Hans Crol was a German goldsmith and instrument maker who worked for Tycho Brahe between c.1584 and 1591. Crol worked on Brahe’s island laboratory of Hven. Crol’s major role was to build instruments for Brahe’s Stjerneborg observatory. These he built these under Brahe’s direct supervision and many of these instruments became famous including the great equitorial armillary, the large (155cm) revolving azimuth quadrant, the improved trigonal setant, and the large (233cm) portable brass semicircle.
Crol was also a sharp eyed observer and in November 1585 be observed a comet with another Brahe assistant Elias Olsen Morsing. He also kept a observation journal in Latin between 1586 and 1590. The fact he could write Latin was unusual for an artisan. Further evidence of this ability in Latin comes from this note on solar parallax,
“N.B.—Confer altitudinem meridianam cum his circa 90 gradum, atque bine erue parallaxin ♀ . Nam refractione caret in ista altitudine citima iuxta 90 gradum.”
Crol complained to a visiting scholar, Georg Ludwig Frobenius, that he, “had been with him [Brahe] for six years without receiving any wages except a few clothes”. He also complained to Frobenius that he could not get away from Brahe’s Island. Crol died on Hven in 1591.
Brahe praised Crol saying,
“my goldsmith, named Johannes Crol, who lived with me here in the country and took care of my instruments, of which he had made many with his own hands, and served me in this diligently and faithfully for many years.”
- Robert, Christianson, J. R. (John (2000). On Tycho’s island : Tycho Brahe and his assistants, 1570-1601. Cambridge, U.K.: Cambridge University Press.
- Dreyer, J. L. E. (1910-11-11). “Note on Tycho Brahe’s opinion about the Solar Parallax: (Plate 4.)”. Monthly Notices of the Royal Astronomical Society. 71 (1): 74–76.