Editing René Descartes (section)

=== Magnetism ===
[[File:Descartes magnetic field.jpg|thumb|Descartes's 1664 diagram of effluvia emmited by magnets. It is a predecessor of the concept of [[magnetic field]].]]
Descartes proposed a theory to explain magnetism and explain the observation in [[De Magnete|''De Magnete'']] by [[William Gilbert (physicist)|William Gilbert]]. Descartes considered that 'effluvia' were emitted by a magnet, the effluvia rarefied the air creating pressure differences, and thus forces.<ref>{{Cite book |last=Cao |first=Tian Yu |url=https://books.google.com/books?id=vaCsDwAAQBAJ&dq=descartes+magnetism+effluvia+rarefied&pg=PA22 |title=Conceptual Development of 20th Century Field Theories |date=2019-10-03 |publisher=Cambridge University Press |isbn=978-1-108-47607-2 |language=en}}</ref>