But, however that may be, there is no doubt that the whole world owes a deep debt of gratitude to the men who have worked out this most beneficent of inventions. It is difficult to think of a single one which has ever brought such a load of benefits to poor, struggling humanity as this has. The ship in distress, the lighthouse man on his lonely islet, the explorer in the Polar regions, the pioneer settler in the new lands—in fact, just those who most need some connecting link with their fellows—are the people to whom the wireless telegraph brings aid and comfort. All honour to the men who have done it.
CHAPTER XIII
HOW PICTURES CAN BE SENT BY WIRE
The sending of a message by telegraph is easily understandable. Various combinations of two simple signs, such as short sounds and long sounds, can readily be made to indicate letters by which the words can be spelt out.
Nor does the sending of sound over a wire make a very great demand upon the credulity. We all know that sound consists of innumerable little waves in the air, and by the simplest of devices these can be converted into variations in an electric current, which variations, by means equally simple, can be made to re-convert themselves back into sound waves at the other end.
But to transmit a picture is another matter altogether. It seems barely possible in the case of a drawing such as a pen-and-ink sketch, which consists of a comparatively small number of definite lines; but with a shaded sketch or a photograph, with its gradations of light and shadow—to transmit such would seem to be beyond the bounds of possibility, did we not know that it has been done. The description of the methods will therefore constitute a not uninteresting subject for a chapter.
It is worthy of remark that an attempt along these lines was made many years ago by a man named Caselli, and a description of this pioneer apparatus will form a good introduction to the later developments.
In Fig. 13 we see a square which represents a sheet of tinfoil, upon which is drawn, in non-conductive ink, a simple geometrical figure. The ink may be grease, or shellac varnish, indeed there are many substances which are available for use as an insulating ink. Across the square there are a number of parallel dotted lines, but these, it must be understood, are not actually drawn upon the foil—their purpose will be apparent in a moment.