ON SOME MARVELS IN TELEGRAPHY. 241 



must remind the reader that this is only a convenient way 

 of expressing the fact that the wire assumes a certain condi- 

 tion when it connects two such plates, and is capable of 

 producing certain effects. Whether in reality any process is 

 taking place which can be justly compared to the flow of a 

 current one way or the other, or whether a negative current 

 flows along the circuit one way, while the positive current 

 flows the other way, are questions still unanswered. We 

 need not here enter into them, however. In fact, very little 

 is known about these points. Nor need we consider here 

 the various ways in which many pairs of plates such as I 

 have described can be combined in many vessels of dilute 

 acid to strengthen the current. Let it simply be noted that 

 such a combination is called a battery ; that when the ex- 

 treme plates of opposite kinds are connected by a wire, a 

 current of electricity passes along the wire from the extreme 

 plate of that metal which is least affected, forming the posi- 

 tive pole, to the other extreme plate of that metal which is 

 most affected and forms the negative pole. The metals 

 commonly employed are zinc and copper, the former being 

 the one most affected by the action of the dilute acid, usually 

 sulphuric acid. But it must here be mentioned that the 

 chemical process, affecting both metals, but one chiefly, 

 would soon render a battery of the kind described useless ; 

 wherefore arrangements are made in various ways for main- 

 taining the efficiency of the dilute acid and of the metallic 

 plates, especially the copper : for the action of the acid on 

 the zinc tends, otherwise, to form on the copper a deposit of 

 zinc. I need not describe the various arrangements for 

 forming what are called constant batteries, as Daniell's, 

 Grove's, Bunsen's, and others. Let it be understood that, 

 instead of a current which would rapidly grow weaker and 

 weaker, these batteries give a steady current for a consider- 

 able time. Without this, as will presently be seen, tele- 

 graphic communication would be impossible. 



We have, then, in a galvanic battery a steady source of 

 electricity. This electricity is of low intensity, incompetent 



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