THE LAWS OF LIFE. 247 



chemical action constitutes a single current in that 

 direction ; the oxygen being also attracted, there 

 arises in the air a double current, one towards and 

 one away from the flame. Now the hydrogen 

 current towards the flame and the nitrogen current 

 from the flame being on opposite sides are in the 

 same direction ; and it may be conceived, in theory 

 at least, that by a mechanical arrangement of tubes 

 these two currents might be united, so that the 

 impulse of the current of nitrogen from the flame 

 should serve to augment the momentum of the 

 hydrogen current towards the flame, facilitating by 

 so much its union with the oxygen. 



In a zinc and platinum galvanic battery the pro- 

 cess which takes place is the same the element 

 added is a resistance to the freely circulating 

 currents we have been considering. For the par- 

 ticles of the zinc are attracted to the point of 

 chemical union in the same way as those of 

 hydrogen are attracted, but the cohesion of its 

 structure resists their motion. Hence there is 

 produced in it a tension, which, while on the one 

 hand it represents the motion of its particles to- 



