This file is from Wikimedia Commons and may be used by other projects.
The description on its file description page there is shown below.
Summary
DescriptionHuygens Refracted Waves.png
English: from Christiaan Huygens 1678 Traité de la Lumiere, showing how waves lead to refraction.
Date
Source
Christiaan Huygens 1678 Traité de la Lumiere
Author
Christiaan Huygens
Licensing
Public domainPublic domainfalsefalse
This work is in the public domain in its country of origin and other countries and areas where the copyright term is the author's life plus 100 years or fewer.
You must also include a United States public domain tag to indicate why this work is in the public domain in the United States.