"The Eye of the Submarine."
The improved periscope, showing all directions at one glance.
At sea, where the. aim is to locate a vessel, the distortion is
less disturbing.
THE
SCIENCE- HISTORY
OF THE UNIVERSE
FRANCIS ROLT- WHEELER
Managing Editor
IN TEN VOLUMES
THE CURRENT LITERATURE PUBLISHING COMPANY
NEW YORK
1909
INTRODUCTIONS BY
Professor E. E. Barnard, A.M., Sc.D.,
Yerkes Astronomical Observatory.
Professor Charles Baskerville, Ph.D., F.C.S.
Professor of Chemistry, College of the City of New York.
Director William T. Hornaday, Sc.D.,
President of New York Zoological Society.
Professor Frederick Starr, S.B., S.M., Ph.D.,
Professor of Anthropology, Chicago University.
Professor Cassius J. Keyser, B.S., A.M., Ph.D.,
Adrain Professor of Mathematics, Columbia University
Edward J. Wheeler, A.M., Litt.D.,
Editor of 'Current Literature.'
Professor Hugo Munsterberg, A.B., M.D., Ph.D., LL.D.,
Professor of Psychology, Harvard University.
EDITORIAL BOARD
Vol. I — Waldemar Kaempffert,
'Scientific American.'
Vol. II — Harold E. Slade, C.E.
Vol. Ill — George Matthew, A.M.
Vol. Ill — Professor William J. Moore, M.E.,
Assistant Professor of Mechanical Engineering, Brooklyn
Polytechnic Institute.
Vol. IV — William Allen Hamor,
Research Chemist, Chemistry Department, College of the
City of New York.
Vol. V — Caroline E. Stackpole, A.M.,
Tutor in Biology, Teachers' College, Columbia University.
Vol. VI— Wm. D. Matthew, A.B., Ph.B., A.M., Ph.D.,
Assistant Curator, Vertebrate Paleontology, American
Museum of Natural History.
Vol. VI — Marion E. Latham, A.M.,
Tutor in Botany, Barnard College, Columbia University.
Vol. VII — Francis Rolt-Wheeler, S.T.D.
Vol. VII— Theodore H. Allen, A.M., M.D.
Vol. VIII— L. Leland Locke, A.B., A.M.,
Brooklyn Training School for Teachers.
Vol. VIII— Franz Bellinger, A.M., Ph.D.
Vol. IX— S. J. Woolf.
Vol. IX — Francis Rolt-Wheeler, S.T.D.
Vol. X — Professor Charles Gray Shaw, Ph.D.,
Professor of Ethics and Philosophy, New York University.
Leonard Abbott,
Associate Editor 'Current Literature/
Digitized by the Internet Archive
in 2012 with funding from
The Institute of Museum and Library Services through an Indiana State Library LSTA Grant
http://archive.org/details/sciencehistoryofv3rolt
THE
SCIENCE - HISTORY
OF THE UNIVERSE
VOLUME III
PHYSICS
By GEO. MATTHEW
ELECTRICITY
By PROFESSOR WM. J. MOORE
Copyright, 1909, by
CURRENT LITERATURE PUBLISHING COMPANY
CONTENTS
CHAPTER PAGE
I An Analysis of Matter i
II The Properties of Matter 21
III Heat 49
IV The Sources of Light 61
V The Speed of Light 72
VI Reflection and Refraction 83
VII The Nature of Light 98
VIII Sound 116
ELECTRICITY
I The Nature of Electricity 141
II Electrostatics, Atmospheric Electricity.. . 155
III Fundamental Discoveries 176
IV Electro-Magnetic Machinery 189
V Development of Power Transmission 211
VI History of Electric Lighting 225
VII Development of Electro-Chemistry 248
VIII The Telephone 259
IX Electric Railways 280
X The Electro-Magnetic Telegraph 293
XI Wireless Telegraphy 310
PHYSICS
CHAPTER I
AN ANALYSIS OF MATTER
When a child first opens his eyes on the world about
him a confusing array of experiences thrust themselves
upon his notice. The clothes in which he is wrapped, the
incomprehensible voice-sounds that come to his ears, the
ever-changing personalities of his environment — every-
thing is wonderful, strange and fearsome because of its
strangeness. So must the world of nature have seemed
strange to early man, strange and terrifying. The sights
and sounds of the forest, the wind rushing through the trees
or lashing the rivers into foam, thunder and clouds and
lightning, clear sun and quiet stars — all spoke to man in
his earlier development in personal voices. Each new
object of sense constituted for him an object for suspicious
investigation or superstitious fear. Familiarity may or
may not breed contempt, but that it does induce a form of
indifference is certain.
When a leaf rustles in the forest to-day, the rational
explanation of a breath of wind takes the place of the old-
time fear of a wood-demon ; when a tidal wave rushes up
a river, the modern knowledge of tides releases man from
a blind terror. And this goes even farther, for when a
lightning-flash strikes, the law of the association of ideas
will lead the mind to correlate the incident with Benjamin
Franklin and with the harnessing of the lightning to many
2 PHYSICS
everyday uses. Having passed the stage of superstitious
wonder, man at once attempts to classify the phenomena
of nature among those experiences of whose character
already he feels himself sure.
The earliest recorded beginnings of physical science
were made, so far as history can testify, by the Chaldean
astrologers. Their study of the stars, however, directed
as it was rather to the prediction of individual and national
destinies than to determining the real nature of the ma-
terial universe, laid the ground-work for further study,
but bequeathed little of practical importance in physics.
No great names in science have been bequeathed to the
world by Assyria or Chaldea. They may have furnished
material for the imaginative genius of the Greeks, but the
latter alone were capable of formulating into a system the
vague wisdom of the Orient. As John Lord remarks,
"The East never gave valuable knowledge to the West; it
gave the tendency to Egyptian mysticism, which in its
turn tended to superstition. Instead of astronomy, it gave
astrology; instead of science, it gave magic, incantations
and dreams."
The Chaldean and Assyrian civilizations which gave
birth to the astrology of the Magi flourished and declined
. in the fertile valleys of the Tigris and Euphrates. Nearly
a thousand years before them, however, there had been
developing in the fecund region of the Nile the people
who produced the first of those marvelous pyramids which
remain to-day the greatest monuments of history. Some
considerable knowledge of physics and the elementary
application of machines the Egyptians must have pos-
sessed, or at least the builders of the pyramids, whoever
they were. The stones are much larger than those used
in architecture to-day. The columns of the Egyptian tem-
ples still standing in ruins are immense. Travelers look
with astonishment and admiration at the gigantic struc-
tures whose walls, lintels, columns and entablatures are
formed of material cut in extraordinary dimensions. No
AN ANALYSIS OF MATTER 3
scientific works remain to show how the ancient builders
of Egypt managed to carry and put in place such large
blocks of stone. Mural paintings, sculptures and inscrip-
tions are the only means of conveying such slight informa-
tion as has been handed down to the present generation.
It has been held by some students of antiquity that the
pyramids were designed as institutions to embody cosmic
discoveries ; for example, that certain specific measure-
ments of the structure bear a definite ratio to such matters
as the exact length of the earth's circumference and di-
ameter, the length of an arc of meridian and standard
units of measure. Other theorists, with far more prob-
ability in their favor, believe the pyramids to have been
constructed as the tombs of the great kings whose names
are graven in the interior and whose sarcophagi (with
their mummies) are often found in the central chamber.
Still others have declared that the pyramids were used for
astronomical study.
Whatever other purpose the pyramids may have served,
they seem to have been little adapted for observatories.
It is a matter of common knowledge that an object viewed
through a roll of paper is better seen in detail than when
looked at without such aid. Place a lens in either end of
the roll, adjust the focus of the lenses and a telescope is
made. The eye takes in a great deal more than the mind
perceives. In gazing at an object, especially at a distance,
the detail of the object is obscured by the light reflected
from hundreds of other objects in the neighborhood. The
simple roll of paper overcomes this difficulty in exactly the
same way that the ventilating passages, the so-called "tele-
scopes" of the pyramids, might do. A star is visible in
broad daylight when viewed through such a long, narrow
passage as were these nine-inch "telescopes" of the pyra-
mids. A fatal defect in this telescope thesis, however, is
the fact that the earth revolves, and a star visible for a
few seconds at the aperture of the passage would be lost
almost immediately.
4 PHYSICS
In their astronomical observations and in their arith-
metical calculations the Egyptians were inferior to the
Chaldeans. They were familiar with the true meridian
and the length of the sidereal year. They did not know
the signs of the zodiac, however, nor are there any inscrip-
tions of Egyptian origin such as are found on the Assyrian
bricks, wherein appear the square and cubic multiplication
tables and the three hundred and sixty degrees of the
Fig. i — Great Pyramid, Showing 'Telescopic' Passages.
circle. The Egyptian "zodiac" of the temple at Derderah
is now known to be a production comparatively modern
in origin, even showing Greek influence.
The Hellenic philosophers made the first definite classi-
fication of elements, asserting that earth, air, fire and
water were the four indivisible substances out of which
the whole world was made up. They knew a god of the
water, Poseidon (Neptune); a god of earth, Anteus; a
AN ANALYSIS OF MATTER 5
god of fire, Pluto, while each of the four winds was a
deity. However simple and clear such a division might
seem, modern science has proved that each of these sup-
posed elements is divisible into several elementary sub-
stances. Thus ordinary water, for instance, is known to
be compounded of oxygen and hydrogen ; air is a mixture
of nitrogen, oxygen, carbonic acid gas and a number of
other elements more recently isolated, among which helium
is of especial interest ; and so numerous are the component
parts of earth that it seems most strange how it ever could
have been conceived as an element at all. Despite all
errors in explaining the phenomena of nature, however,
Greece must be credited with having made the first real
beginning of that "classified knowledge" out of which has
developed the natural science of modern times.
Thales, the founder of the Ionic school of philosophers,
is reported to have determined the course of the sun from
solstice to solstice and to have calculated eclipses. He at-
tributed an eclipse of the moon to the interposition of the
earth between the sun and moon, and an eclipse of the sun
to the interposition of the moon between the sun and earth,
and thus taught the rotundity of the earth, sun and moon.
He also held that water is the principle of all things — a
somewhat egregious error from the modern point of view.
As early as two hundred and eighty years before the pres-
ent era Aristarchus, Hippocrates and Galen made many
scientific advances, but Physics was not yet strongly dif-
ferentiated from its attendant sciences.
The mantle of the Greek philosophers was caught up by
Pliny, who perished in the eruption of Vesuvius in 23 a.d.
His Natural History in thirty-seven books treats of every-
thing in the natural world — of the heavenly bodies, of the
elements, of thunder and lightning, of the winds and sea-
sons. Like nearly all the Greek and Roman philosophers,
however, and many great theorists of later date, Pliny con-
tented himself with theorizing.
In mathematics, metaphysics, literature and art the
6 PHYSICS
Greeks displayed wonderful creative genius, but in natural
science they achieved comparatively little. "It would not
be correct to say that they possessed little or no aptitude
for observing natural phenomena," says Florian Cajori in
his 'History of Physics,' "but it is true that as a rule,
they were ignorant of the art of experimentation and that
many of their physical speculations were vague, trifling
and worthless. As compared with the vast amount of
theoretical deduction about nature, trie-number of experi-
ments known to have been performed by the Greeks is
surprisingly small. Little or no attempt was made to
verify speculation by experimental evidence. As a con-
spicuous example of misty philosophizing we give Aris-
totle's proof that the world is perfect: The bodies of
which the world is composed are solids, and therefore have
dimensions. Now, three is the most perfect number — it
is the first of numbers, for of one we do not speak as a
number, of two we say both, but three is the first number
of which we say all. Moreover, it has a beginning, a
middle and an end.' "
Mechanical subjects are treated in the writings of
Aristotle. The great peripatetic had grasped the notion of
the parallelogram of forces for the special case of the
rectangle. Pie attempted the theory of the lever, stating
that a force at a greater distance from the fulcrum moves
a weight more easily because it describes a greater circle.
Aristotle's views of falling bodies are very far from
the truth. Nevertheless they demand attention, for the
reason that, during the Middle Ages and Renaissance, his
authority was so great that they play an important role
in scientific thought. He says : "That body is heavier
than another which, in an equal bulk, moves downward
quicker." In another place he teaches that bodies fall
quicker in exact proportion to their weight. No statement
could be further from the truth.
A modern writer endeavors to exonerate Aristotle as a
physicist. "If he could have had any modern instrument
AN ANALYSIS OF MATTER 7
of observation — such as the telescope or microscope, or
even the thermometer or barometer — placed in his hands,
how swiftly would he have used such an advantage !"
But in the case of falling bodies, the experiment was
within his reach. If it had only occurred to him, while
walking up and down the paths near his school in Athens,
to pick up two stones of unequal weight and drop them
together, he could easily have seen that the one of, say, ten
times the weight did not descend ten times faster.
Immeasurably superior to Aristotle as a student of
Fig. 2 — Archimedes and the Lever.
mechanics is Archimedes (287-212 B.C.). He is the true
originator of mechanics as a science. To him belongs the
honor of enunciating the theory of the center of gravity
(centroid) and of the lever. In his 'Equiponderance of
Planes' he starts with the axiom that equal weights acting
at equal distances on opposite sides of a pivot are in equi-
librium, and then endeavors to establish the principle that
"in the lever unequal weights are in equilibrium only
when they are inversely proportional to the arms from
which they are suspended." His appreciation of its effi-
ciency is echoed in the exclamation attributed to him :
"Give me where I may stand and I will move the world."
While the "Equiponderance" treats of solids or the
8 PHYSICS
equilibrium of solids, the book on "Floating Bodies" treats
of hydrostatics. The attention of Archimedes was first
drawn to the subject of specific gravity when King Hieron
asked him to test whether a crown, professed by the maker
to be pure gold, was not alloyed with silver. The story
goes that the philosopher was in a bath when the true
method of solution flashed on his mind. He immediately
leapt from the bath and ran home, shouting, "I have found
it !" To solve the problem, he took a piece of gold and a
piece of silver, each weighing the same as the crown, the
piece of silver being almost twice the size of the gold. He
then determined the volume of water displaced by the gold,
the silver and the crown respectively, and from that cal-
culated the amount of gold and silver in the crown. The
proportion of greater displacement in the crown above the
piece of pure gold showed the extent of the alloy.
In his "Floating Bodies" Archimedes established the
important principle, known by his name, that the loss of
weight of a body submerged in water is equal to the weight
of the water displaced and that a floating body displaces
its own weight of water. Since the days of Archimedes
able minds have drawn erroneous conclusions on liquid
pressure. The expression "hydrostatic paradox" indicates
the slippery nature of the subject. All the more must we
admire the clearness of conception and almost perfect logi-
cal rigor which characterize the investigations of Archi-
medes.
Archimedes is said to have shown wonderful inventive
genius in various mechanical inventions. It is reported
that he astonished the court of Hieron by moving heavy
ships by aid of a collection of pulleys. To him is ascribed
the invention of war engines and the endless screw
("screw of Archimedes") which was used to drain the
holds of ships. This genius, "the greatest scientist before
Galileo," perished in the siege of Syracuse by the Romans
(212 B.C.).
About a century after Archimedes there flourished
AN ANALYSIS OF MATTER 9
Ctesibius and his pupil Heron, both of Alexandria. They
contributed little to the advancement of theoretical investi-
gation, but displayed wonderful mechanical ingenuity.
The force-pump is probably the invention of Ctesibius.
The suction pump is older and was known in the time of
Aristotle. According to Vitruvius, Ctesibius designed the
ancient fire-engine, consisting of the combination of two
force-pumps, spraying alternately. The machine had no
air-chamber, and therefore could not produce a steady
stream. Heron describes the fire-engine in his "Pneu-
matica." During the Middle Ages the fire-engine was
unknown. It is said to have been first used in Augsburg
in 1518.
Ctesibius is credited with the invention of the hydraulic
organ, the water-clock and the catapult. Heron showed
the earliest application of steam as a motive power in his
toy, called the "eolipile." It was the forerunner of Bar-
ker's water-mill and the modern turbine. Heron wrote an
important book on geodesy, called "Dioptra."
The Greeks invented the hydrometer, probably in the
fourth century a.d. There appears to be no good evidence
for attributing its origin to Archimedes. The hydrometer,
a device in common use to-day for measuring the densities
of water, milk and acids, is described in full by Bishop
Synesius in a letter to Hypatia. It consisted of a hollow,,
graduated tin cylinder, weighted below. Immersed in a
liquid, the depth to which it sank constituted a measure of
the relative weight or density of that liquid. It was first
used in medicine, to determine the quality of drinking-
water, hard water being at that time considered unwhole-
some. According to Desaguliers, it was used for this pur-
pose as late as the eighteenth century.
Since in such distant days, and with theories so diverse
from those of modern times, the study of matter and of
its properties began, the question arises whether the initial
problem has yet been solved. Theories have been multi-
plied, modified, rejected, confirmed. Through centuries the
io PHYSICS
evidence of experiment has accumulated; much has been
learned of the nature and behavior of matter under varying
conditions, but the complexity of the problem has become
more evident the further it is studied and the complete
answer is not yet. The world is rife to-day with stores
of knowledge undreamed of a few centuries ago, but since
every addition to the sum of information brings with it a
new series of problems, human reason halts before the
attainment of a conclusive knowledge as to the real es-
sence of that which it calls Matter.
The Greek-Roman Asclepiades conceived matter to con-
sist of extremely small, but still divisible and fragile,
formless and mutable collections of atoms, cognizable in-
deed by the understanding, but not by the senses. These
atoms originally moved about uncontrolled in a general
vacuum and burst in pieces through accidental collisions.
By union of the finest fragments thus engendered, the
"Leptomeres," originate the visible bodies, whose differ-
ences of form and varying peculiarities have their founda-
tion in the different association of the leptomeres into
different bodies.
In a quaint series of inquiries by John Abercrombie,
'The Investigation of Truth,' published in Edinburgh
three-fourths of a century ago, Matter is defined as "a
name which we apply to a certain combination of proper-
ties or to certain substances which are solid, extended and
divisible and which are known to us only by these prop-
erties."
Francis Bacon, "the wisest, brightest, meanest of man-
kind," as Pope styled him, conceived of matter as made
up of two "tribes of things," the "sulphureous" and "mer-
curial," which, he says, "seem vastly extensive, so as to
enter and occupy the whole material world."
Sir Isaac Newton regarded matter as "the coexistence
of the smallest particles which are themselves extended
and material" and which, through a power whose nature he
did not further analyse, hang together. Newton, therefore,
AN ANALYSIS OF MATTER n
adhered to the atomistic school, of which the Greek De-
mocritus of Abdera was the great classic expositor. He
did not believe in the infinite sub-divisibility of matter.
In his "Treatise on Light" the great philosopher con-
cludes that "it seems extremely probable that the Creator
so formed Matter that its primary particles, out of which
all possible bodies afterward arose, was firm, hard, im-
penetrable and movable." These particles therefore could
not through any known force be divided, hence all bodies
composed of these minute granules possessed interstices,
because otherwise their parts could not be separated from
one another, and matter was therefore divisible only until
its atoms were reached. Moreover, these primary particles
possessed not only a power which subjected them to cer-
tain immutable laws of motion, but also the capacity of
being set in motion through other influencing causes, for
example gravity, fermentation and cohesion.
In accordance with these premises, Newton justly com-
bated the theory of his great contemporary, Cartesius,
that matter occupied all space. His excellent development
of the idea of the resistance of a medium led to conclusions
which inevitably contradicted Cartesius' theory of filled
space. In such a compact mass as the latter theory as-
sumed, a mass which would be absolutely impenetrable, all
motion must find an unlimited resistance. Cartesius as-
sumed, it is true, that this subtle material was so finely
divided as scarcely to exist at all, but Newton showed that
this was only empty assertion. He based his opposition to
the theory on the ground that the smallest subdividing of
matter would not appreciably diminish the resistance
which "filled space" would present to a moving body, espe-
cially since the body in motion would enforcedly have a
density not greatly dissimilar to the resisting medium.
Therefore, he argued, a medium wherein bodies move
without perceptible retardation must be immensely more
attenuated than the bodies themselves. On the other hand,
a cannon-ball projected into the "filled space" of Cartesius,
12 PHYSICS
be that medium ever so finely divided, would lose more
than half its motion before it had moved a distance of
thrice its diameter. It would be impossible on this sup-
position for a man to move from a given spot, much less
the heavenly bodies, whose courses show no perceptible
retardation, as would inevitably be the case were they to
be advancing through an absolutely dense medium.
The belief in "filled space" did not originate with Car-
tesius. It is rather remarkable that the two thinkers who
of all men in history most powerfully have swayed philo-
sophic thought, Aristotle and Kant, were both exponents
of the doctrine that space is continuously filled.
The great ancient expositor of the atomic theory was
Democritus of Abdera. He taught that the world consists
of empty space and an infinite number of indivisible, in-
visibly small atoms. Bodies appear and disappear only by
the union and separation of atoms. Even the phenomena
of sensation and thought he affirmed to be the result of
their combination.
Newton's belief in the granular, or atomic, nature of
matter has been abundantly upheld by the evidence of
modern research. It is true that the chemical atom is no
longer considered the ultimate unit of material structure.
One brilliant writer on this subject has recently advanced
a series of exhaustive arguments in favor of the New-
tonian thesis. He points out, however, that it is by no
means an impossible conclusion that matter in the form
of interstellar ether may have properties quite different
from those which are observed of matter in the mass.
It has been remarked above that Newton did not attempt
to describe the nature of force; he merely assumed its
existence as evidenced by the behavior of matter. This
was natural, for reason must commence with an assump-
tion and arrives at conclusions based simply upon the
evidence of the physical senses. While force is generally
conceived rather as an object of thought than of sense,
AN ANALYSIS OF MATTER 13
yet it should not be forgotten that force has just as real
an existence as matter.
Many and various definitions of matter have been made
in the course of scientific history. It has been described,
for example, as "that which occupies space," or as "the
receptacle of energy," or again as "the permanent possi-
bility of sensation." All these may be brought under one
of two general heads — either matter must be defined, as
Bacon defined it, in terms of its properties, or it must be
defined in terms of its coexistent phenomenon — force. It
is clear that the physical world may be comprehended
within the limits of these two notions — Force and Matter.
Force is that which acts upon Matter, Matter is that by
which man apprehends Force.
Force is by no means such a vague and various thing
as is sometimes supposed. There is to-day a very general
tendency among scientific writers to endeavor to reduce
all force to a single underlying principle. The establish-
ment of the theory of the Conservation of Energy; the
ready transmutation in everyday experience of various
forms of Force, such as the conversion of sound into elec-
tricity and of the latter into heat, light, motion or chemical
energy; the advances in the study of radio-activity and
the general acceptance of the kinetic theory of gases all
point to an ultimate unification under some one great
principle of the various forms of force.
Gravity alone seems incapable of classification with
other forces, and this is due to its independence of any
quality but mass. Temperature will affect the conductiv-
ity of an electric wire, solution is greatly influenced by
pressure, light has a determinative effect upon physical
life as upon many chemical reactions, but gravity is not
affected by these conditions of temperature or of the inter-
vening medium. Its nature is utterly unknown.
Electricity has long been held to be a form of force. It
acts upon matter to change its condition; it is not an object
of sense in a current-carrying wire or a charged Leyden
14 PHYSICS
jar. It seems to be typical of what is popularly under-
stood by the name force. Yet the study of the cathode
rays by Sir William Crookes and his great co-workers in
this field of research — Roentgen, Hertz, Rutherford and
others whose names are perhaps even more familiar — has
made it apparent that something closely resembling ma-
terial particles are actually discharged from the cathode
or negative pole of an electric conductor when the current
passes. So strong indeed is the accepted belief that the
nature of electricity is material rather than dynamic that
a distinguished American chemist recently formulated the
thesis that electricity is one of the elements.
To obtain a clear understanding of the most modern
theories with regard to the nature of matter, a brief de-
scription of the apparatus used by investigators is inevi-
table. Imagine an electric bulb or oval vessel of glass.
In this are placed two electrodes, which may be either
metallic points or bulbs, or, in short, any poles separated
by smaller or greater intervals and charged with electricity.
Their electrification will be maintained, for example, by
placing them in connection with the terminals of an elec-
tric current of high voltage. A short tube provided with
a stop-cock allows the bulb to be exhausted of air. When
the electric tension passes a certain limit a current is
established.
If the vacuum is maintained at something less than a
thousandth of an atmosphere this current appears as a
soft rose-colored glow passing within the bulb from the
positive to the negative pole. Sir William Crookes pushed
the exhaustion of air in his experiments to a prodigious
degree, the pressure being only one millionth of an at-
mosphere. Concerning Crookes' experiments, M. A.
Dastre writes: "The English scientist claimed that when
exhausted to this point the residue no longer has the prop-
erties of ordinary gases. According to him it is a hyper-
gas as different from the true gaseous state as the latter is
from the liquid state and forming a fourth condition of
AN ANALYSIS OF MATTER 15
matter, following the solid, the liquid and the gas proper;
this he called radiant matter. Crookes desired to deter-
mine the nature of this fourth state of matter. In reality,
the gas, rarefied to the millionth of an atmosphere, has not
acquired, by this fact alone, an entirely new character;
but it has acquired it most certainly when electrification is
added to the rarefaction, and it is then that it constitutes
the emanation or the cathode ray."
The vacuum must not be pushed too far; if one goes
beyond the millionth of an atmosphere — and the perfection
of mechanism allows going much further than that — the
gaseous residue cannot be electrified; electricity will not
A Common Form of X-ray Tube.
pass through; there is no longer a current. The electric
force is incapable of penetrating absolute vacuum. The
importance of this principle is very great from the theo-
retical point of view; it furnishes, in fact, a new test for
matter.
But in Crookes' tube, in which the vacuum has been
pushed to one millionth, the current behaves itself rather
differently from what it does in the tubes where the rare-
faction is less. The path of the current has lost much of
its brilliancy; it no longer appears as an uncertain glow,
wavering, striated, of a hue intermediate between rose and
violet. All the remainder of the interior of the bulb now
remains dark. The electricity passes as before between the
positive electrode and the cathode or negative po-le. The
principal flow has been joined by a secondary one; from
16 PHYSICS
all points of the tube the positive currents are directed
toward the cathode and go to reinforce the principal cur-
rent. These positive charges which descend from all
points of the exterior, form the counterpart of the negative
charges, which can be seen fixed on the cathode rays.
Their existence, their development, their circulation result
in consequence from the existence^ the development and
the inverse circulation of the negative electricity that car-
ries with it the cathode ray.
Such is the cathode afflux ; it is composed of the current
directed toward the positive electrode and of secondary
currents directed from all parts of the recipient toward the
cathode. This cathode afflux has, besides, the character
and the properties that physicists and chemists attribute to
the electric current. It touches directly the cathode.
The afflux, however, is in fact perfectly distinct in every
respect from the cathode radiation which follows it. The
latter is formed of a pencil of rays perpendicular to the
surface of the cathode. It traverses the tube in a perfectly
straight line without being disturbed by the rays flowing
toward the cathode in an opposite direction, of which we
have just been speaking; it passes by them and through
them unchecked.
This new pencil implanted perpendicularly on the
cathode is not luminous. It is not directly visible; it forms
a dark spot in the Crookes tube. It would entirely escape
observation if it did not excite a peculiar fluorescence
opposite to the cathode at the points where it meets the
sides of the tube. The material of the glass becomes il-
luminated at these points and presents a luminous brilliant
spot of a green color.
Crookes conceived the idea of arranging in the interior
of the tube, in the path of the pencil of rays between the
cathode and the wall, a cross of aluminum. He then saw
outlined against the clear fluorescent background the exact
silhouette of the cross.
If the cathode is a mirror with spherical concave surface
AN ANALYSIS OF MATTER 17
the perpendicular lines at the surface form 3 conic pencil
and converge toward a focus. The effects peculiar to
cathode rays are magnified by this concentration, in the
same manner that the effects of luminous rays are in-
creased in the focus of a lens. In this manner Crookes
was able to show the heating action of his supposed radiant
matter; that is to say, of cathode rays. He succeeded in
Fig. 4 — Cathode Radiation.
fusing, at one of these foci, not only glass but a wire of
iridium-platinum, an operation which requires a tempera-
ture of more than 2,000°-
When the cathode rays are reflected from a sheet of
platinum within the tube the marvelous phenomena of
X rays, or Roentgen rays, are produced. These rays are
different in character from the cathode rays in that they
pass readily through wood, flesh, cardboard and even thin
sheets of metal. Their serviceability in locating and deter-
mining the nature of a fracture in a bone is too well
known to need comment.
i8 PHYSICS
The cathode projectile does not depend upon the nature
of the cathode. It has been proved to be composed of
hydrogen. It has its origin necessarily in the breaking up
of an atom of hydrogen. (Villard showed that the cathode
rays exhibit the spectrum of hydrogen, and if every trace
of this gas is removed the cathode emission is suddenly
suppressed.)
"Hydrogen," observes M. Dastre in the article quoted
above, "instead of being the final expression of simplicity
and of lightness, as chemists believe, appears to be a quite
complex edifice and rather heavy, since the current of the
Crookes tube removes from the stones which represent it
but the thousandth part of its mass. These stones are the
fragments of atoms, or the atomic corpuscles of J. J.
Thompson. The atom is no longer indivisible."
The infinitesimal mass of an atom is a fact sometimes
lost sight of in discussing the constitution of matter. It
has been estimated from experimentation with colored so-
lutions of a known concentration that the weight of an
atom of hydrogen is less than 0.0000000000019008 oz. and
its diameter is less than 0.000000002 in.
Following this line of inquiry as to the ultimate con-
stitution of matter, there has recently appeared an article
by Dr. W. D. Home which reads in part as follows:
"From considerations based (partly) on very elaborate
mathematical calculations it is now maintained that mat-
ter is composed of electricity and nothing else. Electricity
here is not considered as a form of energy any more than
water is a form of energy, but as a vehicle of energy,
which can be moved from place to place and whose energy
must be in the form of motion or of strain. In motion it
constitutes current and magnetism; under strain it con-
stitutes charge, and in vibration it constitutes light."
Continuing, the same writer says: "Sir Oliver Lodge
describes the atom of matter as constituted of an indi-
vidualized mass of positive electricity diffused uniformly
over a space the size of an atom, perhaps spherical in
AN ANALYSIS OF MATTER 19
shape and about one two hundred millionth of an inch in
diameter. Throughout this small spherical space some eight
hundred minute particles of negative electricity, all ex-
actly alike, are supposed to be scattered, flying vigorously
about, each repelling every other and yet all contained
within their orbits by the mass of positive electricity. The
positive electricity is very much attenuated and constitutes
perhaps only about one per cent of the mass of the atom,
while the negative electrons are correspondingly dense
and so inconceivably small that the eight hundred are less
crowded in their atom than are the planets in the solar
system. Atoms of different kinds of matter are supposed
to be constructed in the same general manner and of the
same kind of electrons, but the number of electrons in an
atom are proportional to the atomic weight of the element.
Thus oxygen would have sixteen times as many electrons
in its atom as has hydrogen. When the crowding becomes
excessive, as in the very heavy atoms of uranium (the
heaviest substance known), thorium and radium, having
atomic weights well over two hundred, the atoms become
radio-active, probably due to numerous collisions between
the electrons, some of which are being constantly shot
away."
This perspicuous summary of the so-called electron the-
ory is highly suggestive of the fundamental unity of force
and matter. Moreover, the electron theory seems, so far,
most in accord with the results of recent investigation into
the physical basis of the material universe.
Curiously enough, the medieval alchemists who, next
after the Greeks, attempted to establish an orderly classifi-
cation of the elements, actually anticipated one of the most
modern theories regarding the properties of matter. They
believed in the Philosopher's Stone, which, if it could but
be discovered, would make possible the transformation of
any or all of the baser metals into gold. Recent investi-
gation has shown that something like a true Philosopher's
Stone actually exists and is known in the world to-day. It
20 PHYSICS
is a well accepted belief that the earth in its passage through
space gathers up constantly minute quantities of the gas
helium, so called because its spectrum was found first in
the analysis of light from the sun and before the discovery
of the element in the terrestrial atmosphere. The theory
has lately been advanced that under the influence of helium
the nobler metals, silver and gold, are slowly disintegrating
and their electrons recombining through immense periods
of time to form the baser metals, iron, copper, tin, zinc, etc.
In a discussion of modern views on matter, Sir Oliver
Lodge observed that the facts recorded in connection with
the study of radio-activity constituted a phenomenon quite
new in the history of the world. "No one," he says, "hith-
erto has observed the transition from one form of matter
to another, tho throughout the Middle Ages such a transmu-
tation was looked for. The evolution of matter likewise has
been suspected by a few chemists of genius. It was per-
ceived, on the strength of Mendeleeff's law (the periodic
law), that the elements form a kind of family or related
series, and it was surmised that possibly the barriers be-
tween one species and the next were not absolutely in-
frangible, but that temporary transitional forms might
occur. All this was speculation, but here in radio-active
matter the process appears to be going on before our
eyes."
CHAPTER II
THE PROPERTIES OF MATTER
The foregoing brief inquiry into the essence of matter
leads naturally to a consideration of its properties. Of
these properties the first and foremost is that of weight.
The term "ponderable matter" has long been used to dis-
tinguish matter in the mass, whereby is plainly indicated
the most fundamental property of matter as such. Even in
ancient times it was realized that any consideration of mat-
ter would deal primarily with questions bearing a definite
relation to weight, and the development of the knowledge
of the laws concerning the attraction of bodies for each
other is closely allied to the inner history of Physics.
In that renascence of learning and thought which suc-
ceeded the gloom of the Dark Ages in Europe arose many
great lights of science. Copernicus outlined the system
which subsequently became known by his name. Kepler
grappled with the problem of determining the paths of the
planets. Galileo laid the foundation of experimental sci-
ence. The belief in the earth as the center of the universe
was then overthrown. Copernicus taught that the earth
was not flat, but spherical ; that it rotated on its axis and
revolved around the sun; that seasons are due to the in-
clination of the earth's axis. He defined gravity as "noth-
ing other than a certain natural appetite innate in the parts
of matter by the divine providence of the Artificer of the
universe, so that they assemble themselves in an exact
unity, combining in the form of globes." The marvelous
22 PHYSICS
mathematical insight of Kepler proved the accuracy of the
Copernican theory, and he demonstrated that the elliptical
orbit of Mars would accord exactly with this theory and
with no other.
The famous experiments of Galileo with falling bodies
constituted as clear a proof of a principle as ever man has
made. The young investigator was the first actually to try
out the assertion of Aristotle that falling bodies would
descend with a velocity proportionate to their weight — a
stone weighing ten pounds would fall ten times as fast as
a stone weighing but one pound. Galileo did not believe
this, and having found from experimentation that it was
not so, openly proclaimed his conviction that Aristotle was
wrong. His opinions were hotly opposed by the learned
professors of the University of Pisa. By agreement the
case was put to the test, and from the top of the leaning
tower of Pisa Galileo allowed a small cannon ball and a
large bomb to drop together. "The multitude saw the balls
start together, fall together and heard them strike the
ground together. Some were convinced, others returned
to their rooms, consulted Aristotle, and, distrusting the
evidence of their senses, declared continued allegiance to
his doctrine."
Galileo then experimented with a polished brass ball
rolling down a smooth incline, in order to establish the
ratio between the distance traversed and the time of fall-
ing. Clocks did not exist in his day, and he resorted to a
very interesting and ingenious device for measuring the
time elapsing during the progress of this experiment.
Attaching a small spigot to the bottom of a water pail, he
caught the escaping water and measured its weight, com-
paring the increase of weight with the distance traversed
by the ball. From these experiments he found the distance
to increase very closely as the square of the time.
Galileo's reflections had brought him to the confident
belief that Copernicus' theory of the solar system was as
true as that of Aristotle was false. He taught and wrote
THE PROPERTIES OF MATTER 23
much in support of this doctrine and by his sarcastic rail-
lery against the narrow prejudice of his contemporaries
incurred the enmity of many. As an old man of nearly
seventy he published a brilliant defence of the Copernican
system which aroused such fierce antagonism that he was
forced publicly to abjure and to curse his "detestable
heresy" — viz., that the earth moves round the sun. His
"E pur si muove" (But it does move !), uttered as he came
forth from his trial, has become historic.
The extraordinarily active mind of this investigator
seemed ever to be discovering new and interesting phe-
nomena. It is said of Galileo that while he was praying in
the cathedral at Pisa his attention was drawn to the lamps
which had been lighted and left irregularly swinging above
the altar. His mind at once set off on the question as to
whether the period of a pendulum would vary exactly with
the amplitude (width) of its vibration. He timed one of
the swinging lamps by his pulse and found that the period
of vibration was exactly the same, no matter whether the
pendulum was swinging violently or dying down to rest.
