Hadley and Ferrel
PDFGeorge Hadley
George Hadley was born in London on February 12, 1685 and died on June 28, 1768. He was the youngest of John Hadley, who became a recognized astronomer, inventor of the octant, precursor of the sextant for navigation. George Hadley was called to the London Bar as a lawyer in 1709 and has always been interested in his older brother’s work, contributing to it with a contribution that he cites in his own publications. His personal interest in science focused on meteorology and more particularly on the study of winds in the tropics, which was a real challenge for the marine expeditions of the time. Although he approached these areas as an amateur, George Hadley became a sufficiently enlightened expert to publish in 1735, in the journal Philosophical Transactions of the Royal Society, the article Concerning the Cause of the General Trade Winds which, for the first time, showed that the westerly inclination of trade winds and the equatorial eastern current were consequences of the Earth’s rotation. No photograph or portrait of George Hadley appears to be available, but the profile of John Hadley, his elder, is well known.
William Ferrel
William Ferrel, born on 29 January 1817 and died on 18 September 1891 in the United States, was a self-taught teacher who had studied the most advanced scientific works of his time, including Philosophiæ Naturalis Principia Mathematica by Isaac Newton (1686) and the Traité de Mécanique Céleste, a five volume work by Pierre-Simon de Laplace written between 1799 and 1825. His best-known article, Essay on the winds and current in the ocean, was published in 1856 in the Nashville Journal of Medicine and Surgery. This article echoes and complements George Hadley’s predictions, showing that the Earth’s rotation is not limited to bending the trade winds to the west and generating the equatorial eastern current. It shows that it influences all atmospheric circulation and requires the presence of three cells in each hemisphere, whereas Hadley considered only one from the equator to the pole. It thus explains the existence and high speed of the polar Jet Stream at high altitude. William Ferrel also contributed to the understanding of tides (1853), supplementing Laplace’s predictions with the contribution of friction. William Ferrel was later recruited into the United States Army, where he participated in meteorological studies in a unit which became the National Weather Service.