SCIENCE IN THE INDUSTRIAL WORLD 



larly useful where the same messages are to be sent to a 

 number of different places, as the perforated strip of 

 paper can be made in multiples at a single punching. 



Many different types of telegraph recorders have 

 been invented since the time of Morse's first instrument, 

 several of these being the experimental inventions of 

 Morse himself. The principles involved in these 

 recorders have been both chemical and mechanical, the 

 mechanical ones, as a rule, predominating. Practical 

 chemical recorders are used, however, utilizing the 

 well-known fact of chemical decomposition by the 

 electric current. For example, if a strip of paper is 

 saturated with some chemical which is easily decom- 

 posed by electricity, and in this decomposition changes 

 color, the pressure of an electrical needle upon this strip 

 of paper will produce a mark. If the strip is arranged 

 on rolls which pass it beneath the position of the needle 

 at a uniform rate of speed, dashes and dots may be 

 made by the needle's contact with the paper for a 

 longer or shorter time. This method is found to be 

 entirely practical, and the principle is utilized in many 

 recording devices. 



It is quite beyond the scope of this work to go into 

 details of the hundreds of telegraphic devices, for signal- 

 ing, etc., the numbers of which are being multiplied al- 

 most daily, and which have become practical necessi- 

 ties in civilized communities. But it is interesting 

 to remember that such widely divergent mechanisms as 

 the dial-signaling apparatus with which the captain of 

 the ocean liner communicates his commands to the 

 engineer far below in the engine-room, the Atlantic 



