236 



SCIENTIFIC RECREATIONS. 



wire surrounding it. When the electric current passes through the coil, it 

 will turn out of the upright position to either one side or the other, accord- 

 ing to the direction of the current, from its tendency to assume a position 

 at an angle thereto (fig. 248) ; if the current be stopped even for an instant, 

 then the needle, or magnet, will again assume its upright position. The 

 pivot of this magnet is brought forward, and has on its front part another 

 needle, which turns with it ; this is visible on the outside of the apparatus, 

 and is looked at to ascertain the movement of the one within. There is 

 also an arrangement called a " commutator," so contrived, that by moving a 



Fig. 245.- The circuit. 



handle to the right or left, a connection shall be made with either end of 

 the battery, and thereby cause the direction of the current and needle to be 

 changed at pleasure ; also by moving the handle into an upright position 

 the current shall be stopped ; and finally, by a third movement, a bell shall 

 be rung. Now, as has already been explained, when the current goes in one 

 direction, the magnetic needle is deflected in that direction ; and when the 

 current is reversed the position of the needle is also reversed, and when the 

 current is cut off the needle will resume its perpendicular position. If two 

 such needles and two such handles be at each station, when the handles at 

 one station are moved, the needles at the other station will take on a similar 



Fig. 246. 



Fig. 247. 

 Magnetic needles. 



movement ; and when the handles at that station are moved, the needles at 

 the first station will be moved to correspond. This constitutes the system 

 of communication kept up by the electric telegraphs in England ; but it 

 remains to be shown how all the letters of the alphabet and numerals can 

 be represented by the movements of the two handles. These handles can 

 ;be placed in eight positions (besides the upright one) by a single movement 

 of each hand, as may be seen in fig. 249 ; and these eight signals if repeated, 

 or made twice in rapid succession will make eight more, and by being 

 repeated three times will constitute a third eight, making twenty-four ; 

 finally, by a rapid motion right and left, they may be caused to signify a 



