been discovered and notions of multiple glacial
and 'Crollean' interglacial epochs were being debated. Many of the
major mechanisms of climatic change had been proposed, if not yet
fully explored: changes in solar output, changes in the Earth's
orbital geometry, geographical changes, and changes in atmospheric
transparency and composition. New climate theories were being
introduced and new work was being done on heat budgets,
spectroscopy, and the carbon dioxide content of the atmosphere. The
stratographic sequence had not been worked out and many geologists
still thought that glacial 'drift' deposits had been carried by
icebergs. Through such tempestuous theoretical waters, Croll kept a
steady course, negotiating between cosmic and terrestrial physics
on the one hand (as exemplified by Herschel and Lord Kelvin) and
geology on the other, as practiced by Lyell, Darwin, and the Geikie
brothers.
In 1875, Croll published his
major book, Climate and Time, a work delayed several years
due to ill health, but a work widely admired for the profound
impression it produced on geologists around the world. The leading
geologist of his day, Charles Lyell, revised his Principles of
Geology in response to Croll's theory.
Croll's work was widely discussed, but by the end of the 19th
century, his theory was generally disbelieved. However, the basic
idea of orbitally-forced insolation variations influencing
terrestrial temperatures was further developed by Milutin
Milankovitch and eventually, in modified form, triumphed in
1976.
He corresponded with Charles
Darwin on erosion by rivers. In 1876, he was elected Fellow of the
Royal Society, and awarded an honorary degree by the University of
St Andrews. He retired in 1880 because of ill health, and died in
Perth in 1890.
