The electric light owes its existence to the intense heat that the electric current produces, and heat lies at the root of every system of artificial illumination. For instance, suppose we take a common match and light it, we light it simply because by the friction of the two surfaces together we generate heat, the heat burns the substance of which the match is made. We are able to light a common candle because we have applied heat to the wick, the heat liquefies the wax of which the candle is made, the wax is decomposed, it combines with the oxygen of the air, intense heat is produced at that point, carbon is consumed, and the consequence is light. So with all our various modes of artificial illumination. Gas, as you are well aware, produces intense heat, and the result of that heat is light. There are various ways in which gas is applied to produce heat and the necessary consequence--light. Here is a Sellon gas burner, in which the combustion of gas raises the temperature of a fine platinum cap, and the result is, as you see, a very beautiful light. In one lamp we have a cap or mantle, in the other case there is merely a flat disk gauze of platinum. The combustion of the gas produces intense heat, which raises the network to a very high state of temperature, though in the present case the light is not so good as it should be, probably through the pressure in the supply main not being sufficiently great. In another case we have a gas jet surrounded with a network of some vegetable matter, linen or cambric, steeped in a solution of salts of zirconium, and a few other rare earths, and the intense heat of the gas causes a very high temperature, and, as you see, a very brilliant effect is produced. You will see from this that in all cases of artificial illumination bodies have to be raised to a high state of temperature. I hold in my hand a piece of magnesium wire; it is really flat magnesium tape, but it is called wire. If I heat that, you will observe that a very brilliant light is produced, due to the very high temperature at which it burns. Now, if I take a lump of coal and heat it--it requires to be raised to a certain temperature before the oxygen is directed upon it--and subject it to a jet of oxygen, you will see that it burns with very much more intense light than you are accustomed to in the ordinary fire. If I take a piece of iron wire and place it in a jar of oxygen, you see what a very brilliant effect the combination of oxygen and iron produces through the iron being raised to a very high temperature.