HISTORY AND PROGRESS. 57 



at the lowest point and closes an electric circuit, by which 

 the paper is lifted up against the type- wheel, and the letter 

 printed. 



The key-board used to elevate the contact pins is shown 

 in Fig. 27. It consists of twenty-eight keys, alternately 

 white and black, marked with the twenty^six letters of the 

 alphabet, a full stop, and a blank, corresponding to an empty 

 space in the type- wheel. Below each of the keys is a mov- 

 able lever, whose fulcrum is at K", and which terminates at the 

 bottom of one of the contact pins K K, arranged in a circle 

 in the metal box A, in the top and bottom of which are 

 holes for the ends to protrude the upper holes being long, 

 to allow of a radial motion. Each pin is held down by the 

 pressure of a small spring, but may be elevated by pressing 

 down the corresponding key of the piano-board. 



Fig. 28 gives a vertical section of the printing instrument 

 and key-board. The section shows a white key, hinged at 

 K", connected to its lever K', a contact pin, k, on the right, 

 and also to a black key, whose lever reaches to a contact pin 

 on the left of the box A. The contact pins are provided with 

 shoulders to limit their movements in each direction. 



The horizontal arm, which travels over the circle of con- 

 tact points, is attached to the bottom of the vertical arbor Q, 

 to which motion is imparted by the bevelled wheel G 2 , on 

 the shaft G. It is made up of three principal parts the 

 arm r, jointed at a ; the resting piece, or earth-contact, r ; 

 and the shovel r. The vertical shaft Q is of brass, and is 

 divided electrically into two parts by an insulating ring of 

 ivory, q. The lower part is supported by the central pedestal, 

 which is insulated from the box A by a non-conducting ring. 



The continuation of the jointed arm r, which is held by 

 the portion of the shaft above the insulating ring q, is 

 pressed down by a spring, which keeps a small screw in 

 the middle of the continuation in metallic contact with the 

 second piece r , supported by the portion of the shaft below 

 the ring. The shovel r is of steel. 



"When a key is depressed, the corresponding contact pin 

 is elevated, and if the arbor Q is in motion, the extremity 



