ScienceWeek

ON THOMAS HARIOT (1560-1621) AND THE LAW OF REFRACTION

The following points are made by Hans C. von Baeyer (New Scientist 2001 11 August):

1) Hariot was a mathematician, deriving fundamental theorems in cartography, trigonometry and algebra, and adding the symbols > and < to the mathematical lexicon. He worked on mirrors and lenses, and built telescopes contemporaneously with Galileo. With these telescopes, Hariot independently discovered the phases of Venus, made the first map of the Moon, and anticipated Galileo in observing sunspots and measuring the periods of the satellites of Jupiter. His observations of the comet of 1607, the comet later to become famous as "Halley's comet", were good enough to be used in cometary orbital calculations 200 years later.

2) Among Hariot's wide-ranging interests was the phenomenon of refraction. During Hariot's time, the laws of refraction were eagerly sought by the designers of optical instruments as well as by astronomers who wanted to correct for the effect of Earth's atmosphere on starlight. The inherited lists and rules of thumb for describing refraction were known to be incomplete and in places highly inaccurate. Unlike the eminent astronomer Johannes Kepler (1571-1630), who disdained painstaking experimentation and relied instead on various approximate formulas arrived at by speculation, Hariot perfected a simple technique for observing refraction, and with this technique he discovered the correct law of refraction by 1602, 19 years before Willebrord Snell (1580-1626), who is usually given credit for the discovery.