Later experiments confirmed this conclusion and led
likewise to the discovery that the length only of a pen-
dulum affected the time of its oscillation. A slender wire,
with a small steel ball for a bob, swings to and fro in
exactly the same period as a heavy iron bar whose center
of gravity is at an equal distance from the point of suspen-
sion. Galileo found out that the swing of a pendulum
varied as the square root of its length. Thus a pendulum
four feet long will vibrate half as fast as a pendulum a
foot long.
The pendulum is used to-day in experimenting upon the
attraction due to gravity in different parts of the earth,
and by its help the flattening toward the poles of the
curved surface of the earth can be exactly determined.
The attraction due to gravity varies inversely as the square
of the distance from the center of the earth. Thus a
pendulum which possesses at New York a length of 39.1
5 — Foucault's Experiment Showing Rotation of the
Earth.
THE PROPERTIES OF MATTER 25
inches will vibrate once every second at that point of the
earth's surface. As it moves toward the poles the pendu-
lum vibrates more rapidly. If the change of location is
made in the direction of the equator the vibration is
slower; this for the reason that the pull of the earth is
less, since at the equator the pendulum is farther from the
center of gravity of the earth.
Of the same character was the famous Foucault experi-
ment to show the rotation of the earth. On this experi-
ment it was shown that a pendulum at rest, if of sufficient
length, would oscillate owing to the motion of the earth,
the various factors operating throughout the pendulum,
each point of which was at a varying distance from the
center of the earth.
The discovery that a pendulum of fixed length always
vibrated in the same period led naturally to the invention
of the pendulum clock. For this invention credit has been
ascribed to several unknown men, but it is probable that
the honor should be divided between Galileo and his
famous Dutch contemporary, Christian Huygens. The
significance of this invention in the history of physical
science is great indeed, when account is taken of the in-
numerable forms of experimentation which have been
reduced by its aid to exact sciences.
While Galileo, Kepler and Copernicus had completely
overthrown the ancient theory of Aristotle that the earth
is the center of the universe, and had mathematically
proved that the solar system revolves about the sun as a
center, they did not show the "why" of these new and
startling discoveries. The puzzle stared philosophers in
the face, What is it that causes the planets to move in
their orbits? To this question Descartes proposed the
novel and striking explanation of a series of whirls or
vortices. All space, he argued, was filled with a fluid, the
parts of which, acting on each other, caused circular
motion. Thus the fluid was formed into a multitude of
vortices of various density and size. A huge vortex round
26 PHYSICS
the sun carries with it the earth and all the other planets.
Each planet in the same way is the center of a vortex of
its own and draws bodies to itself in much the same way
that a log of wood is drawn into the center of a whirlpool.
Cohesion between the different parts of a body he ex-
plained in the same manner as* the result of infinitesimally
small vortices.
Unsatisfactory as this vortex theory seemed and quite
out of accord with the laws which Kepler's intellect had
formulated, yet the weight of authority lent to it by the
great name of Descartes resulted in its persistence as a
generally accepted theory until the middle of the eight-
eenth century.
Greatest of all natural scientists of this or any time
and first to formulate completely and finally the laws of
matter was the great English mathematician and physicist,
"prince of philosophers," Sir Isaac Newton. It was re-
served for his .genius to show why the apple which falls
from a tree falls down to the earth and not up to the
clouds ; how the earth, this infinitesimal point in space,
does not rush headlong into the sun or fly off at a tangent
into the void beyond the solar system; why the wave re-
bounds from the cliff and why the pendulum swings to and
fro. Newton's Law of Universal Gravitation is the cate-
chism of astronomy; his Three Laws of Motion have be-
come the basis of physics and the bed-rock of the science
of mechanics. That which is known as Newton's Law of
Universal Gravitation is in brief as follows :
Any two bodies in the universe attract each other with
a force which is directly proportional to the product of the
masses and inversely proportional to the square of the dis-
tance between them.
The term mass, as used here and generally in a physical
discussion, refers to a constant quality of weight in a
body. As a pendulum varies in its swing at different
points upon the earth's surface, so a pound of iron at the
equator will weigh less than a pound in Greenland. The
THE PROPERTIES OF MATTER 27
influence of the earth acts upon all bodies exactly as tho
its whole mass were concentrated at the center. Hence a
pound weight at the surface of the earth, 4,000 miles from
its center, would weigh, according to Newton's law of
gravitation, heavier and heavier as it approached the
center. Similarly if the weight were carried away to a
distance of say 4,000 miles from the surface of the earth,
it would weigh only one-fourth as much as it did at the
surface, since it is twice as far away from the earth's
center. Or again, a body which would weigh 1,000 ounces
at sea level would weigh about 998 ounces at the top of a
mountain four miles high. Nevertheless the mass of the
body — i.e., its power to attract other bodies — would remain
the same.
An athlete who weighs 150 pounds can leap at the sur-
face of the earth over a bar six feet high. Carry him to
the moon and the same muscular effort would carry him
at a bound over an obstacle forty feet high and his descent
on the other side would be comparatively slow. The mass
of the moon being about one-seventh that of the earth,
the same effort would accomplish seven times as much
work, since the resistance to be overcome would be the
mass of the man multiplied by the mass of the moon.
If it is true that the earth attracts the moon, it is equally
true that the moon attracts the earth, as is shown by the
tidal wave which follows the moon in its apparent revolu-
tion around the earth, and this attraction is equal to the
product of the masses of the moon and the earth. Were
the moon brought to a point one-fourth as distant as its
present path around the earth, its speed of revolution
would be enormously increased and its influence on the
water surface of the earth would raise resistless mountain
tides, sweeping the land from east to west as the earth
revolved. Newton's famous apple, detached from the tree,
leaps to meet the earth ; but it is equally true that the earth
leaps up to meet the apple. The relatively great disturb-
28
PHYSICS
ance in the position of the apple is due only to the vastly-
greater mass of the earth.
Newton's great Laws of Motion were stated thus:
( i ) Every body continues in its state of rest or uniform
motion in a straight line unless impelled by external force
to change that state.
Fig. 6 — Gravitation Drawing,
Ascribed to the Pen of
Sir Isaac Newton.
Standing on a moving car, the passenger is thrown vio-
lently forward when the car comes to a sudden stop and
backward when the car starts; he tends in each case to
continue in the previous state, whether that were one of
rest or motion. Water flies from a whirling grindstone,
mud from the spinning wheels of a rapidly driven motor
car. At each instant the world is rushing forward in a
straight line through space, but at the same instant the pro-
digious mass of the sun is acting upon it to pull the earth
into itself. Between these two forces the earth is impelled
in an almost circular orbit around the sun — the centrifugal
THE PROPERTIES OF MATTER
29
force is exactly balanced by the centripetal force which
acts upon the earth exactly as two bits of floating wood in
a quiet pond will come together or as a vessel drifts to
meet an iceberg. The resultant of the two forces acting
upon the earth may be apparent from the following dia-
gram:
S r< jE
Suppose the short side of the oblong, ES, represents the
direction and extent of the sun's attraction for the earth ;
then if ET, the long side, represents the tendency to fly
off at a tangent, the resultant motion will evidently be
between these two. Aristotle knew that if two such forces
were acting at right angles on a body the resultant motion
would be represented by the diagonal of a rectangle of
which the forces were sides. The line EO, representing a
part of the earth's path around the sun, appears as a
straight line only because it is taken as a very small arc
of an enormous circumference.
(2) Rate of change of momentum is proportional to
the force acting and takes place in the direction in which
the force acts.
On a steep slope gravity impels a body more than on a
gentle incline. A sled will gather headway faster on an
30 PHYSICS
abrupt descent. A car will travel faster with a greater
current through the motor. Other things being equal, a
steamer with two propellers making 500 revolutions per
minute would travel twice as fast as the same steamer
under one propeller. Here, however, the resistance of the
water at the bows (which increases for high speeds very
nearly as the cube of the speed) and the whirl of water
astern, which reduces the perfect efficiency of the screw,
would have to be taken account of.
(3) Newton stated his third law thus: To every action
there is an equal and opposite reaction.
This does not mean that a bouncing ball will go on
bouncing forever. Every one knows that it will not. It
does not mean that the "kick" of a gun is exactly equal
to the force with which a bullet leaves the muzzle or that
a pendulum will swing up on one side exactly as far as it
swung down on the other. In all these cases the energy
expended is equal to the work accomplished, but in each
case part of the energy is expended in overcoming resist-
ance and doing work which cannot be seen. A tennis ball
dropped to the floor will rebound about three-fourths as
high as the point from which it fell. Part of the energy
of compression was expended in the flattening of the cover
of the ball and part in overcoming the resistance of the
air. The kick of the gun is taken up by a padding of
clothes ; the pendulum is retarded by friction.
The most elastic solid in the world is steel. To the
majority of people it would appear that some such resilient
material as rubber or ivory is the most elastic. This is
not the case. Within a low range of strains it is true that
rubber has very great elasticity; the tendency of its mole-
cules to resume their former positions after being distended
is very great. Beyond the limit of this tension, however,
the rubber stiffens, the molecules fall asunder and the band
breaks. A steel piano wire, on the other hand, will carry
strains varying from one or two pounds to many hundreds
of pounds, will stretch regularly under the tension and
THE PROPERTIES OF MATTER 31
will always resume its original length. Many hundreds of
stretchings will not measurably increase the length of the
wire. If the elastic limit is reached, however, the mole-
cules will not resume quite their former positions. As
before observed, the elastic limits for steel are very wide
indeed.
A plastic substance such as lead, on the other hand, pos-
sesses almost no elasticity. Its reaction to molecular dis-
placement appears in the form of heat generated among
the molecules. A very little hammering will soon make a
piece of lead too hot to touch, while the same work done
upon a piece of iron of the same weight does not appre-
ciably warm it, for the reaction comes mainly in the re-
bound of the hammer from the iron. Steel is more elastic
than iron and iron more than any other metal.
The extreme elasticity of steel may be gathered from
the results of experimental evidence, whereby it has been
shown that a drawn steel wire one millimeter (?V inch)
in diameter returns completely to its original length so
long as the stretching force is less than 32 kilograms (70
pounds). Within this limit, therefore, steel is said to
possess perfect elasticity. A drawn copper wire of the
same diameter shows perfect elasticity only until the
stretching force has reached 12 kilograms (about 26^
pounds).
Robert Hooke, a contemporary and friend of Newton,
formulated about the end of the seventeenth century what
is known as Hooke's Law, which states :
"Within the limits of perfect elasticity elastic deforma-
tions of any sort, be they twists or bends or stretches, are
directly proportional to the forces producing them."
This means simply that a rubber ball, a steel ball, an
ivory ball or almost any sort of solid body will, if com-
pressed, resume its former shape as soon as the pressure
is removed, provided that the compression has not been
too great. The greater the strain necessary to produce a
small deformation, the greater is said to be the elasticity
32 PHYSICS
of the body. Gases alone possess perfect elasticity for all
degrees of pressure. All gases under pressure tend to ex-
pand indefinitely upon the release of the pressure. By
sufficient pressure and extreme cold all gases may be so
far reduced in volume that they become liquid. The lique-
faction of gases was first successfully accomplished by
Michael Faraday about 1823. Other experimenters fol-
lowed, but no great advance in this direction was made
until 1877, when Cailletet and Pictet, working indepen-
dently, succeeded in liquefying oxygen. Their process
consisted in compressing the gas into a small tube, cooling
it and then suddenly allowing it to expand by removal of
the pressure. The principle is essentially the same as that
in use to-day, and there exists no gas which has not been
examined in the liquid state. Most gases as such are col-
orless ; oxygen gas has no color, but liquid oxygen is milky
white ; hydrogen gas as such is colorless, but liquid hydro-
gen is steel blue.
As before observed, sufficient pressure will reduce most
gases to the liquid state. It is a remarkable fact, however,
that a temperature has been determined for every common
gas above which no amount of pressure, however great,
will succeed in making it liquid. This critical temperature
varies for different gases. Liquid air cannot be produced
at a temperature higher than 2200 (Fahrenheit) below
zero. Hydrogen must be cooled to a temperature of more
than 4000 below zero before it can be liquefied. The terms
"frigid" and "icy" are hopelessly inapplicable to these
terrific degrees of cold, for ordinary ice, as is well known,
is so warm that a vessel of liquid air placed upon a block
of ice will boil violently, while the temperature of liquid
hydrogen is nearly as far below that of liquid air as the
latter is below the freezing point of water.
It might be interesting to note, in passing, that hydro-
gen, which for a long time resisted all efforts at liquefac-
tion, was finally produced by James Dewar in 1902, not
merely as a liquid but as a solid. This he accomplished by
THE PROPERTIES OF MATTER 33
expanding liquid hydrogen into a space continually ex-
hausted by an air pump, reaching thereby the incredibly
low temperature of 430.60 Fahr. below zero.
The history of experimentation upon the weight and
expansive force of gases teems with interesting incidents.
The doctrine that "nature abhors a vacuum" was a part
of the scientific gospel up to the time of that remarkable
group of men who followed Copernicus, Galileo and
Gilbert.
Galileo had proved that air has weight by weighing, a
glass globe, forcing more air into it and weighing it again.
The increase of weight he rightly attributed to the added
air. It did not occur to him, however, that the weight of
air had anything to do with nature's horror of a vacuum.
He was amazed when informed that a lift pump had been
constructed with a tube about forty feet long and that no
amount of pumping would cause the water to rise higher
than about thirty-three feet. He observed that Nature's
horror of a vacuum was an instinct which she did not
always display. Above the water was a vacuum, but the
water refused to fill it. So, said he, Nature's dislike of a
vacuum might be measured by the height of the column
of water which it would support.
Galileo's friend and pupil, Torricelli, musing over this
suggestion, came to the conclusion that the weight of the
water in the suction pipe was supported by the weight of
air upon the cistern outside. Torricelli knew that mercury
was about thirteen times as heavy as water ; he reasoned
that the air ought to support a column of mercury one-
thirteenth as high as the column of water in the* suction
pump. He had a glass tube made about 33 inches long,
closed at one end and completely filled with mercury.
Closing the open end of the tube with his finger, he in-
verted it in a dish of mercury. The mercury sank a little
way in the tube and came to rest with its surface 30 inches
above the free surface of the mercury in the vessel below.
Torricelli had constructed the first barometer.
34 PHYSICS
The name of Pascal is indissolubly associated with the
hydraulic press. He was interested, however, in Torri-
celli's novel experiment and, having tried it, concluded
that "the vacuum is not impossible in Nature and she does
not shun it with so great horror as many imagine." Pascal
reasoned that if one were to ascend a mountain, the pres-
sure of the air at the greater elevation should be less,
because there would be less air overlying the mountain top
than there was overlying an equal area of the plain. Ac-
cordingly he wrote to his brother-in-law, who lived near
the Puy de Dome, an ancient volcano in the Auvergne,
France, asking him to ascend the mountain with a Torri-
cellian tube and observe whether the mercury column
would not fall because of the diminished atmospheric pres-
sure. The experiment was made and it was found that
the mercury column became three inches shorter during
the ascent, but gradually resumed its previous length dur-
ing the descent to the plain.
Pascal also repeated Torricelli's experiment with wine
instead of mercury, and he found, as he had inferred, that,
since wine is less dense than water, the atmosphere bal-
anced a column of it which was longer than the water
column, for of course it would take a longer column of
the lighter fluid to make the same weight.
The hypothesis of Torricelli and Pascal as to the pres-
sure of the atmosphere was thus placed upon a firm experi-
mental basis and was now competent to explain the
phenomena of pumps, but it required the evidence of many
more experiments to secure its general acceptance.
The most remarkable man of this period, however, in
view of the multitude and the ingenuity of his experiments,
was Otto von Guericke, who later became mayor of the
city of Magdeburg. The Magdeburg Hemispheres have
become a familiar word owing to his famous experiment
made in 1654 at Regenburg before the Reichstag and the
German Emperor, Ferdinand III. Two hollow hemispheres
of steel, about 1.2 feet in diameter, were cast for his re-
THE PROPERTIES OF MATTER 35
markable experiment. They were fitted at either end with
heavy iron rings and provided with a tube and stop cock.
The edges were made broad, smoothed and polished to a
perfect plane so that they might fit exactly together. Then
the air was pumped out of the interior, the stop cock
turned off and twelve horses, six at each end, were hitched
to the rings in the hemispheres. Their combined efforts
failed to overcome the pressure on the outside of the
spheres. Another team of horses was attached, and yet
another, and the spheres were finally pulled apart.
A simple calculation will show that this result was in-
evitable, the average horse, it is estimated, being able to
exert a pull equal to about 600 or 650 pounds horizontally.
According to the known formula for the surface of a
sphere of 12 feet diameter, these hemispheres would have
about 652 square inches area. Reckoning the atmospheric
pressure upon the outside of the two hemispheres at 15
pounds to the square inch, and assuming that the internal
pressure has been reduced to a negligible quantity, it is
apparent that the pressure to be overcome would equal,
roughly, 9,780 pounds. According to von Guericke's cal-
culations, a force of 2,686 pounds would overcome the at-
mospheric pressure upon the exterior of the spheres. Here
must be some error !
There is extant a quaint old engraving showing the
horses endeavoring to separate the exhausted hemispheres.
On the occasion of this experiment von Guericke asserted
that if you were to blow your breath into a large exhausted
receiver, you would that moment breathe your last. The
truth of this being doubted, he illustrated the power of
"suction" by a new experiment. "A cylinder of a large
pump had a rope attached to its piston, which led over a
pulley and was divided into branches on which twenty or
thirty men could pull. As soon as the cylinder was con-
nected with an exhausted receiver the piston was suddenly
pushed down by the atmospheric pressure and the men
at the ropes were thrown forward."
36
PHYSICS
debut taf^ "Sed by thedisti^3hed mayor of Mag.
ueourg was his own invention. The unner Lik t
Fig- 7 -Von Guericke's Air PUMp.
THE PROPERTIES OF MATTER 37
periments Touching the Spring of the Air" and stated the
law which has since borne his name :
Under like conditions of temperature and pressure the
volume of a gas varies inversely as the pressure upon it.
"We took then a long glass tube," he writes, "which by
a dexterous hand and the help of a lamp was in such a
manner crooked at the bottom that the part turned up was
almost parallel to the rest of the tube and, the orifice
of this shorter leg being hermetically sealed, the
length of it was divided into inches (each of which was
divided into eight parts) by a straight list of paper, which
containing those divisions, was carefully pasted all along
it. (A similar strip of paper was pasted on the longer leg.)
Then as much quicksilver as served to fill the arch or
bended part of the siphon was poured in so as to be at the
same height in both legs. This done, we began pouring
quicksilver into the longer leg till the air in the shorter
leg was by condensation reduced to take up but half the
space it possessed. We cast our eyes upon the longer leg
of the glass and we observed, not without delight and
satisfaction, that the quicksilver in that longer part of the
tube was 29 inches higher than the other."
Experimentation in measuring the weight of the air was
naturally followed by efforts at more exact estimations of
temperature. The air thermometer of Galileo was an ex-
quisitely sensitive instrument, but having an exposed liquid
surface was subject to barometric influences as well as
those of heat and cold. Fahrenheit, toward the end of this
century, devised the thermometer which bears his name.
He selected his zero at the lowest temperature which he
knew how to obtain and took the highest fixed point at the
temperature of the human body. He divided this space
into twenty-four equal parts and then, finding these de-
grees too large, subdivided each into four parts, thus
making the temperature of the body 960. On this basis
of division the freezing point of water happened to come
at 320 and the boiling point of water at 2120. And there
38 PHYSICS
they stay to this day, despite the fact that all modern
physicists measure temperature on the excellent Centigrade
scale of Celsius, whereon the freezing point of water is
zero and the boiling point ioo°.
Nearly a century after the invention of Fahrenheit's
thermometer and fifty years later than that of the Swedish
astronomer Celsius, need was found for a third type of
thermometer. The experiments of Charles, Dalton, Gay- .
Lussac and others had determined the fact that for every
degree Centigrade of increase in temperature above zero
the volume of a gas increased by 273 of itself. Similarly
a decrease of i° below zero meant a decrease of 273
in volume of the gas. A decrease of 20 meant a reduction
in volume of 273. Hence a fall of 273 ° would mean a
reduction of fyf, or, in other words, the volume of the
gas would be reduced to zero. This was absurd, for the
law of the indestructibility of matter would not allow that
something could become nothing. The explanation, how-
ever, soon was found in the fact that all gases become
liquid before reaching this point, and it is a matter of com-
mon knowledge that liquids are practically non-compress-
ible. The temperature of 2730 Centigrade then was taken
as the zero of the absolute scale, because it was believed
(and there is yet no evidence to disprove it) that at that
temperature the molecular motions of all bodies would
entirely cease, the molecules would be perfectly at rest.
With this thermometer in mind, the statement of the
law of gases, called Charles' Law, or Gay-Lussac's Law,
is simple. It was:
The volume of a gas varies directly as the absolute tem-
perature.
Brief mention herein has been made of the remarkable
experiments of William Crookes upon the so-called cathode
rays in the highly exhausted tubes which have since borne
his name. In the course of his investigations upon the
properties of the newly discovered element, thallium, he
attempted to carry out the necessary delicate weighings
THE PROPERTIES OF MATTER
39
in a vacuum, in order to avoid the effect of the buoyancy
of the air. Irregularities in the weighings which he was
quite unable to explain led him to the invention of his
famous radiometer, an instrument now common enough in
the windows of opticians' stores.
Crookes' Radiometer.
It consists of a delicate paddle wheel with four metallic
vanes, polished on one side and blackened on the other,
mounted so as to revolve in a partially exhausted tube.
Light falling upon the dark surfaces is absorbed, and the
temperature of the residual gas next these surfaces is
therefore raised in accordance with the well-known fact
that "black is a warmer color than white." Higher tem-
perature means greater molecular activity (as will appear
40 PHYSICS
in the chapter on Heat). Hence the vanes are pushed
backward into the region of comparative quiet on the pol-
ished side. When light is withdrawn the revolution ceases
and the brighter the light the faster the revolution. At
first Crookes believed the rotation of the vanes to be due
to ether waves, but by exhausting the bulb to an extremely
high vacuum he found the wheels did not revolve. He
therefore fell back upon the modern Kinetic Theory of
Gases, attributing the motion to the bombardment of the
vanes by the molecules of gas left in the tube.
The examination of the properties of gases began natu-
rally with the study of air. Similarly the inquiries of the
human mind into the characteristics of liquids began with
an investigation of the properties of water. The story of
Archimedes and the crown problem is probably the earliest
historic record of the study of hydrostatics, tho Pliny
makes mention of a Phenician who devised a highly in-
genious scheme for transporting along the Nile two great
columns of an Egyptian temple. The columns were rolled
in huge cylindrical boxes, drawn by oxen to the bank of
the Nile. There the bank was dug away from under them
until they rested on their ends, when two large scows full
of sand were floated underneath them. The sand was
then thrown out, the boats rose and the pillars took the
place of the sand.
No systematic study of displacement and pressure in
liquids, however, was made before the time of Blaise
Pascal. In 1653 there appeared his "Traite de l'equilibre
des Liqueurs," in which he enunciated the law known by
his name — to wit:
Pressure applied anywhere to a body of confined liquid
is transmitted by the liquid so as to act with undiminished
force on every part of the containing vessel.
"Whereby," he said, "it follows that a vessel full of
water is a new principle of mechanics and a new machine
for multiplying forces to any degree we choose."
The hydraulic press is the direct outcome of Pascal's
THE PROPERTIES OF MATTER
4i
principle of transmitted pressure. The mechanical advan-
tage of this machine depends simply upon the relative size
of the surfaces at which the force is applied and the power
produced. If, for instance, the piston of the pump has an
area of 10 square inches and the press itself has contact
with the water over a surface of 1,000 square inches, the
result will evidently be a power 100 times as great as the
force. The press will move, however, only r
some medium other than
matter. This conclusion is involved in the hypothesis of
the granular nature of matter, for force acting at a vacu-
ous distance is unthinkable or at best incomprehensible.
The cohesion of the molecules of a substance thus resem-
bles gravity, which reaches across the enormous inter-
planetary spaces to grasp the masses of the planets and
hold them in their courses round the sun; like gravity
also the cohesive force which renders substances elastic
does not seem to consist of material vibration or ether dis-
turbances. Cohesion acts through infinitesimal spaces upon
bodies infinitesimally small ; gravity spans distances im-
measurable to guide a myriad of suns and systems. Yet
both these forces are conveyed through a medium at once
infinitely rigid, since it is non-compressible, and infinitely
fine, since it is frictionless. The distinguished author of
the electro-magnetic theory of light, speaking of the char-
acteristics of the ether, writes:
"The vast interplanetary and interstellar regions will no
longer be regarded as waste places in the universe, which
the Creator has not seen fit to fill with the symbols of the
manifold order of His kingdom. We shall find them to be
already full of this wonderful medium; so full that no
human power can remove it from the smallest portion of
space or produce the slightest flaw in its infinite continu-
ity. It extends unbroken from star to star, and when a
molecule of hydrogen vibrates in the dog star, the medium
receives the impulses of these vibrations, and after carry-
ing them in its immense bosom for several years, delivers
them, in due course, regular order and full tale, into the
spectroscope."
CHAPTER III
It has been said that the history of man begins with the
discovery of fire. How many conveniences of modern life
are dependent in the last analysis upon the use of fire, it
would be hopeless to attempt to enumerate. The survival
of the human race with its primitive undeveloped physique,
helpless for defense or attack except by virtue of superior
cunning, would never have been possible without the aid
of fire. It is, indeed, a well-known fact that life in any
form is directly dependent for its development upon con-
ditions of temperature. The myriad forms of physical
life that are hourly born upon the surface of the globe owe
their existence to the heat radiated from a gaseous ball,
some 93,000,000 miles away.
All heat in the world — excepting the negligible quantity
reflected from the moon or transmitted from the stars —
must be traced originally either to falling meteorites or to
the sun. The warmth of the air, the rocks and the water is
derived from these sources. Even the heat of a coal or
wood fire is but an expression of solar energy, for it was
the sun's heat which, through the growth of vegetable
tissue, yesterday, or a million years ago, transformed the
incombustible soil into a form apt for the burning.
The heat received by the earth from meteors would be
nearly the same in amount as that which it receives from
the sun by radiation, but for the probable circumstance that
these meteors, reaching the earth's atmosphere at an ex-
49
50 PHYSICS
ceedingly low temperature, radiate most of the heat en-
gendered in their approach into outer space. For practical
purposes, then, the sun may be considered as the original
source of all terrestrial heat. No material body, it is true,
is quite devoid of heat, for as long as its molecules are in
vibration, matter must radiate into the space surrounding
this vibratory energy. Heat as a physical phenomenon,
then, is the vibration energy of molecules of matter —
solid, liquid, or gaseous. Here must be noticed the dif-
ference between "radiant heat," so-called, and molecular
heat. In the form of radiant heat, energy is transmitted
by the sun to the earth. It is converted from radiant heat
into molecular vibration upon contact with the matter of
the earth, and the material bodies, so incited, afford the
phenomenon commonly known as heat.
Anything like an exact study of heat was never possible
before the dissociation of the ideas of the vibratory phe-
nomenon of heat and the sensation of it. By the use of his
sense of touch mainly, man has learned to decide in a gen-
eral way whether a body is hot or cold, and whether it is
gaining heat or losing it. Conclusions based on this sense
of temperature, however, are likely to be very inexact, or
even wholly false. The sensation of heat may often be
mistaken for that of cold, and vice versa. If one hand is
put into ice-cold water and the other into water as hot as
it can endure, and after a minute or two both hands are
thrust into water at blood-heat (980 F.), this same water
will feel cold to one hand and warm to the other. Evidently
the temperature sense is a relative matter. Heat as a sen-
sation must be relegated to the domain of medicine or
psychology; heat as a form of vibration, however, is a
legitimate object of physical investigation.
Previous to the nineteenth century physicists generally
considered heat as an invisible weightless fluid, which by
passing into or out of a body caused it to become hot or
cold. This view accorded readily enough with the facts
observed in the heating of a body held in a flame, or near
HEAT 51
another hot body. It did not account for the heat pro-
duced by friction. In 1798 Benjamin Thompson, Count
Rumford, an American by birth, brought forward the
molecular theory of heat, according to which the increase
in the temperature of a body means simply an increase in
the average velocity of its molecules. This theory, tried
out and carefully tested by the great English physicist,
James Prescott Joule, in an exhaustive series of experi-
ments, has proved thus far the best working hypothesis of
the nature of heat.
"The earliest traces of the theory that heat is matter,"
writes Florian Cajori, "are found in ancient Greece
among Democritus and Epicurus. In modern times it was
advocated by Pierre Gassendi and Georg Ernst Stahl,
author of that erroneous theory of combustion, according
to which a burning body gave off a substance called
'phlogiston.' One such agent paved the way for the other.
In 1738 the French Academy of Sciences offered a prize
question on the nature of heat. The winners of the prize
favored the materialistic theory. At first the only prop-
erties postulated for this material agent, called heat, were
that it was highly elastic and that its particles repelled each
other. By this repulsion the fact that hot bodies give off
heat could be explained. Later it was assumed that the
heat particles attracted ordinary matter, and that this heat
was distributed among bodies in quantities proportional to
their mutual attractions (or their capacities for heat). By
the close of the eighteenth century this theory met with
almost universal acceptance." Marat, afterward famous as
a leader in the French Revolution, gave in 1780 an exposi-
tion of this theory by starting from Newton's corpuscular
theory of light.
Professor Clerk Maxwell, in his 'Theory of Heat,' says :
"We must therefore admit that at every part of the surface
of a hot body there is radiation of heat, and therefore a
state of motion on the superficial parts of the body. Now,
motion is certainly invisible to us by any direct mode of
52 PHYSICS
observation, and therefore the mere fact of a body appear-
ing to be at rest cannot be taken as a demonstration that its
parts may be in a state of motion. Hence, part at least of
the energy of a hot body must be energy arriving from the
motion of its parts. Every hot body is, therefore, in mo-
tion, the movements of the parts being too small to be
observed separately."
Tyndall defined heat as "a mode of motion." It might
more accurately be defined as "a mode of motion of the
particles of a mass ;" the greater the heat, the greater will
be the motion of the particles. In accordance with the
molecular theory discussed in the chapter on the Properties
of Matter, any increase in temperature means simply this,
and nothing more — an increased velocity of the molecules
of the heated substance. If, then, the temperature of a
body be lowered until the point of absolute zero is attained,
there will then be no motion of its molecules — nothing but
mass would remain, absolutely motionless and in a state of
perfect tranquillity and rest.
To speculate as to the probable condition of matter when
the point of absolute zero has been passed, and the molec-
ular motions have become, so to speak, negative, might
be interesting but not profitable. As yet the temperature
of absolute zero has never been attained, and all matter
as known to-day is possessed of some molecular motion —
some heat. The late Lord Kelvin has surmised that the
ether may be constituted of the dissipated dust of atoms
which have lost all vibratory motion of their own. This
is admittedly a guess, and does not affect the generally
accepted belief that ponderable matter is ever in vibration.
The measurement of heat may be considered in any one
of three ways. It is possible first to measure the degree of
heat in a body, as did Galileo with his air thermometer as
early as 1592. Measurements of this kind made with
solids, liquids and gases have resulted in the establishment
of extremely valuable physical data, more especially in
the field of meteorology. Secondly, the actual amount of
HEAT 53
heat in a body may be measured. It is evident that a red-
hot needle possesses a smaller amount of heat than a stove
which is only moderately hot. The determination of the
amount of heat possessed by a body constitutes the science
of calorimetry.
The calorie, or heat unit, is defined as the amount of
heat necessary to raise one cubic centimeter of water
through one degree Centigrade.
Joule reasoned that if the heat of friction were merely
mechanical energy which had been transferred to the
molecules of a heated body, then the same number of
calories must always be produced by the expenditure of a
given amount of mechanical energy. His investigations in
calorimetry, whereby he determined the mechanical power
corresponding to a given amount of heat, first proved expe-
rimentally the identity of various forms of energy. In a
series of experiments lasting over nearly 30 years, he
caused mechanical energy to disappear in as many ways as
possible, and measuring the amount of heat developed,
found it to be for a given amount of energy in each case
the same. Thus was established the principle of the
Mechanical Equivalent of Heat.
The English physicist found that the equivalent of the
calorie in work was equal to 426.4 kilogram meters (= 3,081
ft. lbs.), that is to say, the amount of heat necessary to
raise 1 cubic centimeter of water 1 degree Centigrade
would, if all converted into work, be sufficient to raise
3,081 lbs. through 1 foot of height, or what is the same
thing, to raise 1 pound through 3,081 feet. The mechanical
equivalent of heat is such an important constant in nature
that several physicists since Joule have thought it desirable
to redetermine it. One of the most accurate determina-
tions was made in 1879 by Henry A. Rowland of Balti-
more. He obtained 427 gram meters as the mechanical
equivalent of the calorie.
A third method of measuring the heat of a body is a
relative one. Specific heat is a term used in comparing
54 PHYSICS
the relative amounts of heat necessary to increase equally
the temperature of equal weights of different substances,
for example, glass and water. It has been found that
more heat is required to raise the temperature of a pound
of water, say 10 degrees, than to increase to the same
extent the temperature of an equal weight of almost any
other substance. Therefore, water is taken as a standard
of specific heat, and when the heat necessary to raise the
temperature of glass 10 degrees is found to be five times
as great as that necessary to raise the temperature of an
equal amount of water 10 degrees, the specific heat of glass
is determined at one-fifth or .2. The value to the physi-
cist and chemist of determining specific heats of substances
is great, for a fixed relation has been found to exist be-
tween the specific heats of solids and their atomic weights.
For this significant discovery, science is indebted to the
researches of Berzelius, Regnault, Dulong and Petit.
Matter is variously affected by heat. In general, it in-
creases the volume of a body; but just as magnetism has
sometimes the contrary effect (as, for instance, its con-
tractile influence upon nickel), so heat has sometimes the
effect of reducing a body. Water, for example, is denser
at 400 Fahrenheit than at freezing, which is proven by
the fact that ice floats, having about one-tenth of its vol-
ume out of water. Were it denser than water, this could
not be. Again, type metal contains a small proportion of
antimony, since antimony expands on solidifying, making
the perfectly sharp outline indispensable to good type.
With the exceptions noted, however, the law is general
that bodies contract with cold, and expand with heat. Rail-
way rails are always laid with a slight space between them
to allow for the expansion in the hot days of summer. Iron
bridges frequently have a roller at one end to provide for
the difference of length. The steel suspension cables of
a bridge a mile long will vary in length nearly four feet
between summer heat and winter cold. If the heat applied
to a substance is strong and continuous, the result is a
HEAT 55
change of state ; solid ice becomes water, water becomes a
vapor, A great deal of energy is absorbed in this trans-
formation of state. It takes nearly as much heat to change
a pound of ice into a pound of ice water as to heat the
same water to boiling. It takes more than five times as
much heat to change the water into steam as to raise its
temperature from freezing to boiling. Conversely a great
amount of energy is liberated by the condensation of steam
— a fact well illustrated in the immense power of the steam
engine; and no small amount of heat is set free when
water freezes. The country in the neighborhood of large
lakes is thus appreciably warmed by the congelation of the
water. For exactly the same reason the farmer often
places tubs of water in his cellar that the freezing of the
water may sufficiently warm the air to keep his vegetables
from freezing.
More remarkable than the effect of the freezing of water
upon the surrounding air, is that of evaporation. As the
freezing of water in winter warms the air, so the evapora-
tion of water in the open seasons of the year will cool it.
The amount of evaporated water which can exist in the
air depends upon the temperature. If the air has absorbed
all the water vapor which it is capable of holding, it is
evident that a fall in temperature will succeed in condens-
ing a part of the suspended water-vapor which then falls
as rain, or settles as mist. If the air is not completely
saturated, it is evident that considerable cooling may take
place before the "dew-point" is reached and condensation
of water begins. In the hot days of the summer months
the air is capable of taking up and holding in suspension a
large amount of moisture. On such days the oppressive-
ness of the heat is greatly augmented by the "muggy"
condition of the atmosphere. The excessive moisture of
the human body cannot escape into the air, for the latter
is already surcharged with moisture, or nearly so. The
grateful effect of a breeze is thus made clear, for the
excess of moisture which evaporates from the body has no
56 PHYSICS
opportunity to saturate the air immediately around, before
a fresh supply of air appears to take up the exhalation from
the skin. It was formerly held by scientific inquirers that
the dew fell from the upper regions of the atmosphere.
That idea has been quite swept away within recent times,
and it is now known that the formation of dew is due to
the condensation of water-vapor in the air close to the
ground. A heavy dew is said to be the forerunner of fine
weather. It actually indicates an unusual fall in tempera-
ture from the heat of the day — nothing more.
