Letter from A [Alexander] Larmor, 336A Oxford Road, Manchester, to Joseph [Larmor] Alexander would be glad if Joseph would come after finishing at Cambridge. He gives thanks for a copy of the London Mathematical Society Proceedings. He found the result from [George Gabriel] Stokes's optics from which he deduced a formula only holds if 'm' is positive. He expands upon his thinking, and what would occur in a spherical wave front. He has been reading [Augustin-Jean] Fresnel's works, applying this to Rayleigh, and he describes Fresnel's treatment, making clear that as slits become wider, bands come closer together. Alexander has found a missing link in his own proof, in the part treating the complete duality of two tetrahedrons, and he explains this. [Arthur] Schuster has suggested that he compare the iron spectrum between poles with that given by a spark between a pole and a solution of iron salt. 6 March [1887]