112 THE ELECTRIC TELEGRAPH. 



and the similarity in the behayiour of galvanic and frictional 

 electricities has also been spoken of. 



When Siemens and Halske were engaged in the construc- 

 tion of their subterranean line between Berlin and Frank- 

 fort-on-the-Maine, and Kramer his between the Prussian 

 capital and Cologne, in 1848, they were both astonished to 

 observe a phenomenon resulting from the two facts alluded 

 to above. 



Dub says : " Whilst Kramer was able to speak with the 

 greatest ease on an overland line from Berlin to Magdeburg, 

 he found it absolutely impossible to do the same on a subter- 

 ranean line. With the greatest trouble and slowness, accord- 

 ing to his own account, it was scarcely possible for him to 

 accomplish a satisfactory correspondence between Potsdam 

 and Magdeburg. Siemens and Halske found the same diffi- 

 culty with their instruments, particularly on the line between 

 Erfurt and Halle, which set all their efforts at defiance. An 

 exchange of the apparatus was also without result. Bad 

 insulation was, at first, supposed to be the cause of the dis- 

 turbances ; but it soon appeared that the better the insula- 

 tion, the greater became the difficulty. Kramer says that he 

 has often left his bureau and destroyed the insulation of his 

 line at a thousand paces distance, in order to be able to 

 forward a despatch with greater ease." 



Dr. Werner Siemens, writing about the same date, in a 

 paper* presented to the Academy of Sciences in Paris, says 

 that when the extremity, B, of a covered wire was insulated, 

 and the other end, A, made to communicate with a battery 

 of which the opposite pole was to earth, the instant of contact 

 being established, a current of short duration was observed in 

 those parts of the wire not too remote from the battery, in 

 the same direction in which the current traversed the line, 

 when the end B was brought into contact with the earth. 

 When the wire was perfectly well insulated, he did not 

 observe, after the first instant, the least trace of current. On 

 replacing, suddenly, the battery (by means of a key), by a 



* Memoire sur la Telegraphic Electrique, 1850. 