The formation of condensed particles of water-vapor in
the upper regions of the atmosphere is generally conceded
to be due to the impalpable dust particles which float every-
where in the terrestrial atmosphere rising to considerable
heights. As water vanishes so strangely into the thin
vapors of the air, so solid bodies have been observed by
every one to disappear and dissolve in liquids.
There are probably few persons, if any, who have not
noticed that sugar dissolves more readily in hot water than
in cold, while salt is about equally soluble in both. In
general, the solutions of solids in water or any other sol-
vent are made easier by the application of heat. So also
with solutions of liquids, for the viscosity of most liquids
is reduced by the application of heat, they become less
dense, and therefore mix more readily with the molecules
of the liquid in which they are dissolved. Solution is such
a familiar, everyday phenomenon that the complete disap-
pearance of solid material in a liquid is taken as a matter
of course. Yet it is truly a wonderful thing that a lump
of sugar or a teaspoonful of salt dissolved in a glass of
water will not raise the level of the water, and so soon as
solution is complete will leave absolutely no visible trace of
its presence. As the temperature is raised more of the
solid may be made to disappear. Even boiling water, how-
ever, will take up but a limited quantity of a solute, and
on cooling this may readily be seen by dropping in a
crystal of the dissolved material or otherwise disturbing
HEAT 57
the mixture, causing it to exhibit the beautiful and fasci-
nating phenomenon of crystallization.
A strange contrast to this condition of things is found
in the fact of the solution of gases in liquids. Here the
effect of temperature is quite the reverse of what has just
been observed. The cooler the liquid, the greater the quan-
tity of gas which may be dissolved in it. The quantity of
gas which may be dissolved by a single pint of water is
amazing, in some instances almost incredible. Hydrogen
chloride, for example, is soluble to the extent of over 300
pints in a single liter of water; and the same quantity of
water will dissolve without artificial pressure 1,148 pints of
ammonia gas.
The effect of heat on a liquid — or indeed on any body —
being recognised as an increase of its molecular velocities,
the question arises as to how this increase of velocity is
transferred from one part of matter to another. The most
direct way for this to take place is by the transference of
energy from one molecule to the next. In general this
is accomplished most readily by the molecules of a solid,
especially solids of exceptional density such as metals.
For example, a short copper or iron wire held for a mo-
ment in a hot flame soon becomes too hot at the other end
to hold. A silver wire will conduct the heat of the flame
to the hand even more quickly. A stone feels colder to
the hand than a piece of wood at exactly the same tem-
perature, for the obvious reason that the stone, being a
better conductor, carries off the heat of the body more
rapidly. The tongue will freeze fast in winter to the
blade of an ax, a fact well known in cold countries where
the bit of a horse's bridle cannot be put directly in his
mouth if it has been out in the frosty air. The same ax
blade lying in the summer sun will feel hotter than any
other part of the ax.
Liquids, however, are poor conductors, as has been
shown by the fact that burning alcohol on the surface of
water will register no perceptible heat in an instrument so
58 PHYSICS
sensitive as the air thermometer whose bulb is placed but
half an inch below the surface of the water. Gases are
almost non-conducting. "Dry air," writes a physicist of
to-day, "is a practical vacuum as regards the rays of heat."
Liquids and gases, however, may carry considerable
heat by the motions of comparatively large masses of
themselves in a heated condition. This transference of
heat by the movement of masses of a liquid or gas is
termed "convection." The term thus describes the man-
ner in which temperature is adjusted by winds in the at-
mosphere and currents in bodies of water.
Yet another method of the conveyance of heat is that
by which most heat in the universe is carried — viz., radia-
tion. The heat which is received from an open fire is not
carried by conduction or convection. Not by convection,
for the movement of masses of air is all toward the fire,
not away from it; not by conduction, for gases have been
shown to be very poor conductors. The only other pos-
sible explanation of the passage of the heat rays must then
be found in a non-material form of energy. To this form
of heat transference the term "radiation" has been applied.
Radiation thus explains the sensation of heat felt from a
burning house, even when the house is at a considerable
distance and the wind is blowing toward the fire. The
method by which the heat of the sun is conveyed to the
earth will likewise readily be seen to be the method of
radiation. There could evidently be no mass movements
nor yet molecular movements where is neither mass nor
molecule. This radiant property must then be a function
of the ether, not of matter in the mass. According to re~
cent scholars, radiant heat must now be classed with light
under the head of electricity.
The three forms of heat transference — conduction, con-
vection, radiation — are all to be seen in the consideration
of the common steam or water radiator. Convection brings
masses of hot water or steam from the furnace to the radi-
ator. Conduction transfers the heat to the outside of the
HEAT 59
radiator. Radiation carries the heat to every part of the
room to be heated.
The application of heat to mechanical purposes has been
astonishingly slow of development. From the time of the
invention of Heron's eolipile there elapsed 1,000 years be-
fore the idea of heat as a source of motive power was
turned to practical account. Steam fountains were de-
signed in the seventeenth century, but they were merely
modifications of the eolipile and applied for ornamental
purposes only.
The first successful attempt to combine the principles and
forms of mechanism then known into an economical and
convenient machine was made by Thomas Newcomen, a
blacksmith of Dartmouth, England. Assisted by John Gal-
ley, Newcomen constructed an engine — an "atmospheric
steam engine." In 171 1 such a machine was set up at Wol-
verhampton for the raising of water. Steam passing from
the boiler into the cylinder held the piston up against the
external atmospheric pressure until the passage between
the cylinder and boiler was closed by a cock. Then the
steam in the cylinder was condensed by a jet of water. A
partial vacuum was formed and the air above pressed the
piston down. This piston was suspended from one end of
an overhead beam, the other end carrying the pump-rod.
The fly-wheel was introduced in 1736 by Jonathan Hulls.
The next great improvements were introduced by James
Watt in Scotland. Becoming interested in the steam en-
gine and its history, he began to experiment in a scientific
manner. He took up the study of chemistry under the
guidance of Joseph Black, the originator of the doctrine of
"latent heat." Observing the great loss of heat in the
Newcomen engine, due to the cooling of the cylinder by
the jet of water at every stroke, he began to ponder on
the possibility of keeping the cylinder "always as hot as
the steam that entered it." He himself tells how there
flashed through his mind the happy thought of how this
could be done. "I had gone to take a walk," he says, "on a
6o PHYSICS
fine Sabbath afternoon. I had entered the Green by the
gate at the foot of Charlotte Street and had passed the old
washing-house. I was thinking upon the engine at the
time, and had gone as far as the herd's house when the
idea came into my mind that, as steam was an elastic body,
it would rush into a vacuum, and if a communication were
made between the cylinder and an exhausted vessel, it
would rush into it and might be there condensed without
cooling the cylinder."
This improvement it is by right of which James Watt
may justly be called the "inventor" of the steam engine.
The steam engine as such has practically reached its maxi-
mum of efficiency. Only about 22 per cent, of the heat
energy furnished by the coal consumed is actually con-
verted into work, even in the best triple expansion engines.
The efficiency of the locomotive is even lower, being about
17 per cent.
The steam turbine, the latest development of the steam
engine, is in principle very much like the common wind-
mill, the steam being driven at an angle against a multi-
tude of little blades set into a revolving cylinder of steel —
the shaft. In large sea-going vessels this engine is rapidly
replacing the old-fashioned "reciprocating" machine, for
its efficiency is higher, it occupies less than one-tenth the
floor space and it runs without jarring the ship. The
highest speeds ever attained by vessels at sea — namely,
about forty miles per hour — has been made with the aid
of steam turbines. The construction of a turbine is an
exceedingly difficult operation, for each of the little blades
must be set singly into the shaft at exactly the right angle.
Skilled workmanship and much time are required in this
operation, and in view of the mechanical difficulties of
constructing a turbine, it does not seem so remarkable that
this engine, of which the extremely simple principle was
familiar to Hero of Alexandria (120 B.C.), should have
waited over 2,000 years to see perfection.
The efficiency of the steam engine is measured by the
HEAT
61
fall in temperature which the steam undergoes in passing
from the boiler through the cylinder (thus driving the pis-
tons) to the condenser. It is evident that as this heat is
made to disappear, work must be produced. The greater the
fall in temperature, then, the higher the efficiency of the
engine. Unfortunately the steam engine is limited in this
— Principle of the Turbine.
regard, for the highest temperature that can safely be
maintained in the boiler is about 2000 Centigrade, the
steam being then under a pressure of 15 atmospheres, or
225 pounds upon every square inch of surface. The lowest
practicable limit of temperature in the condenser is about
300. Hence the loss of heat and the resulting efficiency
62 PHYSICS
will be measured by a fall of 170 ° (2000 — 300). A perfect
steam engine should render about 36 per cent, of its heat
energy into work, but owing to friction and other causes
no steam engine has ever been made which approaches this
degree of efficiency.
The gas engine has a considerably larger range of tem-
perature fall possible in its mechanism. The explosion
of the gases takes place at a very high temperature. Engi-
neers predict that the gas cylinder engine and turbine en-
gine will before long supplant the corresponding types of
steam-driven machines.
In conclusion, then, heat must not be considered as a
weightless fluid, for the interchange of heat and mechani-
cal energy is not consistent with this belief. Nor is heat
"latent" any more than the lifting power of a steam crane
is latent. All the evidence of to-day points to the conclu-
sion that heat is only one of the many forms of vibration.
The effect of heat upon any material body is an in-
creased rate of vibration of its molecules. The heat that
reaches the earth from the sun, however, traverses the
intervening space without heating it, as the intense cold
of the upper regions of the atmosphere clearly indicates.
It is therefore a property of the ether that it transmits
vibrations without being itself affected by them. In mat-
ter, on the other hand, all parts of a conductor must
become hot when heat is transferred from one end of it to
the other. Convection cannot be considered as a form of
vibration at all, since it does not represent the transmis-
sion of energy from particle to particle of a mass so much
as the change of location of a relatively large amount of
heat. It cannot proceed, however, without the aid of either
conduction or radiation, inasmuch as the heat given by
one mass to another can be received only through the
medium of matter or ether. As before observed, ether-
borne heat energy is now regarded as nothing more or less
than electricity.
CHAPTER IV
THE SOURCES OF LIGHT
Rising from underneath the world, and flooding all
nature with the growing splendor of its Light, the morn-
ing sun has ever been to man a symbol of the power of
goodness. The unparalleled poetic imagination of the
Greeks clothed this symbolic object with personal attri-
butes, and formulated the fiery chariot and flying steeds
of the Sun God Apollo, the Baldur of the Norsemen, the
Christ of early German legend. A growing Christianity
synchronized with the effacement of the personal and
divine attributes of Light. The third century in Europe
saw the development of an established Church — Christian,
and an established Science — Greek. The Properties «of
Matter, Light, Sound, Heat, as defined by Aristotle, be-
came the accepted creed of Europe.
A science not less dogmatic than theology ruled the
thoughts of men until near the end of the sixteenth cen-
tury, until Roger Bacon and Bruno and Galileo, with
other less illustrious but not less courageous investiga-
tors, had suffered contempt and persecution, and even
languished in prison for the splendid heresy of Experi-
mental Truth. The conception of Force — intangible, ir-
resistible, indestructible — was long in making its way into
any system of popular philosophy ; the world, as a cosmos
of Substance possessed of varying Qualities, was all-suffi-
cient explanation for medieval thought of the phenomena
of Sense and the fabrications of Reason.
63
64 PHYSICS
Light, like other things now conceded to be forms of
force, was deemed a substance or a quality of substance.
Generally it was held to be a substance, possessed, like
other substances, of such qualities as elasticity (reflec-
tion) and solubility (absorption). The law of the angle
of incidence and reflection was* known to the Egyptians
and the Greeks; the Assyrians were familiar with the
lens ; the Arabs imitated from Greece and developed a
system of optics involving a knowledge of mirrors, plane
and spherical, lenses and prisms, the straight-line propa-
gation of light, shadows and semishadows, or penumbrae.
That light travels in straight lines was one of the arti-
cles of faith of the Platonic school. Not all the Greek
philosophers, however, maintained this view, and the vari-
ance of their opinions foreshadowed the uncertainty con-
cerning light which has characterized all subsequent dis-
cussion of its exact nature. Aristotle wrote more volumi-
nously than any of the Greeks upon this question, but his
conclusions are dubious and obscure. Through his in-
fluence the Scholastics were led to regard light as some-
thing immaterial, rather a quality of bodies than a sub-
stance, and they sought to find in the bodies themselves
something analogous with the color sensation of the eye.
Both Euclid and Plato, however, conceived of light as
a. something projected from the eye upon an illuminated
body, causing sight as soon as it met another substance,
which emanated from the body. Pythagoras and Democ-
ritus held that visible bodies projected something into
the eye whereby they became visible.
The Greeks knew something of spherical and parabolic
mirrors. The story is told of Archimedes that when the
Romans were besieging his native city, Syracuse, he de-
fended it by the use of mirrors reflecting the sun's rays,
which focused upon the ships of the Romans as they came
near, setting them on fire. The terrific heat developed
in a modern solar engine makes this tale not so impos-
sible as might at first sight appear, altho it is likely that
THE SOURCES OF LIGHT 65
the men, rather than the ships of the Romans, were the
sufferers under the fierce reflection from the mirrors of
the Greeks.
That the latter had gathered much other evidence with
regard to the phenomena of light is unquestioned, for
in a fragment of a Greek document discovered in Egypt
mention is made of various familiar optical illusions.
They had observed, for example, that a ring on the bot-
tom of an empty vessel, just hidden by the edge, becomes
visible when water is poured into the vessel, and Cleo-
mides observed that in the same way the sun may be
visible when it has actually sunk below the horizon. The
Greeks had noticed, also, that the sun appears larger
when rising or setting than when high in the heavens;
they were familiar with the fact that light glances off
from a mirror at the same angle as that at which it
strikes.
Among the Romans no investigators of natural phe-
nomena appeared to add anything of moment to the dis-
coveries of the Greeks. Lucretius made some interesting
comments on magnetism; Seneca observed and taught the
identity of the colors in the edge of a piece of glass with
those of the rainbow; he did not explain why they were
identical; he remarked that a globular glass vessel, full
of water, magnifies objects, from which he was led to
conclude that there is nothing so deceptive as sight, an
inference not particularly ingenious nor highly illumi-
nating as an explanation.
Abu 'Ali al Hasan ibn al Hasan ibn Al Haitam rose
into favor under one of the Caliphs of Egypt as a result
of a plan (which he never carried out) to regulate the
flow of the Nile for purposes of irrigation. He made a
study of plane and spherical mirrors, and understood,,
also, the principle of parabolic reflectors, such as are used
to-day in searchlights or the headlights of locomotives,
in which all the rays leave the mirror in parallel lines.
He knew that a ray of light is flashed back from the
66 PHYSICS
surface of water at the same angle as that at which it
strikes; he knew, also, that a beam of light entering
water is bent from its course — refracted, to use the mod-
ern tern. He was aware of the fact of the apparent en-
largement of the sun's diameter on approaching the hori-
zon, and correctly explained it as due to the fact that
the sun's diameter is then estimated by the size of less
distant terrestrial objects, a view admitted by most sci-
entists to-day. Al Hazen (as he is more briefly known)
also first described the human eye with exactitude of de-
tail, and originated the famous and difficult problem in
optics known as Al Hazen's problem : "Given the position
of a luminous point and of the eye, to find the spot at
which reflection takes place on a spherical, cylindrical or
conical mirror."
Earlier even than the mirror appears the record of
the lens. Among the ruins of Nineveh is reported to
have been found a lens of rock crystal. Burning-glasses
were manufactured at an early date in Greece. In Aris-
tophanes' comedy of The Clouds is found mention of "a
fine transparent stone with which fires are kindled," and
by which, standing in the sun, one can, "tho at a distance,,
melt all the writing" on a waxen tablet of the times.
From the millennium of the beginning of this era Euro-
pean thought for 500 years plodded blindly along the
road that Grecian philosophy had pointed. Roger Bacon,
the one great man in all his time who dared to make
a place for original thought and experimental science,
was crushed to silence by a ten years' imprisonment for
heresy. Petrus Ramus in Paris was forbidden, on pain of
corporal punishment, to teach or write against the great
Aristotle. With Petrus Ramus must likewise be mentioned
Franciscus Patritius, a learned Italian, fiercely persecuted
by the Aristotelians on account of his heretical theory that
Light and Darkness together produce Warmth and Cold.
From the various theories of the philosophers of Greece
it is evident that the Nature of Light, even in those early
THE SOURCES OF LIGHT 67
times, was a much-mooted question. Previous to the
time of Newton opinions as to its exact constitution were
divided; some held it to be a real substance, others, espe-
cially the followers of Aristotle, considered it a property
or quality of matter. Early in the seventeenth century
Descartes formulated a new hypothesis as to the nature
of light. He held that it is neither material nor a prop-
erty of matter, but a vibration of that something of which
matter is composed, its "second element." He assumed
that the whole universe is filled with minute spheres of
this elemental substance. Through the constant motion
of the particles of luminous bodies these little spheres
are jarred, and since there is no empty space in the uni-
verse beside them, one sphere immediately touching an-
other, this jar or disturbance is immediately distributed
in straight lines. As an explanation of this thesis he com-
pares the propagation of light with the motion imparted
to the whole length of a stick when one end of it is
pushed. A similar disturbance, in his opinion, may be
caused by the eye, from which he explains how cats and
other animals whose eyes glitter can see in the dark.
Against this Cartesian hypothesis it has been urged that
through these rows of spheres light would be propagated,
not in straight lines alone, but in every direction, as
pressure is transmitted in all directions by water. Des-
cartes, however, had a large following for a time in his
belief as to the nature of light.
Later appeared two main theories of light, viz., the
Corpuscular Theory and the Undulatory Theory. The
former theory was essentially that of the Greeks, altho
they adorned it with various fanciful hypotheses. The
great exponent of this theory in more recent times was
Sir Isaac Newton, who based his acceptance of it on
the conviction that the rectilinear propagation of light
was explainable only on this basis. Sound waves, he ar-
gued, may be heard around corners; water waves swing
round a jutting point of land. Since light travels in
68
THYSICS
straight lines, the great philosopher concluded that it
must be due to the projection from luminous bodies of
extremely minute particles or corpuscles at a tremendous
A contrary view was advocated by Christian Huygens
about the end of the seventeenth century. This famous'
Dutch physicist regarded light, like sound, as a form of
Fig. 12 — Bell Cannot be Heard in Vacuum.
wave motion. A very serious difficulty confronted this
theory at the outset. Sound, as is well known, cannot
traverse a vacuum. Von Guericke, the Madgeburg Ma-
gician, had shown, some years previously, that a clock
cannot be heard to strike in a receiver exhausted of air.
Light, however, can be seen through such a vacuum with-
out difficulty, and travels without perceptible retardation
through the enormous interstellar spaces — possibly vacua
— infinitely better than can be gotten by the best means
artificially. Some medium, Huygens reasoned, must be
there to transmit these vibrations. He boldly assumed
THE SOURCES OF LIGHT 69
such a medium and called it the Luminiferous or Light-
bearing Ether. The fact that other forms of undulatory
motion, such as sound waves and water waves, can sweep
around corners, he did not explain.
At first sight the corpuscular theory of light would,
seem to be by far the simpler and more obvious explana-
tion of the two, and for more than a hundred years the
weight of Newton's authority threw the balance in favor
of this theory. So many facts opposed to this theory have
appeared, however, in modern experimentation that the
corpuscular theory is to-day practically abandoned. Light
is admittedly a form of vibration.
Light, it has been said, is a form of vibration, but it is
evidently not the same vibration as that which takes place
in the molecules of a heated conductor ; nor is it the same
as the series of condensations and rarefactions of the air
that is called sound. These latter are vibrations of matter,
and light is evidently a vibration of a different nature, for
no amount of light applied to one side of an iron door will
shine through to the other side. Heat, on the contrary,
or sound will very quickly be transferred by conduction
to the farther side of the door. Light as it reaches the
earth from the sun must be considered as something close-
ly analogous to radiant heat, if not identical with it. Re-
cent study of the effects of radiation show that light and
radiant heat are actually the same. Modern theory re-
gards light as a form of radiant heat whose wave lengths
are such that they directly affect the optic nerve.
The great source of light on the earth — far transcending
all others — is the sun. It is by no means the only source.
The moon, tho intermittent in the amount of its light and
shining in full radiance for only a few nights each month,
must nevertheless be reckoned as a valuable adjunct illu-
minant to the sun. The light from stars and planets, too,
is considerable. Walter Hough, in his 'Development of
Illumination,' says : ''Under the clear night sky of the
Arizona deserts the atmosphere seems charged with star
70 PHYSICS
mist; eminences miles away may be outlined, the dial of
a watch may be read, and a trail followed with little dif-
ficulty. These are the conditions under which night jour-
neys are made to avoid the burning sun." The planet
Venus, he continues, at certain times sheds light sufficient
for the traveler over open country.
"There are at times nights of remarkable luminescence.
Clouds become phosphorescent, and often under certain
states of electric stress, during high winds, glimmer with
a faint light not amounting to a discharge of the electric
fluid. Frequently successive flashes of 'heat lightning' aid
the traveler in finding his way. It is possible, also, that
the soil over certain regions may become phosphorescent
under the light of the sun and retain the property during
the night, as certain gems are phosphorescent after being
submitted to sunlight. Snow has this property. Gaseous
emanations of a phosphorescent character are occasionally
abundant enough to produce temporary illumination, and
the phosphorescent light of tropical seas has drawn forth
many remarks on its beauty."
Most of the work in the cities of to-day is done by dif-
fused light. The direct rays of the sun are found, in al-
most all cases, too powerful for purposes of reading or
writing, but the diffused light reflected in a thousand dif-
ferent directions from all surfaces not perfectly black or
smooth supplies an abundance of light, soft, yet bright
enough for use. Since the introduction of artificial illu-
minants it has ever been the aim of inventors to produce
a light resembling this diffused daylight. The old sperm
oil lamps and tallow dips of Europe which came over with
the colonists to America were there superseded by petro-
leum lamps. The addition of the argand chimney of glass
— the invention of which dates back only to about 1780 —
facilitated the development of the first really practical ar-
tificial illuminant. Even to-day this old type of chimney
and burner may be seen in the 'student lamp,' so popular
for reading purposes. The invention of the argand lamp,
THE SOURCES OF LIGHT 71
with the brilliantly luminous kerosene, soon made nights'
reading a general practice. Everybody could now read —
even the poor — and everybody did. It is an interesting;
coincidence that is brought out by a recent writer on
illumination, Dr. David T. Day, that the progress of the
countries of the civilized world to-day is in nearly every
case directly proportional to their consumption of kero-
sene.
The arc lamp and incandescent light of Edison marked
a step forward toward the production of an ideal artificial
light. But the arc light is not constant, and even when
surrounded with a large globe not sufficiently diffused for
reading purposes; the incandescent bulb, notwithstanding
the improved tantalum and osmium filaments gives a glare
too concentrated for ease in working. The nearest ap-
proach to diffused daylight has been made in the Hewitt
mercury vapor lamp, where a small quantity of mercury
in a long vacuum tube is first vaporized and then rendered
luminous under the influence of the electric current. This
lamp, however, is open to objection on the ground of its
color. The ideal lamp has yet to appear.
CHAPTER V
THE SPEED OF LIGHT
Among all the properties of light none is more striking
than its speed. Previous to the seventeenth century this
had always been supposed to be infinite, and the discovery
of the gradual propagation of light is one of the most
wonderful achievements of that wonderful period in the
history of physics — the Renaissance. The first attempt
to measure the speed of light was made by Galileo. He
ascertained the time for one person to signal with a lamp
to another and receive back the signal. The experiment
was tried at night, when the two observers were close to-
gether and again when they were nearly a mile apart. If
a difference in time could be detected, then light wouldi
travel with finite velocity. Galileo was not able from his
experiments to settle the question.
About thirty years later a young Dane, Olaf Romer,
was observing the eclipses of Jupiter's moons.
It was noticed that the times of revolution of these
moons in their orbits were not the same at all periods of
the year, and were greater than the average when the
apparent size of Jupiter was diminishing. Considering it
in the highest degree improbable that the actual motions
should be affected with any inequality of this sort, Romer
became convinced that the observed irregularities must be
explained on the supposition that the velocity of light is
finite. He said that the discrepancy could be accounted
for by assuming that it took time for light to come from
72
THE SPEED OF LIGHT 73
Jupiter to the earth. On November 9, 1676, an eclipse
took place at 5 h. 35 m. 45 s., while by computation it
should have been at 5 h. 25 m. 45 s. On November 22 he
explained his theory to the French Academy more fully,
and said that it required light 22 minutes to cross the
earth's orbit. (The more correct value is now known to
be 16 minutes and 36 seconds.) Like the news of so many
other great discoveries, Romer's announcement fell upon
deaf ears. It was fifty years before the scientific world
recognised the truth and the value of his contribution to
knowledge.
Romer computed the velocity of light to be 309,000 kilo-
meters (about 186,000 miles) per second. Subsequent de-
terminations made by astronomers and physicists have
corrected this computation but little. The most accurate
estimates of this figure are those made by Jean Leon Fou-
cault, inventor of the gyroscope and originator of the
Foucault pendulum, in France, and Albert R. Michelson,
of the United States Navy, in America. The speed found
by Michelson as the result of more than a hundred trials,
lasting over some two months of daily experimentation,
averaged 299,740 kilometers, or 186,300 miles per second.
The speed of light in a vacuum is estimated as but slightly
greater than in air.
The velocity of light in water was a pregnant question
in determining the true nature of light. The discussion of
this problem belongs to very recent times. It shows what
remarkable influence the opinions of Isaac Newton exer-
cized, and illustrates how easy it is even for scientific
men to "take sides" in a discussion where only truth is
sought. According to the adherents of the Newtonian
school the speed of light in water — a denser medium than
air — should be greater than its speed in air, just as the
speed of sound in iron is greater than in wood. But if
light be a vibrational phenomenon the speed should be less
in water than in air. This was the fact which the ex-
ponents of the undulatory theory — of whom Thomas
74 PHYSICS
Young in England and Fresnel, Malus and Foucault in
France were the leading lights — were called upon to dem-
onstrate if the Newtonian theory was to be refuted.
Foucault took up the idea, constructed a sort of "light
siren" which made more than^ 1,000 revolutions per sec-
ond, and reflecting a beam of light showed a deviation of
the ray upon a mirror at a distance. This deviation he
found to be greater when the ray of light was passed
through water, and his experiment gave conclusive proof
that the Newtonian theory of light was false. The speed
of light in water was found to be just about three-fourths
of the speed in air. That light in passing from air
through a dense medium, such as water or glass, suffers
a retardation, was a natural inference.
That a distant light gives less illumination than one
which is near was early a fact of common observation.
The exact extent to which distance would affect the
amount of light received, however, is not so generally-
known. The earth receives a certain amount of light
from the sun, an amount varying with the latitude and the
seasons. At first blush it might seem as if this light would
increase in direct proportion to the nearness to the sun,
as if, supposing the earth were half as far away, the light
would be twice as great, and the heat received on the earth
would only be doubled. That such is not the case is now
known to every student of the elements of physics.
It has been estimated, indeed, that if the earth were
moved half way from its present position toward the sun,
the whole face of nature would be changed. Life as it
now exists would be impossible — no trees, grass, or any
verdure would cover the face of the earth; water would
be unknown, existing only as a prodigious enveloping veil
of vapor through which the sun's rays would pass with
considerable loss of energy. Enough would be trans-
mitted, however, so that metals such as tin and lead and
even zinc would be liquids, mercury a gas, sulphur a
boiling fluid mass. An intense glare would illuminate the
THE SPEED OF LIGHT 75
glowing rocks and naked soil — a light the like of which
cannot be conceived by aid of any comparison with the
physical world of to-day. And yet the sun would then
be distant more than forty millions of miles from the sur-
face of the earth. How bright must be the illumination
which the sun casts upon the little planet Mercury, so
much nearer to him than the Earth, it is utterly impossible
to imagine. There is no standard of comparison. Yet
Mercury is distant 37,000,000 miles from the sun.
The sense of perspective is a universal faculty- A ship
grows continually smaller in approaching the horizon; a
near-by fly crossing the path of vision looks larger than
an eagle; a penny held close to the eye will obscure the
world. Light, as before observed, travels in straight lines
from every illuminated point. From a lighted candle rays
of light radiate in every direction straight away from the
flame. The artist familiarly represents the light of a
candle by an illuminated circle around it, which rapidly
shades from white to dark gray or black shadow. This
iluminated circle represents in reality a hollow sphere or
shell of light, and each radiant vibration coming from the
source of light is spread over the surface of the sphere.
It is a well-known fact that if the radius of such a sphere
be made to increase, the area of the sphere will also in-
crease, but much faster than the radius — in fact, as the
square of the latter. The surface of a two-inch ball is
four times as great as that of an inch ball ; the surface of
a three-inch ball is nine times as great as that of an inch
ball. Similarly the light which from a point withirrf
would reach the surface of a hollow sphere one foot in
diameter would be spread over nine times the same
area if the radius of the sphere were three feet. Hence
each point on the surface of the larger sphere would
receive only one-ninth as much light.
The amount or intensity of light, then, varies not ex-
actly as the inverse of the distance, but inversely as the
square of the distance from the source of light. In gen-
76 PHYSICS
eral, as any light wave advances its energy is being
distributed over a surface which increases directly as the
square of the distance the wave has traveled. It must
be noted, however, that this law of intensity applies only
to the direct light from a luminous body; for the total
illumination on a given surface4 is usually very much in-
creased by the light reflected from near-by non-luminous
bodies. Hence it is that white walls and furnishings add
so much to the total amount of light in a room. The law
of the Intensity of Light is evidently analogous to that of
gravity, where it was seen that a pound weight at the
surface of the earth (4,000 miles from its center) would
weigh only % lb. at the distance of 4,000 miles from the
surface (8,000 miles from its center, or twice as far away
as at the surface). It is this strangely persistent law of
inverse squares which, more than any other fact of
physics, points to the ultimate unification of all Force
under one head. The law holds true for gravity, electric
and magnetic attraction and repulsion, light, sound, heat
and so-called "radiant heat," together with numerous
other less fundamental physical relationships.
An ingenious yet extremely simple instrument for meas-
uring the amount of light received from a given source
was invented about the end of the eighteenth century by
an American, Benjamin Thompson, afterward Count
Rumford. In front of a ground glass screen he fixed an
opaque rod, placing a bright lamp and a candle at such
distances from the rod that the shadows thrown by each
light upon the screen appeared equally bright. Measuring
the distance of each light from the shadows cast, he
found the lamp to be four times as far away as the candle,
from which, by the law of inverse squares, he perceived
that the lamp was twice as bright as the candle.
Some fifty years later another light-measuring instru-
ment was produced by the famous chemist Robert Wilhelm
Bunsen. This admirably simple device consisted of a
sheet of white paper with a grease spot on it. The ex-
THE SPEED OF LIGHT
77
periment may easily be made by any one. If the paper is
equally illuminated from both sides the grease spot will
be hardly visible, but if the light upon one side is made,
ever so little brighter than upon the other, the spot will
at once appear on the darker side brighter (and on the
brighter side darker) than the rest of the paper. The
obvious reason of this is that the matt surface of the white
paper reflects back more and transmits less of the light
which falls upon it than does the part covered with a film
of grease. If now a standard light be placed on one side
Fig. 13 — Simple Mode of Measuring Intensity of Light.
of this paper, any other light whose "candle-power" is to be
determined may be shifted back on the other side until the
grease spot is no longer visible, when by measuring the
distances of the two lights from the paper screen the
relative intensity may easily be determined.
Incandescent electric lamps, arc lights and in fact all
common illuminants are measured in candle power. One
British standard candle power is the rate at which light is
emitted by the flame of a sperm candle weighing 1/a of a
pound and burning 120 grains per hour. The amount of
light from such a source, however, has been shown to
vary as much as 20 per cent., hence the standard is some-
what unsatisfactory. Ordinary electric glow lamps are
equivalent to 16 standard candles and are therefore called
78 PHYSICS
16 c.p. (candle-power) lamps. Other varieties of pho-
tometer ("light-measurers") have subsequently been in-
vented, one of which, Wheatstone's, produces very beau-
tiful luminous effects.
Similar in many ways to the measurement of the light
of the sun is the accurate estimation of solar heat.
In 1883 Samuel Pierpont Langley invented the bolome-
ter, briefly described as an exquisitely delicate thermopile.
Langley's invention was a part of his careful and elaborate
preparation for that remarkable trip to the (then almost
unknown) summit of Mount Whitney, in southern Cali-
fornia, where the summits of the Sierra Nevada, rising
precipitously in the dry air to a height of nearly fifteen
thousand feet over the Mojave Desert to the eastward,
furnished a suitable location for the study of the influence
of the earth's atmosphere upon the radiations from the
sun. "I spent nearly a year," says Langley, "before as-
cending the mountain in inventing and perfecting the new
instrument which I have called the 'bolometer/ or 'ray-
measurer.' The principle on which it is founded is the
same as that employed by my late lamented friend, Sir
William Siemens, for measuring temperatures at the bot-
tom of the sea, which is that a smaller electric current
flows through a warm wire than a cold one.
"One great difficulty was to make the conducting wire
very thin and yet continuous, and for this purpose almost
endless experiments were made, among other substances
pure gold having been obtained by chemical means in a
plate so thin that it transmitted a sea-green light through
the solid substance of the metal. This proving unsuitable,
I learned that iron had been rolled of extraordinary thin-
ness in a contest of skill between some English and Ameri-
can iron-masters ; and, procuring some, I found that fifteen
thousand of the iron plates they had rolled, laid one on
the other, would make but one English inch. Out of this
the first bolometers were made. The iron is now replaced
by platinum, in wires, or rather tapes, from a two-thou-
THE SPEED OF LIGHT 79
sandth to a twenty-thousandth of an inch thick, all but
invisible, being far finer than a human hair. This thread
acts as tho sensitive, like a nerve laid bare to every indi-
cation of heat and cold. It is, then, a sort of sentient
thing; what the eye sees as light it feels as heat, and what
the eye sees as a narrow band of darkness (the Frauen-
hofer line) this feels as a narrow belt of cold; so that,
when moved parallel to itself and the Frauenhofer lines
down the spectrum, it registers their presence."
Langley's fascinating story of his experimental trip to
Mount Whitney, told in the records of the Royal Institu-
tion, is full of thrilling imaginative touches. A few lines
may serve to show something of the immense difficulties
which he had to overcome in getting his results. He
writes: "We commenced our slow toil northward with a
thermometer at no° in the shade, if any shade there be
in the shadeless desert, which seems to be chiefly inhabited
by rattlesnakes of an ashen gray color and a peculiarly
venomous bite. There is no water, save at the rarest in-
tervals, and the soil at a distance seems as tho strewed
with sheets of salt, which aids the delusive show of the
mirage.
"At last, after a seemingly interminable journey, we
pitched our tents and fell to work (for you remember we
must have two stations, a low and a high one, to compare
the results) ; and here we labored three weeks in almost
intolerable heat, the instruments having to be constantly
swept clear of the red desert dust which the hot wind
brought. Close by these tents a thermometer covered by a
single sheet of glass and surrounded by wool rose to 237°
in the sun, and sometimes in the tent, which was dark-
ened for the study of separate rays, the heat was abso-
lutely beyond human endurance.
"Finally our apparatus was taken apart and packed in
small pieces on the backs of mules, who were to carry it
by a ten days' journey through the mountains to the other
side of the rocky wall, which, tho only ten or twelve miles
80 PHYSICS
distant, arose miles above our heads; and, leaving these
mule-trains to go with the escort by this longer route, I
started with a guide by a nearer way to those white gleams
in the upper skies that had daily tantalized us below in the
desert with suggestions of delicious, unattainable cold.
That desert sun had tanned our faces to a leather-like
brown, and the change to the cooler air as we ascended
was at first delightful. But the colder it grew the more
the sun burnt the skin — quite literally burnt, I may say ; so
that by the end of the third day my face and hands, case-
hardened, as I thought, in the desert, began to look as if
they had been seared with red-hot irons, here in the cold,
where the thermometer had fallen to freezing at night; and
still, as we ascended, the paradoxical effect increased.
The colder it grew about us the hotter the sun blazed
above. It almost seemed as tho sunbeams up here were
different things, and contained something which the air
filters out before they reach us in our customary abodes.
Radiation here is increased by the absence of water-vapor,
too; and, on the whole, this intimate personal experience
fell in almost too well with our anticipations that the air
is an even more elaborate trap to catch the sunbeams than
had been surmised, and that this effect of selective absorp-
tion and radiation was intimately connected with that
change of the primal energies and primal color of the sun
which we had climbed toward it to study.
"We suffered from cold (the ice forming three inches
deep in the tents at night) and from mountain sick-
ness, but we were too busy to pay much attention to
bodily comfort and worked with desperate energy to util-
ize the remaining autumn days, which were all too short.
