SCIENCE OF COMMON THINGS. 



301 



Telegraph, magnetic, principles of. 



Intelligence, how conveyed by. 



Fig. 96. 



vents the point from resting upon the paper when the telegraph is not in 

 operation. 



1940 Why is it necessary, in conveying the telegraph wires, to support 

 them upon glass or earthen cylinders f 



These are used for the purpose of insuring the perfect 

 insulation of the wires, since but for this the electricity 

 would pass down a damp pole to the earth, and be lost. 



1941 Is there any truth in the idea that many persons have, that some 

 principle passes along the telegraphic wires when intelligence is transmitted ~? 



This supposition is wholly erroneous ; the word cur- 

 rent, as something flowing, conveys a false idea, but we 

 have no other term to express electrical progression. 



1943 How can we, gain an idea of what really takes place, and of the 

 nature of the influence transmitted ? 



The earth and all matter are reservoirs of electricity ; 

 if we disturb this electricity at Boston by voltaic influ- 

 ence, its pulsations may be felt in New York. Suppose 

 the telegraphic wire were a tube, extending from 

 Boston to New York, filled with water. Now, if one 

 drop more is forced into it at Boston, a drop must fall 

 out at New York, but no drop was caused to pass from 

 Boston to New York. Something similar to this occurs 

 in the transmission of electricity. 



