WHA T THE ELECTRIC LIGHT IS. 15 



the electric light. If, instead ot employing a generator of 

 high tension, a generator of electricity in quantity is used, such 

 as a battery, especially the battery with acids, the effects are 

 different : the discharge cannot spontaneously be produced 

 between the opposed electrodes if these be separated by 

 even an extremely small interval. In this case it is ne- 

 cessary to bring the electrodes into contact, so as to develop 

 a calorific effect, and since the. surrounding gases are then 

 made conductors by the heat, the electrodes may afterwards 

 be separated from each other and the discharge be made 

 to take place through the gaseous medium, but not with 

 more than a very small separation of the electrodes. 



It must not be supposed that any one source of electricity 

 is especially suitable for producing the electric light : what- 

 ever the source may be, it can always be arranged so as to 

 supply the desired effect. For instance, a battery is capable 

 of giving tension effects if a large number of well insulated 

 cells joined by their opposite poles are employed. Gassiot 

 has succeeded in obtaining sparks with a battery of 3,000 

 small cells containing water only, each cell insulated by glass 

 supports; and Warren de la Rue has obtained still more 

 important results with chloride of silver batteries. In another 

 direction, Gaston Plante, with his polarization batteries and 

 his rheostatic machine, has succeeded in producing by vol- 

 taic discharges sparks of 4 centimetres in length. By a re- 

 verse method the intensity of a generator can be increased 

 at the expense of its tension, by condensing its charges, or 

 by arranging for quantity the elements which co-operate in 

 the production of the electricity. Thus, an induction ma- 

 chine is able to give effects of quantity, if thick wire is used 

 for the induced coil, and if the different coils brought into 

 action are so connected that the induced currents, instead 

 of passing from one coil to another, shall issue simultane- 

 ously from each individual coil, and all traverse the same con- 

 ductor at once. In this case, as in the former, the pre- 

 ponderance of intensity over tension may be varied at will 



