THE PRINCIPLES OF ENERGY 37 



radio-activity. As the result of the physical research based on 

 this, it became very probable that an atom (which is still the 

 smallest particle of matter as such that can exist) is really com- 

 plex, and consists of a system of electrons. An electron is not 

 material, but is an unit charge of electricity, the smallest charge 

 that can exist. In the centre of the atom there is an electron, 

 and revolving round this there are others, much in the way the 

 planets are revolving round the sun in the solar system. Now 

 one or more of the electrons can be expelled from the system, and 

 then the latter becomes a new kind of chemical atom. Different 

 atoms contain different numbers of revolving electrons. 



What is an electron ? All we can say about it is that it is elec- 

 tricity, and not material. Thus, materiality dissolves into energy, 

 and the latter is the fundamental physical reality. Mass disappears, 

 but inertia remains, only the latter is now electro-magnetic inertia. 



The Capacity for Doing Work. 



Things, then, remain as they are unless something is done to 

 them. A train remains at rest unless work is done upon it, 

 causing it, for instance, to attain a velocity of thirty miles per 

 hour three minutes after it has started to move. Conversely, the 

 train will continue to run after the steam has been shut off unless 

 work is done upon it, causing it to stop, and such work may be 

 done by the application of the brakes, or by the friction of the 

 air, or that of the wheels on their bearings or upon the rails. The 

 mechanical work that is done in both these cases is measured in 

 horse-power. 1 h.p. being the amount of work done by raising 

 a weight of 33.000 pounds 1 foot high in one minute. 



The water in a steam boiler will remain at one temperature 

 unless work is done upon it. Heat must be supplied to the water 

 by the combustion of coal in the furnace. Now we can express 

 the amount of heat in units, which are called Calories, each 

 Calorie generated in a second being 5-62 h.p. Thus to raise the 

 temperature of the water in the boiler that is, to change its 

 state in a certain way so much work must be done. 



An electric tram will stand still upon the rails for ever unless 

 work is done upon it. When the switch is closed electric current 

 enters the motors, and the latter revolve propelling the car and 

 giving it a speed of, say, ten miles per hour in one half- minute. 

 We measure this work done by the current in units, called kilo- 

 watts, each of the latter being 1-341 h.p. 



