PHYSICS OF NINETEENTH CENT. ELECTRICITY. 569 



larger scale at p., of which c 3 is the plan. The trough is filled with 

 water, and the letters are indicated by the gas which rises from the ends 

 of the wires by the decomposition of the water. When a message was 

 to be sent, the attention of the observer at the receiving station was 

 called by means of a bell rung by clockwork, and the clock was set in 

 motion by a current from the sending station at the required moment 

 through an ingenious adjunct to the trough. Over the wires marked 

 B and c in d and c^ is shown in the figure what appears like a small 

 inverted spoon. It is, in fact, a small hemispherical bowl attached to 

 one end of a long lever, the other arm of which is bent twice at right 

 angles, the whole being capable of taking up the position shown by 

 the dotted lines in d- A leaden ball slides on the upper arm, and is 

 so adjusted that when the water in the hemispherical bowl is displaced 

 by gas rising from the wires B and c (as shown in Q>), the oowl rises 

 to the top, and the lead ball slips off through the funnel-shaped vessel, 

 and in falling acts on a detent, which releases the clockwork, and then 

 the bell is rung. The polar wires of the pile terminate in metallic 

 pegs, which are placed by the sender in the terminals where the letters 

 he wishes to signal are marked. He would begin his operations by 

 placing one at B, the other at c, and then after a sufficient interval for 

 the setting in action of the alarum apparatus, and for obtaining the 

 requisite attention at the receiving station, he would begin to spell 

 out the letters of the message two at once. For gas will be seen to 

 move from two of the terminals in d ; and, as the reader is already 

 aware, there will be twice as much hydrogen as oxygen gas (page 376) 

 a difference which is at once appreciable to the eye. It will be 

 noticed that the pegs terminating the polar wire have different shapes. 

 Suppose that with the V-shaped peg is attached to the negative pole of 

 the pile ; if they be placed as shown at B 2 , the observer at d would see 

 hydrogen gas issuing from the " A " wire, and oxygen from the " F " 

 wire ; and he would read the letters a-f, it being agreed that the letter 

 indicated by the large stream of gas should be read first in order. If 

 the sender places the pegs as at BJ, the letters indicated would there- 

 fore not be ch but he. By certain expedients afterwards suggested it 

 would be possible to reduce the number of wires to two. 



When QErsted had announced his discovery of the action of the 

 current upon the magnetic needle, Ampere at once suggested the 

 application of the principle to telegraphy. At first it was intended to 

 use as many needles and as many wires as there are letters in the 

 alphabet. But in order that the action of a single wire (as represented 

 in Fig. 272) should be distinct and rapid, a rather powerful current is 

 required ; and as such currents cannot be sent through long circuits 

 except by very great battery power, practical success would not have 

 been attained for the electric telegraph had not the same expedient 

 which furnished electric science with one of its most useful instru- 

 ments of research, also supplied the means of making the current from 



