Johannes Phocylides Holwarda (Jan Fokkesz, Jan Fokker, Johann Holwarda, Johannes Fokkes Holwarda, Jan Fokkens Holwarda, Jan Fokkes van haylen) (February 19, 1618—January 22, 1651) was a Frisian astronomer, physician, and philosopher. He was a professor of philosophy at the University of Franeker from 1639 to 1651.Pieter Willem van der Horst, The Sentences of Pseudo-Phocylides (Brill, 1978), 63.
Born in Holwerd, he is best remembered for his discovery of the length of Mira's (Omicron Ceti's) varying appearance cycle. In a systematic study in 1638, he found that Mira disappeared and reappeared in a varying cycle of about 330 days.Mira, Omicron Ceti
Holwarda was also a supporter of "atomism". His Philosophia Naturalis, seu Physica Vetus-Nova, published posthumously in 1651, defines matter and form: matter is extended and divided into atoms while form is the texture of atoms. According to Phocylides, bodies are formed from atoms and a lack of atoms. Atoms, which he distinguished as simple or compound, are solid corpuscles that receive motion directly from God.Antonio Clericuzio, Elements, Principles and Corpuscles: A Study of Atomism and Chemistry in the Seventeenth Century (Springer, 2001), p. 187.
The lunar crater Phocylides is named after him.the-moon » Phocylides
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