DEVELOPMENTS IN PHYSICAL SCIENCE 455 
friend, they can not put you in jail on such a charge as that.” “Yes, 
but they have,” replied the prisoner. 
When our physicist says that radium can not remain at a higher 
temperature than its surroundings and continue to radiate heat, as that 
would be contrary to the second law of thermodynamics, the answer is 
—yes, but it does. 
When he says that it can not continue to radiate energy without 
receiving energy from some other body, as that would be contrary to the 
principle of the conservation of energy, the answer is—yes, but it 
does it. 
When some one says that helium or carbon dioxide can not appear 
in sealed tubes which contained no trace of these substances to begin 
with, the answer is—yes, but they do. 
Let us suppose that we have a mass of gun powder and that it is 
possible to, and we do, cause it to explode, one grain at a time, each 
erain firing its neighbor—as in the fuse of a fire cracker. The tem- 
perature of the mass of gunpowder will be higher than its surroundings 
and it will give off heat and other forms of energy, and continue to do 
so so long as the powder lasts. No one would think of calling this an 
exception to the law of the conservation of energy, or the second law 
of thermodynamics. The source of the energy is the atomic potential 
energy of the powder itself. 
Let us suppose that we have a sphere with frictionless surface ro- 
tating at an enormous speed. Suppose that particles of matter are 
thrown off at frequent intervals. These particles, on account of their 
high speed, possess considerable energy. Thus the sphere con- 
tinues to give off energy without receiving any, as long as any mass 
remains. ‘I'he source of the energy is the kinetic energy stored in the 
sphere at the outset, of which energy we are conscious only when we 
have some method of detecting and slowing down the projected 
particles. 
Thus the energy radiated by radium might be stored within the 
radium atom as potential energy and liberated by a sort of atomic—or 
sub-atomic explosion. Or it might be stored as kinetic energy—of re- 
volving electrons and liberated gradually as these electrons escape from 
their orbits. It might be stored in both forms. In any case it is intra- 
atomic energy because stored within the atom itself, and liberated only 
by atomic change—disintegration. In neither case would there be a 
violation of the principle of the conservation of energy or of the second 
law of thermodynamics. Sooner or later all the energy will have been 
radiated. The fact that the supply is destined to last so long is what 
appeals to us as wonderful. And soitis. The world is full of wonder- 
ful things to any one who pauses long enough to think. 
In this paper I have endeavored to give a general notion of the trend 
of physical science rather than an enumeration and description of dig- 
