184 THE ELECTRIC TELEGRAPH. 



in which plunge five amalgamated contacts for short-circuiting 

 the batteries when the type-box has passed through, and the 

 prepared paper is going under the bridge. This is done by 

 a catch on the waggon itself, which, passing by, turns the 

 shaft carrying the five contacts. 



The waggon when at rest is held at the top of the rail- 

 way by the catch, which, being in communication with the 

 electro-magnet, is released by the first current which passes 

 through the line. This circuit is closed by means of the key, 

 K. Thus the waggons of both stations are made to start 

 together. They are impelled by similar weights, and their 

 speed regulated by means of fans which enable the operators 

 to adjust the two instruments to practical synchronism. 



The waggons occupy from ten to twelve seconds in passing 

 under the bridge. In this time, therefore, the message, set 

 up in the type-box, is transmitted, and another received on 

 the upper half on the prepared paper. 



In the instrument shown in Fig. 95, the type-box passes 

 first under the bridge ; when the waggon has got half way, 

 it short-circuits the batteries and leaves the line clear for the 

 reception of a message on the paper on the farther half. 



About twenty words are on the average set up in each 

 type-box. Thus a speed of transmission and reception of 

 twenty words in six seconds, or of two hundred words per 

 minute, is easily attained, not counting the time lost in 

 changing the type-boxes and removing the paper. 



The paper intended for receiving permanent printing by 

 the Bonelli instrument for distribution to the public, is pre- 

 pared by being saturated in a solution of nitrate of manga- 

 nese, which yields, under the action of the current, a light 

 brown-coloured precipitate. That which is termed " fugitive 

 printing," as for press work, by which the impressions are 

 not necessarily of a permanent character, is done with paper 

 prepared with a solution of iodide of potassium, which gives 

 letters at first an iodine colour, but which in course of time 

 lose their intensity. 



The speed said by the operators to be attainable in perma- 

 nent work is 300 words per minute, and the fugitive printing 



