239 



SCIENTIFIC RECREATIONS. 



to the earth (fig. 251), and in order that these may be quite dry, an inverted 

 cup of metal, glass, or earthenware is placed over it, or the whole is blown 

 or moulded in one piece. If the support for the wires were not kept from 

 the rain, the wet would form a conducting surface, and allow the electricity 

 to escape into the earth. 



The Telegraph Alphabet, in the two-needle instrument, now not 

 generally used in England, is given below. 



TWO-NEEDLE ALPHABET. 



Of both Needles together. 



Moving to right. 

 Moving to left. 



Twice to right. 

 Twice to left. 



One to right, one to left. 

 One to lelt, one to right. 



Two to right, one to left. 

 One to right, two to left. 



In the single needle instrument the letters are indicated by right and 

 left vibrations, from A one right, to B one right and left, and so on, increas- 

 ing to Z. This mode is now generally used. 



The manner in which the current passes is shown by the following 

 illustrations (figs. 252, 253). 



For the sake of clearness, the diagram has been drawn with simple 

 lines only. In the real needle-machine the construction is much more 

 complicated ; perspective drawings of it may be seen in Lardner's " Electric 

 Telegraph," and numerous other works. In fig. I , B is a single cell of a 

 battery containing a plate of copper, C, and a plate of zinc, Z, immersed in 

 sulphuric acid and water. H is the handle of the instrument, turning from 

 left to right, and vice versa, like the handle of a door, consisting of two 

 pieces of brass insulated from each other by being inserted in an axis of 

 ivory. To the ends of the two pieces of brass are fixed the wires, CW and 

 zw, leading from the copper and zinc ends of the cell respectively. Fixed 



* Monvel's u Course of Physics." 



