Gregorie moved to London in 1662, where he befriended Robert Moray of the Royal Society and published Optica Promota. In Optica Promota, Gregorie proves a reflective sine law that, unbeknownst to him due to his rural location when he worked on the book, Descartes had already proven (known as Descartes law of sines). In fact, though Gregorie puts forth many ideas about lunar, solar, and stellar parallax and other astronomical ideas and applications, many of these had already been promoted by other current astronomers. Gregorie simply wasn’t aware of the current knowledge at the time the book was written. He did, however, describe a method for the use of Venus’s transit in order to measure the distance of the Earth to the Sun (or the Astronomical Unit). Edmund Halley, the English astronomer, would later promote Gregorie’s method and it would become the basis of the first effective measurement of the Astronomical Unit.
Gregorie’s most important contribution to astronomy in the Optica Promota was his design for a new telescope, located in the Epilogue. Gregorie believed that a telescope that utilized both mirrors and lenses, rather than one or the other, would correct several defects in the current design of telescopes. In his new design, the “catadioptrical” telescope, a parabolic mirror reflects parallel incident rays to a primary focus. The light is then reflected back through a hole in the center of the first mirror by a small concave elliptical mirror to a secondary focus, and from there through a plano-convex lens to the eye. Gregorie used the available books in Aberdeen on optics and astronomy to create this telescope, including Kepler’s Paralipomena. Gregorie was unable to actually create the telescope, but in 1663 Robert Hooke created a six foot telescope of Gregorie’s design. However, Isaac Newton, with whom Gregorie would later correspond, objected that Gregorie dialed to polish the conical mirrors correctly and in about 1668 Newton reveals an improved design to Gregorie’s original telescope. Gregorie actually wanted to build an observatory at St. Andrews, where he taught, and teach the “new” science, but the students had rebelled against the faculty and administration would not permit Gregorie to do so.
Some of Gregorie’s most important additions to scientific knowledge actually came in the form of mathematics. Gregorie began to embrace his mathematics side in Italy, where he moved in late 1663, to study under Evangelista Torricelli’s pupil Stefano degli Angeli. Gregorie published Vera circuli et hyperbolae quadratura in 1667 and Geometrioe pars universalis in 1668. Gregorie determined that quadrature of the circle (making a square with a straight edge and a compass that had the same area as a circle) was impossible. Additionally, he proposed that the areas of a circle and hyperbola could be obtained in the form of infinite convergent series. He was also one of the first modern mathematicians to think about transcendental numbers, such as pi and e. Furthermore, his work provided the basis for the Taylor series, a way to make sine, cosine, and logarithmic functions be able to be described in polynomial terms.
James Gregorie died in 1675 in Edinburgh, Scotland. He was showing his students Jupiter’s satellites through a telescope when a stroke blinded him. He died a few days later.
Works Cited
"James Gregory (Astronomer and Mathematician)." Wikipedia. 09 Oct. 2007 .
"James Gregory." Dictionary of Scientific Biography. 6th vol. New York: Charles Scribner's Sons, 1981.
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