66 



current of electricity for a motive power, it must be con- 

 verted into magnetism, which is easily done by wrapping 

 insulated copper wire, in many turns, around soft iron of 

 any convenient shape. 



One of the many practical uses of the electric current 

 he explained by the use of apparatus which was put up 

 in a circuit about the hall. It represented a circuit of 

 street gas-lights, s.uch as have been in use in Ward Three 

 in this city since last fall, and though the winter has been 

 an unusually severe one, they have proved themselves 

 equal to it, and have worked with perfect success through 

 the severest storms. The apparatus consisted substan- 

 tially of an electro magnet, an armature, ratchet wheel 

 and pawl. Two wires led from the battery at the cen- 

 tral station to the first light in the circuit, and thence to 

 each one in its turn. When a current was scut out on the 

 lighting wire, the magnet was charged, the armature of 

 which actuates the pawl and ratchet wheel, thus opening 

 the cock to let on the gas, at the same time, by an inter- 

 ruption of the current at the tip, lighting the gas; At 

 the expiration of the half second of time which it takes 

 to turn on and light the gas, the current was sent forward, 

 by the action of a cam and spring, to the next light, and 

 so on to the end of the circuit. A reversal of the switch 

 at head quarters sent out a current on the other wire, 

 which by a similar operation turned off the gas at the rate 

 of four burners in one second. 



After explaining the apparatus very fully and minutely, 

 in its capacity as a burglar alarm, etc., the lecturer passed 

 on to the consideration of some other branches of electri- 

 cal science. The subject of ocean telegraphy was taken 

 up and treated as fully as the tiuie would permit, by the 

 use of actual working apparatus and diagrams. 



After speaking of the importance of international tele- 



