RECENT WONDERS OF ELECTRICITY. 673 



energy to it, and it sets the whole air of this room in motion, and 

 every tympanum of every ear present is struck by the little bullets of 

 air that are thrown into vibration, and the result is the effect called 

 sound. As another illustration, I will take coal. I take a small piece 

 of coal and warm it in an iron cup, so as to cause it to give out a little 

 kinetic energy in the shape of heat, and, on placing it in this jar of 

 oxygen [experiment performed], you see that the mere insertion of 

 coal, slightly heated, in an atmosphere of oxygen, produces a most 

 brilliant effect, which is the result of the conversion of the potential 

 energy existing in the carbon, or coal, into the kinetic energy seen in 

 tbe shape of motion, heat, and light. We have even more brilliant 

 effect of this conversion of potential into kinetic energy. Here is a 

 piece of magnesium wire which, when heated [light applied], has its 

 potential energy converted into kinetic energy, and a most brilliant 

 light is the result. But we need not go to light, and we need not go 

 to heat, for instances of energy. I have shown you that energy is a 

 form of motion ; that it is so found in sound, heat, and light ; but we 

 also have energy as magnetism. There is a little toy-duck floating on 

 the basin of water before me, and I merely hold in front of it a mag- 

 net, when you will see that a sort of affection is set up between the 

 duck and the magnet, by the duck following the motion of the mag- 

 net round the basin. That is another form of energy. The last form 

 of energy that I wish to draw your special attention to is that due to 

 electricity. You have all seen the vivid flashes of lightning and have 

 heard the dreadful roar of thunder ; in those two effects we have en- 

 ergy. It is in its potential form when it exists in a charged cloud, 

 and in its kinetic form when that charged cloud gives its charge up to 

 the earth, and in flying to the earth produces that dreadful effect that 

 we call lightning, with its accompaniment, the roar of thunder. Thus, 

 you have illustrations of energy in its different forms, electrical, mag- 

 netical, chemical, heat, light, and motion. 



Now comes the question, How is this energy transferred from 

 place to place ? You may have all stood upon the sea-beach and have 

 seen the waves dashing upon the rocks, and sent up in the air in white 

 and brilliant spray. You have seen the waves rolling over and over 

 again in glorious breakers upon the sands. You have probably seen 

 wrecks dashed to pieces by the force of waves, all which effects are 

 the result of energy which has been imparted to the water by a storm 

 miles and miles away, the energy of that storm having been transferred 

 by the waves of the water till it meets with the resistance of the shore 

 and produces those effects I have mentioned. Again, energy is trans- 

 ferred by air- vibrations. The explosion of a gun can be heard to a 

 distance of twenty to twenty-five miles ; and instances are known where 

 the bombardment of a town has been heard at a distance of one hun- 

 dred miles. It is well known that the roar of the cannon at Waterloo 

 was heard on the English coasts, at a distance of over one hundred 



TOL. XX. 43 



