James Gregory (1638-1675) was a Scottish mathematician, astronomer, and first Regius Professor of Mathematics at the University of St Andrews. He was the first to state and prove a version of the Fundamental Theorem of Calculus and was the first to write a textbook concerning Calculus, which is why calculus was taught at St Andrews a hundred years before it was on the curriculum at the University of Cambridge. He invented the Gregorian telescope, which is still used today, and discovered the principles of diffraction gratings, where he was able to observe light travelling in different directions by using a bird feather. He also worked to find the areas of the circle and hyperbola using a modification of the method of Archimedes (c.211BCE).
Gregory was elected to the Royal Society of London before travelling to St Andrews and there starting his family. After a while, he moved to the University of Edinburgh.
Most notably, Gregory is thought to have laid the very first meridian line 200 years before the Greenwich meridian was established. This meridian runs several degrees west of the Greenwich meridian, making it around 12 minutes behind GMT. The brass meridian on South Street represents the line which Gregory initially carved into the floor of his laboratory (now King James’ Library). Outside Parliament Hall, you can see his plaque.