Here, as below, the sunlight entered a darkened tent and
was spread into a spectrum, which was explored through-
out by the bolometer, measuring on the same separate rays
which we had studied below in the desert, all of which
were different up here, all having grown stronger, but in
very different proportions."
THE SPEED OF LIGHT 81
The delicately constructed bolometer of Langley has
been brought in comparatively recent years to very high
perfection so as to record a change of temperature of
,0000001 of a degree Centigrade. Prof. C. B. Boys in
1888 constructed a similar instrument capable of indicat-
ing so minute quantities of radiant heat that in the absence
of atmospheric absorption the heat radiated from a can-
dle two miles away would be distinctly registered. A still
more perfect instrument lately completed in America simi-
lar to the radiometer of Dr. Crookes reached a marvelous
degree of sensitiveness to radiant energy.
Experiments were made on the heat of a candle situated
2,000 feet from the concave mirror which focused its rays
upon the instrument. The feeble radiations of the candle
at this great distance sufficed to turn the indicator through
nearly a hundred scale divisions, and even the face of an
observer when placed in the position before occupied by
the candle produced a deflection of 25 scale divisions. As
a tenth of a single scale division could readily be observed,
it will be seen, to speak figuratively, that with this radiom-
eter one might note the approach of a friend while yet
some miles distant, merely by the glow of his countenance.
CHAPTER VI
REFLECTION AND REFRACTION
A strange phenomenon of light which long puzzled
the scientific world was that of polarization, or two-sided-
ness. A crystal of tourmaline held between the eye and a
light source will appear transparent. A second crystal
placed in front of it will also allow the light to pass as
long as the two crystals are held lengthwise. If one of
them be turned at a right angle to the other the light is
cut off. The explanation of this was a hard nut for
Young to crack. He cracked it thus : "It is possible," he
wrote in a letter to a friend, "to explain in this (undula-
tory) theory a transverse vibration propagated in the
direction of the radius and with equal velocity, the motions
of the particles being in a certain constant direction with
respect to that radius transverse to the ray; and this is
Polarization."
Thus Young explained that what happened in the prog-
ress of a light ray is the same thing as that which happens
in the progress of a water wave ; a stick of wood may be
seen to rise and fall with the waves, but it does not ad-
vance with them, for the vibration is transverse to the
direction of propagation. The apparent motion of the
water in a wave is a forward motion ; the actual motion is
up and down. So is it with light. The analogy may be
carried further, for when the wave approaches the shore,
the lower part of it is arrested and the upper part is still
carried forward by the impulse from behind. The result
82
REFLECTION AND REFRACTION 83
is that the wave now takes a downward as well as a for-
ward motion, and this effect becoming more and more pro-
nounced the top of the wave curls completely over the
water below and crashes as a breaker on the shore.
In light this change of direction also takes place when-
ever the light wave passes from air to a denser medium,
such as water. If a ray of light strike the water at an
angle, the lower part of the wave being arrested at the
surface of the water, the ray bends downward into the
water. A "normal" or perpendicular to the surface of
the water would therefore form a larger angle with the
ray in the air than in the water. The ray is said to be
bent toward the normal in passing from a rare to a
denser medium. Imagine the same ray to be shot back
again, and it will obviously be bent from the normal as it
leaves the water. It is evident from the water-wave an-
alogy that the more the wave is stopped at the surface of
the new medium the greater will be the bending.
In a substance like diamond, where the light travels less
than half as fast as in air, the bending is very great, and
the colors of which the white light is composed are much
scattered and broken. Hence appear the magnificent lights
in the diamond. In crown glass, where the wave travels
two-thirds as fast as in air, there is less stoppage and con-
sequently less refraction of the ray. In water, as has been
remarked, the speed is three-fourths of the speed in air,
hence the bending is still less.
Owing to this bending downward of a ray of light as it
enters the water, it is evident that an observant trout will
sight a fisherman some seconds before the latter sees the
trout, and in the same way the setting sun will be visible
to a fish in the water as shining apparently some degrees
above the horizon. The effects of refraction are interest-
ing, sometimes startling. It has been noted above that a
ray of light passing from water into air suffers a bending
away from the normal to the surface. That is, it tends to
lie down and run along the surface. This tendency is more
84 PHYSICS
marked as the angle of incidence increases. When the
ray of light strikes the under surface of the water at a
long angle it does not pass into the air, but runs along the
surface of the water. Increase the angle ever so slightly,
and the ray is actually bent down again through the water,
affording the striking phenomenon of total reflection.
A familiar example of total reflection is found in the
mirage. This reflection may take place whenever a ray of
light passes from one layer of air to another of different
density. The image of an inverted ship is observed com-
monly enough at sea before the ship itself comes over the
horizon. The images of distant shores may be seen in like
manner. The rays of light from the ship pass upward and
reach some stratum of air which is warmer and conse-
quently rarer than the air above the water immediately
surrounding the vessel. From this rarer medium the
image is bent down by total reflection and projected to
some distant point. In the sandy plains of Egypt and other
hot countries a similar phenomenon is due to similar
causes. In this case, however, the image formed is re-
flected from a cooler stratum of air than that immediately
above the burning sand of the desert. The inverted pic-
ture of trees thus formed in the sky is precisely analogous
to the reflection of trees on the shore of a still lake. The
reflecting medium in both cases is denser than that sur-
rounding the object.
As the amount of light varies inversely as the
square of the distance from the source, so it also varies
with the angle at which the light falls. If the rays
are projected vertically upon a surface, the amount of
light will be greater than that received when they reach
the surface at an angle. Hence the amount of light,
as well as the amount of heat, which reaches the polar
regions is far less than that which falls upon the equator.
The same amount of light is spread over a larger surface.
Anything like accurate measurement of the amount of
light received upon an object must always take into ac-
REFLECTION AND REFRACTION 85
count the light due to reflection — for every visible surface
reflects; if it did not it would not be visible. The scatter-
ing of the rays which results from a rough surface is
utilized in minimizing the glare from a too brilliant source
of light, such as the incandescent mantle of the Welsbach
gaslight or the dazzling core of the electric arc. Ground
glass globes enclose the lights and diffuse the intense
brightness by scattering the rays which pass through the
roughened surface. The great difficulty from an eco-
nomic standpoint, with this method of softening the radi-
ated light, is that nearly one-half of the illuminating
power is wasted in the resistance offered by the semi-N
opaque glass globe. Diffuse reflection takes place at all
points of the roughened surface.
The famous Mirror Maze, composed of several mirrors
at various angles and scores of panes of clear glass, is
so confusing that even extreme watchfulness will not
prevent the observer from running into a pane of glass,
not being able to perceive it. The reflection of any object
in a plane mirror is a virtual, not a real image. There
is no actual image where the object appears to be, and
the virtual image so formed will be exactly as far in
the rear of the»mirror as the object itself is in front of it.
This would follow inevitably from the well-known Law
of Reflection, which, so far back as the time of Archime-
des, was well understood as a fundamental principle of
all mirrors of every shape and description.
If two mirrors are placed so as to touch at right an-
gles, a candle placed in the angle will show three images
reflected, no matter how the observer stands. By making
the angle of the mirrors continually smaller, more and
more images will be brought into view. When the angle
of the mirrors is 60 degrees (the angle of an equilateral,
triangle) five images will appear, and seven if the mirrors
are inclined at an angle of 45 degrees. When the angle
is made small enough so that the mirrors are almost paral-
lel, the number of reflections become practically infinite.
86 PHYSICS
An interesting and striking fact with regard to these mul-
tiple images is that every image so formed, as well as
the luminous object itself, will lie on the circumference
of a circle of which the juncture of the mirrors is the
exact center. This, again, may readily be shown to be
an obvious result of the familiar sLaw of Reflection.
Sir David Brewster, of the University of Edinboro,
invented early in the nineteenth century a reflecting in-
strument through which he became better known than
by any of his more elaborate contributions to science.
The kaleidoscope, a simple little device to be had to-day
in almost any toy shop, was constructed by him with three
plane mirrors. These were made of equal width and
length, and fitted into a tube closed at one end by a disk
or plate of ground glass, behind which irregular bits of
colored glass or porcelain were allowed to tumble and
turn in any direction. The latter were held in place by
another disk of clear glass. When viewed from a small
aperture in the farther end of the tube these bits of col-
ored glass showed by their multiple reflections in the three
mirrors an amazing variety of beautiful symmetrical de-
signs apparently without number or end. So great at
one time was the demand for these kaleidoscopes that
it» was found impossible to supply it. A more complicated
series of images of great diversity is made by placing
six mirrors together so as to form a regular hexagon,
each angle of which is exactly twice the angle of an
equilateral triangle, or 120 degrees. This is the forim
in which mirrors have been combined to produce the re-
markable vistas of crystal mazes, of which a noteworthy
example has recently been constructed in Paris, wherein
the turn of a lever transports the observer from a forest
grove to the interior of a Hindu temple or the wonderful
Arabian palace of Aladdin.
The image formed by a glass mirror is not reflected"
by the glass. Back of every such mirror will be found"
a thin layer of some metallic substance, which forms a
REFLECTION AND REFRACTION 87
much better reflecting surface than the glass. A beam of
light falling on the mirror will be partly reflected from
the front surface of the glass, but mainly from the metal-
lic hinder surface. Thus it becomes apparent why a
mirror, especially a thick one, forms two or more distinct
images of an object seen at an angle in the glass. A
consideration of the law of Total Reflection will show
how many such images may actually be formed, reflected
back and forth from the two surfaces of the mirror, and
growing rapidly dimmer, so that usually not more than
one or two are plainly to be seen.
A certain astronomical observer, not many years ago,
betrayed in this connection an unconscious vein of humor.
By means of the reflections from a plate of clear glass
he announced the discovery of a large satellite circling
the planet Venus ! On account of these repeated images
in glass mirrors, they are usually replaced, in physical
observatories, by metallic reflectors.
The great law of Reflection, that the Angle of the In-
cident Ray equals the Angle of the Reflected Ray, was
found to hold true for all angles and all surfaces. The
law applies with equal rigor to a plane mirror or to a re-
flecting surface of any other type, spherical, cylindrical,
conical, concave or convex. Nearly a thousand years
ago the famous Image Problem of the Arab Al Hazen, to
which reference has already been made, was formulated,
calling for a proof of the images formed in plane, spheri-
cal and conical mirrors. The spreading of the rays of
light will obviously change the appearance of the image
formed in any convex reflecting surface, while the oppo-
site effect will produce an opposite change in the image
formed in a concave reflector.
The image formed by looking in the bowl of an ordi-
nary spoon is seen to be inverted. No matter which way
the spoon is held, sidewise or upside down, this will al-
ways be found true — unless the spoon is large and brought
very close to the face. Looking at the back of the spoon,
88 PHYSICS
however, the image is seen to be erect, no matter how near
or how far away the spoon is held. The reason is easily-
seen. Every ray of light from an object must glance off
from the polished metallic surface at the same angle as
that at which it strikes. In a concave surface, such as the
hollow of a spoon, these rays must evidently meet some-
where and then cross. Evidently the image formed after
they cross will be upside down and left side right. Such
an image is real, for it is actually formed where it ap-
pears to be, and in this respect differs from the images
formed in plane or convex mirrors, which apparently exist
where experience proves they cannot exist, viz., behind
the reflector. If the reflection in a concave surface is
made by an object held close to the mirror, it will form
an enlarged erect virtual image; the rays of light do not
pass through the focus, or crossing point of the mirror,
hence there is no inversion, and the image, but for the
enlargement, is exactly like that formed in a plane mirror.
It appears behind the surface.
Parabolic mirrors which have come into such general
use for powerful lighting purposes — as, for example, in
the headlights of automobiles and locomotives — show but
a slight modification of the concave spherical mirror. The
change, tho slight, is important, for all the rays of
light from the lamp within the reflector now strike the
side walls at such an angle that they pass out in parallel
lines; therefore, except for the light lost in absorption, at
the metallic surface every bit of illumination is centered
in the one direction. The illuminating power of these re-
flectors, when furnished with a brilliant light, is enor-
mous. The parabolic mirror is said to have been known
since the time of Archimedes.
The convex surface of the back of an ordinary spoon
forms, as has been said, an erect image, which appears
reduced and at a distance of several inches behind the
spoon. Withdraw the spoon slowly, and the image con-
tinues to recede and diminish, until at a certain point the
Muscles of Eye which Direct
Movements.
Cross section of Globe of
Eye.
Vertical Section of Retina.
(After H. Muller.)
i., layer of rods and cones; 2.,
rods; 3., cones; 4., 5., 6., ex-
ternal granule layer ; 7., in-
ternal granule layer; 9., 10.,
finely granular gray layer;
11., layer of nerve-cells; 12.,
14., fibers of optic nerve; 13.,
membrana limitans.
Connection of Rods and Cones
of Retina with Nervous
Elements. (After Sappey.)
i., 2., 3., rods and cones seen
from in front; 4., 5., 6., side
view.
REFLECTION AND REFRACTION 89
diminution seems to stop and the image remains constant
no matter how far away the spoon is moved Here, as be-
fore, a converging point of the rays of light will be found,
this time behind the mirror; but there will be no crossing,
for the rays will exactly meet and the image be reduced to
a point only when the object has been removed to a dis-
tance theoretically infinite.
In general, it has been said of all real images that they
are those formed by the reflected rays themselves, whereas
virtual images are formed by their imaginary prolonga-
tions. The real image is always inverted and the virtual
image erect. By analogy with the phenomena of images
in convex and concave mirrors, the process of image
formation through the ordinary convex lens will readily
be understood. The process here, as has been shown,
is one of refraction, not of reflection of light. But the
bending of the rays to a focus on either side of the lens
will determine, as before, the form of the image, whether
erect or inverted. Images formed by refraction through
a convex lens must in all cases when the object is outside
the focus be real, since the figure is actually formed and
may be shown on a screen exactly where it appears to be.
If the object is placed inside the focus of the lens — i.e.,
between the focus and the lens itself — an enlarged virtual
image will be seen. This is the case in ordinary reading
glasses; the light rays from all extremities of the object
(letters or what-not) under examination are twice re-
fracted by the double convex surface of the lens, and the
eye sees these points of the object along the line last
traveled by the light. Hence the object appears greatly
magnified — its extremities appearing to be much farther
apart than in reality they are. The more convex the lens
the greater is its magnifying power, but the greater, at
the same time, the difficulty in using it without some cor-
rection of the spherical aberration which increases with
the curvature of the lens. Double convex lenses, used as
magnifying glasses, are frequently called simple micro-
90 PHYSICS
scopes, as distinguished from the powerful compound mi-
croscope, which by the aid of brilliant illumination pro-
duces an image many thousand times larger than the
original. The focus of all convex lenses was seen to be
the place where rays of ligtrt traveling straight to the
lens are bent together by refraction and meet There
will evidently be two such foci formed, one on either side
of every double convex lens. These are the so-called con-
jugate foci of the lens. In concave lenses there is no real
Fig. 14 — Angles or a Lens.
focus possible, since all rays will be refracted in a direc-
tion away from the perpendicular through the center of the
lens. All images through such a lens will therefore be
virtual images.
The earliest lenses were made in Europe of rock crystal,
altho lenses of glass appaer to have been known to the
Greeks. The lenses of Hans Lippersley, of Middleburg,
the inventor of the binocular telescope, were made of rock
crystal. (These small instruments, it is interesting to
note, sold at that time (1608) for the large sum of 900
gulden.) Galileo's lenses, one of them concave the other
convex, were made of glass. Sparing neither expense nor
labor, he succeeded in constructing an instrument which
magnified an object nearly a thousand times and brought
it more than thirty times nearer. He went to Venice to
REFLECTION AND REFRACTION 91
display his telescope. "Many noblemen and senators,"
says he, "altho of great age, mounted the steps of the high-
est church towers at Venice to watch the ships, which
were visible through my glass two hours before they were
seen entering the harbor."
In the early telescopes lenses were made with very great
focal lengths — the beams converging in some cases at a
distance of 10, 20, 30, 40 and in one instance of 123 feet
from the center of the lens. These lenses were mounted
on high poles, and being unprotected by a tube gave very
inferior results. The purpose of these great clumsy ob-
jectives was the avoidance of the color dispersion which is
always observable at the edges of a simple lens of pro-
nounced curvature. Since the prism has shown that the
blue rays of light are bent more than the red, they must
come to a focus behind a lens a little sooner than the red
rays. This is the explanation of the fact that so manyj
common lenses, reading glasses, etc., make it appear that
the objects behind them are surrounded with a colored
halo. This is more noticeable in lenses of much curvature,
for the difference in focus between the red rays and the
blue is then emphasized.
Leonhard Euler suggested that lenses made out of two
different materials of different refractive powers would
probably cure this "chromatic aberration." He tried to
produce such a lens, but failed. A London optician, John
Dolland, taking up Euler's idea, began a series of tests
in making lenses which were achromatic — i.e., showing no
color dispersion. Years of repeated failure in this direc-
tion were finally crowned with success, and Dolland pro-
duced a lens made of crown and flint glass which was
perfectly free from color and entirely accurate. His
accomplishment created a sensation throughout Europe
and greatly facilitated from that time the growth of as-
tronomy. Lenses began to increase in diameter and
telescopes in size. Herschel, the discoverer of the two
inmost moons of Saturn, added immense concave mirrors
92 PHYSICS
to his telescopes whereby the light-gathering power of the
instrument was vastly increased. At Parsonstown in Ire-
land was completed a gigantic reflecting telescope with a
mirror 6 feet across and a tube 58 feet long and 7 feet
in diameter, so that a certain ecclesiastic, Dean Peacock,
once walked through it with uplifted umbrella.
The achromatic lenses which made possible these great
telescopes were likewise instrumental in the development
of microscopes, to which they were early applied. The
first microscope was constructed in the beginning of the
seventeenth century by Zacharias Johannides, a Dutch
optician. The eyepieces of his microscope were made at
first concave; subsequent improvements made both lenses
convex.
Spectacles also were manufactured with achromatic
lenses, greatly increasing their comfort and serviceability.
The inventor of spectacles must rest his claim to this
honor upon an inscription dated some three hundred years
before the invention of achromatic lenses. Upon the
tomb of Salvino Armato in Florence is carved below the
bust o£ this nobleman the inscription :
Here lies
Salvino Armato d'Armati,
of
Florence,
Inventor of Spectacles
May God pardon his sins
a.d. 1317.
In the tall lighthouses that to-day guard the coast of
every civilized country is found the peculiar echelon or
annular lens. To avoid the spherical aberration, and the
loss of light inevitable in refractors of such magnitude as
those of the lighthouse lights, these lenses are made in
concentric rings of glass, which focus in one point, the
outermost ring being some two feet in diameter. The
light placed in this focus is not too widely distributed, and
becomes brightly visible over a distance of more than
REFLECTION AND REFRACTION 93
forty miles. Some conception of the power of these lenses
may be had from the fact that when inverted and used
to condense the solar rays, gold, platinum and quartz are
melted in the intense heat, and less refractory substances,
as lead, tin and zinc, are almost immediately reduced to a
vapor.
Far more perfect than any previously produced were the
glass lenses made in Munich by Joseph Frauenhofer. The
talented son of a poor glazier, Frauenhofer combined a
thoro* practical skill with an unusual degree of theoretic
insight. "By his invention of new and improved meth-
ods, machinery and measuring instruments for grinding
and polishing lenses, by his having the superintendence,
after 181 1, also of the work in glass melting, enabling him
to produce flint and crown glass in larger pieces, free of
veins, but especially by his discovery of a method of com-
puting accurately the forms of lenses, he has led practical
optics into entirely new paths, and has raised the achro-
matic telescope to a perfection hitherto undreamed of."
So writes Lommel in his preface to Frauenhofer's 'Gesam-
melte Schriften.'
Among the many other applications of the lens which'
have made a necessary place in present-day life, the
camera deserves especial notice. Baptista Porta, a Nea-
politan physician and contemporary of the great Gilbert,
invented an instrument now familiar enough to every
school boy of a practical turn of mind — the camera
obscura. A simple box, light proof, and painted black
within and without, received through a lens the image of
external objects and reflected it from a sloping white
paper screen on to a plate of ground glass in the top of the
box. To imitate in the form of a fixed photograph the
beautiful colored image thus thrown on the plate subse-
quent artists and scientists have sought in vain ; the "color
photography" thus far accomplished has been a compli-
cated and difficult procedure, rewarded by only partial
success.
94
PHYSICS
The camera obscura may hardly be considered the ante-
cedent of the photographic camera of to-day, which re-
sembles the pin-hole camera in structure more nearly.
Yet the essential principle of the modern camera was not
different from that of the camera obscura. With an ad-
justable or focusing lens and the* substitution of a sensitive
film or plate for the former plate of ground glass, the
transformation was accomplished. In modern days many
people take photographs, and there is more or less
familiarity with the nature of the chemical changes that
are worked by the exposure to the light of the silver salts
upon the "sensitive" plate. If exacting Reason, however,
demand in this connection an explanation of why the
change takes place, it must be answered in brief that the
energy of the light ray probably effects a rapid alteration
of the structure of the atoms of the silver salt employed,
in much the same way as has been noted before in the dif-
ferent forms of copper and iron. When the velocity of
waves of light is remembered, it becomes clear that a 1/-,*
second exposure means that these atoms have been ham-
mered thousands of times by light waves in that brief
period.
The art of photography is of very recent development,
depending of necessity upon a certain advance in the sci-
ence of chemistry. Pictures on metal were produced in
1827 by Joseph Nicephore Niepce, whose assistant and
successor in this work, Daguerre, has given his name to
the improved metallic photographs which are still called,
after him, daguerreotypes. These first efforts at a photo-
graph were clumsy contrivances, requiring from five to
seven minutes' exposure, during which the photographee
must sit with iron face and rigid figure, immovable. The
face of the sitter had also to be dusted with white pow-
der, and the print, when completed, was faint, and in cer-
tain lights invisible, on account of the brilliant polish of
the metallic surface upon which the print was made.
Tinting the picture was commonly resorted to in the en-
REFLECTION AND REFRACTION 95
deavor to make the result more life-like. From the slow
and troublesome methods of the old daguerreotype to the
magnificent black and white instantaneous carbon prints
of to-day is a long stride.
It frequently happens in human history that after an
invention has been made and perfected, the further prog-
ress of knowledge reveals the fact that the wonderful in-
vention already existed in Nature in a state of develop-
ment far more advanced. The old scoop dredge, tho it
still has its special use, has been largely replaced by a
huge iron hand like a man's hand; the phonograph is a
clumsy imitation of the auricular nerve and tympanum
of the human ear ; the eye has been described as a camera
with a self-adjusting shutter and focusing automatically.
Without going too minutely into the physical structure of
the eye, its essential parts may briefly be summed up.
Covering all the exposed front of the organ is a tough
elastic membrane (cornea), which lets through the light,
but protects the delicate mechanism immediately behind.
This interior part it is which lends character and color
to the eye, the iris or colored ring appearing of various
hues — as ranging from a light gray-blue, which is largely
destitute of the orange-brown coloring pigment, to a brown
so deep as almost to seem black. "Helmholtz," writes
Cajori in his history already referred to, "irreverently
disclosed the fact that in blue eyes there is no real blue
coloring matter whatever; the deepest blue is nothing but
a turbid medium. The optic action is the same as in the
case of smoke which appears blue on a dark background,
tho the particles themselves are not blue ; or in case of the
sky, which, according to Newton, Stokes and Rayleigh,
looks blue through the agency of extremely fine dust sus-
pended in the air. This dust, when illuminated by sun-
light, reflects a greater proportion of the shorter waves of
bluish light and transmits a greater proportion of longer
waves of reddish light."
The 'pupil' of the eye is the shutter, which, by the ex-
96 PHYSICS
pansion or contraction of the iris, lets in more or less light
to the sensitive film or 'retina' at the back of the organ.
Close behind the pupil and its encircling iris the crystal-
line lens refracts incident light from objects near or re-
mote, and by the aid of the enveloping 'ciliary' muscle
may be so far contracted as to focus the vision with equal
readiness upon a tiny shell in the hand or a mass of rocks
on a far-distant mountain. Through the glassy liquid
which fills all the remaining interior of the eye the light
is transmitted to the retina, where a chemical change is
constantly being effected upon the exposed film of this
optical photographic camera, the optic nerves reporting
to the brain at every moment the nature of these changes.
With all its beauty and delicate adjustment, however,
the human eye has many imperfections. No voice has
spoken of the physics of the eye with more authority than
has the extraordinarily versatile and learned Helmholtz.
To him the eye is indeed a crude instrument. The German
physicist indicates its defects with considerable force. "A
refracting surface which is imperfectly elliptical," he
says, "an ill-centered telescope, does not give a single illu-
minated point as the image of a star, but according to the
surface and arrangement of the refracting media, elliptic,
circular, or linear images. Now the images of an illumi-
nated point, as the human eye brings them to focus, are
even more inaccurate: they are irregularly radiated. The
reason of this lies in the construction of the crystalline
lens, the fibers of which are arranged around six diverg-
ing axes, so that the rays which we see around stars and
other distant lights are images of the radiated structure
of our lens; and the universality of this optical defect is
proved by any figure with diverging rays, being called
'star-shaped.' It is from the same cause that the moon,
while her crescent is still narrow, appears to many per-
sons double or threefold."
"Now, it is not too much to say," he remarks again,
"that if an optician wanted to sell me an instrument which
REFLECTION AND REFRACTION 97
had all these defects, I should think myself quite justified
in blaming his carelessness in the strongest terms and
giving him back his instrument."
The mechanical process of the eye has never, until
comparatively recently, been understood. Helmholtz and
others, basing their experiments upon the observations of
Thomas Young, Louis Joseph Sanson and Max Lagen-
beck, have explained the manner in which the eye focuses
and the means employed to control the admission of light.
The sense of color, however, is still a matter of contro-
versy. The most acceptable theory of color sense is that
promulgated by Young and developed by Helmholtz,
based on the phenomenon of color blindness to the three
shades which occupy respectively the ends and the center
of the prismatic ribbon, viz., red, green and violet. Color
blindness to red is common and to green not uncommon,
while the inability to recognise violet is known. Young
showed that the rotation of colored disks of red, green and
violet produces the impression of gray. These, therefore,
may be taken as the three primary colors, by combination
of which all the intermediate colors may be produced.
CHAPTER VII
THE NATURE OF LIGHT
To the phenomenon of total reflection was added in the
very beginning of the nineteenth century another bit of
evidence which the exponents of the corpuscular theory of
light found difficult to explain away. This was the phe-
nomenon of interference. Two plates of glass touching at
one end and separated at the other by a fine hair will form
between them a thin wedge of air. If a bright light is held
near the plates they will be seen crossed with dark and
bright bands. Thomas Young, a brilliant young English
physicist, experimenting with these plates and studying the
dark bands, stated in a famous paper on light that they
were due to the interference of light waves from the two
surfaces of the wedge of air included between the plates of
glass. He showed how the waves of light from these two
surfaces might be proved to meet at intervals and produce
the appearance of darkness, just as two sound waves may
be combined to produce silence.
This remarkable paper, by far the most valuable con-
tribution to the study of optics since the time of Newton,
attracted no favorable attention and was received with
open scorn and contempt by the editor of the Edinboro
Review. The young scientist is represented by this illus-
trious organ as deficient in "the powers of solid thinking"
and his theories dismissed as "feeble lucubrations without
any traces of learning, acuteness or ingenuity/' John
Tyndall, that great and fascinating Irish scientist, writes
THE NATURE OF LIGHT 99
of Young: "For twenty years this man of genius was
quenched — hidden ^rom the appreciative genius of his
countrymen — deemed, in fact, a dreamer, through the
vigorous sarcasm of a writer who had then possession of
the public ear. To the celebrated Frenchmen, Fresnel and
Arago, he was first indebted for the restitution of his
rights." The soundness of Young's reasoning has been
abundantly attested to by the verdict of later investigators,
and the known fact of the "interference" of light is to-
day held to be one of the compelling arguments in favor
of light as a form of vibration.
Difficult of explanation as the fact of interference proved
from a corpuscular basis, still more did prismatic disper-
sion prove itself an occasion of falling. Every one is
familiar with the beautiful color effects obtainable with
the aid of a triangular prism of glass, and has noted how
a beam of "white" light may be spread out into a band
of colors as the ray is bent through the prism. In this
spreading out it is evident that some of the rays are bent
more than others. Unless the corpuscles of light were
infinite in variety, this would be simply inexplicable as a
corpuscular phenomenon. The prism as an instrument of
optical study found its first great master in Isaac Newton.
The observation of its effects had been noted by the Roman
philosopher Seneca, and in the period of the Renaissance
the breaking up of white light into colors was discussed
by Grimaldi, Descartes, Hooke and others. But it re-
quired the supreme genius of Newton to make clear the
true idea of the dispersion of light. With rough appli-
ances fashioned by his own hands he conducted his ex-
periments. In his treatise on "Opticks' he quaintly re-
marks, "I procured me a triangular glass prisme, to try
therewith the celebrated phenomena of colors. And in
order thereto having darkened my chamber, and made a
small hole in my window-shuts to let in a convenient quan-
tity of the sun's light, I placed my prisme at his entrance,
that it might be thereby refracted to the opposite wall."
ioo PHYSICS
He goes on to say how surprised he was to find that
the ray of light, after passing through the prism, instead
of being thrown upon the wall in the form of a round spot,
was spread out into a beautiful colored ribbon, or spec-
trum, red at one end, yellow in the middle, and bluish
green at the other end. "Comparing the length of this
colored spectrum with its breadth," he continues, "I found
it about five times greater — a disproportion so extrava-
gant that it excited me to a more than ordinary curiosity
of examining from whence it might proceed.
"Then I began to suspect, whether the rays after their
trajection through the prism, did not move in curve lines,
and according to their more or less curvity tend to divers
parts of the wall. And it increased my suspicion, when I
remembered that I had often seen a tennis ball struck
with an oblique racket, describe such a curve line. For, a
circular as well as a progressive motion being communi-
cated to it by that stroke, its parts on that side, where the
motions conspire, must press and beat the contiguous air
more violently than on the other, and there excite a reluct-
ancy and reaction of the air proportionably greater. And
for the same reason, if the rays of light should possibly
be globular bodies, and by their oblique passage out of the
medium into another, acquire a circulating motion, the)'
ought to feel the greater resistance from the ambient^
aether, on that side, where the motions conspire, and thence
be continually bowed to the other. But notwithstanding
this plausible ground of suspicion, when I came to ex-
amine it, I could observe no such curvity in them. And
besides (which was enough for my purpose) I observed,
that the difference betwixt the length of the image, and
the diameter of the hole, through which the light was
transmitted, was proportionable to their distance.
"The gradual removal of these suspicions at length led
me to the experimentum crucis, which was this: I took
two boards, and placed one of them close behind the prism
at the window, so that the light might pass through a
THE NATURE OF LIGHT 101
small hole, made in it for the purpose, and fall on the other
board, which I placed at about twelve feet distance, hav-
ing first made a small hole in it also, for some of that in-
cident light to pass through. Then, I placed another prism
behind the second board." On turning the first prism
about its axis, the image which fell on the second board
was made to move up and down upon that board, so that
all its parts could successively pass through the hole in
that board, and fall upon the prism behind it. The places
Fig. 15 — Experiment Showing Refraction and Division of
Light Rays, Until Green Ray Will Not Subdivide Further.
where the light fell against the wall were noted. It was
seen that the blue light, which was most refracted in the
first prism, was also most refracted in the second prism,
the red being least refracted in both prisms. "And so the
true cause of the length of that image was detected to be
no other than that light is not similar or homogeneal, but
consists of difform rays, some of which are more refran-
gible than others."
No more complete or illuminating explanation of the
nature of light through the agency of the prism has ever
been given than this. Newton showed here the real reason
of the dispersion, adducing the analogy of the rainbow,
altho he clung through it all to the corpuscular theory,,
postulating the existence not only of the flying particles
constituting light, but also of an ether — all the mechanism,
in fact, needed for the wave theory, and more.
102 PHYSICS
It was not until the beginning of the present century
that this experiment of Newton's (repeated as it had been
in the meantime by many philosophers) was found by Dr.
Wollaston to possess certain peculiarities which defied all
explanation. He found that, by substituting a slit in the
shutter of the darkened room for the round hole which
Newton had used, the spectrum was intersected by certain
dark lines. This announcement, altho at the time it did
not excite much attention, led to further experiments by
different investigators, who, however, vainly endeavored
to solve the meaning of these bands of darkness. It was
observed by the great Munich optician that they never
varied, but always occupied a certain fixed position in the
spectrum ; moreover, he succeeded in mapping them to the
number of nearly six hundred, for which reason they have
been identified with his name, as "Frauenhofer's lines."
It was one of the greatest contributions to science. Acci-
dentally he discovered in the spectrum of a lamp the double
line in the orange, now known as the sodium, line. He was
endeavoring at the time to determine how the refraction
through glass would take place for different colored lights.
The observation of the sodium line was a chance inci-
dent of his experiments. In oil and tallow light, and in
fact in all firelight, he saw this same bright, sharply defined
double line "exactly in the same place and consequently
very useful." Examining the spectrum of sunlight cast
through a small telescope upon a prism, he remarked "an
almost countless number of strong and feeble vertical lines
which, however, were darker than the other parts of the
spectrum, some appearing to be almost perfectly black."
He also examined starlight with his primitive spectro-
scope and found many of the solar lines in the spectrum
of the planet Venus. For nearly forty years the scientific
world, absorbed in theories concerning the nature of
light itself, or the newly announced atomic theory of
Dalton and the laws of chemical combination and compo-
sition, failed to see the meaning and significance of this
THE NATURE OF LIGHT 103
discovery of Frauenhofer. The great astronomer J. F. W.
Hersche!, the electrician Wheatstone, William Henry Fox
Talbot, Sir David Brewster and others remarked on
various similar phenomena in spectral experimentation,
but none succeeded in finding the clue to the mystery.
Many famous men between 1850 and i860 turned their
attention to this riddle.
Herschel pointed out that metals, when rendered incan-
descent under the flame of the blowpipe, exhibited vari-
ous tints. He further suggested that as the color thus
shown was distinctive for each metal, it might be possible
by these means to work out a new system of analysis.
Bunsen and Kirchhoff in i860 discovered that each
metal when in an incandescent state exhibited through the
prism certain distinctive brilliant lines. They also found
that these brilliant lines were identical in position with
many of Frauenhofer's dark lines ; or to put it more clear-
ly, each bright line given by a burning metal found its
exact counterpart in a dark line on the solar spectrum. It
thus became evident that there was some subtle connection
between these brilliant lines and the dark bands which had
puzzled observers for so many years. Having this clue,
experiments were pushed on with renewed vigor, until, by
happy chance, the vapors of the burning metals were ex-
amined through the agency of the electric light. That is
to say, the light from the electric lamp was permitted to
shine through the vapor of the burning metal under exam-
ination, forming, so to speak, a background for the ex-
pected lines. It was now seen that what before were bright
bands on a dark ground were now dark bands on a bright
ground. This discovery of the reversal of the lines
peculiar to a burning metal, when such metal was exam-
ined in the form of vapor, led to the enunciation of the
great principle that "vapors of metals at a lower tempera-
ture absorb exactly those rays which they emit at a
higher."
To make this important fact more clear, suppose that
io4 PHYSICS
upon the red-hot cinders in an ordinary fire-grate is
thrown a handful of saltpeter, also called nitrate of potash
or more commonly niter. On looking through the spec-
troscope at the dazzling molten mass thus produced
(instead of the colored ribbons which the sunlight gives)
all is black, with the exception of a brilliant violet
line at the one end of the spectrum and an equally brilliant
red line at the other end. This is the spectrum peculiar to
potassium; so that, if not previously aware of the presence
of that metal, and if requested to name the source of the
flame produced, the spectroscope would have enabled such
answer without difficulty. Now suppose this burning
saltpeter to be again examined under altered conditions.
Place the red-hot cinders in a shovel and remove them to
the open air, throwing upon them a fresh supply of the
niter. If the vapor now be examined while the sunlight
forms a background to it, it will be seen that the two
bright colored lines have given place to dark ones. This
experiment will prove the truth of Kirchhoff's law so far
as potassium is concerned, for the molten mass first gave
the bright lines, and afterward by examining the cooler
vapor it was evident that they were transformed to bands
of darkness ; in other words they were absorbed.
The simple glass prism as used by Newton, altho it is
the parent of the modern spectroscope, bears very little
resemblance to its gifted successor. The complicated and
costly instrument now used consists of a train of several
prisms, through which the ray of light under examination
can be passed by reflection more than once. By these
means greater dispersion is gained; that is to say, the re-
sulting spectrum is longer, and consequently far easier of
examination.
