Joseph-Nicolas Delisle
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Joseph-Nicolas Delisle was a French astronomer and cartographer. Delisle is mostly known for the Delisle scale, a temperature scale he invented in 1732.
Delisle's observatory in Beryozovo (marked a.), from Continuation de l'histoire générale des voyages, vol. 72 (1768)
Explication de la carte des nouvelles decouvertes au nord de la mer du Sud, 1752
Arago spot
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In optics, the Arago spot, Poisson spot, or Fresnel spot is a bright point that appears at the center of a circular object's shadow due to Fresnel diffraction. This spot played an important role in th
Notation for calculating the wave amplitude at point P1 from a spherical point source at P0.
The on-axis intensity at the center of the shadow of a small circular obstacle converges to the unobstructed intensity.
Numerical simulation of the intensity of monochromatic light of wavelength λ = 0.5 μm behind a circular obstacle of radius R = 5 μm = 10λ.
Arago spot experiment. A point source illuminates a circular object, casting a shadow on a screen. At the shadow's center a bright spot appears due to diffraction, contradicting the prediction of geometric optics.