236 PLEASANT WAYS IN SCIENCE. 



this line of communication to Paris in one hour after the 

 French troops had entered that city. Thus the message 

 was conveyed at the rate of more than 120 miles per hour. 



Various other devices were suggested and employed 

 during the first half of the present century. The sema- 

 phores still used in railway signalling illustrate the general 

 form which most of these methods assumed. An upright, 

 with two arms, each capable of assuming six distinct posi- 

 tions (excluding the upright position), would give forty-eight 

 different signals; thus each would give six signals alone, 

 or twelve for the pair, and each of the six signals of one 

 combined with each of the six signals of the other, would 

 give thirty-six signals, making forty-eight in all. This num- 

 ber suffices to express the letters of the alphabet (twenty- 

 five only are needed), the Arabic numerals, and thirteen 

 arbitrary signals. 



The progress of improvement in such methods of sig- 

 nalling 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 mes- 

 sage from Plymouth, really intended to convey news of a 

 victory. The words transmitted were, "Wellington de- 

 feated ; " 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 de- 

 feated at," etc., the interruption of the message would have 

 been of less consequence. 