Since the middle of the nineteenth century the analytical
eye of this wonderful instrument has looked into the ma-
terial universe and aided the chemist to the discovery of
elements previously unsuspected and unknown. It has
shown the composition of sun and stars, by the correspond
Red Yellow Green Blue Violet Ultra- Violet
A
iiiiiiiiiiiiiiiiiiiiii
B
J;.J_ ' '• :.----
,MljMljMl„lM,|p,LljnluJnIlMllnlMl|lllLllMlIililillXllln.il
T !
L,: : ' . ' ' '^ LiUmlmlmU, ] limLilnnlnlnlmiLnlnnlnn Imilnnlnnlnn
Spectra: A., electric spark, negative pole; B, Potassium chloride,
vaporized; C, rluminum; D., chloride of gold, vaporized ; E., Strontium
chloride, vaporized; F., phosphoretted hydrogen.
THE NATURE OF LIGHT 105
dence of their spectra with those of terrestrial matter, to
be in general identical with that of the earth. Nor are
its services to be measured merely in qualitative units, for,
in examining incandescent bodies, by a careful study of
the absorption lines a very exact estimate of the 'quantity'
present can be arrived at. This method of analysis is so
delicate tl ' in experiments carried on at the mint a differ-
ence of one ten-thousandth part in an alloy has been
recognised. Neither must it be supposed that the services
of the spectroscope are confined to metals, for nearly all
colored matter can also be subjected to its scrutiny. Even
the most minute substances, when examined by the micro-
scope in conjunction with the prism, show a particular
spectrum by which they can always be identified.
While the spectroscope succeeded in proving that a cer-
tain yellow flame was the flame of sodium and a certain
reddish flame was that of calcium, it did not show why
the flame of one kind of substance should be brighter than
another. The flame of burning wood, for instance, is less
bright, generally speaking, than that of a burning kero-
sene lamp; the flame of phosphorus burning in oxygen is
dazzling in its brilliancy; a ribbon of the metal magnesium
(commonly used as a powder in flashlight photographs)
burns in ordinary air with an intensely brilliant white
light. The brightness of these flames cannot be due
wholly to temperature, as has often been maintained, for
there may be a solid such as iron or carbon burning in
oxygen at a high temperature, with brilliant incandes-
cence, or glowing, but without flame, while on the other
hand the lambent flame of boric methide or of camphor
shows that flame may exist without a high temperature.
A piece of burning camphor, in fact, may easily be held in
the unprotected palm by changing it from hand to hand —
a trick sometimes resorted to by stage jugglers. Again,
the ordinary Bunsen burner found in every chemical labo-
ratory will produce, by adjusting the air supply, either a
yellow, luminous flame of relatively low temperature, or a
106 PHYSICS
much hotter, non-luminous flame, whereas the temperature
in the exceedingly brilliant electric arc is extreme, reach-
ing in the electric furnace as high as 3,000 degrees Cen-
tigrade.
The real nature of flame was long a matter of conjec-
ture. The "phlogiston" (fire-substance) of the eight-
eenth century, in fulfilment of the hope expressed by that
erratic genius, Count Rumford, is to-day interred, it is
true, in the same tomb with "caloric" (heat-substance).
But the death of phlogiston did not bring with it the ex-
planation of the luminosity of flame. Sir Humphrey
Davy — inventor of the Davy Safety Lamp — regarded the
luminosity as due to the incandescence of solid particles
suspended in the flame, and this theory* until about the
middle of the nineteenth century, went unchallenged! The
presence of solid particles, either in the flame itself or in
immediate contact with the burning gas, was held to be es-
sential.
There is no doubt that the introduction of solid particles
in a fine state of division into a flame of feeble luminosity
will usually impart to it a considerable degree of bril-
liancy by the incandescence of the solid particles, or per-
haps in seme cases by reflection of the light from their
many surfaces, and it is usual to refer to the black deposit
which is formed upon a glass rod or similar body, when
held in the flame of a candle or gas, as a proof that such
flames contain solid particles.
Nevertheless luminous effects have been produced where
the solid particle hypothesis could not account for them,
such, for example, as the luminosity of the flame of hy-
drogen burning in oxygen under pressure; moreover, in
many of the brightest flames the temperature is such that
fuliginous matter could not exist in them. In many cases
it seemed, therefore, to be a more satisfactory explanation,
that the luminosity of flames depends on the existence
of a comparatively high temperature and on the presence
of gases or vapors of considerable density.
THE NATURE OF LIGHT 107
The effect of high temperature is seen in the greater
brightness of the flames of sulphur, phosphorus, and, in-
deed, all substances when burnt in pure oxygen, as com-
pared with the result of their combustion in air. Direct
evidence of the effect of high temperature is also afforded
by the combustion of phosphorus in chlorine, for while
at ordinary temperatures only a feeble light is produced
by this combustion, strongly heated phosphorus vapor
burns in hot chlorine with a dazzling white light.
A comparison o-f the relative densities of gases and
vapors shows that the brightest flames in general are those
which contain the densest vapors.
Hydrogen burning in chlorine produces a vapor more
than twice as heavy as that resulting from its combustion
in oxygen, and the light produced in the former case is
stronger than in the latter. Carbon and sulphur burning
in oxygen produce vapors of still greater density, and
their combustion gives a still brighter light. Phosphorus,
also, which has a very dense vapor, and yields, in burn-
ing, a product of great vapor density, burns in oxygen
with a brilliancy almost blinding.
The luminosity of a flame is increased by compressing
around it the surrounding gaseous atmosphere, and it is
diminished by rarefying it. Thus, mixtures of hydrogen
and carbonic oxide with oxygen emit but little light when
they are burnt or exploded in free air, but exhibit intense
luminosity when exploded in closed vessels so as to pre-
vent expansion of the gases at the moment of combustion.
The density, then, of the gases formed in combustion,
and the temperature at which combustion takes place,
were thus held by some physicists, notably E. Frankland,
to be the sole determining factors in the brilliancy of a
flame. As for the particles of solid matter, it is known
that while in some instances they may increase the lu-
minosity, in other cases they produce the opposite effect,
rendering the flame less bright. All these known facts
were thought during the latter half of the nineteenth cen-
108 PHYSICS
tury completely to have disposed of the solid par-
ticle idea in the brightness of flames. As a matter of fact,
it is evident that the "dense vapor'' theory advocated by
E. Frankland and others, while it adds much interesting
information to what already is known of the nature of
flame, does not in the least disprove the fact that a flame
is bright when it contains particles of solid glowing car-
bon, and it is not luminous when it does not.
Such brilliant and thorough investigators as Heumann,
Burch, Smithells, Techla, and especially Vivian B. Lewes,
established the fact toward the end of the century that in
the burning of ordinary illuminating gas that remarkable
illuminant acetylene is first formed and subsequently de-
composed. Lewes' careful experimentation showed that
in the dark part of the flame there occurs a transforma-
tion of gases, and that at the point where luminosity just
begins seventy to eighty per cent, of the compounds
formed is acetylene, and this in a gas flame in which less
than one per cent, of acetylene is originally present. Im-
mediately above this point the increasing heat of the
flame breaks up the acetylene gas into its two constituents,
carbon and hydrogen. The hydrogen burns in contact
with the oxygen of the air. The carbon is heated to in-
candesce by the combined influence of the burning hydro-
gen and the so-called "latent heat" of the chemical separa-
tion— hence the flame.
The real nature of flame is even to-day very commonly
misapprehended. A popular idea exists that wood burns.
Wood, strictly speaking, does not any more burn in air
than it floats in water. The flames seen burning at the
surface of a wood fire are due to the combustion of vola-
tilized solid material, and their luminosity is generally
conceded to-day to be due, as above shown, to the presence
of finely divided particles of glowing carbon. Dr. Percy
has accurately denned flame thus: "Ordinary flame is gas
or vapor of which the surface, in contact with atmospheric
air, is burning with the emission of light." This defini-
THE NATURE OF LIGHT 109
tion leaves little to be desired, for it very properly directs
attention to the gas or vapor necessary to a flame, as well
as to the fact that the flame itself is hollow.
Dr. Robert Montgomery Bird has summed up the es-
sential teachings of modern study of flame briefly as fol-
lows :
When the hydrocarbon gas leaves the jet at which it is
burned those portions which come in contact with the
air are consumed and form a wall of flame, which sur-
rounds the issuing gases. The unburnt gas in its pas-
sage through the lower heated area undergoes a number
of chemical changes, brought about by the heat radiated
from the flame walls; the principal change being the con-
version of hydrocarbons into acetylene, hydrogen and
methane. The temperature of the flame rapidly increases
with the distance from the jet, and reaches a point at
which it is high enough to decompose acetylene into car-
bon and hydrogen with a rapidity almost that of an ex-
plosion. The latent heat so suddenly set free is localized
by the proximity of carbon particles, which by absorbing
it become incandescent and emit the larger part of the
light given out by the flame ; altho the heat of combustion
causes them to glow somewhat until they come into con-
tact with oxygen and are consumed. This external heat-
ing gives rise to little of the light.
There have been opponents to this theory of the cause
of luminosity — as there are, fortunately, of all theories —
but the evidence is so strong and covers so many points,
and so many investigators have confirmed one part, or an-
other of the work, that it has been generally accepted as
a true statement of the facts with which it deals.
Visible light, as Frauenhofer long since pointed out,
reaches the eye in vibrations numbering from 4,000 to
7,000 billion per second. No other vibrations are useful
to us for seeing purposes, for no others have any effect
upon the retina of the eye. The analysis of the apparently
white light of the sun and the combining of the spectral
no PHYSICS
colors so formed to reproduce white light dates back to the
time of Newton. Frauenhofer, however, devised a means
of studying the solar spectrum without a prism. On plates
of glass he ruled very fine parallel lines very close together,
making the first grating. The beautiful iridescence of such
substances as mother of pearl has been shown by the sim-
ple microscope to be due to a multitude of fine lines in the
surface, the refracting edges of which disperse the pris-
matic colors like any true prism. Such a surface was the
grating of Frauenhofer, and the great advantage of this
instrument over the prism lay- in the fact that the lower
part of the spectrum where the red rays occur was very
much spread out, whereas the simple prism dispersed the
red end of the spectrum so little that examination of its
characteristics was rendered difficult. Frauenhofer also
experimented successfully with gratings made of very fine
wire, .04 to .6 mm. (.002 to .03 inch) in thickness.
By the aid of similar gratings, John William Draper, of
New York, not only confirmed the measurements of the
light waves which Frauenhofer had made, but determined
the temperature (5250 C.) at which all solid and liquid
substances become incandescent and glow with a red heat.
He proved also that below this red heat invisible rays are
emitted whose vibration lengths may be measured. Lewis
Morris Rutherford, whose magnificent work in radio-
activity has rendered him justly famous, produced other
and better gratings made of thin sheets of metal, and
Henry A. Rowland, of Johns Hopkins University, within
very recent years ruled gratings so fine that they con-
tained more than 100,000 lines to the inch — from fifty to
a hundred in the width of a fine human hair — gratings
which have never been surpassed. With the aid of these
wonderfully fine gratings Rowland has prepared large
photographic maps of the solar spectrum and prepared a
system of standard wave lengths now universally adopted.
The wave length of every line in the solar spectrum has
been measured through this means, and there are few of
THE NATURE OF LIGHT in
the common terrestrial elements which have not now been
identified in the atmosphere of the sun.
The discovery of the invisible rays below the red of the
solar spectrum dates back to Sir William Herschel, who
in 1800 determined their existence by means of a ther-
mometer. He noticed that the thermometer rose regularly
when it was moved from the violet toward the red end of
the spectrum, and it occurred to him to try the region be-
yond the extremes of the visible colors. To his delight he
found a regular series of radiations below the red. "It is
sometimes of great use in natural philosophy," the great
astronomer observed, "to doubt of things that are com-
monly taken for granted, especially as the means of resolv-
ing any doubt, when once it is entertained, are often
within our reach."
"This discovery," says Thomas Young in his 'Lectures'
of 1807, "must be allowed to be one of the greatest that
has been made since the days of Newton." Yet the ma-
jority of physicists failed for more than half a century to
see the importance of this discovery of Herschel. It was
only a few years after the discovery by Herschel of in-
fra-red radiation from the sun that Johann Wilhelm Ritter
and Wollaston proved the existence of dark chemical rays
in the ultra-violet region of the spectrum. Macedonio
Melloni, the inventor with Leopoldi Nobili of the thermo-
pile, was the first to arrive at a thoro realization of the
identity of radiant heat and light. "Light," said he, "is
merely a series of calorific indications sensible to the or-
gans of sight, or vice versa, the radiations of obscure
heat are veritable invisible radiations of light." He argued
that where there is light of any sort there must be some
heat, and moonlight ought to show some heat effects. He
experimented, at first unsuccessfully, in this direction, but
finally with a lens more than three feet in diameter suc-
ceeded in getting feeble indications of heat from the rays
of the moon. The thermopile which he used was a simple
instrument based on the well-known principle that a cold
ii2 PHYSICS
wire is, in general, a better conductor of electricity than a
warm wire. Hence any simple galvanometer or other cur-
rent-measuring apparatus showed by a deflection of the
needle when any part of the electric conductor was heated.
The measurements of radiant heat made by Melloni in
solids and liquids were paralleled by the investigations of
Tyndall upon the diathermancy of gases. Tyndall pos-
sessed extraordinary powers of popularizing difficult scien-
tific subjects. His first great lecture, delivered in 1853 in
England, took his audience by storm. He came to Amer-
ica and delivered in 1872 and 1873 several lectures on
light which were enthusiastically received. His famous
"Belfast Address" brought upon the brilliant Irishman the
charge of "infidelity," for he was as independent in thought
as outspoken in expression and held ever to the principle
that Truth has nothing to fear from its enemies.
Tyndall pointed out (as had Melloni before him) an
error of wide prevalence concerning the influence of color
and absorption. Benjamin Franklin records of himself
that having placed patches of different-colored cloth of
the same weight upon snow and allowed the sun to shine
upon them, he found that they absorbed the solar rays to
different degrees and sank to different depths in the snow.
He concluded from this experiment that dark colors were
the best absorbers and light colors the worst. For the
visible rays of the sun this conclusion is in general true,
but the solar rays consists of radiations running far out-
side the visible spectrum, about seven times the length of
the solar spectrum having been detected in the infra-red
radiations, and perhaps twice as much as is visible in the
invisible ultra-violet.
The visible spectrum of "white" light has been shown
by recent measurements to be only about one-tenth of the
actual measurable solar spectrum. In the invisible region
of the spectrum effects are often observed which are the
exact opposite of those seen in the prismatic spectrum.
Tyndall proved this in a clever manner. He coated the
THE NATURE OF LIGHT 113
bulb of a delicate mercury thermometer with the white
powder alum and the bulb of a second thermometer with
powdered iodine. Exposing both bulbs at the same dis-
tance to the radiations from an ordinary gas jet, he found
the alum-coated thermometer rose nearly twice as high
as the other; alum was a better absorber than iodine.
"The radiation," he remarked, "from the clothes which
cover the human body is not at all, to the extent sometimes
supposed, dependent on their color. The color of animals'
fur is equally incompetent to influence radiation."
Some of the first results of the invention of Langley's
bolometer were to show that the maximum heat of the
solar spectrum is in the orange, not in the infra-red, as
Herschel had supposed. It proved, moreover, that the
white light from the sun is not the sum total of the solar
radiations — that the sun's true color is blue and only the
orange veil of the terrestrial atmosphere works through its
selective absorption on sunlight, letting through the red
rays and absorbing the blue, to produce the effect of white.
Strictly speaking, we should say with Professor Langley
that the atmosphere absorbs all the colors, but selectively
taking out more orange than red, more green than orange,
more blue than green. "As there are really an infinite
number of shades of color in the spectrum," says Langley,
". . . it is merely for brevity that we now unite the
more refrangible colors under the general word 'blue,'
and the others under the corresponding terms 'orange' or
'red.' "
Newton showed that white light is compounded of blue,
red, and other colors ; by turning a colored wheel rapidly
all blend into a grayish white. Arrange them so that
there is too much blue, and the combined result is a very
bluish white, that of the original sun ray. Alter the pro-
portion of colors so as to virtually take out the excess of
blue, and the result is colorless or white light. White,
then, is not necessarily made by combining the "seven col-
ors," or any number of them, unless they are there in
ii4 PHYSICS
just proportion (which is in effect what Newton himself
says) ; and white, then, may be made out of such a bluish
light as we have described, not by putting anything to it,
but by taking away the excess which is there already.
Langley and T. W. Very showed by studying the radia-
tions of the firefly "that it is possible to produce light
without heat, other than that in the light itself; that this
is actually effected now by nature's processes; that nature
produces this cheapest light at about one four-hundredth
part of the cost of the energy which is expended in the
candle flame, and at but an insignificant fraction of the
cost of the electric light."
Langley showed also that the amount of energy neces-
sary to produce the sense of color varies enormously with
the color. The sensation of red, for example, requires
that the energy of the waves which enter the eye shall be
100,000 times as great as the energy necessary to produce
the impression of green. Far down below the visible red
of the solar spectrum the delicate filament of Langley's
bolometer groped its way until a point was reached at
which the solar radiations seem to be suddenly cut off.
From terrestrial sources, however, he obtained still fur-
ther wave lengths which exceeded in length .03 of a mil-
limeter (or more than .001 of an inch).
Rubens and Nichols, using a modified form of Crookes'
radiometer, found still longer wave lengths, equal to about
1 -100 the length of the shortest Hertzian waves. Thus
radiations of almost every length, from the great electric
oscillations of Hertz several miles long down to the ultra-
violet rays less than .000009 °^ an inch, have been defi-
nitely measured. Enormous strides have been made in the
measurement of all kinds of radiations, thanks to the in-
vention of the Hertz receiver — the "electric eye," as Sir
W. Thompson calls it — a simple instrument, "nothing but
a bit of wire or a pair of bits of wire adjusted so that
when immersed in strong electric radiations they give mi-
nute sparks across a microscopic air gap." Thus Sir
THE NATURE OF LIGHT 115
Oliver Lodge. It was the theory of that great mathe-
matician James Clerk-Maxwell, that light and electricity
are fundamentally one, upon which Hertz conducted his
studies leading to the production of those wonderful waves
which to-day, through the improvements of Marconi, con-
vey messages a thousand miles through empty air. In a
lecture delivered a few years before the close of the nine-
teenth century Lodge said of such oscillations :
"Light is an electro-magnetic disturbance of the ether.
Optics is a branch of electricity. Outstanding problems
in optics are being rapidly solved now that we have the
means of definitely exciting light with a full perception of
what we are doing and of the precise mode of its vibra-
tion.
"It remains to find out how to shorten down the waves
— to hurry up the vibration until the light becomes visible.
Nothing is wanted but quicker modes of vibrations.
Smaller oscillators must be used — very much smaller —
oscillators not much bigger than molecules. In all prob-
ability— one may almost say certainly — ordinary light is
the result of electric oscillation in the molecules of hot
bodies, or sometimes of bodies not hot — as in the phenome-
non of phosphorescence.
"Any one looking at a common glowworm must be
struck with the fact that not by ordinary combustion, nor
yet on the steam engine and dynamo principle is that easy
light produced.
"So soon as we clearly recognise," he concludes, "that
light is an electric vibration, so soon shall we begin to
beat about for some mode of exciting and maintaining an
electrical vibration of any required degree of rapidity.
When this has been accomplished the problem of lighting
will have been solved."
CHAPTER VIII
There is no more general instinct in man than the love
of the music of Nature. Often, too, the light accents of
almost inaudible sounds are more eloquent and persuasive
than the louder vibrations heard in a world where every
smallest particle of matter vibrates. The whole physical
universe is but a fathomless ocean of vibrations, altho only
a few of these appear as audible sound. Yet in human his-
tory no physical sense has had such fateful influence as
that of hearing. The vocal Memnon of Egypt, the oracles
of Greece, the war-trumpets of Rome, the vibrant harp-
strings of the Scandinavian skald, the shrill call of the
bagpipes, the booming tree-drums of the South American
Indians, the violin of Rouget de Lisle, the triumphant
crash of the modern regimental band or massed symphony
orchestra, finally the human voice in all time — it needs
but a glance at a few such examples to prove how surpass-
ing is the influence of the sounds that impinge upon the
ear on the mind.
It is said that Apollo was once wandering along the
shore of the Mediterranean Sea and found there the shell
of a dead turtle with a few strings of dried flesh stretched
across it. He held it up and delighted himself with the
musical sound which it made in the wind. He plucked
the strings and found they made a pleasing sound together.
Such was the origin of the lyre. Pythagoras constructed
on this model an instrument of a single string — the mono-
116
SOUND 117
chord — which was capable of producing notes of various
pitch. The string was stretched above a board, and run-
ning over a bridge was attached to weights by means of
which the tension on the string could be adjusted.
Strange theories the Greeks had as to the nature of
sound. Not the least curious of these theories was that
enunciated by Alcmaeon of Crotona, who wrote: "We
hear with the ear because it contains a vacuum" ! Lit-
tle as they knew of what is called to-day the science of
sound, however, the Greeks carried the theory of music to
a high degree of development. They were familiar with
the diatonic scale of C and wrote massive bass melodies,
using the natural notes, these melodies being classified as
"modes," according to the note upon which the melody
ended. They had six such modes ending on every note
of the scale except the seventh. The accompaniment was
put in above the melody in a manner exactly the reverse
of that now generally in use. The so-called Ionian Mode
corresponded to the modern scale of C natural, the Mixo-
lydian to that of G natural, the iEolian to the scale of A
minor. These same modes, adopted from the Greek by
St. Ambrose and added to by St. Gregory, became the
basis of many of the grand melodies still extant in the
ritual of the Catholic Church. The Greeks also recog-
nised three genera or varieties of modulation — the
Diatonic, the Chromatic and the Enharmonic. The latter
contained intervals smaller than a semi-tone — the least
difference of pitch to which modern ears are accustomed.
The peripatetic school of philosophers held that the higher
the pitch of a sound the greater was its velocity; they
also believed that the source of a sound determined the
speed of its transmission, errors which were not disproved
until early in the seventeenth century.
Oracles played an important part in the history of Gre-
cian development, as in fact in that of most ancient
nations. The simple device of a speaking tube made it
possible to produce those mysterious voices whose super-
n8 PHYSICS
natural revelations so swayed the imagination of an un-
sophisticated people. Such were the cryptic and potent
utterances of the famous Greek oracle at Delphi. To the
modern mind, accustomed to wonder at nothing, to ex-
plain everything, the faith of men in the oracular utter-
ances of antiquity seems as barbarous, childish; yet the
roar of trains and machinery, the whistles, bells and rat-
tling wheels of commerce cannot drown the quiet voice
of the savant, the * man who knows. The oracle still
speaks, but speaks to-day from the mysterious retirement
of the laboratory with an authority as absolute as that
which bid the Athenians defend their city with wooden
walls.
It is apparent that the multitude of sounds which reach
the ear must be conveyed to it by some material medium.
In most cases this medium is the air; indeed, the striking
fact has long since been pointed out that but for this at-
mospheric ocean the world would be plunged for us in
perpetual silence. The bell-jar experiment of Francis
Hauksbee, made in the seventeenth century, proved that
no sound is audible in a vacuum. The ringing of a bell
became rapidly fainter when the air was exhausted from
the bell-jar under which it was placed.
The fact that air is not the only conductor of sound nor
the best is well known. Tapping a table, the sound is
heard much more distinctly when the ear is placed close to
the wood; the Indian places his ear near the ground to
note the sound of approaching footsteps; an oncoming
train is heard through the rails long before the sound of
it reaches through the air; the detonation of a distant
explosion comes with a double shock, the sound traveling
faster through the earth than through the air. In general,
then, the more dense the medium is, the better conductor
does it become of sound waves. Liquids transmit the
vibrations of sound better than gases. Stones clapped
together under water produce a sharp stunning effect upon
the ear placed under water to hear them. The bell signals
SOUND 119
installed on the American coast give practical evidence of
the superior transmitting power of water over air.
The velocity of sound in air was investigated in the six-
teenth century by Marin Mersenne. Noting the difference
in time between the flash and the report of fire-arms at
known distances, he got 1,380 feet per second as the speed
of propagation of sound waves. This result was far from
accurate. Pierre Gassendi, making similar experiments,
used guns large and small and disproved the Aristotelian
theory that the velocity of sound was dependent upon
source and pitch. To any one indeed in modern days this
idea of the peripatetic school must appear absurd, for the
pitch and the source of sounds from a modern orchestra
are as various as musical genius can make them, yet when
played together the sounds of all reach the ear at the same
moment.
That the source of sound does not affect the speed of its
transmission is not, however, universally true. Captain
Parry, on his Arctic expedition, found that violently loud
sounds would travel faster than softer ones. During artil-
lery practice it was shown that by persons at distance from
the guns the report of the latter was heard before the
command of the officer to fire. In a series of experiments
upon the velocity of sound in rocks Mallet showed that
with a charge of 2,000 pounds of gunpowder the average
velocity of the sound of a blast was 967 feet per second,
while a charge of 12,000 pounds produced a speed of trans-
mission of 1,210 per second. Through iron the speed of
sound has been shown to be still faster. M. Biot, experi-
menting with an iron tube 3,120 feet long, found the
speed of sound through this tube to be 9 or 10 times as
fast as in air. It is now generally conceded that the speed
of sound in iron is actually about five times as fast as in
air and through water about four times as fast.
The great law of Inverse Squares which has been shown
to be so general in physics applies also to Sound. If four
bells of the same kind are placed at a distance of 20 yards
120 PHYSICS
from the ear and another at a distance of 10 yards the
single bell produces a sound as loud as that of the four.
How far a sound is audible depends upon its loudness.
The report of a volcano at St. Vincent was heard at
Demerara, 300 miles away, and the cannons of the battle
of Waterloo are said to have been audible at Dover.
The study of sound in music, the classification of tones
and their combination reached a high point of development
long before any complete analysis had been made of the
cause of sound and the manner of its transmission. About
the end of the seventeenth century Joseph Sauveur, a poor
adventurer who found his way on foot to Paris seeking his
fortune, became professor of mathematics at the College
Royal. He published important papers on the discovery
of "overtones" in strings, using paper riders to locate the
points of greatest and least motion when the strings were
set in vibration. He had observed and explained the phe-
nomenon of sympathetic vibration. From the "beats"
produced by organ pipes of nearly equal length he deter-
mined the vibration rates of the notes given forth by each.
Two pipes were tuned in the ratio of 24-^25. When air
was blown into these four beats per second were observed,
from which Sauveur concluded that the higher pitched
pipe was producing 100 vibrations per second.
The experiments of William Noble and Thomas Pigott
at Oxford had proved that the vibration of a string is
greatest at the center and that it may also be made to
vibrate in halves, thirds, fourths, fifths, etc. The strings
of a harp or piano, for example, vibrate chiefly as a whole
— that is, throughout their entire length. The harder the
string is plucked or struck, the louder is the sound and the
more ample is the motion of the string. Thus amplitude
of vibration was seen to be a determining factor in the
loudness of a sound.
Not only nearness and amplitude of vibration, but echo
as well may increase the intensity of a sound. Speaking
tubes, megaphones and such devices depending upon this
SOUND 121
principle were in use long before the theory of sound was
generally understood. The effect here is evidently one of
reinforcement by echo, which in smooth tubes is so great
that M. Biot observed that a conversation could be carried
on in a low tone through a small tube 1,040 yards long.
For very long distances, however, it is evident that the
speaking tube is not a practicable device, as it would re-
quire 8 minutes for the sound to travel from one town to
another 100 miles away — less than */10 of the distance
easily and instantly bridged to-day by the wireless tele-
graph.
The "father of acoustics" introduced about the end of
the eighteenth century a new chapter in the study of
sound. Ernst Florens Friedrich Chladni, educated for
the law, proved himself a much better scientist than law-
yer. He experimented with vibrating plates covered with
sand. The collection of the sand at the nodes, or points
of least vibration, formed the famous "figures of Chladni."
These were exhibited before Napoleon, and the conqueror
of Europe presented him with 6,000 francs to enable him
to translate into French his Akustik. Chladni invented a
torsional pendulum in which the motive force of gravity
was replaced by the molecular resistance of a rod to the
effect of twisting; he made many calculations of the abso-
lute rate of vibration of sounding bodies and determined
the velocity of sound in other gases than air by filling
organ pipes with the gas and noting the resulting pitch.
Felix Savart, the greatest master of his time in the
theory of sound, invented a simple but effective instrument
to show that the vibration rate of a body is the sole factor
in the pitch of the note which it produces. A toothed
wheel was made to rotate rapidly against the edge of a
card. By increasing or decreasing the speed of rotation
the pitch of the note produced could be raised or lowered
at will. A dial indicated the number of shocks per second
made by the teeth of the wheel striking the card.
Caignard Latour invented about the same time an in-
122 PHYSICS
strument often heard to-day in connection with steam
whistles — the siren — so called because it could produce
sounds audible in water as well as in air. A current of
air blown through holes in a swiftly revolving disk pro-
duced notes which could be regulated to give any desired
pitch. This apparatus of Latoirr was used by Savart with
certain improvements to determine the limits of audible
Sound Vibration Measurement.
sounds. He found that he could hear tones of bodies
vibrating at the rate of 48,000 per second. The lower limit
of audible vibration he placed at 16 or 14 per second. With
the same velocity the siren gives the same sound in water
as in air and all gases. Thus the number of vibrations
per second, irrespective of the material of the vibrating
body, was proved to be the sole factor in determining
pitch. It is interesting to note that the siren has been ap-
plied to find the rapidity of motion in the buzzing wings
of insects. The tiny gauze pinions of the gnat have thus
been found to vibrate 15,000 times in a second.
About the middle of the last century was invented an
instrument so similar to the human ear that it deserves
some attention. E. Leon Scott produced an apparatus
SOUND
123
which he called the Phonautograph, so beautifully con-
structed as to register not only the vibrations produced by
solid bodies, but also those produced by wind-instruments,
by the voice in singing, and even such noises as that of
thunder or the report of a gun. A small cask of plaster of
Paris, perhaps a foot and a half long, was closed at one
— Mechanism of the Ear.
end but for a small circular space over which was fitted a
flexible membrane. Plaster of Paris was selected on ac-
count of* its absence of elasticity and its very slight sus-
ceptibility tc vibration. A stylus or blunt needle in con-
tact with the membrane recorded the vibrations of the
latter upon a revolving cylinder. A movable piece, called
the subdivider, enables the experimenter to adjust at will
the arrangement of the lines of greatest and least vibra-
124
PHYSICS
tion. Comparing the ellipsoid cask with the auditory
canal, the stretched membrane with the tympanum or
drum of the ear and the subdivider with the chain of little
bones which touch the tympanum, the likeness of this in-
strument to the organ of hearing becomes singularly
apparent.
Before the researches of Savart it was generally as-
Fig. 1 8 — The Phonautograph.
sumed that sounds above 18,000 per second and below 32
per second were inaudible to human ears. M. Despretz,
investigating the same subject, disputed Savart's results,
maintaining that the higher and lower limits of audible
sounds were respectively 73,700 vibrations and 32 vibra-
tions per second. It is probable that the ears even of
trained experts will vary greatly in their sensibility to
sounds of extreme pitch. The intensity of a sound will
SOUND 125
also evidently make it audible when another less intense
sound of the same pitch cannot be heard at all.
The question of the quality of sounds was first clearly
explained by the great Helmholtz. His *Lehre von den
Tonempfindungen' has gone through many German and
English editions. This wonderful investigator, mathema-
tician and physicist showed that musical tones were due
to regularity of vibration, discordant tones to irregularity.
Musical tones he distinguished by their Intensity, Pitch
and Quality. The Quality of a sound he found depended
upon the number of "upper partials," or "overtones," pres-
ent in the vibration of any body. The electrician Georg
S. Ohm was the first to point out that there is only one
form of vibration which will give rise to no "overtones,"
but consists only of the fundamental note. This was the
vibration peculiar to the pendulum and tuning fork.
Helmholtz's experiments showed analytically the composi-
tion of vowel qualities, how the infinite subtleties of inflec-
tion in the human voice are due not so much to the loud-
ness or softness^ of the instrument as to the number and
position of these upper tones present with and sounding
with the fundamental. "If only the unevenly numbered
partials," says he, "are present (as in narrow stopped or-
gan pipes, piano strings struck in their middle points, and
clarinets), the quality of tone is hollow, and, when a large
number of such upper partials are present, nasal. When
the prime tone predominates the quality of tone is rich,
but when the prime tone is not sufficiently superior in
strength to the upper partials the quality of tone is poor."
Helmholtz designed a series of glass globes, "resonators,"
which he had made of such size as to correspond with the
vibration numbers of the upper partials of a given funda-
mental tone. When the fundamental tone was sounded^
he held each one of these resonators to his ear, and if that
particular overtone were present it would at once be rein-
forced and exposed by the resonator. Thus he proved,
beyond question the fact that it is the overtones of any
126
PHYSICS
given note which lend to it its peculiar character, tone-
color or timbre.
Rudolf Konig, the eminent instrument maker of Paris,
constructed a series of resonators which were an im-
provement upon the design of Helmholtz. He made his
Manometric Mirror.
resonators cylindrical in form, having over one end a
close-fitting cap, by means of which the cylinder could be
drawn out and tuned to a nicety. Then he conceived the
brilliant idea of arranging these resonators on a frame
connected with a manometric mirror, whereby the presence
of each and every overtone could be instantly detected by
the dentations of the flame.
But Helmholtz was not content with the analysis of
tones according to their quality. He verified his results
by the synthesis of the same tones from their constituents.
SOUND
127
By means of a series of electro-magnets he succeeded in
making all possible combinations of overtones and produc-
ing notes of every quality.
Professor Ganot's Elements de Physique thus sum-
marizes the facts which the inestimably valuable researches
of Helmholtz have contributed to the study of tone-color :
Fig. 20 — Manometric Flames.
Different tones produce variant flame effects.
1. Simple tones, as those produced by a tuning-fork with
a resonance box, and by wide covered pipes, are soft and
agreeable without any roughness, but weak, and in the
deeper notes dull.
2. Musical sounds accompanied by a series of har-
monics, say up to the sixth, in moderate strength are full
and musical. In comparison with simple tones they are
grander, richer and more sonorous. Such are the sounds
of open organ pipes, of the pianoforte, etc.
128 PHYSICS
3. If only the uneven harmonics are present, as in the
case of narrow covered pipes, of pianoforte strings struck
in the middle, clarinets, etc., the sound becomes indis-
tinct; and when a greater number of harmonics are
audible the sound acquires a nasal character.
4. If the harmonics beyond the sixth and seventh are
very distinct the sound becomes sharp and rough. If less
strong, the harmonics are not prejudicial to the musical
usefulness of the notes. On the contrary, they are useful
as imparting character and expression to the music. Of
this kind are most stringed instruments and most pipes
furnished with tongues, etc. Sounds in which the har-
monics are particularly strong acquire thereby a peculiarly
penetrating character, such as those yielded by brass in-
struments.
M. Jul. Ant. Lissajous designed a method of tracing by
means of a stylus the vibrations of two tuning forks,
known as 'Lissajous' figures/ Nathaniel Bowditch, of
Salem, Mass., had also previously to Lissajous' experi-
ments succeeded in producing the same figures.
From the evidence of the researches of Helmholtz it is
evident that a pure tone is almost never heard. The notes
of a violin, or of a beautiful voice, or of a piano sound, it
is true, like simple tones. They are not simple — in fact,
the most pleasing tones which can be heard are as a rule
very complex. A note struck on the piano sounds forth
simultaneously a number of other notes. These may not
at first appear, but if the note struck is held down for a
few minutes even the untrained ear will infallibly distin-
guish other notes of higher pitch which seem to take shape
and stand forth separately from the sounding interior of
the instrument. These auxiliary tones are frequently
classed under the general head of "haromnics." Helm-
holtz called them "upper partials." Tyndall gave them the
name of "overtones." The strings of a violin or 'cello may
likewise be made to produce different notes by setting them
into vibration with the bow in the usual way and merely
SOUND 129
touching the vibrating string at various points. Violin
soloists become phenomenally skilled in the use of these
harmonics, which can be produced with equal readiness on
the stopped or on the open strings. The same effects may-
be observed in a piano if the string happens to be access-
ible. From any string under tension harmonic effects may
be obtained. Let the A string of a 'cello, for example, be
bowed and at the same time lightly touched in the middle
by a finger. A note will at once appear which is the
octave above the open string, and the string will be seen to
be vibrating in two sections in place of one. A paper rider
will remain quiet when placed in the middle of the string,
but if the latter is made to vibrate throughout its whole
length the rider will be violently thrown off. Again, the
string may be divided by a touch and made to vibrate in
thirds or fourths or fifths. Dividing the string in thirds
is clearly equivalent to multiplying its vibration number
by 3. Each of these divisions will therefore give out a
note whose vibrations are three times as frequent as those
of the fundamental ; in musical terms this note is said to
be an octave and a fifth above the open string. If the
vibration number of the A string be taken at 213 vibrations
per second, the octave and fifth (E') will then vibrate
three times as frequently, giving 639 vibrations per second.
