176 THE ELECTRIC TELEGRAPH. 



An idea of the time saved by this system may be gleaned 

 from the signals representing the word " telegraph " by 

 the Stoehrer and Morse codes respectively : 



Stoehrer:'. ...._. .. 



t e I e g rap h 



Morse: o 

 t e leg 



Taking the dot as unit of time and the dash as equal to 

 two of them, whilst the spaces between the dots and dashes 

 of" a letter are equal to one dot, and those between the dif- 

 ferent letters equal to the length of a dash, the time required 

 for transmitting the word " telegraph " by Stoehrer's code 

 will be 44 units, whereas by Morse's it will occupy 61. 



VI. ELECTRO- CHEMICAL TELEGRAPHS. 



99. Bain's Chemical Telegraph. Mr. Alexander Bain has 

 been, since the year 1845, the author of several improve- 

 ments and inventions in telegraphy. The most important 

 of these is his electro-chemical telegraph, patented in England 

 in 1846. 



The sending apparatus is a simple Morse contact key. 

 The receiving apparatus consists of a circular disc of chemi- 

 cally prepared paper stretched upon a similar disc of metal 

 kept in rotation by clockwork. On the upper surface of the 

 paper rests the point of a style, which, while the disc revolves, 

 is drawn towards the periphery so as to travel over the paper 

 in a spiral curve. When the circuit is closed, the salt with 

 which the paper is prepared becomes decomposed under the 

 style. 



On a base board are erected the clockwork or driving 

 portion of the instrument, and the recording disc which it 

 turns round. The clockwork is regulated by the fly, and 

 is connected with the recording disc by the shaft, to which it 



