Lord Rayleigh1842–1919
Moiré fringes to test gratings, 1874
English physicist who in 1881 explained Talbot’s self-imaging gratings, predicting the distance at which the pattern repeats.
Moiré Circles
Two sets of rings, drawn a little apart. Where they disagree, a second family of curves appears that neither one contains.
About this pattern
Concentric grating interference · Lord Rayleigh's test, 1874
Rayleigh used exactly this to judge how accurately a grating had been ruled, because the interference figure is far coarser than either set of lines and so magnifies any error in them. With two sets of evenly spaced rings the fringes are hyperbolas, one for each whole number of rings' difference, the same construction as the two-slit figure, drawn rather than lit.
Behind the mathematics