126 GALVANIC ELECTRICITY. 



298. THE EARTH, USED AS A CONDUCTOR. 



What ^s said 



of the earth It would seem requisite to extend both ends 



as^conduc- of the wire f orming the coil through all 



the intervening distance, and then to con- 

 nect them with the opposite poles of the battery ; but 

 it is found, in practice, that one is sufficient, and that 

 all the middle portion of the second wire may be dis- 

 pensed with. The remaining ends, one connected 

 with the helix, and the other with the battery, being 

 made to terminate in large plates, and buried in the 

 ground, the earth between them is found to take the 

 place of the second wire, and complete the circuit. 



Mention some 299. APPLICATIONS OF THE TELEGRAPH. 



remarkable There are many applications of the tele- 



applications t 



of the tele- graph beside the one of transmitting intel- 

 graph. ligence to distant places. In the city of 



Boston, an alarm of fire is instantaneously communi- 

 cated throughout the city, and the bells rung by tele- 

 graphic apparatus. 



In Marseilles, France, a single clock is made by sim- 

 ilar means to indicate the time on dials, placed in the 

 street lamps of the city. Electro-magnetic apparatus 

 has also been employed with the most remarkable suc- 

 cess in increasing the dispatch and accuracy of astro- 

 nomical observations ; making it possible to accomplish 

 during a single night in the study of the heavens, what 

 formerly cost a month of labor. 



300. PHYSIOLOGICAL EFFECTS OF GAL- 



Describe the 



physiological VANisM. The nerves of animals are ex- 

 fanism f ? ff<a ' tremel 7 susceptible to the galvanic influ- 

 ence. The apparatus represented in the 



