It is difficult to name the unknown. In the ancient world all the
unknown was included in the idea of God. It remained for the
evangelist to declare that God is a _spirit_--thus separating the
natural forces of the material world from the Supreme Power who is
from eternity.
This century has been the epoch of investigation into the nature of
the imponderable forces. Sound and light and heat have been known as
the principal agents of sensation since the first ages of man-life on
the earth; but their nature has not been well understood until within
the memories of men still living. Electricity was also vaguely
known--but very indistinctly--from ancient times. It has remained for
the scientific investigators of our age to enter into the secret parts
of nature and lay bare to the understanding many of the hitherto
unknown facts relating to the imponderable agents.
The laws of heat, of acoustics, of light, have been clearly arranged
and taught; but they have not been placed beyond the reach of new
interpretation and possibly not beyond the reach of complete
revolution and reconstruction. That which has been accepted as
definitely known with regard to these agents has now to be reviewed,
and possibly to be learned over again from first principles.
As to electricity in its various forms and manifestations, that
sublime and powerful agent began to be better known just before the
middle of the century. Since that time there has been almost constant
progress in the science of this great force, until at the present time
it is handled, controlled and understood in its phenomena almost as
easily as water is poured into a vessel, air compressed under a
piston, or hydrogen made to inflate a balloon.
It has remained, however, for the last half decade of the great
century to come upon and investigate a hitherto unknown force in
nature. Certain it is that the new force exists, that it is
everywhere, that it is a part of the profound agency by which life is
administered, that its control is possible, and that its probable
applications are as wonderful--perhaps more wonderful--than anything
ever hitherto discovered by scientific investigation.
It is not unlikely that since the day, or evening, on which Galileo,
with his little extemporized telescope, out in the garden of the
Quirinal, at Rome, compelled bigotry to behold the shining horns of
the crescent Venus, thus opening as if by compulsion the sublime
vista of the heavens and bringing in a new concept of the planetary
and stellar worlds,--no such other discovery as that of the so-called
Röntgen rays has been made. The results which seem likely to flow from
this marvelous revelation surpass the human imagination. Let us try in
a few words to realize the discovery, and define what it is.
It was on the eighth of November, 1895, that Dr. William Konrad
Röntgen, of Würzburg, made the discovery which seems likely to
contribute so much to our knowledge of the mysterious processes of
nature. On that day Dr. Röntgen was working with a Crookes tube in his
laboratory. This piece of apparatus is well known to students and
partly known to general readers. It consists of a glass cylinder,
elongated into tubular form, and hermetically closed at the ends. When
the tube is made, the air is exhausted as nearly as possible from it,
and the ends are sealed over a vacuum as perfect as science is able to
produce. Through the two ends, bits of platinum wire are passed at the
time of sealing, so that they project a little within and without. The
interior of the tube is thus a vacuum into which at the two ends
platinum wires extend. Electrical communication with outside apparatus
is thus supplied.
It has long been known that on the discharge of an electrical current
into this kind of vacuum peculiar and interesting phenomena are
produced. The platinum wires at the two ends are connected with the
positive and negative wires or terminals of an induction coil. When
this is done, the electrical current discharged into the vacuum seems
to flash out around the inner surfaces of the tube, in the form of
light. There are brilliant coruscations from one end to the other of
the tube. The tips of the platinum wire constituting the inner poles
glow and seem to flame. That pole which is connected with the positive
side of the battery is called the _anode_, or _upper_ pole, and that
which is connected with the negative, or receptive, side of the
battery, is called the _cathode_, or lower pole. It was in his
experimentation with this apparatus, and in particular in noticing the
results at the cathode or lower end of the tube, that Professor
Röntgen made his famous discovery. It was for this reason that the
name of "cathode rays" has been given to the new radiant force; but
Dr. Röntgen himself called the phenomena the X, or unknown, rays.
In the experimentation referred to, Röntgen had covered the glass tube
at the end with a shield of black cardboard. This rendered the glow at
the cathode pole completely invisible. It chanced that a piece of
paper treated with platino-barium cyanide for photographic uses was on
a bench near by. Notwithstanding the fact that the tube was covered
with an opaque shield, so that no _light_ could be transmitted,
Professor Röntgen noticed that changes in the barium paper were taking
place, _as though_ it were exposed to the action of light! Black lines
appeared on the paper, showing that the surface was undergoing
chemical change from the action of some invisible and hitherto unknown
force!
This was the moment of discovery. The philosopher began experimenting.
He repeated what had been accidentally done and was immediately
convinced that a force, or, as it were, invisible rays were streaming
from the cathode pole of the tube through the glass, and through a
substance absolutely opaque, and that these rays were performing their
work at a distance on the surface of paper that was ordinarily
sensitive only to the action of light.
Certain it was that _something_ was doing this work. Certain it was
that it was _not light_. Highly probable it was that it was not any
form of _electricity_, for glass is impermeable to the electrical
current. Certain it was that it was _not sound_, for there was no
noise or atmospheric agitation to produce such a result. In a word, it
was demonstrated then and there that a hitherto unknown, subtle and
powerful agent had been discovered, the applications of which might be
of almost infinite range and interest.
Professor Röntgen soon announced his discovery to the Physico-Medical
Society of Würzburg. It was at the December meeting of this body that
the new stage in human progress was declared. The news was soon
flashed all over the world, and scientific men in every civilized
country began at once to experiment with the cathode light--if light
that might be called that lighted nothing.
In Röntgen's announcement he stated that there had been by the
scientists Hertz and Lenard, in 1894, certain antecedent discoveries
from which his own might in some sense be deduced. There was, however,
a great difference between the discovery made by Röntgen and anything
that had preceded it. His stage of progress in knowledge was this,
that during the discharge of _one_ kind of rays of force from the
cathode pole in a Crookes tube _another kind_ of rays are set free,
which differ totally in their nature and effects from anything
hitherto known. It is this fact which has indissolubly connected the
name of Konrad Röntgen with that great bound in scientific knowledge
which seems likely to modify nearly all the other scientific knowledge
of mankind.