(These figures, while not quite accurate, are close enough
to illustrate by a rough computation how the values of
harmonics were determined.) Dividing the same string of
213 vibrations per second into four parts, a note is ob-
tained two octaves above the open string (A'), and the
vibration number of this note will, in the same manner, be
four times that of the fundamental, giving therefore the
number 852. The division of the string into fifths pro-
duces a note which has five times the vibration frequency
of the fundamental. This note will prove to be C"# — two
octaves and a third above the original note. A little care-
ful experimentation will show that several still higher
harmonics may readily be produced by this one string.
130 PHYSICS
The harmonics produced by sounding a note on the piano
and listening for its overtones will usually appear the
wrong order, the higher harmonics, on account of their
more dissonant relation with the fundamental coming to
the fore first.
The natural series of overtones follows in whole tones
after the seventh. But none of these are exactly in tune,
and after the G" A" B" C'"# have been passed a partial
tone appears which cannot be located by the notation in
common use to-day.
In the pitch generally recognised by physicists C has a
vibration frequency of 256 per second. "International
Standard Pitch," so called, is made slightly higher than
this in the endeavor to lend a more brilliant quality to the
instruments. The pitch of a given note, therefore, is not
always constant. A brief consideration, however, will
show that not only is this the case, but that the tone-
relations of a note are not constant and that the same note
in different natural scales must have a different vibration-
rate. The fact is that the natural scale in use to-day is
not natural but artificial ; the diatonic scale is not diatonic.
For purposes of modulation it became necessary to "tem-
per" the natural series of notes which would occur as
overtones from a given fundamental. Thus the "perfect
fifth" (G) above the note C is actually about 1/M of a
semi-tone flat, and the F next below it is made sharp to a
still greater extent, while the other notes of the scale are
tempered more than these. A perfectly "tuned" piano has
not a single note (excepting the octaves) in tune. The
complex nature of the apparently simple major scale may
easily be made apparent.
The scale from C to C has in it eight natural notes
(white) and five "accidentals" (black). Excluding the
octave, this makes then twelve notes. Theoretically the
major scale was originally derived from the first few over-
tones of a given fundamental. All the natural notes of the
scale, except the seventh, are found in the overtones of the
SOUND 131
note C. But the interval from the first to the second note
of the scale is not the same as the interval from the second
to the third. The introduction of minor melodies and a
minor scale made the problem still more difficult, for the
ratio between E& in the "perfect" scale and C is not at all
the ratio between D# in the "perfect" scale and the same
note C. Consequently D# and E^ must both be altered to
some intermediate note, since in an instrument (like the
piano) of fixed pitch the same key must be struck to repre-
sent both these notes. The problem was finally solved by
dividing the notes from C to its octave above (C) into
twelve equal steps or intervals, and by this means pro-
ducing a "tempered" scale of which the notes, black or
white, could be played in any key. For this instrument
NATURAL TEMPERED
c 24 24
c# & 25.43
d 27 26.94
d# et>. . 28.55
e 30 30.25
f 32 32-05
f# gb 33-96
g 36 35-98
g# a& 38.12
a 40 40.38
a** bb 42.80
b 45 45-33
cw 48 48
so tuned Johann Sebastian Bach, the greatest of all great
composers, wrote his Das Wohltempenrte Klavier, show-
ing that with these fixed and tempered notes music could
be played in any key whatsoever. It is related of the
great Handel that he could not bear to hear music played
in the tempered scale, and had constructed for himself an
organ provided with keys to produce every one of the
132 PHYSICS
notes theoretically necessary for a perfect scale. This
would really require a keyboard containing about twenty
notes to the octave, and more than this if such acci-
dentals as double sharps and flats be accurately repre-
sented! A glance at the accompanying table will show
how each note of the tempered scale compares with its
true value in the natural scale.
It is a problem for the "musical" physicist of the future
to devise a keyboard adapted to play in perfect tune the
perfect scale in every key.
Musical instruments are among the earliest recorded
human inventions. In the Hebrew scriptures mention is
made of one Jubal, who became "the father of all such as
handle the harp and the organ." The Hebrews had many
musical instruments — harps, trumpets and flutes of various
styles. The Egyptian inscriptions likewise portray types
of all these instruments. They developed also an organ, a
set of pan-pipes with bellows. From the Phenicians the
Greeks are said to have imitated the cithara, zither or lyre.
The Sabeca of the Chaldeans was the precursor of the
modern harp, the Psauterin of the clavichord, from which
evolved the modern piano. The bagpipes were known
from the very beginning of history in Syria, Phenicia and
Egypt. Such early instruments as these were designed
rather to accompany singing and religious ritual than for
solo performances. The use of instruments unaccom-
panied by the human voice is an essentially modern idea.
The infinite combinations of tone heard in a modern
orchestra are the product of four main classes of in-
struments :
(i) The Strings.
(2) The Wood Wind Instruments.
(3) The Brass Instruments.
(4) The Percussion Instruments.
More than half of a well-balanced orchestra to-day is
made up of stringed instruments — the Violins, Violas,
'Cellos and Bass Viols. As the latter three are identical
SOUND
133
in general construction with the violin, the difference
being mainly one of size, a word concerning the latter
will of course apply to all in this group.
The vibration of the strings alone of a violin, made by
drawing a bow across them, would have so little resonant
value that the sound would be almost inaudible and the
instrument about as serviceable in an orchestra as a jew's-
harp. The tone must therefore be reinforced, and this is
1 and 3, Portable Harps to*
taab of Ttaaesm lit.
Fig. 2i — Early Stringed Instruments.
done by the body of the violin, every part of which is
forced into vibration when the strings vibrate. A just
proportion in the construction of the violin "box" is the
secret which the great Cremona violin makers — the Guar-
nerii and Stradivarii — discovered. The wood must not be
too thick, for the vibration then will be dull and smoth-
ered, nor too thin, for then the tone of the instrument lacks
body, richness, mellowness. The material must be per-
fectly seasoned, so that no subsequent contraction of the
134 PHYSICS
fiber may strain and destroy the perfect proportion of the
parts of the instrument. The adjustment of the bass-bar
beneath the heaviest string and supporting one foot of
the bridge; of the sound post which supports the other
foot of the bridge; the adjustment, carving out and pro-
portioning of the bridge itself ; the length of neck and size
of head; the varnish which fills and protects the surface
of the wood ; the shape of the body ; the position, size and
shape of the sound-holes — all these and other conditions
affect the construction of a perfect instrument. By bow-
ing nearer to or farther from the bridge the tone is made
either bright or soft and mellow. If the vibration is ex-
cited near the bridge, a large number of the higher over-
tones are brought out; if farther away the fundamental
and primary overtones assume greater prominence, for the
larger the segments in which the principal vibrations oc-
cur the less will the tone be affected by the higher partials.
If the string is bowed too far from the bridge it loses its
sonorous quality and becomes feeble in tone. The violin
string, therefore, is bowed at points which vary from x/8 to
V12 of the string-length from the bridge, and the instru-
ment is thus able to produce more varieties of tone-color
than are found in any other one instrument.
In the others of this class the quality of tone grows
gradually more somber as the instruments increase in size
and weight, and the greater size of string necessitates
bowing farther from the bridge. Even the bass viol (or
violone), however, may be used occasionally as a solo in-
strument, giving a magnificently rich, ponderous tone.
The production of sound in the brass instruments de-
pends upon the use of overtones. The fundamental
("pedal") notes of these instruments are seldom heard.
In the bugle, the simplest of the brasses, the second, third,
fourth and fifth overtones are alone used. For example, a
C bugle will produce among its natural overtones the
notes G, C, E', G', and with these four notes, by aid of
change of rhythm, all the military signals may be pro-
SOUND 135
duced. A trombone, if in this key, would add to these
notes the octave C. Here, however, a new principle is
introduced — by means of the slide the length of the trom-
bone tube may be increased. Suppose the slide to be
pushed out about an inch and a half, it is clear that the
pitch of the whole instrument will be lowered ; it will give
exactly the same series of overtones, but each will be
found about a semi-tone below its original pitch, thus
producing the notes F#, B, D#, F#. (It should be noted
that a trombone is exactly an octave lower than a bugle,
cornet or trumpet in the same key.) Pushing the slide
out another inch and a half again lengthens the tube and
again lowers the instrument a semi-tone, giving the series
F, Bb, D, F. This is actually the key in which the orches-
tral trombone lies with slide closed. By repeating this
process of lowering the slide all the semi-tones in the scale
may be produced as far as the compass of the instrument
extends. The pedal note of the trombone may similarly
be lowered by means of the slide.
In all the brass instruments other than the slide trom-
bone the overtones are lowered by means of finger valves
which introduce different lengths of pipe into the vibrat-
ing tube. The trombone is not infrequently (especially in
brass bands) provided with such valves in lieu of the slide,
and the physical principle of the instrument then becomes
identical with that of the French horn, cornet, trumpet
and tuba.
The French horn produces a tone singularly soft among
the brasses, sounding often more like some wood wind
instrument. The quality of tone of this instrument has
been explained on the basis of the conical bore of the tube
and the immense bell at the end of it. The sound is soft-
ened and mellowed by the oblique reinforcement of echo
from the walls of the tube. The trumpet, on the contrary,
by far the most brilliant instrument in existence, is said
to owe its superiority in this regard to the cylindrical bore
136 PHYSICS
and small bell of the tube. The vibrations are not lost as
in the spreading walls of the French horn, cornet, etc.
The wood wind instruments are of three types. The
flute and piccolo (or octave flute) are made to sound by
the breath of the player blown across a hole in the instru-
ment and striking the opposite edge. Different notes are
produced by the keys, which open holes in the side of the
flute, thus causing the air within to vibrate in various sec-
tions at the will of the player.
The oboe, English horn (or tenoroon) and bassoon have
two thin reeds in the mouth-piece which set into vibration
the column of air within the instrument. The extremely
reedy tone of this instrument has caused it to be used a
great deal for pastoral effects in what is called "descrip-
tive" music. This penetrating, soft, but reedy quality,
when brought down into the bass register as in the bas-
soon, has an effect sometimes ludicrous, sometimes terrify-
ing, always peculiarly characteristic. The "flutes" of the
Egyptians are believed by some authorities to have been
in reality of the oboe type. It is probable that they fre-
quently used reeds in the end of the pipes and that the
latter would be classed to-day as either oboes or clarinets.
The clarinet principle is not essentially different from
that of the oboe, except that it has one reed instead of
two. The instrument is made in several pitches. A high
clarinet in E& is much favored in band music, but appears
seldom in orchestra. There are also a bass and an alto
clarinet which are recognised by composers, these instru-
ments being identical in principle with the A and B^
clarinets of an orchestra. The quality of these instru-
ments partakes of both the soft floating notes of the flute
and the highly nasal character of the oboe.
Altho there is probably no instrument so primitive as
the drum, yet the kettle drums of the modern orchestra
are by no means primitive instruments. Their value is
chiefly in the tremendous energy which they add to
rhythmic effects, but they can also be tuned through a
SOUND 137
surprisingly wide range of notes, altho of low pitch and
dull quality of tone, producing no definite musical tone-
color. The copper hemisphere above which the sheepskin
head is stretched acts as a perfect resonator, and the tone
of the drum, partly on account of this large reflecting
surface, has an amazing carrying power.
Of other percussion instruments, such as the cymbals,
snare drum, tambourine, xylophone, etc., which have come
down with little or no change from the earliest times, onl^
passing mention need be made.
A familiar but very beautiful instrument, different sm
principle from any of those heretofore mentioned, is the
^Eolian harp. In this the strings are set in motion by the
varying currents of wind upon them. Since no resonator
reinforces the tone of the strings, the quality of the sound
is exceedingly soft and ethereal, altho distinct enough in
point of pitch.
Sound, therefore, like Light and Heat, may be con-
sidered in a double aspect, that of the physicist and that
of the artist or musician. The Laws of Physics cannot
be considered merely as cold abstractions, for the reason
that they are so intimately related to the esthetic interests
of life and the advancement of human well-being. The
better understanding of the Properties of Matter has led
to this era of Mechanical Knowledge, the comprehension
of the principles of heat has enabled man to obviate
much climatic inclemency; the length of available time
for labor and pleasure has been increased by artificial
lighting, and speech is dependent upon the hearing of
the Sound. And even yet the vast domain of these great
subjects is scarcely known, but half explored, and the
twentieth century waits to welcome the Newton of the
future.
ELECTRICITY
PROF. WM. J. MOORE
ELECTRICITY
CHAPTER I
THE NATURE OF ELECTRICITY
So rapidly have the applications of electricity to the
wants of industry followed one another during the past
thirty years that it may seem as tho the whole science
had been practically developed in that time, and yet the
real foundation work, which make the almost innumerable
electrical contrivances of to-day possible, was mainly laid
long before that period. It is Gilbert, Franklin, Volta,
Galvani, Davy, Arago, Faraday, Maxwell and many others
who have enabled the modern experts to put much of tho
science on a mathematical basis, and who made long
strides toward that final goal which is still so far away—
the answer to the question, What is Electricity ?
Many are the philosophers who are still devoting their
lives to it, and occasionally some fact is discovered which
disarranges many existing ideas and leads to new and un-
explored fields. The new theories which have been ad-
vanced, however, have striven rather to elucidate some
unexplained points of the old theories than to disprove
them.
Thales in 600 B.C., who discovered the attraction of
amber for light bodies, said that amber had a soul. Gil-
bert, in 1600 a.dv is accredited with the following hypothe-
sis: Friction, because it heats a body, causes it to emit
rays of a subtle unctuous material, which is cooled agaia
142 ELECTRICITY
on coming into contact with the air, loses its expansive
force, and draws itself together again, bringing back such
light bodies as come in the way of the electrified body.
According to Hauksbee, the emanations of matter which
start from an electrified body spread in the form of rays
or physical lines, which possess a kind of continuity in
themselves so that those parts of each ray or line which
reach out furthest into space receive the impulse from
those parts which are nearest to the body.
The eighteenth century brought out two theories which
for a time seemed to explain most of the phenomena then
observed: one was the two-fluid theory of Symmer and
the other the single-fluid theory of Franklin. Both these
theories assumed electricity to be a fluid.
Franklin assumes the existence of one electric substance
or fluid which attracts the particles of ordinary matter,
but repels itself. In the ordinary state, bodies are charged
with a normal quantity of this electrical substance. If this
charge be either increased or decreased, the body becomes
'electrified'; if it be increased, the body is charged with
a 'plus' or positive charge; if the body has a less quantity
of electricity than in its normal state, it is said to be
charged with a 'minus' or negative charge.
The two-fluid theory thought out by Symmer sup-
poses that instead of there being one fluid there are two
fluids having opposite properties to each other. The mole-
cules of either fluid repel one another, but attract those
of the opposite kind of fluid. Bodies in their normal con-
dition, or when unelectrified, contain equal quantities of
both fluids held together by their mutual attraction, so
neutralizing each other. By friction or by induction the
two fluids may be separated; the positive fluid passes to
one of the bodies and accumulates on its surface, thus
leaving an excess of negative electricity on the other.
These two theories were convenient to use in explain-
ing the action of frictional and influence machines, the
electrophorus, the condenser and many other forms of
NATURE AND FORCE 143
electrostatic apparatus. Indeed, these theories are still
applied to a certain extent as affording a convenient means
of expressing these electrostatic actions. They contain a
large element of truth, and the later theory of Maxwell
and the electron theory are elaborations of them.
Franklin's opinion on the nature of electricity may best
be stated in his own words, and the following is an extract
from his paper entitled 'Opinions and Conjectures con-
cerning the Properties and Effects of Electrical Matter
arising from Experiments and Observations made at Phil-
adelphia, 1749':
"(1) The electrical matter consists of particles ex-
tremely subtile, since it can permeate common mat-
ter, even the densest metals, with such ease and free-
dom as not to receive any perceptible resistance.
"(2) If any one should doubt whether the electrical
matter passes through the substance of bodies, or only
over and along their surfaces, a shock from an elec-
trified large glass jar, taken through his own body,
will probably convince him.
"(3) Electrical matter differs from common matter
in this, that the parts of the latter mutually attract,
those of the former mutually repel each other. Hence
the appearing divergency in a stream of electrified
effluvia.
"(4) But tho the particles of electrical matter do
repel each other, they are strongly attracted by all
other matter.
"(5) From these three things, the extreme subtilty
of the electrical matter, the mutual repulsion of its
parts, and the strong attraction between them and
other matter, arise this effect, that when a quantity
of electrical matter is applied to a mass of common
matter, of any bigness or length, within our obser-
vation (which hath not already got its quantity), it is
immediately and equally diffused through the whole.
"(6) The common matter is a kind of sponge to the
144 ELECTRICITY
electrical fluid. And as a sponge would receive no
water if the parts of water were not smaller than the
pores of the sponge, and even then but slowly, if there
were not a mutual attraction between those parts and
the parts of the sponge ; and .would imbibe it still fast-
er if the mutual attraction among the parts of the
water did not impede, some force being required to
separate them; and fastest, if, instead of attraction,
there were a mutual repulsion among those parts
which would act in conjunction with the attraction of
the sponge — so is the case between electrical and
common matter.
"(7) But in the common matter there is (generally)
as much of the electrical as it will contain within its
substance. If more is added, it lies without upon the
surface, and forms what we call an electrical atmos-
phere, and the body is said to be electrified.
"(8) 'Tis supposed that all kinds of common matter
do not attract and retain the electrical with equal
strength and force, for reasons to be given hereafter.
And that those called electrics per se, as glass, etc.,
attract and retain it strongest and contain the great-
est quantity.
"(9) We know that the electrical fluid is in common
matter because we can pump it out by the globe or
tube. We know that common matter has near as
much as it can contain because when we add a little
more to any portion of it, the additional quantity does
not enter but forms an electrical atmosphere. And
we know that common matter has not (generally)
more than it can contain, otherwise all loose portions
of it would repel each other as they constantly do
when they have electric atmospheres. . . .
"(15) The form of the electrical atmosphere is that
of the body it surrounds."
Such are the essential parts of Franklin's primitive
theory, propounded for the purpose of giving a consistent
NATURE AND FORCE MS
account of the phenomena of electric attraction and re-
pulsion so far as they were known in his time. It ip curi-
ous to observe how some of his ideas were quite in keep-
ing with the latest theory — the electron theory — described
later.
Various theories were propounded from time to time for
a long time after the enunciation of the single and two
fluid theories, but none served better as a working basis.
In the latter part of the nineteenth century, however, a
new theory dealing with electricity as obeying the laws
of mechanics was formulated by Clerk Maxwell, the great
English physicist. Maxwell's ideas were founded on the
observations made by Faraday, who discovered that the
nature of the insulating material, or dielectric, between
the plates of a condenser had a great deal to do with the
quantity of electricity which would flow into it under the
influence of a given electromotive force. This fact led
Maxwell to believe that the dielectric was the real seat of
the charge, that the conductor acted merely to distribute
the charge over the different portions of the dielectric in
contact with it. When a flow of current takes place along
a wire it is due to the differences existing in the dielectric
about the wire. The following extract from 'Maxwell's
Theory and Hertzian Oscillations,' by H. Poincare, trans-
lated by Frederick K. Vreeland, may serve to give some
idea of the action in and about an electric circuit.
"If we undertake to compress a spring," he says, "we
encounter an opposing force which increases as the spring
yields to the pressure. If, now, we can exert only a lim-
ited pressure, a moment will arrive when we can no longer
overcome the reacting force; the movement will cease, and
equilibrium will be established. Finally, when the pres-
sure is removed, the spring will regain its original form,
giving back all the energy that was expended in compress-
ing it
"Suppose, on the other hand, that we wish to move a
body immersed in water. Here again we encounter a re-
146
ELECTRICITY
action, which depends upon the velocity, but which, if the
velocity remain constant, does not go on increasing as the
body yields to the pressure. The motion will thus continue
as long as the motive force acts, and equilibrium will
never be established. Finally, when the force is removed,
the body does not tend to return to the starting point, and
the energy expended in removing it cannot be restored ; it
Fig. 1 — Model Illustrating Flow of a Displacement Current.
The pressure in the vessel represents the voltage of the battery ;
the height of the column, the displacement in the dielectric ;
the flow of water, the charging current. The energy ex-
pended may be recovered.
has been completely transformed into heat through the
viscosity of the water.
"The contrast is manifest, and it is important to dis-
tinguish between elastic reaction and viscous reaction.
Now, the dielectrics behave toward the motion of elec-
tricity as elastic solids do toward the motion of matter,
while the conductors behave like viscous liquids. Hence
there are two kinds of currents : the displacement currents
of Maxwell, which traverse the dielectrics, and the ordi-
nary conduction currents which flow in conductors.
NATURE AND FORCE
147
"The former, having to overcome a sort of elastic re-
action, must be of short duration, for this reaction in-
creases as long as the current continues to flow and equi-
librium must soon be established.
"Conduction currents, on the other hand, must overcome
a sort of viscous resistance, and hence may continue as
long as the electromotive force which produces them.
"To take a hydraulic analogy, suppose that we have
a closed vessel containing water under pressure. If we
put this vessel in communication with a vertical pipe, the
Fig.
-Model Illustrating the Flow of a Conduction
Current.
The flow continues undiminished as long as the pressure is main-
tained. The energy expended in friction takes the form of
heat and is lost. (From Vreeland & Poincare, Maxwell's
Theory.)
water will rise in it, but the flow will cease when the
hydrostatic equilibrium is established. If the pipe be
large, there will be no appreciable friction nor loss of
head, and the water thus raised may be used to do work.
We have here an illustration of displacement currents.
"If, on the other hand, the water be allowed to run
out through a horizontal pipe (Fig. 2), the flow will con-
tinue as long as there is water in the reservoir ; but if the
pipe be small, there will be a considerable less of energy,
and heat will be produced by the friction. This illustrates
the action of conduction currents.
"Altho it is impossible and unnecessary to try to im-
148
ELECTRICITY
agine all the details of the mechanism, we may say that all
takes place as if the displacement currents had the effect of
compressing a multitude of minute springs.
■'When the currents cease, electrostatic equilibrium is
established; and the tension of the spring depends upon
the intensity of the electrostatic field. The energy accu-
mulated in these springs — that is, the electrostatic energy
of the field — may be restored whenever they are allowed to
unbend; and it is thus that mechanical work is produced
Fig. 3 — Old and New Ideas of the Charging of a Condenser.
Formerly the electricity was supposed to accumulate on the sur-
face o,f the plates as shown by the dotted lines. The circuit
was considered unclosed. Maxwell assumes that the current
does not stop at the surface of the conductor, but continues
to flow through the dielectric until checked by the elastic re-
action. The circuit is thus completed. (From Vreeland &
Poincare, Maxwell's Theory.)
when charged conductors are allowed to obey their elec-
trostatic attractions. These attractions are thus due to
the pressure exerted on the conductors by the compressed
springs. Finally, to pursue the analogy to the end, a dis-
ruptive discharge may be attributed to the breaking of
some springs which are unable to stand the strain.
"On the other hand, the energy expended in producing
conduction currents is lost, and converted into heat, like
the work done in overcoming friction or the viscosity of
NATURE AND FORCE 149
fluids. This is why a conductor is heated by the passage
of a current.
"From Maxwell's point of view, none but closed cur-
rents exist. To the early electricians this was not the
case. They considered as closed the current which cir-
culates in a wire joining the two terminals of a battery.
But if, instead of joining these terminals directly, they
were connected respectively to the two plates of a con-
denser, the momentary current which flowed while the
condenser was being charged was considered as unclosed.
It flowed, they said, from one plate to the other through
the wire connected to the battery, and stopped at the sur-
faces of the plates. Maxwell, on the contrary, considers
that the current continues, in the form of a displacement
current, across the insulating layer which separates the
plates, and is thus completely closed. The elastic reaction
which the current encounters in traversing the dielectric
explains its short duration.
"Currents may manifest themselves in three ways: by
their heatinj effects, by their action on magnets and on
other currents, by the induced currents which they gen-
erate. We have seen above why conduction currents pro-
duce heat and displacement currents do not. Yet, accord-
ing to Maxwell's hypothesis, the currents which he im-
agines should, like ordinary currents, produce electromag-
netic, electrodynamic, and inductive effects.
"Why could these effects not be observed? Because a
displacement current, however feeble, cannot continue
long in one direction ; for the tension of our hypothetical
springs, continually increasing, will soon check it Thus
we cannot have in a dielectric either a continuous current
of long duration or a sensible alternating current of long
period; but the effects should be observable if the alterna-
tions are very rapid.
"And here wt have, according to Maxwell, the origitt
of light: A light wave is a series of alternating currents,
flowing in a dielectric, in the air, or in interplanetary
150 ELECTRICITY
space, changing their direction 1,000,000,000,000,000 tii >es
in a second. The enormous inductive effect of these rapid
alternations produces other currents in the neighboring
portions of the dielectric, and thus the light waves are
propagated from place to place. -The velocity of propa-
gation may be known analytically to be equal to the ratio
of the units — that is, to the velocity of light.
"These alternating currents are a kind of electrical
vibration ; but are they longitudinal, like those of sound, or
transverse, like those of FresneFs ether? In the case of
sound, the air undergoes alternate condensations and rare-
factions; but the ether of Fresnel acts as if it were com-
posed of incompressible layers capable only of sliding
upon each other. If the currents flowed in unclosed cir-
cuits, the electricity would necessarily accumulate at one
end or the other of the circuits, and we should have a con-
dition analogous to the condensations and rarefactions of
air; the vibrations would be longitudinal. But, as Max-
well admits only closed currents, those accumulations are
impossible, and the electricity must behave like the incom-
pressible ether of Fresnel: its vibrations must be trans-
verse.
"Thus we reach all the conclusions of the wave theory
of light. This, however, was not enough to enable the
physicists, who were attracted rather than convinced, to
accept absolutely Maxwell's ideas: all that could be said
in their favor was that they did not conflict with any
known facts, and that it were indeed a pity if they were
not true. The experimental confirmation was lacking, and
remained so for twenty-five years.
"It was necessary to find, between the old theory and
that of Maxwell, a discrepancy not too minute for our
crude methods of observation. There was only one such
from which an experimentum crucis could be derived. To
do this was the work of Hertz."
Maxwell's electromagnetic theory, which led to the
recognition of light as an electrical phenomenon and to
NATURE AND FORCE 151
many other grand generalizations, was more a mathemati-
cal than a physical theory. What it chiefly accomplished
was to express, in mathematical language, the experi-
mental results of Faraday. Maxwell, however, avoided
giving any description of the molecular constitution of
the media through which electrical energy was trans-
mitted.
Professor Fleming, in his pamphlet on the "Electronic
Theory," says:
"It seems tolerably clear from all the facts of electroly-
sis that electricity can only pass through a conducting
liquid or electrolyte by being carried on atoms or groups
of atoms which are called ions — i.e., wanderers. The
quantity thus carried by a hydrogen atom or other monad
element, such as sodium, silver, or potassium, is a definite
natural unit of electricity. The quantity carried by any
other atom or group of atoms acting as an ion is always
an exact integer multiple of this natural unit. This small
indivisible quantity of electricity has been called by Dr.
Johnstone Stoney an electron or atom of electricity. The
artificial or conventional unit of electric quantity in the
centimeter-gram-second system, as defined by the Brit-
ish Association Committee on Electrical Units, is as fol-
lows:
" 'An electrostatic unit of electric quantity is the charge
which, when placed upon a very small sphere, repels an-
other similarly charged sphere, the centers being one cen-
timeter apart, with a mechanical force of one dyne. The
dyne is a mechanical unit of force, and is that force which,
acting for one second on a mass of one gram, gives it a
velocity of one centimeter per second. Hence, by the law
of inverse squares the force in dynes exerted by two equal
charges Q at a distance D is equal to Q2/D2. Two other
units of electric quantity are in use — the electromagnetic
unit, which is thirty thousand million times as great as
the electrostatic unit, and the practical unit called the
coulomb or ampere-second, which is three thou&and mil-
152 ELECTRICITY
Hon times the electrostatic unit. We can calculate easily
the relation between the electron and the coulomb — that is,
between Nature's unit of electricity and the British Asso-
ciation unit — as follows:
" 'If we electrolyze any electrolyte, say acidified water,
which yields up hydrogen at a negative electrode, we find
that to evolve one cubic centimeter of hydrogen at o° C.
and 760 mm., we have to pass through the electrolyte a
quantity of electricity equal to 8.62 coulombs. For 96,540
coulombs are required to evolve one gram of hydrogen and
11,200 cubic centimeters at o° C. and atmospheric pressure
weigh one gram. The number 8.62 is the quotient of 96,-
540 by 11,200.
" 'From various sources calculations indicate that the
number of molecules of hydrogen in a cubic centimeter is
probably best represented by the number twenty million
million million=2 X iq19' Hence it follows, since there are
two atoms of hydrogen in a molecule, that in electrostatic
units the electric charge on a hydrogen atom or hydrogen
ion is
96540 w 3 ^ I0?a = 65„ of a C. G. S. electrostatic unit = 22,n of a coulomb.
11200X4X1019 IO11 1020
" 'Accordingly, if the above atomic charge is called one
electron, then the conventional British Association elec-
trostatic unit of electric quantity is equal to 1,540 million
electrons, and the quantity called a coulomb is nearly five
million million million electrons. The electron or the elec-
tric charge by a hydrogen atom or ion is evidently a very
important physical constant.'
"It is, in fact, Nature's unit, from which all other physi-
cal units may be brought into agreement with natural
quantities. And thus we see that electricity is atomic in
nature and in structure; that is to say, we can have it only
in amounts which are all exact multiples of a certain unit,
which unit cannot be subdivided, and 1,540 millions of
these units equal one coulomb.
"For long it was held that the atom of matter was the
NATURE AND FORCE 153
smallest particle in nature and indivisible, but now we
must assume that atoms are composed by smaller particles.
We are compelled by all the known facts to admit that
Professor Crookes was right when he declared the cathode
rays to be a stream of matter shot from the cathode.
Professor J. J. Thomson, by measuring the deflection of
the stream (of 'radiant matter/ as Crookes called it) in a
known magnetic field, shows that, if the radiant matter
consists of corpuscles or particles, each carries a charge
of one 'electron,' and has a mass of about x/iooo of a hy-
drogen atom, and their velocity is from y$ to y$ the veloc-
ity of light.
"So far as the effects in high vacua are concerned, Pro-
fessor Crookes discovered all we know about cathode
rays, but Lenard conceived the idea that these rays could
penetrate the walls of the vessel containing the vacuum,
and by inserting a window of aluminium in the vessel he
found the rays penetrated the aluminium and that they are
active outside the vessel as they are inside.
"Electrons are found in the mass of gas through which
Rontgen rays have passed. Rontgen discovered that if the
rays from the cathode struck a conductor in the vacuum
bulb, that they penetrated the glass bulb enclosing the
vacuum, and that they also penetrate many opaque bodies
outside, and produce photographs on active plates.
"The atom, it seems, can be divided into two parts of
very unequal size. The small part is negatively electrified,
and is always the same, no matter from what chemical
atom it comes. The remaining larger part is positively1
electrified, but is different in nature, depending on the ele-
mentary atom broken up. It is not settled whether the
particle and its negative charge are separable. It is, how-
ever, becoming common to speak of the two together as
the 'electron.'
"From this point of view the theory of electricity origi-
nates is called the electronic theory. The principal objects
of consideration in this theory are these electrons which
i54 ELECTRICITY
constitute what we call electricity. An atom of matter in
its neutral condition has been assumed to consist of an
outer shell or envelope of negative electrons associated
with some core or matrix which has an opposite electrical
quality, such that if an electron is withdrawn from the
atom the latter is left positively electrified.
"A neutral atom minus an electron constitutes the nat-
ural unit of positive electricity, and the electron and the
neutral atom minus an electron are sometimes called nega-
tive and positive ions. Deferring for a moment a further
analysis of possible atomic structure, we may say that,
with the above hypothesis in hand, we have then to ex-
press our statements of electrical facts in terms of the
electron as the fundamental idea.
"On this theory the difference between conductors and
non-conductors is accounted for by assuming that an elec-
tric current is a procession of electrons, so that a con-
ductor is a substance through which electrons can easily
move; in non-conductors the electrons may be moved, or
vibrated, or displaced to some extent, but spring back
again into their former place.
"The electronic or any theory must account for the
waves set up in the ether around a variable current. This
is explained on the hypothesis that a moving or vibrating
electron, while its motion is being accelerated or reduced,
radiates ethereal waves, and that a flying column of elec-
trons produces a magnetic field in circles round the moving
electrons as a center."
The electron theory has not yet been fully developed.
Many things about it are not clear, but most scientists are
agreed upon the existence of the electron and are awaiting
the results of further experiments to help them decide
upon its exact nature and behavior.
CHAPTER II
ELECTROSTATICS — ATMOSPHERIC ELECTRICITY
In the early days of electrical science many of the ex-
periments in electrostatics were developed which still
form a considerable part of the course usually taught in
present-day schools. The attraction of amber when
rubbed for light bodies was known to the ancient Greeks
as long ago as 600 B.C. About the year 1600, Gilbert, who
had made several discoveries concerning the properties of
the magnet, discovered in glass, sulphur, resin and various
precious stones the same attractive power known to be
possessed by amber. From that time innumerable physi-
cists have extended Gilbert's discoveries and have found a
great number of curious phenomena previously entirely
unknown, and in this way have contributed to found that
branch of physics which, under the name of Electricity,
has attained such important dimensions in modern times.
"If he had used a ball of glass or sulphur previously;
rubbed," sugests Guillemin, "he would have known of the
reciprocity of attraction in the same way as he had shown
that soft iron attracts a magnet. But Gilbert greatly ex-
tended the list of bodies capable, like amber, of being elec-
trified by friction; to those that we have already men-
tioned he added shellac, rock salt, alum and rock crystal.
He also found that electrical attraction took place not
only between light bodies, but between certain solid bodies,
drops of liquids, gaseous bodies, and dense vapors. Again,
he discovered the influence of atmospheric conditions on
electric phenomena.
i55
156 ELECTRICITY
"Boyle discovered the reciprocity of attraction between
non-electrified bcdies and electrified bodies. A very sim-
ple experiment, on the mechanical principle of action and
reaction being equal and opposite, led to this discovery-
On a pivot was placed a small shellac needle electrified by
being rubbed by catskin. Then, on holding his finger near
one end, he found the needle drawn toward his finger.
Otto von Guericke, who made the first frictional electrical
machine, was the first to observe the phenomena of repul-
sion, and he also drew from the globe of sulphur of his
machine visible sparks, accompanied by a crisp crackling
sound, which was in fact the noise of the electric dis-
charge. Here we had for the first time in these early
experiments the production of sparks similar to those
which constitute the electric arc ; tho it is a long step from
these feeble sparks to the dazzling splendor of the electric
light. The experiments of the celebrated burgomaster of
Magdeburg date from the middle of the seventeenth cen-
tury. At the commencement of the eighteenth century,
that was to witness such brilliant discoveries in electricity,
Dr. Wall succeeded in producing most vivid sparks and far
louder crackling; he also had some ideas of the great dis-
covery which made Franklin so celebrated. 'This light
and that crackling,' said he, 'are the same thing as thun-
der and lightning.' The analogy was indeed striking, and
it was not long before it was verified and confirmed.
"Numerous observations on the electrical phenomena
were due to Hauksbee. Among them are very interesting
experiments on the light which is produced in a vacuum
or in a rarefied medium when one introduces some bodies
into it, and develops on their surface electricity by fric-
tion ; or when one excites the exterior of a globe of glass,
the interior of which is a vacuum.
"He observed in particular the effect of heat on the de-
velopment of both attractive and repulsive forces. The
attractions and repulsions of pieces of tinsel by a tube of
glass, rubbed with paper, were found to be more energetic
ELECTROSTATICS 157
when the glass had been heated by friction. The effects
of moisture and warmth that Gilbert had discovered were
proved beyond doubt by the experiments of Hauksbee,'
Dufay and Gray. The following passage occurs in Hauks-
bee's Physico-Mechanical Experiments: 'When the tube
became hottest by the strongest Attrition, the Force of the
Effluvia was rendered manifest to another Sense too,
namely, that of feeling. They did not then only produce
all the forementioned Effects in a more remarkable man-
ner, but were also plainly to be felt upon the Face, or any
other tender part, if the rubbed Tube was held near it.
And they seemed to make very nearly such sort of stroaks
upon the Skin, as a number of fine limber Hairs pushing
against it might be supposed to do/
"The discovery of electrical conductivity was made in
the early part of the eighteenth century by Stephen Gray.
