Electric Lighting.

A very large audience listened to an interesting lecture on "Electric Lighting," given last evening in the lecture room of the Jefferson Physical Laboratory by Dr. Edwin H. Hall. The lecturer gave first a sketcle of the various discoveries in electricity and then explained the theory of the are and incandescent lights. Electricity has been known to mankind for more than 2,000 year, but only during the last ten years has it been used practically for lighting. The electricity generated by friction, when discharged gives a spark of great brilliancy but of very short duration. The discoveries in chemical electricity, by Galvani, and in induced currents, by Faraday, were the greatest strides in our knowledge of the properties of electricity.

The more powerful machines are called "Series machines," in which the current from the dynamo is strengthened by passing through all the large coil of its electric-magnet. The ordinary are light is made by breaking the outside circuit of a Series machine. The carbon tips must be together when the current is started, and the break is made by lifting the upper one a little by a mechanical arrangement. The powerful current, in overcoming the resistance offered by the air, heats the carbon tips to a white heat. In the incandescent lamp the resistance is offered by a filament of carbon encased in an air-tight glass-bulb. The current required to drive an are light will drive twenty-four 16-candle incandescent lamps.

The lecturer illustrated his remarks by numerous experiments, one of which was very beautiful. The magnified image of an are light was thrown upon a screen, and its intense heat shown by burning a clay pipe in the arc.