588 THE APPLICATIONS OF PHYSICAL FORCES. [BOOKV. 



chariot is also composed of two parts v and v which are joined by a 

 screw v. The piece v when the shaft moves round, passes exactly 

 above the holes in the disc, and so long as it is lowered in the posi- 

 tion shown in the figure, the galvanic current reaches the lower part 

 of the shaft, and through the screw v passes away to earth. (See also 

 Fig. 382 of the receiving station.) But when a key is pressed down, 

 its extremity raises a pin g, which in turn raises the piece v of the 

 chariot and insulates the two parts of the shaft a. The current now 

 coming from the positive pole of the battery, follows the path 



FIG. 381. Mechanism of the keys the working of the vertical shaft and the chariot in Hughes's 



telegraph. 



indicated by the arrows (Fig. 382), passing through the points 

 tGKa enters the coils of the electro-magnet E and thence into the 

 line wire L, and so passes on to produce its effect in the apparatus of 

 the receiving station. At each pressing down a key a like effect is 

 produced, and when it is let go the current is interrupted and the 

 effect ceases. So much for sending and interrupting the current. We 

 must now examine what is the alternate action of the current in the 

 sending and also in the receiving apparatus, the movements of which, as 



