SCT. XXIX. VOLTAIC ELECTRICITY. 295 



is neither so sudden nor so intense as that of common 

 electricity, yet it acquires such power from constant 

 accumulation and continued action, that it ultimately 

 surpasses the energy of the other. The two kinds of 

 electricity differ in no circumstance more than in the 

 development of heat. Instead of a momentary evolu- 

 tion, which seems to arise from a forcible compression 

 of the particles of matter during the passage of the com- 

 mon electric fluid, the circulation of the Voltaic electricity 

 is accompanied by a continued development of heat, 

 lasting as long as the circuit is complete, without pro- 

 ducing either light or sound ; and this appears to be its 

 immediate direct effect, independent of mechanical ac- 

 tion. Its intensity from a very powerful battery is 

 greater than that of any heat that can be obtained by 

 artificial means, so that it fuses substances which resist 

 the action of the most powerful furnaces. The temper- 

 ature of every part of a Voltaic battery itself is raised 

 during its activity. 



When the battery is powerful, the luminous effects of 

 Voltaic electricity are very brilliant. But considerable 

 intensity is requisite to enable the electricity to force its 

 way through the air on bringing the wires "together 

 from the opposite poles. Its transit is accompanied by 

 light ; and in consequence of the continuous supply of 

 the fluid, sparks occur every time the contact of the 

 wires is either broken or renewed. The most splendid 

 artificial light known is produced by fixing pencils of 

 charcoal at the extremities of the wires, and bringing 

 them into contact. This light is the more remarkable, 

 as it appears to be independent of combustion, since the 

 charcoal suffers no change, and likewise because it is 

 equally vivid in such gases as do not contain oxygen. 

 Though nearly as bright as solar light, it differs materi- 

 ally from it when analyzed with a prism. Professor 

 Wheatstone has found that the appearance of the spec- 

 trum of the Voltaic spark depends upon the metal from 

 whence the spark is taken. The spectrum of that from 

 mercury consists of seven definite rays, separated from 

 each other by dark intervals ; these visible rays are two 

 orange lines close together, a bright green line, two 

 bluish green lines near each other, a very bright purple 



