286 LIGHT AND ITS ARTIFICIAL PRODUCTION. 



is the source of the luminosity. But while in all flames, and also in 

 the incandescent gaslight, the heating of the carbon or the mantle is 

 produced by the heat developed in the combustion of the gas, in 

 electric lights the heat of combustion of coal or of gas serves first for 

 the production of electric energy, which can be transmitted over con- 

 siderable distances and which, far from the furnace, heats up the fila- 

 ment of the incandescent lamp or the carbons of the arc lamp to a 

 white heat. Naturally a considerable quantity of energy is lost in this 

 roundabout process. For while in a gas flame the heat energy of the 

 gas is directly transformed into light, witli electric lights, for which, 

 for example, the power is originally supplied by a gas motor, the gas 

 first sets in motion the gas motor, this in turn drives the dynamo, and 

 finally the electric current thus produced brings the carbon to incan- 

 descence. Only a few per cent of the heat of combustion of the fuel 

 reappear as light. For this reason, however, this roundabout process 

 furnishes most acceptable light. In it only the i)Ower absolutely neces- 

 sary for heating the carbon filament is conducted into the room, while 

 the noxious products of combustion of coal, of petroleum, of gas, etc., 

 are taken care of in the electric power house. In the incandescent 

 electric lights the only heat introduced into the room is that necessary 

 for raising the temperature of the filament and which the filament 

 radiates in the form of light and heat. 



The gas flame, the petroleum light, the candle, in short, all gaslights 

 in the broadest sense of the word necessitate very much greater heat 

 effects. In all of them there is a continuous current of the products 

 of combustion, together with the carbon particles producing incan- 

 descence. In order to maintain around the flame the high temperature 

 required for the incandescence of the carbon particles a large space 

 must be brought to a high temperature. All parts of the flame, the 

 chimney of the lamp, and the surrounding air must become hot if the 

 combustion temperature of the gas is to reach its highest value, and 

 thus enable the carbon particles or the incandescent mantle to radiate 

 most eificiently. The heat carried off by the products of combustion 

 is partly utilized in the regenerative burner of Fr. Siemens, in which 

 the gas supplied to the burner is first heated by these hot gases. We 

 can thus see why all flames are attended by the evolution of large 

 quantities of heat. But, unfortunately, the flame emits not only heat. 

 The most important product of combustion is carbon dioxide, which is 

 produced at the expense of the oxygen of the air, and with which, 

 together with other noxious gases (carbon monoxide, sulphur dioxide, 

 etc.), the air becomes charged. 



This harmful action accompanies the ordinary gaslight as well as 

 the incandescent gaslight, although in the latter it is much less for 

 the same candle power. While the electric light is much more expen- 

 sive than the incandescent gaslight on account of the very poor return 

 for the heat of combustion of the fuel, its advantages over the free- 

 burning flame is very great from a sanitary standpoint. By giving 