While looking for the reason of the difference between
the two classes he came upon the general fact that all
bodies, without exception, are capable of being electrified,
but that the circumstances must be varied to suit the sub-
stances.
"Let us rapidly review the points that led Gray to this
important discovery. Having electrified a piece of glass
tube, the ends of which were stopped with corks, he was
surprised to find that the corks, which he had not rubbed,
picked up light bodies just as the tube itself did, showing
that the electricity passed from the glass to the cork.
Gray followed up this experiment by lengthening the corks
with sticks of ivory, wood or metal, yet he had the same
phenomena even with stems which ended in a ball of
ivory. Hung from a balcony by a long cord fastened to
the tube the ball still was electrified. He then varied his
experiment to greater and greater distances, until he
found the same effect at the end of a cord 765 feet long.
But Gray found that in order to succeed, certain condi-
tions had to be fulfilled; the cord which carried the elec-
tricity had to be suspended by silk strings, as he found
158
ELECTRICITY
that he got no electrification at all if he suspended it by-
means of metal wires.
"One more experiment of Gray's that was soon repeated
in all laboratories was to show that the human body con-
ducts electricity. It explains the impossibility that had
always been found in trying to electrify such substances
as the metals. Having suspended a child by hair cords,
and having touched him with his electrified tube, he found
that all parts of the child's body had acquired the power
Fig. 4 — The Conductivity of the Human Body :
Experiment.
Gray's
of attracting light bodies. The same effect was produced
when the child stood on a cake of an 'electric' substance,
such as resin, as was produced when he was suspended by
the hair cords. From these experiments, which were then
varied in innumerable ways, two very important conclu-
sions were drawn.
"The first, that electricity obtained by friction could be
transmitted to a distance through any substance that could
not itself be electrified; the second, a corollary to the first,
that this transmission is impossible, or very difficult, if the
transmitting body is one of those capable of being electri-
fied by the method described above.
ELECTROSTATICS 159
"We quoted above Gray's first experiment, which estab-
lished the electrical conductivity of the body. It was a
French physician, Dufay, a member of the Academy of
Sciences, who drew the first spark from the human body.
'Being suspended by silk cords, he found, when electrified,
that, if any one brought his knuckle near to him, he felt
a stinging sensation like a pin-prick, also that the person's
knuckle felt the same sensation. When the experiment
was performed in the dark a little spark was observed.'
"Gray took up the experiments of Dufay and in his turn
found that he could draw sparks from any insulated body
which had been put into contact with rubbed glass; if these
bodies terminated in a point a small luminous cone was
seen, accompanied by a slight noise. In reference to this
Gray repeated Wall's comparison between the spark fol-
lowed by the crackling sound and the lightning followed by
thunder."
Newton's grand discovery of the law of the universal
attraction of matter, when he showed that the force was
proportional to the mass and that it varied in the inverse
ratio of the square of the distance, incited the physicists
of the eighteenth century to discover the law which gov-
erned the strength of electrical forces. Dufay, Hauksbee,
Muschenbroek, /Epinus, and Cavendish were all more or
less instrumental in attaining this end; but we are in-
debted to Coulomb for an exact experimental demonstra-
tion of these laws. Coulomb used for this purpose a simi-
lar apparatus to the magnetic balance. From the figure it
will be seen that it consisted of two spheres so arranged
that they could be charged and the force of repulsion be-
tween them balanced by the torsion of the suspension.
By means of this instrument Coulomb was able to prove
the two laws of electrical attraction:
1. The repulsion between two electrified bodies charged
with the same electricity varies inversely as the square of
the distance between them.
2. The attractions and repulsions vary in the ratio of
i6o
ELECTRICITY
the products of the quantities of free electricity — that is to
say, of the electric charges of the two bodies.
The action of points on metallic conductors in increas-
ing the density of the charge at the point received the at-
tention of Franklin. The following quotation from his
"Experiments and Observations on Electricity, made at
Philadelphia, 1774," describes Franklin's own experiments
on this subject:
Fig. 5 — Coulomb's Method of Proving Electrostatic Laws.
"Place an iron shot of three or four inches diameter on
the mouth of a clean, dry glass bottle. By a fine silken
thread from the ceiling, right over the mouth of the bottle,
suspend a small cork ball, about the bigness of a marble;
the thread of such a length as that the cork ball may rest
against the side of the shot. Electrify the shot, and the
ball will be repelled to the distance of four or five inches,
more or less, according to the quantity of electricity ^
When in this state, if you present to the shot the point of
a long, slender, sharp bodkin, at six or eight inches dis-
ELECTROSTATICS
161
tance, the repellency is instantly destroyed and the cork
flies to the shot. A blunt body must be brought within an
inch and draw a spark to produce the same effect.
"To prove that the electrical fire is drawn off by the
point, if you take the blade of the bodkin out of the
wooden handle and fix it in a stick of sealing-wax, and
then present it at the distance aforesaid, or if you bring it
very near, no such effect follows; but sliding one finger
•Franklin's Experiment on the Action of Points.
along the wax till you touch the blade, and the ball flies
to the shot immediately. If you present the point in the
dark you will see, sometimes at a foot distance and more,
a light gather upon it, like that of a firefly or glowworm;
the less sharp the point the nearer must you bring it to
observe the light; and at whatever distance you see the
light, you may draw off the electrical fire and destroy the
repellency. If a cork ball so suspended be repelled by the
tube, and a point be presented quick to it, 'tis surprising to
1 62
ELECTRICITY
see how suddenly it flies back to the tube. Points of wood
will do near as well as those of iron, provided the wood is
not dry; for perfectly dry wood will no more conduct
electricity than sealing-wax.
"It is calculated that the density of electricity at an
Fig. 7 — Action of Points : Electric Wind.
infinitesimally fine point would be infinitely great, since
it is impossible to charge a pointed conductor in the air
with electricity ; this is proved by experiment. As fast as
electrification is produced, it is given off the point into
the air and disappears. When we examine the extremity
of a point in the dark, there is seen a luminous crest. If,
while the point is in communication with the source of
electrification, one places one's hand before it, a draft
ELECTROSTATICS 163
is at once perceptible, arising from the motions of the
particles of air. This can be still better shown by holding
a candle-flame in front of a long-pointed conductor. The
electric wind is sufficient to bend the flame sharply down,
or even to put it out.
"This movement of the air at the points on electrified
conductors has always been attributed to the accumulation
of electricity, which has been compared to a fluid; but the
following explanation seems to us preferable, as it in-
volves no hypothesis on the nature of electricity, and, be-
sides, it is found to agree with known phenomena. The
molecules of air, in contact with a point electrified to a
great electric density, become charged with the same elec-
trification as the conductor itself. Hence the nearest!
molecules are repelled and others fill their place, which
become electrified in their turn, and so on. Hence the
current of air, which only lasts as long as the electricity is
being supplied. It can be stopped by putting a cap of
sealing-wax over the point."
The explanation of the attraction of an electrified body
for an unelectrified one was not well understood until
the middle of the eighteenth century. John Canton, of
Stroud, seems to have been the first to give the true ex-
planation. His apparatus was similar to that shown in
Fig. 8. If the sphere C be charged with a positive charge
of electricity the end A of the cylinder, which is nearest to
the sphere, will be charged negatively, the other end B
will be charged positively. We can prove this if we bring
an electrified pendulum near to each end in turn. Suppose
the little ball to be charged positively, it is found to be
attracted to the end A when brought carefully toward
it, but when brought toward the end B it is repelled.
The reverse would be the case if the sphere C were
charged negatively.
It may be well here to point out the difference between
a conductor and a dielectric, or non-conductor. A con-
ductor merely connects different parts of the dielectric
164
ELECTRICITY
which surrounds it and with which it is in contact. If,
therefore, this dielectric be suddenly charged in one place
this charge cannot remain at that place because it is in
contact with the conductor, but must flow into the conduc-
tor, along it, and then out into the dielectric surrounding-
it, and this takes places at every point of contact between
the conductor and the dielectric. The office of the conduc-
tor, then, is to distribute the charge to the dielectric. If the
conductor be spherical in shape and there is no other
charge near by, the dielectric will be charged uniformly;
Electrification by Influence.
all about the sphere. If the conductor tapers to a point,
the charge in the dielectric will be most intense about}
the point. Or if the charge about the sphere is influenced
by a neighboring charge, the conducting sphere allows it
to move as the charged body may dictate.
This principle of electrical influence was soon made use
of in constructing a machine for the production of electric
charges and which was the forerunner of the modern
electrical influence machine. This was the electrophorus
of Volta, who gave it the name of "perpetual electro-
phorus" because it preserves for a long time the charges
that it has received.
ELECTROSTATICS 165
"It consists of two parts : a cake of insulating material,
such as resin, sulphur or india-rubber, cast into a wooden
or metal tray, and a metal disk fixed to an insulating
handle of glass or to silk cords. Frequently the disk
is of smaller diameter than the cake, and sometimes it
is made not of metal but of wood, covered on both edge
and faces with tinfoil.
"To use the electrophorus, remove the metal disk and
rub the insulating cake with flannel, woolen cloth or fur.
best of all with a catskin. This produces negative elec-
trification on the resinous cake. This you may prove if
you bring your finger near the cake, for you will observe
small sparks and crackling sounds. Now take the metal
disk by the insulating handle and place it on the rubbed
insulating cake.
"Now pause a moment : let us think what has happened
in this action. While you were putting down the lid on
the cake, even before it touched the cake, it was under,
influence. The cake is negative, hence as you hold the
lid over it there will be a displacement and a rush of elec-
tricity in the lid, causing a positive charge to accumulate
on the lower side, leaving the upper side negative. This
effect will of course increase as the disk is lowered. It
will be noticed that the metal dish in which the cake
stands is also under influence ; but this is of no importance.
"You must now touch with your finger the top of
the lid. Your finger will also be under influence dur-
ing this action, a + charge accumulating on its tip
and then discharging itself with a small spark to fill up
and neutralize the — charge on the top surface. Now lift
up the lid by the handle. You will find that it is positively
electrified, and you can carry away the charge and use
it to give a big spark to any other conductor. You can
then put the lid down again on the cake, touch it, lift it up
again and take another spark as often as you please, the
cake remaining all the time charged with its original
166 ELECTRICITY
charge. The length of spark is roughly proportional to
the size of the electrophorus.
"Mascart in his treatise says that Lichtenberg con-
structed an electrophorus with a cake six feet across and
the disk was five feet across, and. the sparks drawn from
it fourteen to sixteen inches long. Another very large
electrophorus was made by Kleindworth for the Univer-
sity of Gottingen; the cake of resin was 2.25 meters in
diameter and the conducting disk 2 meters.
"The cake sometimes preserves its charge for months,
if it be kept in a cupboard where the air is perfectly dry.
We have said that the insulating cake of the electrophorus
is made of resin, sulphur or india-rubber. All good in-
sulators can be used; mixtures of these substances are
generally used in order to make the cake less brittle."
A short description of the principal static machines
which have been developed is taken from Professor S. P.
Thompson's 'Elementary Lessons in Electricity and Mag-
netism.'
"For the purpose of procuring larger supplies of elec-
tricity than can be obtained by the rubbing of a rod of
glass or shellac, electric machines have been devised. All
electric machines consist of two parts, one for producing,
the other for collecting, the electric charges. Experience
has shown that the quantities of -f- and — electrification
developed by friction upon the two surfaces rubbed against
one another depend on the amount of friction, upon the
extent of the surfaces rubbed, and also upon the nature
of the substances used.
"The earliest form of electric machine was devised by
Otto von Guericke of Magdeburg, and consisted of a globe
of sulphur fixed upon a spindle, and pressed with the dry
surface of the hands while being made to rotate; with this
he discovered the existence of electric sparks and the
repulsion of similarly electrified bodies. Sir Isaac New-
ton replaced Von Guericke's globe of sulphur by a globe
of glass. A little later the form of the machine was im-
ELECTROSTATICS 167
proved by various German electricians; Von Bose added
a collector or "prime conductor," in the shape of an iron
tube, supported by a person standing on cakes of resin to
insulate them, or suspended by silken strings ; Winckler of
Leipzig substituted a leathern cushion for the hand as a
rubber ; and Gordon of Erfurt rendered the machine more
easy of construction by using a glass cylinder instead of a
glass globe. The electricity was led from the excited
cylinder or globe to the prime conductor by a metallic
chain which hung over against the globe. A pointed col-
lector was not employed until after Franklin's famous re-
searches on the action of points. About 1760 De la Fond,
Planta, Ramsden and Cuthbertson constructed machines
having glass plates instead of cylinders. All frictional
machines are, however, now obsolete, having in recent
years been quite superseded by the modern influence ma-
chines.
"The cylinder electric machine consists of a glass cylin-
der mounted on a horizontal axis capable of being turned
by a handle. Against it is pressed from behind a cushion
of leather stuffed with horsehair, the surface of which is
covered with a powdered amalgam of zinc or tin. A flap
of silk attached to the cushion passes over the cylinder,
covering its upper half. In front of the cylinder stands
the "prime conductor," which is made of metal, and usually
of the form of an elongated cylinder with hemispherical
ends, mounted upon a glass stand. At the end of the prime
conductor nearest the cylinder is fixed a rod bearing a row
of fine metallic spikes, resembling in form a rake; the
other end usually carries a rod terminated in a brass ball
or knob. When the handle is turned the friction between
the glass and the amalgam-coated surface of the rubber
produces a copious electrical action, electricity appearing
as a + charge on the glass, leaving the rubber with a —
charge. The prime conductor collects this charge by the
following process : The -f- charge being carried round on
the glass acts inductively on the long insulated conductor,
168 ELECTRICITY
repelling a + charge to the far end; leaving the nearer
end — ly charged. The effect of the row of points is to
emit a — ly electrified wind toward the attracting -j-
charge upon the glass, which is neutralized thereby; the
glass thus arriving at the rubber in a neutral condition
ready to be again excited. This action of the points is
sometimes described, tho less correctly, by saying that the
points collect the -f- charge from the glass. If it is desired
to collect also the — charge of the rubber, the cushion
must be supported on an insulating stem and provided at
the back with a metallic knob. It is, however, more usual
to use only the -f- charge, and to connect the rubber by a
chain to "earth," so allowing the — charge to be neutral-
ized.
"The friction of a jet of steam issuing from a boiler,
through a wooden nozzle, generates electricity. In reality
it is the particles of condensed water in the jet which are
directly concerned. Sir W. Armstrong, who investigated
this source of electricity, constructed a powerful apparatus,
known as the hydro-electrical machine, capable of produc-
ing enormous quantities of electricity, and yielding sparks
5 or 6 feet long. The collector consisted of a row of
spikes, placed in the path of the steam jets issuing from
wooden nozzles, and was supported, together with a brass
ball which served as prime conductor, upon a glass
pillar."
After the invention of the electrophorus by Volta, the
idea naturally suggested itself of performing mechanically
the several operations of bringing the plate near the
charged bed, of touching its upper side, and of removing it
to a. large metallic body where the charge could be stored.
One of the first of these mechanical arrangements was
the revolving doubler of Nicholson, invented in 1788, con-
sisting of a revolving apparatus in which an insulated
carrier can be brought into the presence of an electrified
body, there touched for an instant while under influence,
then carried forward with its acquired charge toward an-
ELECTROSTATICS 169
other body, to which it imparts its charge, and which in
turn acts inductively on it, giving it an opposite charge,
which it can convey to the first body, thus increasing its
initial charge at every rotation.
"In the modern influence machines two principles are
embodied: (1) The principle of influence, namely, that a
conductor touched while under influence acquires a charge
of the opposite kind; (2) the principle of reciprocal ac-
cumulation. This principle must be carefully noted. Let
there be two insulated conductors A and B electrified ever
so little, one positively, the other negatively. Let a third
insulated conductor C, which will be called a carrier, be
arranged to move so that it first approaches A and then
B, and so forth. If touched while under the influence of
the small positive charge on A it will acquire a small
negative charge; suppose that it then moves on and gives
this negative charge to B. Then let it be touched while
under the influence of B, so acquiring a small positive
charge. When it returns toward A let it give up this posi-
tive charge to A, thereby increasing its positive charge.
Then A will act more powerfully, and on repeating the
former operations both B and A will become more highly
charged. Each accumulates the charges derived by in-
fluence from the other. This is the fundamental action of
the machines in question. The modern influence machines
date from i860, when C. F. Varley produced a form with
six carriers mounted on a rotating disk of glass. This
was followed in 1865 by the machine of Holtz and that of
Toepler, and in 1867 by those of Lord Kelvin (the "re-
plenisher" and the "mouse-mill"). The latest forms are
those of Mr. James Wimshurst."
At the present time these machines are used to a limited
extent as a source of high voltages for such work as oper-
ating vacuum tubes, X-ray apparatus, and the like; but
their uncertainty of action, small power and the irregular-
ity of their discharge make the high-tensicn transformer
or Ruhmkorf coil preferable.
170 ELECTRICITY
Cuneus, a pupil of Muschenbroek, a celebrated physicist
of the eighteenth century, was one day trying to electrify
some water in a wide-necked bottle. For this purpose he
held the bottle in one hand, after having placed in the
bottle a metal rod connected to. the machine. When he
thought the water was sufficiently electrified, he tried to
remove the iron rod with one hand without loosing his
hold of the bottle with the other hand. He received a
shock that surprised him. Muschenbroek repeated Cuneus'
experiment, but the shock that he received in his arms,
shoulders and chest was so great that he lost consciousness
and was so frightened that in writing to Reaumur about
this then new discovery, he wrote that for nothing in the
world, not even for the crown of France, would he go
through it again. But some other physicists were less
fearful. Allaman, Lemoinnier, Winckler and the Abbe
Nollet varied the experiment in all sorts of ways, and so
a new piece of apparatus was added to electrical science.
This apparatus, called the Leyden jar, is named after the
place where the experiment was first performed in 1746.
The Leyden jar is only a form of electric condenser, the
essential properties of which have already been explained
in connection with Maxwell's theory.
It is again to Franklin that science is indebted for an
experiment which shows where the charge in such a jar
resides. Franklin constructed a Leyden jar having both
internal and external metallic coatings removable. Having
fitted them to the jar, he connected the inner coating with
an electrical machine and the outer coating with the earth
and charged the jar in the usual manner. He then sepa-
rated the metallic coatings and the jar, and examining each
one for electrification, he found the metallic coatings prac-
tically unelectrified, while the glass jar proved to be highly
electrified. Upon replacing the coatings in the jar, he
was able to obtain a bright spark, just as tho the coatings
had not been removed. This experiment clearly proved
that the important part of such a Leyden jar or condenser
ELECTROSTATICS
171
was the glass or dielectric and that the function of the
conducting coatings was merely to spread the charge over
the glass. Taking such a view, it will be readily seen that
the larger the jar, the greater is the quantity of electricity
which may be stored therein. Large jars are, however,
often inconvenient to handle, so that a 'battery' of such
jars is used having their inner coatings all connected to-
gether to form one large coating, and the outer ones simi-
larly connected. Fig. 10 shows such a battery, the outer
coatings being connected by the tinfoil lining of the box.
Experiment of Cuneus : the Leyden Jar.
From time to time it has been attempted to use for the
dielectric materials other than glass, and thousands of
condensers using paraffined paper are in use on modern
telephone and telegraph circuits. Larger condensers are
used on power circuits. None of these other materials is,
however, as satisfactory as glass, being liable to be dis-
rupted if the pressure of the charge is too great. The op-
portunities for using condensers to advantage are rapidly
172
ELECTRICITY
increasing at present and considerable energy is being
directed toward their development. The desirable qualities
of such a condenser are that its dielectric should be capable
of containing a very large charge, that it should stand
very high electric pressure without disruption, and that its
coatings should be in the most intimate contact with the
Battery of Leyden Jars.
dielectric. In some recent condensers, made in Switzer-
land, the metal coatings are made by chemically depositing
silver upon the inner and outer surfaces of the glass.
The ancients, who knew nothing of electricity, could
not conceive of thunder as anything but the result of a
purely mechanical shock. Seneca, speaking of the fact
that two hands struck together produced a loud noise, con-
cluded from that that the collision of two enormous clouds
ELECTROSTATICS 173
ought to sound with a very great crash. Again, he com-
pares thunder, "the sound of which is very sharp, even
penetrating, to the noise made by the bursting of a bladder
on a person's head." Lucretius also explains thunder by
the shaking of the clouds or their tearing asunder.
The identity of lightning with electricity was first shown
by Benjamin Franklin in a paper published in 1749, two
years before his experiments with the storm clouds. At
that epoch he had just recognised the power of points.
Two ingenious experiments in which this power was put
into play furnished him with a new analogy and suggested
to him to verify by the storm clouds the truth of his con-
jectures. Having suspended by silk threads to the ceiling
of his room a tube of gilt paper, 10 feet in length and a
foot in diameter, Franklin charged it with electricity.
Then, presenting to the tube, at the distance of a foot, the
point of a needle, the tube was instantly discharged; if,
on the contrary, he presented to it a blunt body, an iron
bolt or punch rounded at the end, he found it was neces-
sary to put it within three inches before it could cause the
discharge, which then, he said, took place with a sudden
crackling. Suspending in the same way some great brass
scales, the pans of which were supported by silk cords a
foot from the floor, he electrified one of the pans. The
twisting of the suspending cord caused the scales to turn ;
he placed the iron punch underneath, below a point of the
circumference described. When the pan which was elec-
trified passed over it, it lowered itself, came in contact
with it and thus discharged itself. But if the end of the
punch was furnished with a needle, the point uppermost,
the pan passed above it without approaching, and the dis-
charge took place silently, or if in its course the pan had
come near enough for a spark to strike, it could not, be-
cause it would have been discharged beforehand.
"Now," says Franklin, " if the fire of electricity and
that of lightning be the same, as I have endeavored to
show at large in a former paper, this pasteboard tube and
174 ELECTRICITY
these scales may represent electrified clouds. If a tube
only 10 feet long will strike and discharge its fire on the
punch at two or three inches distance, an electrified cloud
of perhaps 10,000 acres may strike and discharge on the
earth at a proportionately greater distance. The horizon-
tal motion of the scales over the floor may represent the
motion of the clouds over the earth and the erect iron
punch a hill or high building, and then we see how elec-
trified clouds passing over hills or high buildings at too
great a height to strike may be attracted lower till within
their striking distance. And lastly, if a needle fixed on the
punch with its point upright, or even on the floor below
the punch, will draw the fire from the scale silently at a
much greater than the striking distance, and so prevent
its descending toward the punch; or if in its course it
would have come nigh enough to strike, yet being deprived
of its fire it cannot, and the punch is thereby secured from
the stroke.
"I say, if these things are so, may not the knowledge of
this power of points be of use to mankind in preserving
houses, churches, ships, etc., from the stroke of lightning
by directing us to fix on the highest parts of those edifices
upright rods of iron made sharp as a needle, and gilt to
prevent rusting, and from the foot of those rods a wire
down the outside of the building into the ground, or down
round one of the shrouds of the ship, and down her side
till it reaches the water? Would not these pointed rods
probably draw the electrical fire silently out of a cloud
before it came nigh enough to strike, and thereby secure
us from that sudden and most terrible mischief?"
And thus it is that this discovery of Franklin's has been
the means of saving much property from destruction. It
is only of recent years that much has been added to the
knowledge of the action of lightning rods and of their
proper design and application. Hertz's experiments in
electrical oscillations and the proof that lightning dis-
charges were also oscillatory in their character, enabled
ELECTROSTATICS 175
us to gain a better understanding of how to handle these
tremendous discharges. It is now known that lightning
discharges have a frequency of oscillation of about 500,-
000 periods per second.
A recent and most beautiful application of condensers
to the conduction of these lightning discharges to earth
may not be out of place here. If a lightning discharge
strikes an electric line in its course to earth it may find it
easier to pass back to the generator at the power station,
jump through the insulation to the frame and then to the
earth, than to leap over the insulators and down the pole
to the earth ; the result being to destroy the generator. If,
however, condensers are connected at various points along
the line, it may be well to see what should happen.
Every time that a condenser is charged and discharged
a current flows through the wire leading to it, one way
on charging, the other on discharging. If this succession
of charges and discharges takes place slowly, only a small
amount will flow into and out of the condenser, but if it
takes place rapidly the current is proportionately increased
without the pressure being any higher. Suppose such con-
densers to be connected on a line in which the current has
a frequency of 60 oscillations or cycles per second : a small
current will then flow continually. This current is of such
a character that it does not mean a waste of power — but
this is too advanced to be here explained. If, however, a
lightning discharge having a frequency of 500,000 per
second strikes the line, it will pass readily to earth through
the condensers instead of disrupting the insulation of the
generators, the condensers being able to pass 506%0
as much current as would be passed from the line. There
is still much to be learned of electrical disturbances in the
atmosphere and little is yet known of the causes producing
them. It is a field of vast possibilities and one whose study
may result in giving Man a partial control over atmos-
pheric conditions.
CHAPTER III
FUNDAMENTAL DISCOVERIES
There are in all sciences some discoveries which seem
to open vast fields for exploration, and which appear sud-
denly to increase the power of mankind. In electrical sci-
ence the benefits conferred by the discoveries of Volta
and Galvani, Davy, Arago, Ampere, Faraday, Seebeck,
Maxwell and Hertz are only just beginning to be realized.
Volta and Galvani started the investigation of electric
currents, and to-day the earth is full of applications of
them, each one the servant of a human brain. Each day
sees a new device based upon them, and each application
presents them in a new light, which again leads to another
useful appliance of the principles involved.
One hundred years ago men were not so well organized
for scientific research as they are at present, and it may
seem strange that such a simple discovery as electromag-
netic induction should have taken so long to develop after
the production of electric currents. It must be remem-
bered, however, that organization was loose, not bound
tightly together as it is now, when mankind is, as it were,
united into one large concentrated brain. If a discovery
is made at the present time the whole world knows of it
in a few days, and thousands of men stand ready to apply
it to all kinds of industries ; and many men can bring their
vast experience to the immediate aid of the discoverer, so
that the discovery is quickly perfected. All this power
of self-improvement is owed, however, to those whose
176
FUNDAMENTAL DISCOVERIES 177
works have united men so closely. Scientific research
has developed into a business. Large companies have
gathered together the best brains of the world, money and
conveniences are placed at their disposal, the needs of
industry are presented to them and are quickly filled. The
scientific brain is kept in constant touch with the wants
of life, and there is at last accomplished that union of
the scientist and the man of the world — the one with
needs, the other with the means of fulfilling them — that
was lacking in the earlier days.
There are, in general, two classes of scientists. One
is possessed of a mathematical mind, delighting in the
abstract solution of a problem and caring not whether
the result turns out one way or another. He is concerned
rather with the proof of the similarity of processes than
with any difference of detail. To the man with the me-
chanical mind, however, the detection of differences is
all-important. He finds his pleasure in observing differ-
ences in phenomena by the process of experiment, and
his whole idea is to obtain a definite and useful result.
Both classes of men are necessary. Maxwell developed
a beautiful mathematical theory of great comprehensive-
ness, but the proofs waited for the experimental demon-
strations of Hertz. The groundwork of the science is,
however, usually developed through that property of so
few minds — the power of observation.
The discovery of the electric current was an event.
Galvani, an eminent doctor and professor of anatomy
at the University of Bologna, was, one evening in the
year 1780, busy in his laboratory, with some friends,
making experiments relating to a nervous fluid in animals.
On a table, where there was an electric machine used
for the experiments, there had been placed by chance
some recently skinned frogs, intended to make broth of.
"One of Galvani's assistants," says P. Sue in his 'Histoire
du Galvanisme,' "casually put the point of his instrument
near the internal crural nerves of one of the animals;
178 ELECTRICITY
immediately all the muscles of the limbs seemed to be
agitated with strong convulsions. Galvani's wife was
present; she was struck with the novelty of the phenome-
non; she thought she saw that it occurred just at the
moment when a spark was taken from the electric ma-
chine. She warned her husband, who hastened to verify
this curious fact, and he recognised that the muscular
contractions of the frog took place, in fact, every time
that a spark appeared, but ceased while the machine was
at rest."
This observation was the beginning of many experi-
ments with the doctor by which he tried to prove the
identity of the nervous fluid of animals with the supposed
electric fluid. In 1786 he again continued researches of
this kind. "Being anxious one day," says A. Guillemin in
his 'Electricity and Magnetism,' "to see whether the influ-
ence of atmospheric electricity on the muscles of frogs
would be the same as that produced in machines, he had
for that purpose hung up a number of skinned frogs' legs
on the balcony of a terrace of his house. He hooked the
hind legs to the iron of the balcony by a copper wire
which passed under the lumbar nerves. Galvani remarked
with surprise that every time that the feet touched the
balcony the frogs' limbs were contracted with quick con-
vulsions, tho at that moment there were no signs of a
stormy cloud, and, therefore, no particular electric influ-
ence of the atmosphere."
These facts suggested to Galvani the idea that there
existed an electricity belonging to animals, inherent in
their organization; that this electricity, secreted by the
brain, resides specially in the nerves, by which it is com-
municated to the entire body; "that the principal reser-
voirs of this electricity are the muscles, each fiber of
which may be considered as having two surfaces, and pos-
sessing by that means the two electricities, positive and
negative, each of them representing besides, so to speak,
a small Ley den jar, of which the nerves are the conduc-
FUNDAMENTAL DISCOVERIES 179
tors." Hence the comparisons he makes between the mus-
cular contractions in frogs and other animals and the
commotions produced by the discharge of a Leyden jar.
Alexander Volta, then Professor of Natural Philosophy
at Pavia, repeated Galvani's experiments, but he very
soon modified his explanations. According to Volta, the
electricity developed was of the same nature as that which
an electric apparatus produces. It is the contact between
dissimilar metals which gives place to the production of
electricity, one of the metals being charged with a positive,
the other with a negative electrification; these charges
combine in traversing the middle conductor of muscles
and nerves. Then arose between the two celebrated phi-
losophers a discussion, a struggle, honorable to both, and,
above all, profitable to science, which thereby became
enriched by a multitude of new facts. The invention of
the marvelous apparatus which received the name of the
Voltaic pile at last caused the theory of the professor
of Pavia to prevail, tho Galvani's hypothesis on the ex-
istence of a sort of animal electricity is now recognised
as partly true. On the other hand, Volta's ideas have been
somewhat modified.
The outcome of these contentions was the invention of
Volta's pile, first made in 1800. Here, for the first time,
was produced a means of generating a steady and con-
tinuous flow of electric current. Volta's construction was
as follows: Disks of copper, zinc and flannel were cut
out and arranged in a pile in the order, copper, flannel,
zinc, and this order was successively repeated, the flannel
being first dipped in sulphuric acid so that its function
was merely to connect the copper and zinc by the acid.
This arrangement gave a feeble electromotive force be-
tween the elements of each set, which increased when one
connection was made at the lower end of the pile and the
other was moved toward the top. Volta's idea of the
action of the pile was, however, not as it is known to-day.
He believed that the source of the electromotive force was
180 ELECTRICITY
at the contact of the copper and the zinc disks, and that
the moistened cloth served merely as a means of connect-
ing them, whereas the real seat of this force is at the
contact of the acid with the zinc.
This discovery of Volta's was the starting point of
many investigations, in which the metals and the liquids
were tried in all sorts of combinations, many of which
were quite successful, and soon batteries were developed
which were capable of furnishing quite powerful currents.
For sixty years these batteries were the only source of
current available for conducting the brilliant experiments
of that period.
As soon as a source of current was obtainable it was
natural to ascertain the effects of this current on various
bodies. One of the first of these was that of Carlisle and
Nicholson, in 1800, on the decomposition of water. Hav-
ing passed the current of a volatile pile, formed of disks
of silver and zinc, through water, they noticed that at
the end of the copper wire which came from the negative
pole of the pile some gaseous bubbles were given off,
which they ascertained to be hydrogen; the other wire
became rapidly oxidized. On substituting for copper,
platinum, which is not attacked by oxygen, bubbles of
this latter gas were given off in the same way from the
positive wire. That is to say, when two platinum wires
were used, oxygen gas was given off in bubbles from
the surface of the wire by which the current entered
the water, and hydrogen gas was at the same time given
off in bubbles from the surface of the wire by which
the current left the water.
The next fact of great importance was brought to light
twenty years after the discovery of Volta's pile by Oer-
sted, professor in the University of Copenhagen. This
accomplished savant found that the electric current acted
on the magnetic needle. "For a long time," says Guille-
min, " there had been a suspicion of the existence of a
relation between magnetic phenomena and electricity ; peo-
FUNDAMENTAL DISCOVERIES 181
pie had remarked the occurrence of perturbations by the
mariner's compass on ships struck by lightning, or when
their masts presented the phenonemon known by the name
of St. Elmo's fire. It was known that discharges of bat-
teries of Leyden jars affected magnetic needles placed near
the apparatus." But these facts only gave vague ideas
on the relation mentioned above.
In 1820, the year after that in which Oersted made his
discovery, Ampere studied and described the laws of this
action, and showed besides that the currents themselves
acted on currents, and later Arago, Davy and Sturgeon
discovered the magnetizing of steel and soft iron under
the influence of the current from a battery. The experi-
ments of these men were so many points of departure for
a multitude of new experiments which in a short time
completely changed the aspect of this part of the science
by showing that magnetism and electricity are different
manifestations of the same cause.
Oersted expressed his discovery by saying that a current
acts "in a revolving manner" on a magnetic needle. He
does not, however, seem to have understood that the elec-
tric current carried about it a magnetic field, and that it
was the mutual action of this field and of the magnetism
in the needle that produced the deflection. Oersted ex-
pressed the law of the deflection as follows: When an
electric current acts on the magnetic needle, the north pole
of the needle is urged toward the left of the current.
Ampere was the first to use Oersted's discovery to meas-
ure the intensity of currents; but to Schweigger and to
Poggendorf, working independently, is due the happy
thought of multiplying the action of electricity on the
magnetizing needle so as to detect the existence of the
feeblest current. This instrument, then termed the multi-
plier, is now called the galvanometer, and its importance
as a factor in the further development of the science is
seldom appreciated. From this developed the Thomson
galvanometer, in which the needles were made ex-
182 ELECTRICITY
tremely small and light and having a mirror attached,
upon which a beam of light was thrown, and the re-
flected beam was made to pass over a scale. The gal-
vanometer was thereby furnished with a long weightless
pointer, whereby the smallest motion of the needle was
multiplied many times, and extremely small currents could
be detected.
In September, 1820, a little while after the discoveries of
Oersted and Ampere, Arago made the following experi-
ment: He plunged into a mass of iron filings a copper
wire which was connected to the two poles of a battery;
on drawing out the wire, without interrupting the current,
he found it to be covered over its whole surface with
particles of filings arranged transversely. As soon as the
current was broken the iron particles became detached
from the copper and fell down. To assure himself that
this was really temporary magnetism, and not the attrac-
tion of an electrified body for light bodies, he substituted
for the iron filings a non-magnetic substance, such as cop-
per dust or powdered glass, and found that the phenom-
enon did not take place. On placing needles of soft iron,
and then of tempered steel, very near the copper wire and
across it, he saw that the action of the current trans-
formed them into magnetic needles, having their south
poles always to the left of the current, a result in con-
formity with the earliest experiments of Oersted. Shortly
afterward Arago and Ampere noticed that magnetism of
iron or steel is developed much more energetically by plac-
ing the needle inside a spiral coil of wire through which
the current flows. This was the origin of the electro-mag-
net which was later developed by Sturgeon and Henry.
The discovery of the greatest value to electrical science
was that made by Faraday in 183 1. He reasoned that
if magnetism could be produced by the action of the elec-
tric current, the converse should also be true, and after
some experimenting he was successful in demonstrating
it. An interesting account of his experiments is given
FUNDAMENTAL DISCOVERIES 183
below, being an extract from Professor Tyndall's 'Faraday
as a Discoverer':
"In 1831 we have Faraday at the climax of his intel-
lectual strength, forty years of age, stored with knowl-
edge and full of original power. Through reading, lectur-
ing and experimenting, he had become thoroly familiar
with electrical science; he saw where light was needed
and expansion possible. The phenomena of ordinary elec-
tric induction belonged, as it were, to the alphabet of his
knowledge: he knew that under ordinary circumstances
the presence of an electrified body was sufficient to excite,
by induction, an unelectrified body. He knew that the
wire which carried an electric current was an electrified
body, and still that all attempts had failed to make it ex-
cite in other wires a state similar to its own. What was
the reason of this failure?
