h kind of ray. That is, each of the ray families knows a
great deal about all kinds of vibrations of the ether, but is
specializing upon one narrow field. Take, for instance, the rays you are
most interested in; those able to penetrate a zone of force. From my own
very slight and general knowledge I know that it would of necessity be a
ray of the fifth order. These rays are very new--they have been under
investigation only a few hundred years--and the Rovol is the only
student who would be at all well informed upon them. Shall I explain the
orders of rays more fully than I did by means of the educator?"

"Please. You assumed that we knew more than we do, so a little
explanation would help."

"All ordinary vibrations--that is, all molecular and material ones, such
as light, heat, electricity, radio, and the like--were arbitrarily
called waves of the first order; in order to distinguish them from waves
of the second order, which are given off by particles of the second
order, which you know as protons and electrons, in their combination to
form atoms. Your scientist Millikan discovered these rays for you, and
in your language they are known as Millikan, or Cosmic, rays.

* * * * *

"Some time later, when sub-electrons were identified the rays given off
by their combination into electrons, or by the disruption of electrons,
were called rays of the third order. These rays are most interesting and
most useful; in fact, they do all our mechanical work. They as a class
are called protelectricity, and bear the same relation to ordinary
electricity that electricity does to torque--both are pure energy, and
they are inter-convertible. Unlike electricity, however, it may be
converted into many different forms by fields of force, in a way
comparable to that in which white light is resolved into colors by a
prism--or rather, more like the way alternating current is changed to
direct current by a motor-generator set, with attendant changes in
properties. There is a complete spectrum of more than five hundred
factors, each as different from the others as red is different from
green.

"Continuing farther, particles of the fourth order give rays of the
fourth order; those of the fifth, rays of the fifth order. Fourth-order
rays have been investigated quite thoroughly, but only mathematically
and theoretically, as they are of excessively short wave-length and are
capable of being generated only by the