HISTORY AND PROGRESS. 183 



buffer A', and level with the rail, is a hook, D, which engages 

 with an eye at the upper end of the waggon, and holds it 

 until a current traverses the line, and releases it by means 

 of an electro-magnet. 



On the left-hand side of the bridge, over the raised types, 

 is a type- comb consisting of five movable teeth, insulated 

 from each other, which are connected to the ends of five 

 wires going to a similar number of styles at the receiving 

 apparatus. As the waggon, with the types looking upwards, 

 passes underneath the type- comb, the teeth come lightly into 

 contact with the raised portions of the types, and close the 

 circuits whilst the contact lasts. Thus letter after letter 

 is transmitted. The right side of the bridge, which spans 

 the middle of the rails, is appropriated to the reception of 

 messages. It consists of a writing-comb composed of five 

 teeth, made of platinum-iridium alloy, which is not liable to 

 corrosion, insulated from each other, and pressing lightly 

 upon the paper-strip. This comb would produce, if each 

 tooth were traversed at the same time by an electric current, 

 five lines something like the lines on music-paper. As, 

 however, they are each only traversed by a current during 

 the time some portion of a type is underneath the corre- 

 sponding tooth of the type-comb at the sending station, they 

 can only give lines at such intervals and of such length as is 

 determined by the form of the type. 



If the teeth of the type and writing-combs be equally far 

 apart at each of the stations, and the waggons travel over 

 the rails at the same speed, it is evident that a dotted, or 

 rather lined, facsimile of the types on the transmitting 

 waggon will be received on the paper carried by the waggon 

 at the receiving station. 



Any deviation from synchronism is, however, of very small 

 importance, as the difference in one way or the other will 

 only make the letters printed either a little narrower or 

 broader than those of the fount from which the types have 

 been taken, and in this consists the great advantage of the 

 Bonelli arrangement over those of Bain and Bakewell. 



c is an ordinary galvanoscope, and m a mercury trough, 