Everywhere, in the first months of 1896, the experimenters went to
work to verify and apply the discovery of the German philosopher. It
was at once discerned that the new force, since it would freely
traverse opaque bodies and produce afterward chemical changes on
sensitized surfaces similar to those ordinarily produced _by_ light,
might be used for delineating (we can hardly say _photo_ graphing) the
interior outlines and structure of opaque bodies!
On this line of experimentation the work at once began, and with
remarkable success. Röntgen himself was the first man in the world to
obtain, as _if_ by photography, the invisible outline of objects
through opaque materials. He soon obtained a delineation of the bones
of a living hand through the flesh, which was only dimly traced in the
resulting picture. In like manner coins were delineated through the
leather of pocketbooks. Other objects were pictured through
intervening plates of metal or boards of wood. The possibility of
discovering the visible character of invisible things, and even _of
seeing directly through_ opaque materials into parts where neither
light nor electricity can penetrate, was fully shown.
The work of picture taking in the interior of bodies and through
opaque materials was quickly taken up by philosophers in England,
France and the United States. Almost everywhere the physical
laboratories witnessed daily this form of experimentation. Swinton, of
London; Robb, of Trinity College, Dublin; Morton, of New York; Wright,
of Yale University, and in particular Thomas A. Edison, of Menlo Park,
attacked the new problem with scientific zeal, and with startling
results. It remained for Edison to discover that the new force acted
in some respects in the manner of _sound_ rather than in the manner of
_light_. Thus, for example, he showed that the invisible rays not only
_pass through_ substances that are opaque to light and non-conductors
of electricity, but that the invisible rays _run around the edges and
sides_ of plates, then proceeding on their way somewhat in the manner
of sound. A sound made on one side of a metallic plate is heard on the
other side _partly_ by transmission through the plate, and _partly_ by
going around the edges, by atmospheric transmission. The new force
rays act in this manner, and Edison is said to have procured pictures
by means of the invisible agent while it was _going around the corner
_ of an opaque obstruction!
The pre-eminence of Thomas A. Edison as a scientific explorer and
inventor depends upon a quality of mind which enables him more easily
than others--more distinctly than any others--to see the touch of each
new discovery with existing conditions, and the application of it to
the problems of life. Edison catches the premonitory spark struck in
the darkness by some other master's hammer, and with that kindles a
conflagration. Though not the discoverer of the Röntgen ray, he was
able, as it would appear, to understand that discovery better even
than the discoverer. He almost immediately applied the new increment
of knowledge more successfully, we think, than any contemporary
scientist. His experimentation led him directly to the discovery of
the important fact that no photographic apparatus of any kind is
needed to enable an observer to use the X-rays in the delineation or
inspection of objects through opaque substances. He said within
himself: "Why not pass the X-rays through the object to be inspected
and then convert them into visibility, as if by fluorescence."
This scientific question Edison almost immediately solved.
Fluorescence is a property which some transparent bodies have of
producing, either on their surface or within their substance, light
different in color from that of its origin. This happens, for example,
when _green_ crystals of fluor spar afford _blue_ reflections of
light. Glass may be rendered fluorescent, as is seen in the Geisler
and Crookes tubes. Edison conceived the project of using this
phenomenon to get back the invisible rays into visibility.
The substance which he employed was the tungstate of calcium. Taking
crystals of this chemical compound, he spread the same over a cloth or
paper screen, and used that screen to catch and convert the invisible
images carried against it by the X-rays. To his surprise, his
experiment was completely successful. All that is needed in this case
is the cathode light, the object to be examined (as for instance the
hand), and the screen treated with tungstate of calcium. The observer
looks through the screen, or into it, and sees _with the unaided eye_
the invisible interior parts of the object examined, held between the
screen and the cathode light. The invisible rays take the image of the
interior parts of an opaque object, and carry that image to the
screen, where it is reconverted into visibility and delivered to the
eye of the observer, without the aid of any instrument at all! It is
on this simple principle that Edison has invented his surgical and
physiological lamp. The announcement is that with this lamp the
surgeon may look through the calcium tungstate screen and examine, for
example, the fractured bones of the hand, and set them perfectly by
actual inspection of the parts with his eye!
What then _is_ the cathode ray? At the present time its nature is not
understood. That it is a form or mode of motion goes with the
saying--unless it should be presently shown that all the imponderable
forces are really _material_ in their nature; that is, that they are
an inconceivably fine and attenuated form of matter in varying
manifestations.
The cathode rays are not light. They are not sound. They are not
electricity or magnetism. They are not heat. They are not any of the
known forms of force. They seem to be a new transformation of some one
or more of the known agents. It has long been observed that _motion_
is accompanied with _sound_, and that motion also, if increased,
becomes manifest in _heat_. It is known that heat is convertible into
light, and light into electricity.
It is possible that at the bottom of all these phenomena lies the
force of gravitation. This force is absolute and universal. All the
others are partial and limited. All the others, even the newly
discovered cathode rays, are subject to obstruction by certain forms
of matter; that is, to them certain forms of matter are opaque. But
gravitation knows no opacity in the universe. No atom of matter is
exempt from its sway. It streams through all obstructive media as
though such media did not exist. It would appear that heat, light,
electricity, sound, the cathode rays, and all other forms of force in
nature are probably variations, and as it were limited expressions and
manifestations, of _the one supreme force_ that supports the
constitution of the physical universe; and that one supreme force is
_gravitation_!
Stages in Biological Inquiry.