still go on further by the help of Science: beyond the violet we have the actinic or chemical rays, which are used in photography, and which enable us to trace the frequencies for a further two octaves. Beyond this we cannot pierce with our present knowledge; but there may be, and probably are, latent in our nature, senses which, properly developed, will be able to appreciate still more subtle vibrations, and organs which, perhaps, even now are being prepared for the reception of these influences. We have no organs yet developed for receiving and appreciating what are called Wireless waves, but we have already been able to devise physical Receivers, of wonderful sensitiveness, for them and other waves of the same nature, such as those of Radiant heat. In the case of Radiant heat, the Bolometer invented by Professor Langley has been able to receive and record a change of temperature of the one millionth of a degree Centigrade, and can easily make visible the heat of a candle at a distance of one and a half miles. In wireless telegraphy also the Receiver, perfected by Marconi, is affected by rills, made by a splash of electric discharge, over 3000 miles away. If our eyes were sensitive to these frequencies, both of which are composed, as is also light, of electro-magnetic rills, we could see anything that was happening anywhere in the world, for they go through matter as though it did not exist, as light passes through glass; indeed, if our region of Sight waves was only put an octave lower we could not use glass in our windows, it would be too opaque, we should be obliged to have our windows made of thin slabs of carbon or other substances permeable to Radiant heat waves. Science indeed steadily points to electricity and magnetism being a form of motion, and it may be that in these invisible rays we may some day discover the nature of those mysterious forces; and, even far beyond those, as suggested in View Four, we may in the not far distant future be able to appreciate Physical Life itself as a mode of frequency.