The progress of improvement in such methods of signalling promised to be rapid, before the invention of the electric telegraph, or rather, before it was shown how the principle of the electric telegraph could be put practically into operation. We have seen that they were capable of transmitting messages with considerable rapidity, more than twice as fast as we could now send a written message by express train. But they were rough and imperfect. They were all, also, exposed to one serious defect. In thick weather they became useless. Sometimes, at the very time when it was most important that messages should be quickly transmitted, fog interrupted the signalling. Sir J. Barrow relates that during the Peninsular War grave anxiety was occasioned for several hours by the interruption of a message from Plymouth, really intended to convey news of a victory. The words transmitted were, “Wellington defeated;” the message of which these words formed the beginning was: “Wellington defeated the French at,” etc. As Barrow remarks, if the message had run, “French defeated at,” etc., the interruption of the message would have been of less consequence. Although the employment of electricity as a means of communicating at a distance was suggested before the end of the last century, in fact, so far back as 1774, the idea has only been worked out during the last forty-two years. It is curious indeed to note that until the middle of the present century the word “telegraph,” which is now always understood as equivalent to electric telegraph, unless the contrary is expressed, was commonly understood to refer to semaphore signalling,[28] unless the word “electric” were added. The general principle underlying all systems of telegraphic communication by electricity is very commonly misunderstood. The idea seems to prevail that electricity can be sent out along a wire to any place where some suitable arrangement has been made to receive it. In one sense this is correct. But the fact that the electricity has to make a circuit, returning to the place from which it is transmitted, seems not generally understood. Yet, unless this is understood, the principle, even the possibility, of electric communication is not recognized. Let us, at the outset, clearly understand the nature of electric communication.