REFERRING to the interesting letter on the above subject, from Prof. Oliver Lodge and Mr. B. Davies, in your issue for the 29th ult., I should like to mention that I have observed a similar extension of the visible spectrum when thrown upon a fluorescent screen of barium platino-cyanide. I may add that a screen of this description becomes brilliantly luminescent when brought into the vicinity of the brush discharge from a large Wimshurst machine, or, better still, from a Tesla coil. In the latter case the fluorescent surface will become luminescent at a considerable distance from the electrical discharge, if facing the latter; but if the screen is held with its opaque backing towards the discharge, the platino-cyanide will only luminesce if actually penetrated by the streamers of the discharge.