135 
transform into any other form of energy. He may change almost at will 
the relative value of the energy terms on the left side of his energy 
equation, but he can not change their sum. No energy is lost in any 
transformation. The total remains constant. 
~In actual practice, however, when we attempt to transform or use 
energy, we find that more or less heat energy is generated in the process, 
and that this heat energy is dissipated through space. No machine is 
frictionless, no wire is without its electrical resistance. There is no 
motion of matter or electricity that does not result in the generation of 
heat which can not be utilized, heat which soon disappears forever in 
space. This energy is not destroyed, it is lost. It is easy to transform 
energy of any kind into heat energy, but it is impossible to transform 
all of any quantity of heat energy into energy of other kinds. Our best 
steam engines have an efficiency of some twenty per cent., the efficiency of 
the usual engine is not over ten per cent. This means that w waste from 80 
to 90 per cent. of the coal and utilize from 10 to 20 per cent. Our best 
tungsten lamps give us only about 10 per cent. of the energy of the electric 
current required to operate them, and since the engine that drives the dyna- 
mo has an efficiency of, say 10 per cent., the tungsten lamp gives us as light 
only 1 per cent. of the energy of the coal, 99 per cent. being wasted in 
the form of dissipated heat. So we have the principle of the dissipa- 
tion of energy; however we transform energy, a fraction of it—usually ¢ 
large fraction of it—is always dissipated as heat and is forever lost. 
Thus while the total quantity of energy in the universe remains constant, 
the useful or available energy is rapidly diminisning. All forms of energy 
are tending to go into the form of heat, to run down hill as it were, as heat 
is regarded as the lowest form of energy. Consequently this Principle 
of the Dissipation is sometimes called the Principle of the Degradation of 
energy. It makes no difference what the final temperature of the uni- 
verse may be; when all other forms of energy have been transformed into 
heat the heat energy will be useless. We can not use heat energy except 
as it runs down hill, from points of high temperature to points of low tem- 
perature. It is doing this all the time. Diffusion is a property of heat, 
and must result sooner or later in a state of uniform temperature and con- 
sequently in the disappearance of all available energy. 
Perhaps you ask why we shouid worry about the condition of things a 
million years hence? The reply is that we need not do so, but that we 
may well take thought of what the condition may be before the twentieth 
