Huygens–Fresnel principle Arago spot Geometry of corpuscles Commentary

Christiaan Huygens, Augustin-Jean Fresnel optics

Huygens–Fresnel principle

• Huygens considered light to be a luminous disturbance
• of springy corpuscles of ether
• propagated by spherical waves from each point in its path
• that add up to determine light’s direction.
• Huygen’s principle explained
• reflection and refraction,
• but not defraction.
• Fresnel explained defraction
• by adding to Huygen’s principle
• that observation that light waves
• interfere with each other.

Arago spot

• The spot that shouldn’t exist
• in the center of a circular shadow
• helped show that light
• behaves like waves.

Geometry of corpuscles

• Huygens applied
• compass and ruler,
• geometric methods,
• to mythical corpuscles of ether.
• It should perhaps be claimed
• that what he made
• was not a description of light
• but a paper and pencil model of it.