206 THE ELECTRIC TELEGRAPH. 



105. Steinheil 1 s Lightning Discharger. Steinheil* seems to 

 have been the first who supplied the receiving apparatus with 

 an arrangement for protecting it from the effects of atmos- 

 pheric electricity. The method of doing this probably was 

 suggested to him from observing that sparks sprang over 

 from convolution to convolution of the multiplier coils of the 

 apparatus employed on the line between Munich and JSTan- 

 hofen in preference to going through the whole lengths of 

 vhe coils to earth. He concluded justly from this that 

 atmospheric electricity which charged his line resembled, in 

 its disposition to spring over short distances, the better known 

 frictional electricity, and differed in this respect from galvanic 

 electricity. 



The behaviour of the two electricities is in no way more 

 contrasted than in their choice of circuits. If, for example, 

 a galvanic battery be inserted between 

 the points a and I, Fig. 112, the same 

 being already joined by the long spiral 

 wire to, the whole current will pass 

 through the latter and none will go 

 over the space between a and b, how- 

 ever near they may be, if they do not 



make absolutely metallic contact with each other. But if, 

 instead of the galvanic-battery, a charged electric-battery or 

 Leyden jar be substituted, the inner coating, for instance, 

 being connected to a and the outer to 5, it would discharge 

 itself immediately over the small space between a and b, and 

 very little, if any, would pass through the coil w. Thus the 

 way which for galvanic electricity offers an infinite resist- 

 ance, is for static electricity a short circuit. 



Steinheil based the construction of his lightning- guard on 

 this physical law. Instead of bringing the two ends of the 

 line wire into the station, he fixed each of them to a plate of 

 metal 6 inches square, erected over the bureau in which the 

 apparatus was contained. These two plates were insulated 

 from each other by an intervening layer of silk-stuff, which 

 offered an almost infinite resistance to the passage of a voltaic 



* In 1846. Dingler's Journal, 109, p. 302. 



