TOO Human Physiology. 



by the union of one drop of water with four grains of zinc 

 would make a strong flash of lightning. 



Galvanism is a more manageable form of electricity, usually 

 produced by the union of metals with oxygen. An atom ot 

 oxygen seizes upon an atom of zinc, and sets free the force with 

 which the zinc atom held to its fellows. This force, ready for 

 action, passes along a wire from atom to atom with inconceiv- 

 able rapidity, a rapidity like that of light. When the conducting 

 wire passes with many turns round a piece of soft iron, the 

 latter becomes a magnet, having an attractive force proportioned 

 to the intensity of the current and the number of turns in the 

 coil; break the circuit and you have a spark or flash; let it pass 

 from point to point of charcoal in a vacuum and you have the 

 electric light. You can reverse this action and by the motion 

 of permanent magnets produce an electric current. A small 

 stream of water, or a steam engine can be used as well as the 

 chemical action of oxygen and metals. Wilde's Magneto- 

 Electric Engine converts the force of a three horse-power 

 steam engine into electricity, heat, and light. As heat, it melts 

 iron rods 15 -inches long and -inch diameter. The light at 

 two feet distance has three times the intensity of sunshine; and 

 in it at the distance of a quarter of a mile the flames of gas 

 street lamps cast shadows. Galvanism appears to act with the 

 same force through all distances. The same current operates 

 at one point or a hundred. It heats a wire of any length to 

 the same redness; just as the same telegraph wire gives with 

 the same force a message at one or a thousand different places ; 

 facts which seem to me quite irreconcilable with the current 

 doctrines of the conservation of forces. 



Count Rumford, about the beginning of the century, super- 

 intending the boring of cannon at Munich, observed the heat 

 produced by the friction when the borers became dull. Boring 

 in a vessel of water, he made it boil ; and came to the conclu- 

 sion that heat was a mode of motion. A rifie ball flattened 



