d either as a sender or receiver of
current. Two batteries adjusted to the same center line become connected
in series just as if they were connected by ultron wires.

In actual practice, however, two types of batteries are used; both the
_foco_ batteries and _broadcast_ batteries.

_Foco_ batteries are twin batteries, arranged to shoot a positive and a
negative beam in the same direction. When these beams are made
intermittent at light frequencies (though they are not light waves, nor
of the same order as light waves) and are brought together, or focussed,
at a given spot, the space in which they cross radiates alternating
ultronic current in every direction. This radiated _ultralight_ acts
like true light so long as the crossing beams vibrate at light
frequencies, except in three respects: first, it is not visible to the
eye; second, its "color" is exclusively dependent on the frequency of
the _foco_ beams, which determine the frequency of the alternating
radiation. Material surfaces, it would appear, reflect them all in equal
value, and the color of the resultant picture depends on the color of
the _foco_ frequencies. By altering these, a reddish, yellowish or
bluish picture may be seen. In actual practice an orthochromatic mixture
of frequencies is used to give a black, gray and white picture. The
third difference is this: rays pulsating in line toward any ultron
object connected with the rear plates of the twin batteries through
rectifiers cannot be reflected by material objects, for it appears they
are subject to a kind of "pull" which draws them straight through
material objects, which in a sense are "magnetized" and while in this
state offer no resistance.

Ultron, when so connected with battery terminals, glows with true light
under the impact of _ultralight_, and if in the form of a lens or set of
lenses, may be made to deliver a picture in any telescopic degree
desired.

* * * * *

The essential parts of an ultroscope, then, are twin batteries with
focal control and frequency control; an ultron shield, battery connected
and adjustable, to intercept the direct rays from the "_glow-spot_,"
with an ordinary light-shield between it and the lens; and the lens
itself, battery connected and with more or less telescopic elaboration.

To look through a substance at an object, one has only to focus the
_glow-spot_ beyond the substance but on the near side of the object and
slightly