Erasmus Bartholin was a Danish mathematician, physician, and grammarian. He is best remembered for his discovery of double refraction announced in his Experimenta crystalli Islandici disdiaclastici (1669), where he described how Icelandic feldspar (calcite) produces a double image of objects observed through it.
Background
Erasmus Bartholin was born on August 13, 1625, in Roskilde, Denmark. He was the son of Caspar Bartholin (1585-1629) and Anna Cathrine Thomasdatter Fincke (1594-1677), who was the daughter of the professor of medicine of the University of Copenhagen Thomas Fincke.
Education
Erasmus received his first education from private tutors, then he attended a Latin school. He entered the University of Copenhagen in 1642, receiving his Bachelor of Arts in 1644 and a Master of Arts in 1647. From 1647 he studied mathematics at the University of Leiden, traveling to France in 1651 but then going to Italy where he studied at a number of places including Padua from where he received his Doctor of Medicine degree in 1654.
Career
After studying at the University of Leiden for several years studying mathematics, later Erasmus Bartholin traveled in France, and England. Upon his return to Copenhagen, Bartholin was appointed professor of mathematics in 1656 but transferred to an extraordinary chair of medicine in 1657 and to an ordinary one in 1671. He served the University of Copenhagen as dean of the faculty of medicine, librarian, and rector, and was appointed royal physician and privy councilor.
Bartholin wrote little on medicine, although he and his brother Thomas played some part in introducing cinchona bark to Denmark; he also contributed to the journal founded and edited by Thomas, Acta medica et philosophica Hafniensia.
His publications in pure mathematics were fairly numerous, but not of great importance. Besides his own works, he issued in almost every year from 1664 to at least 1674 a Dissertatio de problematibus geometricis consisting of theses propounded by himself and defended by his students.
Bartholin also worked in astronomy. Like many others, he observed the comets of 23 December 1664-9 April 1665. In this effort he was assisted by Ole Romer. He did not reach a conclusion about the true orbits, for he was skeptical of all statements about either the place of comets in the heavens or their physical.
Also in 1664 Bartholin began, at the direction of Frederick III of Denmark, to prepare for publication the collected manuscript observations of Tycho Brahe, which the king had bought from Ludwig Kepler. In this task he was again assisted by Romer. The king’s death prevented the project’s completion, and its only result was Bartholin’s critique of the imperfect Historia coelestis of Albert Curtz.
Views
As an exponent of the Cartesian tradition, Bartholin’s main interest was in the theory of equations; in this he was directly influenced by Frans Van Schooten. In physics, as in mathematics, Bartholin was a fervent admirer of Descartes (of whom he wrote: “Miraculum reliquum solus in orbe fuit”), as is evident in his attempt to deal with the newly discovered phenomenon of double refraction. Having shown that both rays (solita and insolita) are produced by refraction, and given a construction for determining the position of the extraordinary image, he argued that double refraction could be explained in the Cartesian theory of light by assuming that there was a double set of “pores” in the spar.