Letter from R L [Richard Lionel] Hippisley, Royal Engineers, Stanhope Lines, Aldershot, to [Joseph] Larmor He asks Larmor for a reference to any publication in which the 'skin effect' of electric currents in conductors is treated mathematically; Hippisley gives the example of a periodic current in a solenoid surrounding an iron core. He thinks that Oliver Lodge discussed the problem somewhere, in reference to lightning conductors. Larmor may be able to tell him the periodicity in a solenoid necessary for the skin effect of the eddy currents to become noticeable. With some pencilled equations by Joseph Larmor. 7 February [no year]