144 MIKENG INDUSTEY. 



zinc and a copper plate, and their connecting wires, in tlie usual way. They 

 are placed in a little cabinet of shelves in the engine-room. The ground wire 

 leads directly to the earth, in which the end is buried two or three feet deep. 

 The other wire, having three branches, leads to three boxes, each containing 

 a gong-apparatus, there being one for each hoisting compartment. The wire 

 used for this purpose, and for connecting the gong-apparatus with the signal 

 boxes at the stations in the shaft, consists of a small copper twist or rope of 

 seven strands of wire, encased in a rubber coating. The metallic portion, 

 twisted, is about one-tenth of an inch caliber. The whole, including the en- 

 velope, is about one-fifth of an inch thick. 



The gong-apparatus consists of a light wooden box, containing the coil 

 referred to, or, in fact, two coils, 5 or 6 inches long, and 2 or 3 in diameter. 

 Two metallic, upright pieces!, attached to the coils, pass upward through the 

 top of the box. These uprights are each fitted with a perforated knob, one 

 of which receives the wire leading from the battery, the other receiving the 

 wire leading down the shaft. When, therefore, the circuit is completed by 

 the connection of the shaft wire with the ground wire at the station, as be- 

 fore described, the current, passing through the coils, renders them magnetic, 

 and attracts the iron bar by which the gong is rung. The contrivance for 

 this purpose consists of a light iron bar, placed horizontally about half an 

 inch below the coils, the end nearest the coil resting, when not lifted by mag- 

 netic attraction, on an adjustable support; the other end being pivoted, and 

 permitting free angular motion of the bar whenever the magnetic coil exerts 

 its attractive force upon it. The pivoted end forms a right angle like a bell- 

 crank, so that, when one end of the bar is lifted by the coil, the other end, 

 performing a corresponding movement, sets the gong hammer in motion. 

 When the apparatus was first introduced the hammer was attached directly 

 to this bar of iron; but, as it struck the gong with too little force, another 

 arrangement was brought into use, consisting of a clock work, set in motion 

 by a weight, and acting upon a strong spring carrying the gong-hammer, the 

 clock work being restrained from action by a ratchet wheel, the teeth of 

 which are in contact with the end of the iron bar just described. When the 

 bar is lifted by magnetic action the ratchet wheel is released, the clock work 

 set in motion, and the gong struck with force and clearness. 



