(_g_) Radiation charges positively an insulated metal, even when it is an enclosure with walls of the same metal; the metal being certainly uncharged at the beginning of the experiment. The same occurs with sulphur and ebonite. If there is a feeble initial _plus_ charge, radiation increases it. (_h_) While the discharging power of radiation for negative electricity is strongest with zinc and aluminium, and slower with copper and gold, following the Volta series; the E.M.F. set up by radiation, when it charges things positively, is greatest with gold and carbon, and less with zinc and aluminium; again following the Volta series, but inversely. (_i_) If radiation falls on an insulated metal plate connected with an electrometer, in an enclosure of the same metal, the positive electrification shown by the deflection of the electrometer is greater as the plate is further from the walls of the enclosure. The action stops when the metal has attained a certain electric density, constant for a given metal; so the potential of a plate is naturally higher as its capacity is less. It is thus established that radiation acts on the particles of gas in contact with a conductor; they go away with a negative charge, leaving _plus_ on the conductor, until an electric density sufficient to balance this action is attained. (_j_) It is probable that if the solar rays do not produce an effect it is because of the absorbing action of the atmosphere. In fact, if one places a tube whose ends are glazed with selenite between the source of light and the metals being experimented on, the effects become sensibly stronger when the tube is exhausted. APPENDIX VI. ELLIPTICALLY POLARISED ELECTRIC RADIATION. Since the delivery of my lecture to the Royal Institution, on June 1st, Herr Zehnder has published[41] a mode of getting elliptically and circularly polarised electric radiation. He takes a couple of plane polarising grids, such as are depicted in Fig. 21, page 37, and places them parallel to each other at a little distance apart with their wires crossed. If the two grids are close together they will act like wire-gauze, reflecting any kind of polarised radiation equally; but if the warp and woof are an eighth-wave length apart, and the plane of the incident radiation is at 45° to the wires, the reflected radiation will be circularly polarised. A change in the circumstances will, of course, make it elliptical. Such a pair of grids acts, in fact, like a Babinet’s Compensator. [41] _Berichte der Naturforschenden Gesellschaft zu Freiburg i. B._, Bd. IX. Heft 2, June 21, 1894. APPENDIX VII. ON MAGNETISATION PRODUCED BY HERTZIAN CURRENTS; A MAGNETIC DIELECTRIC:[42] BY M. BIRKELAND.