THE ELECTRIC TELEGRAPH. 



Fig. 



Of the various voltaic combinations which have been applied in 

 scientific researches, four only have been found available to any 

 considerable extent in the working of electric telegraphs, the zinc 

 and copper plate combination described above, Daniel's constant 

 battery, Grove's battery, Bunsen's modification of it, and the 

 magneto-electric apparatus. 



32. Daniel's combination, which is extensively used in 

 working the telegraphs on the continent, consists of a 

 copper cylindrical vessel c c, fig. 3, widening near the top 

 a d. In this is placed a cylindrical vessel of unglazed 



porcelain p. In this latter is placed the 

 hollow cylinder of zinc z, already described. 

 The space between the copper and porcelain 

 vessels is filled with a saturated solution of 

 the sulphate of copper, which is maintained 

 in a state of saturation by crystals of the 

 salt placed in the wide cup abed, in the 

 bottom of which is a grating composed of 

 wire carried in a zigzag direction between 

 two concentric rings, as represented in plan 



at G. The vessel p, containing the zinc, is filled with a solution 

 of sulphuric acid, containing from 10 to 25 per cent, of acid when 

 greater electro-motive power is required, and from 1 to 4 per cent. 

 when more moderate action is sufficient. 



33. The following modification of Daniel's system was adopted 

 by M. Pouillet in his experimental researches, and is the form 

 and arrangement used in France for the telegraphs. A hollow 

 cylinder a, fig. 4, of thin copper, is ballasted with sand &, having 



a fiat bottom c, and a conical top d. 

 Above this cone the sides of the copper 

 cylinders are continued, and terminate 

 in a flange e. Between this flange and 

 the base of the cone, and near the base, 

 is a ring of holes. This copper vessel 

 is placed in a bladder which fits it 

 loosely like a glove, and is tied round 

 the neck under the flange e. The satu- 

 rated solution of the sulphate of copper 

 is poured into the cup above the cone, 

 and, flowing through the ring of holes, 

 fills the space between the bladder and 

 the copper vessel. It is maintained in 

 its state of saturation by crystals of the 

 salt deposited in the cup. 



This copper vessel is then immersed in a vessel of glazed 

 126 



Fig. 4. 



