Letter from Geo Fras [George Francis] Fitzgerald, 6 Windsor Terrace, Malahide, to [Joseph] Larmor He has not worked out the case of electromagnetic reflection, noting a difficulty. He describes the corresponding case of a string passing through a hole in a thin board, and the calculation for the force, as a pressure proportional to the energy per unit length of the string. He compares this with the case of a string fastened to the board. The aether and refelecting matter are like the string passing though the hole, he believes. In the case of reflection by matter it is difficult because of the destruction of magnetic induction as the reflector moves, but he has not thought this out. He thinks it cannot be worked by [Christian Andreas] Doppler's principle, giving his reasoning. 15 November 1900