Fig. 72. FBENCH STATE TELEGRAPH. 



THE ELECTRIC TELEGRAPH. 



CHAPTEE VI. 



137. Relation of the deflection to the direction of the current. 138. 

 Galvanometer or multiplier. 139. Method of covering the wire. 

 140. Method of mounting the needle. 141. Method of transmitting 

 signals by the galvanometer. 142. How the current may produce 

 a temporary magnet. 143. Electro-magnet constructed by Pouillet. 

 144. Electro-magnets formed by two straight bars. 145. They 

 acquire and lose their magnetism instantaneously. 146. Magnetic 

 pulsations as rapid as those of the current. 147. How they are 

 rendered visible and counted. 148. Extraordinary celerity of the 

 oscillations thus produced. 149. They produce musical sounds by 

 which the rate of vibration may be estimated. 150. How the vibra- 

 tions may impart motion to clock-work. 151. Their action on an 

 escapement. 152. How the movement of one clock may be trans- 

 mitted by the current to another. 153. How an electro-magnet may 

 produce written characters on paper at a distant station. 154. How 

 the motion of the hand upon a dial at one station can produce a like 

 motion of a hand upon a dial at a distant station. 155, How an 

 agent at one station can ring an alarum at another station. 156. Or 

 may discharge a gun or cannon there. 157. Power of the bell or other 

 signal not dependent on the force of the current. 158. Mechanism of 

 telegraphic alarum. 159. Various alarums in telegraphic offices. 

 160. Magneto-electricity. 161. Method of producing a momentary 

 magneto-electric current. 162. Application of an electro-magnet to 

 produce it. 



LABDNER'S MGSEUM OF SCIENCE. o 193 



No. 39. 



