THE ELECTRIC TELEGRAPH. 



the line -wire upon which it is transmitted, the more or less perfect 

 state of the insulators, and in fine on the weather. 



If the current become so feeble that the attraction of the 

 magnet is less than the force of the spring s, the armature g o will 

 remain upon the stop t, from which the magnet is too feeble to 

 remove it. If, on the other hand, the spring have not sufficient 

 force to overcome the friction and inertia of the armature g o, and 

 the small portion of magnetism which may be retained by the 

 electro-magnet after the current has been suspended, the armature 

 will remain upon the stop ', the spring being unable to produce 

 its recoil. 



Since therefore the forces against which the spring s acts, and 

 which it ought to exceed, and those which act against it and 

 which ought to exceed it, are variable, it is clear that the mainte- 

 nance of the efficiency of the apparatus requires that the spring s 

 shall from time to time be adjusted, so as to be kept in that 

 relation to its antagonistic forces, which are necessary for the due 

 performance of the telegraph. 



It has been already shown that very sufficient and very simple 

 means of adjustment for this purpose have been supplied in 

 the French telegraphs. The hands which appear in the upper 

 corners of the instrument (fig. 70) are intended for this purpose, 

 and being turned by the key, the springs connected with them are 

 increased or diminished in their force, according as the key applied 

 to them is turned the one way or the other. Similar adjustments 

 are provided in the German instruments. 



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