"Faraday never could work from the experiments of
others, however clearly described. He knew well that
from every experiment issues a kind of radiation, lumi-
nous in different degrees to different minds, and he hardly
trusted himself to reason upon an experiment that he had
not seen. In the autumn of 1831 he began to repeat the
experiments with electric currents which, up to that time,
had produced no positive result. And here, for the sake
of younger inquirers, if not for the sake of us all, it is
worth while to dwell for a moment on a power which
Faraday possesed in an extraordinary degree. He united
vast strength with perfect flexibility. His momentum was
that of a river, which combines weight and directness with
the ability to yield to the flexures of its bed. The intent-
ness of his vision in any direction did not apparently di-
minish his power of perception in other directions; and
when he attacked a subject, expecting results, he had the
faculty of keeping his mind alert, so that results different
from those which he expected should not escape him
through preoccupation.
"He began his experiments 'on the induction of electric
184 ELECTRICITY
currents' by composing a helix of two insulated wires,
which were wound side by side round the same wooden
cylinder. One of these wires he connected with a voltaic
battery of ten cells, and the other with a sensitive gal-
vanometer. When connection with the battery was made,
and while the current flowed, no effect whatever was ob-
served at the galvanometer. But he never accepted an ex-
perimental result until he had applied to it the utmost
power at his command. He raised his battery from ten
cells to one hundred and twenty cells, but without avail.
The current flowed calmly through the battery wire with-
out producing, during its flow, any sensible result upon the
galvanometer. During its flow — and this was the time
when an effect was expected ; but here Faraday's power of
lateral vision, separating, as it were, from the line of ex-
pectation, came into play — he noticed that a feeble move-
ment occurred when he made contact with the battery;
that the needle would afterward return to its former posi-
tion and remain quietly there unaffected by the flowing
current. At the moment, however, when the circuit was
interrupted the needle again moved, and in a direction
opposed to that observed on the completion of the circuit."
This result and others of a similar kind led him to the
conclusion, in his own words, "that the battery current
through the one wire did in reality induce a similar cur-
rent through the other; but that it continued for an in-
stant only, and partook more of the nature of the electric
wave from a common Ley den jar than of the current from
a voltaic battery." The momentary currents thus gener-
ated were called induced currents, while the current which
generated them was called the inducing current. It was
immediately proved that the current generated at making
the circuit was always opposed in direction to its generator,
while that developed on the rupture oj: the circuit coin-
cided in direction with the inducing current.
"It appeared," says Tyndall, "as if the current on its
first rush through the primary wire sought a purchase in
FUNDAMENTAL DISCOVERIES 185
the secondary one, and by a kind of kick impelled back-
ward through the latter an electric wave, which subsided
as soon as the primary current was fully established.
Faraday, for a time, believed that the secondary wire,
tho quiescent when the primary current had been once
established, was not in its natural condition, its return to
that condition being declared by the current observed at
breaking the circuit. He called this hypothetical state of
the wire the electrotonic state; he afterward abandoned
this hypothesis, but seemed to return to it in after-life. The
term electrotonic is also preserved by Professor DuBois
Reymond to express a certain electric condition of the
nerves, and Professor Clerk Maxwell has ably denned
and illustrated the hypothesis in the tenth volume of the
'Transactions of the Cambridge Philosophical Society.' "
The mere approach of a wire forming a closed curve
to a second wire through which a voltaic current flowed
was then shown by Faraday to be sufficient to arouse in
the neutral wire an induced current; the withdrawal cf the
wire also generated a current having the same direction
as the inducing current; those currents existed only dur-
ing the time of approach or withdrawal, and when neither
the primary nor the secondary wire was in motion, no
matter how close their proximity might be, no induced
current was generated.
'Faraday/' remarks Tyndall, "has been called a purely
inductive philosopher. A great deal of nonsense is, I
fear, uttered in this land of England about induction and
deduction. Some profess to befriend the one, some the
other, while the real vocation of an investigator, like
Faraday, consists in the incessant marriage of both. He
was at this time full of the theory of Ampere, and it can-
not be doubted that numbers of his experiments were exe-
cuted merely to test his deductions from that theory."
Starting from the discovery of Oersted, the celebrated
French philosopher had shown that all the phenomena of
magnetism then known might be reduced to the mutual
186 ELECTRICITY
attractions and repulsions of electric currents. Magnet-
ism had been produced from electricity, and Faraday, who
all his life long entertained a strong belief in such recip-
rocal actions, now attempted to effect the evolution of
electricity from magnetism. Round a welded iron ring he
placed two distinct coils of covered wire, causing the coils
to occupy opposite halves of the ring. Connecting the
ends of one of the coils with a galvanometer, he found
that the moment the ring was magnetized, by sending a
current through the other coil, the galvanometer needle
whirled round four or five times in succession. The ac-
tion, as before, was that of a pulse, which vanished imme-
diately. On interrupting the current, a whirl of the needle
in the opposite direction occurred. It was only during the
time of magnetization or demagnetization that these
effects were produced. The induced currents declared a
change of condition only, and they vanished the moment
the act of magnetization or demagnetization was complete.
The effects obtained with the welded ring were also ob-
tained with straight bars of iron. Whether the bars were
magnetized by the electric current, or were excited by the
contact of permanent steel magnets, induced currents
were always generated during the rise and during the sub-
sidence of the magnetism. The use of iron was then
abandoned, and the same effects were obtained by merely
thrusting a permanent steel magnet into a coil of wire. A
rush of electricity through the coil accompanied the in-
sertion of the magnet ; an equal rush in the opposite direc-
tion accompanied its withdrawal.
The precision with which Faraday describes these re-
sults and the completeness with which he defined the
boundaries of his facts are wonderful. The magnet, for
example, must not be passed quite through the coil, but
only half through, for if passed wholly through the needle
it is stopped as by a blow, and then he shows how this blow
results from a reversal of the electric wave in the helix.
He next operated with the powerful permanent magnet of
FUNDAMENTAL DISCOVERIES 187
the Royal Society, and obtained with it, in an exalted de-
gree, all the foregoing phenomena, and now he turned the
light of these discoveries upon the darkest physical phe-
nomenon of that day.
Arago* had discovered in 1824 that a disk of non-mag-
netic metal had the power of bringing a vibrating mag-
netic needle suspended over it rapidly to rest, and that on
causing the disk to rotate the magnetic needle rotated
along with it. When both were quiescent, there was not
the slightest measurable attraction or repulsion exerted
between the needle and the disk ; still, when in motion the
disk was competent to drag after it not only a light
needle, but a heavy magnet. The question had been probed
and investigated with admirable skill by both Arago and
Ampere, and Poisson had published a theoretic memoir on
the subject; but no cause could be assigned for so extraor-
dinary an action. It had also been examined in this coun-
try by two celebrated men, Mr. Babbage and Sir John
Herschel ; but it still remained a mystery. Faraday always
recommended the suspension of judgment in cases of
doubt.
"I have always admired," he says, "the prudence and
philosophical reserve shown by M. Arago in resisting the
temptations to give a theory of the effect he had discov-
ered, so long as he could not devise one which was perfect
in its application, and in refusing to assent to the imper-
fect theories of others." Now, however, the time for the-
ory had come. Faraday saw mentally the rotating disk,
under the operation of the magnet, flooded with his in-
duced currents, and from the known laws of interaction
between currents and magnets he hoped to deduce the
motion observed by Arago. That hope he realized, show-
ing by actual experiment that when his disk rotated cur-
rents passed through it, their position and direction being
such as must, in accordance with the established laws of
electromagnetic action, produce the observed rotation.
Introducing the edge uf his disk between the poles of
188 ELECTRICITY
the large horseshoe magnet of the Royal Society, and con-
necting the axis and the edge of the disk each by a wire
with a galvanometer, he obtained, when the disk was
turned round, a constant flow of electricity. The direction
of the current was determined by the direction of the mo-
tion, the current being reversed when the rotation was
reversed. He now states the law which rules the produc-
tion of currents in both disks and wires, and in so doing
uses for the first time a phrase which has since become
famous. When iron filings are scattered over a magnet,
the particles of iron arrange themselves in certain deter-
mined lines called magnetic curves.
In 1 83 1 Faraday for the first time called these curves
"lines of magnetic force," and he showed that to produce
induced currents neither approach to nor withdrawal from
a magnetic source, or center, or pole was essential, but
that it was only necessary to cut appropriately the lines of
magnetic force. Faraday's first paper on Magneto-electric
Induction, which is here briefly condensed, was read be-
fore the Royal Society on the 24th of November, 1831.
Faraday delighted in investigation for the sake of the
processes themselves. He had no inclination to follow up
his discoveries with their practical application. The atti-
tude of his mind is best described in his own words. "I
have rather," he writes in 1831, "been desirous of dis-
covering new facts and new relations dependent on mag-
neto-electric induction than of exalting the force of those
already obtained, being assured that the latter would find
their full development hereafter."
CHAPTER IV
ELECTRO-MAGNETIC MACHINERY
As previously related, the relations of electricity and
magnetism were established by the investigations of Oer-
sted, Ampere, Arago, Faraday, and others ; but the one to
whom the most credit is due is Faraday. He not only
made discoveries of the greatest importance, but he fol-
lowed up these discoveries with such true explanations of
their principles that these explanations have become the
basic laws of electro-magnetic induction. Faraday, how-
ever, did not care to make practical use of his discoveries,
being sure that others would do so. What were some of
these discoveries which have been of such great value to
succeeding generations? One of them was a modification
of Arago's experiment in which Faraday rotated a metallic
disk between the poles of a magnet, and, by connecting one
wire to the shaft of the disk and another in rubbing con-
tact with its rim, produced a steady deflection on the gal-
vanometer. This was really the first electro-magnetic gen-
erator. Here Faraday produced a continuous current
without that drawback to direct current machines of
the present day — the commutator.
It has from time to time been attempted to build ma-
chines based on Faraday's experiment, but the voltage
generated was not sufficient for practical purposes. Re-
cently, however, owing to the introduction of the steam
turbine with its high speed, generators have been built of
large powers and voltages of 600 or more which are based
i9o ELECTRICITY
on this principle. In this experiment of Faraday's, then,
was the beginning of the modern electric generator with
its almost unlimited power of changing mechanical into
electrical energy or vice versa. Faraday did not at first
use an electro-magnet, but in hi-s first public demonstra-
tions used a very powerful permanent magnet. Faraday
made many other experiments in the induction of cur-
rents, culminating in the production of an apparatus
known as Faraday's ring, the ancestor of the modern al-
ternating current transformer.
'The first development of Faraday's discovery," says
Henry Morton in his 'Electric Lighting,' "was made by
Pixii, of Paris, who in 1832 constructed an apparatus in
which a large steel magnet was rotated so that its poles
continuously and successively swept past those of an elec-
tro-magnet, or U-shaped bar of soft iron whose ends were
surrounded with coils of copper wire. This motion gen-
erated in the copper wire rapidly alternating electric cur-
rents, which were 'commuted' or made to pass out of the
machine in a constant direction by a simple 'commutator'
on the axis of the revolving magnet, which shifted the
connections each time the direction of the current was
changed.
"In the machine of Pixii, near the top, are seen the cop-
per-wire coils wound on cores of soft iron, like thread on
a spool. Immediately below these is the permanent mag-
net, of a U shape and so supported that it can be rapidly
rotated about a vertical axis midway between its poles, so
that each pole is caused to approach, pass and recede from
in succession each of the iron cores of the coils. Im-
mediately below the bend of the U-magnet are the com-
mutator segments, pressed upon by the contact brushes,
and below these again is the gearing by which the
magnet is made to rotate. Machines operating on the
same principle, but varying in construction (as, for exam-
ple, by rotating the electro-magnet or coils of copper wire
while the steel permanent magnet remained stationary),
ELECTRO-MAGNETIC MACHINERY
191
were brought out by Saxton, of Philadelphia, in 1833; by
Clark, of London, in 1834; and by Page, of Washington, in
1835. None of these machines, however, was of suffi-
cient size to be available for the production of a practical
electric light, altho they all exhibited a capacity for this
effect on a minute scale.
"The first magneto-electric machine of a magnitude
sufficient to operate a practical electric lamp was that pro-
Fig. 11 — Pixit's Magne-
to-electric Machine,
1832.
Fig. 12 — An Alliance Dynamo
Used in the South Foreland
Lichthouse, 1858.
duced by the united labors of M. Nollet, Professor of
Physics at the Military School of Brussels, and his assist-
ant constructor, Joseph van Malderen, under the auspices
of a corporation composed of French and English capi-
talists and known as the 'Alliance Company.' Strange to
say, this machine was built with the absurd object of
using it to decompose water and employ the resulting gases
in the production of light."
This machine, with some modifications by Mr. Holmes,
of England, was, under the superintendence of Faraday;
i92 ELECTRICITY
himself, introduced into two of the English lighthouses,
at South Foreland and at Dungeness. Its preliminary
trial was made in 1857. The electric light was first thrown
over the sea from the South Foreland on the evening of
December 8, 1858, and from Dungeness on the 6th of
June, 1862. Fig. 12 shows in outline one of the Alli-
ance machines, as modified by Mr. Holmes, which was
long since put in operation at the South Foreland light-
house. The outer framework supports twenty-four com-
pound steel permanent magnets, and a drum inside car-
ries thirty-two armatures or spools of copper wire wound
on iron cores. As these pass from pole to pole between
the magnets currents are developed which are carried off
by commutators on the farther end of the shaft, not
shown.
The electric light was not introduced into the French
lighthouses until December 26, 1863, when it was installed
at La Heve, near Havre. It was also used for lighting
works of construction, such as the Cherbourg Docks, and
on some vessels, for example, on the Lafayette and the
Jerome Napoleon. Altho Faraday lived to see the little
spark which he had developed from a magnet and coil of
wire in his laboratory grow into these magnificent illu-
minators of sea and land, it was not until after many years
and numerous new developments that the electric light
approached the commercial utility which it to-day pos-
sesses. These Alliance machines, on account of their
great size and multitude of parts, were very expensive.
Thus the two machines placed in the Dungeness light-
house, with their engines, appliances, and lamps or "regu-
lators," cost £4,760, or nearly $24,000. The two located at
Souter Point in like manner cost £7,000, or about $35,000,
and the machines and accessories for the two lights at
South Foreland cost £8,500, or about $42,500. The same
characteristics caused them to be liable to accident and
injury and costly in repairs. The world therefore waited
for some further development before it could enjoy gen-
ELECTRO-MAGNETIC MACHINERY 193
erally the advantages of electricity as a means of illumina-
tion.
The first of these came when Dr. Werner Siemens, of
Berlin, constructed a machine in which the revolving coil
or armature was made of the form shown in Fig. 13,
and was entirely enclosed between the ends of the per-
manent magnets. To construct this armature a long, solid
cylinder of soft iron is taken, and two deep grooves are
cut on opposite sides through its entire length, so that its
cross-section is such as appears at F in the accompanying
figure. Insulated copper wire is then wound lengthwise
in these grooves, its ends being united to the section x, y
of the commutator. Journals on which this armature ro-
tates are provided at either end, and at one end also a pul-
ley by which it may be driven by a belt.
This armature secured a great concentration of action
by bringing the revolving armature into a highly concen-
trated field of magnetic force and allowing it to have a
very rapid angular velocity of rotation. But the chief
value of this improvement consisted in its serving as a
step toward another, which was most remarkable in its re-
sults and excited the liveliest interest all over the world
when it was announced.
This next step was taken by Wilde, of Manchester. He
took a small magneto-electric machine, such as had been
constructed by Siemens, and carried the current from its
commutator to the coils of very large electro-magnets,
which constituted the field magnets of a similar machine,
which, however, differed from the other, or Siemens ma-
chine, both in size and in having its field constructed of
electro-magnets in place of permanent magnets. Fig.
14 shows such a combination, in which the first or small
magneto-electric machine is mounted on the top of the
other, and sends the current from its commutator through
the coils of the electro-magnet below, between whose ex-
panded poles another Siemens armature is made to re-
volve. Under these circumstances the current developed
194
ELECTRICITY
in the armature of the upper machine by its permanent
steel magnets will develop a more than tenfold greater
magnetic force in the poles of the electro-magnet of the
lower machine; and the second armature, rotating in this
powerful magnetic field betwen the poles of this large
electro-magnet, will develop a more than tenfold greater
current than that of the smaller machine. This method of
multiplying or creating magnetic force was a wonderful
Fig. 13 — Siemens' Shut-
tle Armature.
Fig. 14 — The Wilde Dynamo.
discovery, and, combined with the use of electro-magnets
in place of permanent magnets for the production of the
magnetic field, gave an important increase in power and
efficiency to the machine ; for as compared with perma-
nent magnets the power of electro-magnets is vastly
greater.
This advance, made by Wilde on April 13, 1866, was
quickly followed by another, made almost simultaneously
in Europe by Varley, Siemens, and Wheatstone, and near-
ly a year earlier in this country by Mr. M. G. Farmer,
ELECTRO-MAGNETIC MACHINERY 195
whose work in another department of electric lighting is
to be treated in more detail farther on. This develop-
ment may be indicated by the term "self-exciting," and
consisted in the discovery that if the commutator is so
connected with the coils constituting the field magnets that
all or a part of the current developed in the armature will
flow through these coils, then all permanent magnets may
be dispensed with, and the machine will excite itself or
charge its own field magnets without the aid of any charg-
ing or feeding machine.
There is in all iron, unless special means have been taken
to remove it, a little magnetic force. This small magnetic
force, called "residual magnetism," in the iron cores ot
the field magnets will produce a little current in the ar-
mature when it is revolved. This current flowing through
the coils of the field magnets will increase their magnetic
force, and thus cause them to develop more current in the
armature, which in turn, flowing through the coils of the
field magnets, will further increase their magnetic force,
and so on until maximum, determined by the structural
conditions of the machine and the amount of driving force
applied to the pulley of the armature, is reached. In prac-
tice such machines are each complete within themselves.
When started they develop for a few moments only very
feeble currents; but within a few seconds they "wake up"
by degrees, and reach their maximum in less time than
it takes to read this paragraph.
One other radical improvement in dynamo-electric ma-
chines remains to be recorded, namely, that due to the
French inventor Gramme. The essence of this lay in the
structure of the armature. While previous to Gramme all
armatures had been constructed either like spools of cotton
or like balls of yarn wound on blocks, he made his arma-
ture by starting with an iron ring (itself consisting of a
coil of soft iron wire), and winding the copper wire on
this by passing the end of the wire again and again
through the ring. A Gramme armature ring, cut and bent
196
ELECTRICITY
out partly, and with some of its copper coils removed, is
shown in Fig. 15. The cut ends of the iron wires con-
stituting the ring-core are shown at A, and B shows a por-
tion of the copper-wire coils wound around this ring-core.
The copper wire is continuous throughout as regards its
electric connection, but at frequent intervals a loop of this
Section of a Gramme Ring Armature.
wire is carried out and attached to a segment of the com-
mutator.
This armature being rotated in a magnetic field — i.e.,
between the poles of powerful field magnets — tends to
deliver a substantially continuous current to "brushes"
touching the commutator segments at points midway be-
tween the poles of the field magnets. It will be remem-
bered that the iron ring constituting the core of the
ELECTRO-MAGNETIC MACHINERY 197
Gramme armature was made of iron wires, and not of a
solid piece or ring of iron. The object of this was to pre-
vent the formation of electric currents in this ring-core
itself, commonly called Foucault currents, which would be
a cause of inconvenience by heating the armature and of
loss by wasting energy in the useless production of this
heat. The Siemens armature had no such provision, and
accordingly very serious difficulties were experienced in
the running of machines using such armatures by reason
of the intense heat there produced. Arrangements were
in fact made in many machines to relieve this symptom by
running cold water through the armature, made hollow
for that end; but this did not cure the disease or prevent
the loss of efficiency caused by the conversion of the driv-
ing energy into useless heat in place of useful current.
The desirable end was, however, soon secured by "lami-
nating the armature core" — that is, making it up out of a
great number of thin sheets of iron insulated from each
other and held together by one or more bolts. The merit
of this invention appears to have ben assigned by the
United States Patent Office to Edward Weston, September
22, 1882.
A Weston generator of about 1890 is shown in Fig. 16.
In comparing this with a modern machine, the most
marked feature is the large and heavy field magnet. Edi-
son's first generators, of which some are still in opera-
tion, also contain these tremendous field magnets. These
large field magnets were made necessary because the idea
of embedding the wires in the armature in slots had not
yet been originated. The fields were therefore made
powerful in order to force the requisite magnetic flux
across the large air gap into the armature.
By the later improvement of embedding the wires in
slots in the armature, the air gap was much reduced and
the fields made proportionately lighter. This decreased
very considerably both the weight and cost of the machine.
A change in the design of direct current generators of
193 ELECTRICITY
considerable importance was occasioned by the desirability
of connecting them to slow-speed engines of the Corliss
type — engines of low steam consumption. To accomplish
this many poles were arranged in a circular yoke, and
these were called "multipolar" generators. Upon the in-
troduction of the high-speed steam turbines, however, the
number of poles was again decreased to two, four, or six,
1 6 — A Weston Dynamo of 18
and the weight of a machine of given power was greatly
reduced. Herein lies one of the advantages of the steam
turbine for driving generators.
The dynamo is first of all a generator of alternating
currents, and the commutator was added for the purpose
of rectifying them. This commutator was always a source
of trouble, mainly on account of sparking and the wearing
away of the brushes and commutator surface. On the
other hand, continuous currents are, in many cases, much
easier to handle than alternating ones, and it was this fact
ELECTRO-MAGNETIC MACHINERY 199
which caused so much effort to be spent on the develop-
ment of direct current apparatus. Direct currents could
be transmitted with less loss of voltage in the line and
direct current motors were quite well developed before
1890. These two very important facts caused the direct
current to reign supreme. In the latter part of the 8o's,
however, its overthrow began, and ever since it has
gradually been declining before the advance of its more
flexible rival — the alternating current. At that time Ni-
kola Tesla took out patents covering the principles of the
induction motor — a motor which, on account of its me-
chanical simplicity, rapidly found favor, altho inferior
to the direct current motor in many respects. The funda-
mental principle of these motors lies in the production of
a rotating magnetic field, which field drags along with it,
at a somewhat slower speed, a cylindrical armature called
the rotor.
An idea of how a rotating field is produced by the action
of polyphase currents is given in Professor S. P. Thomp-
son's 'Elementary Lessons in Electricity and Magnetism.'
"It is obviously possible," he says, "by placing on the ar-
mature of an alternator two separate sets of coils, one a
little ahead of the other, to obtain two alternate currents
of equal frequency and strength, but differing in phase by
any desired degree. Gramme, indeed, constructed alter-
nators with two and with three separate circuits in 1878.
If two equal alternate currents, differing in phase by one-
quarter of a period, are properly combined, they can be
made to produce a rotatory magnetic field. And in such a
rotatory field conductors can be set rotating, as was first
suggested by Baily in 1879.
"Consider an ordinary Gramme ring (Fig. 17) wound
with a continuous winding. If a single alternating current
were introduced at the points A A' it would set up an oscil-
latory magnetic field, a N pole growing at A, and a S pole
at A', then dying away and reversing in direction. Simi-
larly, if another alternate current were introduced at B B'
200 ELECTRICITY
it would produce another oscillatory magnetic field in the
B B' diameter. If both these currents are set to work but
timed so that the B B' current is *% period behind the A A'
current, they will then combine to produce a rotatory mag-
netic field, tho the coil itself stands still. This is quite
analogous to the well-known way "in which a rotatory mo-
tion, without any dead points, can be produced from two
oscillatory motions by using two cranks at right angles to
one another, the impulses being given l/$ period one after
the other. The above combination is called a diphase
Ia'
Fig. 17 — Connections for Producing a Rotating Field From
Two-phase Currents.
Fig. 18 — Connections for Producing a Rotating Field From
Three-phase Currents.
system of currents. If the B B' current is *4 period later
than the A A' current the rotation will be right-handed.
"Another way of generating a rotatory field is by a tri-
phase system (or so-called 'dreh-strom') of currents. Let
3 alternate currents, differing from one another by y$
period (or 1200), be led into the ring at the points ABC.
The current flows in first at A (and out by B and C), then
at B (flowing out by C and A), then at C (out by A and
B), again producing a revolving magnetic field. This is
analogous to a 3-crank engine, with the cranks set at 1200
apart."
One of the important features of these motors is their
successful operation at high voltage — 11,000 or more. An-
other feature is their mechanical simplicity, there being
ELECTRO-MAGNETIC MACHINERY 201
no commutator, rings, brushes or other parts to collect
dirt and thus interfere with the operation of the machine.
As previously stated, alternators are usually wound to
generate two or three phase currents, altho they may be
built for other phases. In the last few years, however,
the three-phase generator has practically controlled the
field on account of the wide use of three-phase currents.
Historically the generators have developed in the order
of single, two, and three phase.
The first generators to come into commercial use were
single-phase — i.e., had a single winding in the armature.
A notable instance of the use of these generators was the
first plant of the Telluride Power Company in Colorado,
where a single-phase generator was connected to a water
wheel and the electrical energy developed again converted
into mechanical energy by an exactly similar machine used
as a motor. When an alternating current generator is
used as a motor i't is called a synchronous motor, for the
reason that its speed must be absolutely synchronous with
that of the generator. Alternating current generators are
thus reversible in their action, just as are direct current
generators. They are not, .however, usually self-starting,
but require auxiliary motors to bring them up to speed.
After the development of the induction motor — it being
necessary to have polyphase currents for the production of
the rotating magnetic field — two-phase generators came
into use. Probably the largest of these are located in the
first and second Niagara Falls power houses, where there
are twenty-one, each one being of 3,750 kilowatts or 5,000
horse-power capacity. In transmitting this power to
Buffalo, it is first changed to three-phase by a simple con-
nection of transformers — known as Scott's connection —
because 25 per cent, of copper is saved thereby. In the
more recently constructed generators three-phase windings
are almost exclusively used, principally because of the
advantage of three-phase transmission. It is a notable
fact, however, that these generators were used in the
202 ELECTRICITY
Frankfort-Lauffen transmission of 1891 in Germany,
transmission being effected, then as now, by three wires.
These alternators are now built in sizes as large as 7,500
and 10,000 kilowatts, or 10,000 and 13,300 horse-power.
In 1893 the rotary converter was brought out. This
machine is the connecting link between alternating and
direct currents, usually serving to convert alternating into
direct current, altho it may be used in the reverse way. In
construction it is similar to a direct current generator,
with the addition of collecting rings for the introduction
of the alternating current. Many of the converters now
in use are six-phase, the change from three to six phase
being accomplished by the transformers used to reduce the
voltage. These machines serve to connect the superior
qualities of the alternating current for transmission pui -
poses with the more perfect ones of the direct current
motor for traction purposes. On account of the degree of
perfection which has been attained recently with the al-
ternating current motor, it would seem that the days of the
rotary converters are numbered.
The induction coil and the alternating current trans-
former are founded on the same principles, but differ
somewhat in the purposes to which they are applied. Each
depends upon the fact that if the magnetic flux passing
through a coil is changed in value, an electromotive-force
will be set up in the coil which will be proportional to the
rapidity of that change. There are several ways of pro-
ducing the flux through the coil. One is by the introduc-
tion of a magnet into the coil, in which case the magnetic
flux may be caused to change by moving the magnet in and
out of the coil, there being established an electromotive-
force in one direction upon its introduction, and in the
reverse direction upon its withdrawal. Another method
is to cause the flux created by another coil to pass through
the first one and to vary this flux by changing the current
in the second coil. The coil causing the flux is called the
ELECTRO-MAGNETIC MACHINERY 203
primary, and that in which the electromotive-forces are
set up, the secondary coil.
The best way of making the flux set up by the primary
coil pass through the secondary coil is to wind the two
coils on the same core. It will here be evident that an
electromotive- force will be induced, not only in the sec-
ondary coil, but in the primary as well, since each turn of
wire surrounding the changing magnetic flux is equally
affected. This electromotive-force is called the electro-
motive-force of self-induction, and acts in such a way as
to retard the establishment of a current in a coil, and to
maintain it when it is attempted to stop it. In other
words, it causes the circuit to act as tho it possessed in-
ertia. From these statements it would appear, then, that
the higher the electromotive-force which it is desired to
set up, the more rapidly must the magnetic flux be changed
and the greater must be its value. A flux withdrawn from
a coil infinitely fast would produce an infinitely high elec-
tromotive-force, but this is no more possible than it is to
stop a heavy fly-wheel instantly. Having now in mind
what is desired in an induction coil, let us see how the
various methods for producing these results gradually
developed.
The credit for all discoveries in electromagnetic induc-
tion is usually given to Faraday. One should not, how-
ever, in this connection forget Professor Henry, whose
discoveries were made without a knowledge of Faraday's
works, and but a few months after them. Faraday dis-
covered the effect of one coil upon another, but Henry
was the first to discover the electromotive-force of self-
induction, and published his discovery in 1832. In his first
experiments Henry used copper tape or ribbon wound in
the form of a spiral, and, upon passing a current through
this spiral and suddenly interrupting it, he obtained a
bright spark, and if the two ends of the coil were touched
by the hands at the instant of break, a shock was felt.
When the current was alternately made and interrupted
204 ELECTRICITY
by rubbing one of the wires over a rough metal plate,
vivid sparks were obtained. In 1836 the Rev. N. J. Cal-
lan, of Maynooth College, constructed an electromagnet
with two separate insulated wires, one thick and the other
thin, wound on the iron core together. The thick wire
was copper, and through this the current was passed. The
thin wire was iron, having one end attached to the thick
winding. Upon making and breaking the current, he ob-
tained severe shocks from the iron wire circuit. Later
he extended his experiments by constructing a larger ap-
paratus of sufficient power to kill small animals.
In 1837, Sturgeon, the inventor of the electromagnet,
constructed a coil on Callan's plan, but of a shape re-
sembling the wooden coil. He applied to his coils a
make-and-break arrangement, consisting of a wire dipping
in a mercury cup in one case and of a notched zinc disk in
the other. He made experiments with solid iron cores,
and noticed that when the interruptions of the current be-
came too rapid, the effect was much diminished. He
draws attention to the fact that G. H. Bachhoffner had
tried a divided iron core and had observed that a bundle
of fine iron wires used as a core gave far better shocks
than when a solid iron bar was employed. Sturgeon there-
fore made use of the iron wire core in constructing his
coils, one of which was exhibited to the London Electrical
Society in August, 1837.
The next advance was made by Callan in September,
J^37, when he constructed two coils, each with its pri-
mary and secondary windings separate. These coils he
connected together with their primaries in parallel and
their secondaries in series, so that the secondary electro-
motive-forces added together. He surmises that if a hun-
dred such induction coils could be aranged with their
secondaries in series and their primaries in parallel, it
would be possible to have a shock equal to 100,000 or 200,-
000 single cells.
In 1838, Professor Page, of Washington, constructed a
ELECTRO-MAGNETIC MACHINERY 205
coil closely resembling modern coils. The two windings
were entirely separate and he used the iron wire core. In
addition he made a very important improvement. It has
been seen that the value of the electromotive-force de-
pends upon the suddenness of the collapse of the magnetic
flux. Page noticed that the spark produced in his mer-
Sturgeon's Induction Coil.
cury contact breaker was quite prolonged, so that the cur-
rent producing the flux in the core was not stopped as sud-
denly as it should be, and he conceived the idea of cover-
ing the mercury with oil or alcohol in order to suppress the
spark, and this proved a valuable addition. This device
was revived many years after by other inventors, par-
ticularly by Foucault. Page was the first to notice that
206 ELECTRICITY
when a metallic sheath or tube is interposed between the
primary and secondary circuits, it more or less annuls
the action. Between 1838 and 1850 Page made many in-
duction coils. With one of his coils he found he could
obtain sparks y2 inch long in air. He also noticed the
effect of rarefying the air upon the length of the dis-
charge. With a coil giving only Vie-inch sparks in air,
he obtained a discharge of about 4^2 inches in rarefied air.
In 1850 he constructed a very large coil, from which he
obtained sparks 8 inches long with a battery of 100 Grove
cells.
It is to Ruhmkorff, a skilful mechanician of Paris, that
modern electricians are indebted for many of the me-
chanical improvements in coil construction, and for the
addition of the condenser which is used to suppress the
spark at the break of the primary circuit, thus performing
the same function as the oil on the mercury in Page's in-
terrupter. So many of these coils were constructed by
Ruhmkorff that this type of coil is commonly called by his
name. One of the largest of these coils was made by hirn
in 1867, the secondary containing 62 miles of wire. This
coil could give sparks 16 inches in length. In its con-
struction Ruhmkorff employed a method of winding the
secondary so that no two neighboring parts should be at
a very different potential. He had before been troubled
with internal sparking of the secondary. Instead of wind-
ing the wire in layers, he wound it in small flat sections
which were placed side by side on the core and connected
in series. This method of winding was also employed by
E. I. Ritchie, of Boston, who constructed a large coil
in i860 capable of producing sparks of 21 inches with only
three bichromate cells. One of the largest of this type of
coil ever built was constructed by A. Apps in 1876,
and is known as the Spottiswoode coil. The secondary of
this coil contained no less than 280 miles of wire in 341,-
850 turns, and produced sparks 42 inches in length.
The evolution of the alternating current transformer
ELECTRO-MAGNETIC MACHINERY 207
from the induction coil was but a short step. The first
intimation of it came in 1856, when C. F. Varley, of Lon-
don, took out patents on an induction coil in which the
iron wire core was extended and folded back on itself out-
side the coil, so that the ends overlapped and completed the
magnetic circuit. J. B. Fuller, of New York, seems, how-
fl-Jl_ft
J
Fig. 20 — Varley's Induction Coil (1856), With Closed-circuit
Divided Iron Core.
ever, to have been the first to recognise the value of the
transformer as early as 1879, but his death caused the
failure of his plans. A number of other inventors at-
tempted to adapt the induction coil to the operation of
lights, but they all worked with the idea of connecting the
primaries in series, but the loading of each secondary was
208 ELECTRICITY
found to affect all the others, and the plan was not suc-
cessful. The last experiment with this series arrangement
of primaries was made in 1883 on the Metropolitan Rail-
way in England. A Siemens alternator was put down at
the Edgeware Road Station, and -a high-pressure alternat-
ing current was led through the primary circuits of a
series of secondary generators which reduced the pres-
sure. The high-pressure current was transmitted through
the primary coils of secondary generators. The length
of the primary circuit was 16 miles and the primary coils
of the secondary generators were placed in series upon it.
Incandescent and arc lamps were worked at these various
stations. The impossibility of independent regulation pre-
vented the system from being a success.
The advantages of operating the transformer primaries
in parallel from the same mains were first pointed out by
Rankin Kennedy in 1883, but were not appreciated and
acted upon until they were again brought forward in 1885
by Messrs. Ziperowsky, Deri and Blathy, of Budapest.
In August, 1885, the investigations of these gentlemen
were made known in a series of technical papers, and in
which the reasons for adopting the parallel mode of ar-
ranging induction coils were given fully, as well as de-
scriptions of transformers suitable for this method of
working. In the summer of 1885 tne Inventions Exhibi-
tion was held at South Kensington, and part of the exhibit
of the Edison and Swan United Electric Company con-
sisted of a pair of 10 hp. Ziperowsky-Deri transform-
ers working in parallel between a pair of high-pressure
leads, and reducing the pressure from 1,000 to 100 volts.
The current for these transformers was supplied by a self-
exciting alternator, and the primary current was convened
by a pair of No. 10 B. W. G. insulated copper wires a
distance of 800 yards to the place where the transformers
were placed. The system was set in operation in London
in July, 1885. The transformers were clpsed magnetic
ELECTRO-MAGNETIC MACHINERY 209
circuit transformers and the lamps were arranged on the
secondary circuit in parallel.
"This was the first occasion," says J. A. Fleming in his
'Alternate Current Transformer,' "on which transformers
with their primary circuits arranged in mains were ex-
hibited operating incandescent lamps arranged in parallel
on their secondary circuits. This small installation was
worked throughout the summer and autumn of 1885 with
perfect success. From and after this date the system of
parallel working was universally adopted."
Transformers may be divided into four classes, de-
pending on the disposition of the iron core. These are :
(1) Transformers with open or incomplete iron mag-
netic circuits.
(2) Transformers with closed or complete iron mag-
netic circuits.
(3) Transformers with an iron core.
(4) Transformers surrounded by an iron shell.
The first type was soon found to produce poor results,
altho good for the induction coil, and closed magnetic
circuits were used.
There are two common types of transformers, viz., con-
stant potential and constant current. The first are used
in such work as incandescent lighting, operating motors,
etc., in which the voltage must be held constant. The
second are employed to supply arc lamp circuits in which
it is necessary to keep the current constant but vary the
voltage to suit the number of lamps. Both transformers
may operate from the same constant potential mains. In
the constant potential transformer both primary and sec-
ondary windings remain fixed and the windings are inter-
laced as much as possible, so that all the magnetic flux
created by the primary winding must also pass through
the secondary winding. In the constant current trans-
former, however, this magnetic leakage is utilized to pre-
vent the increase of the secondary current. The fact that
the secondary and primary currents in a transformer are
2»o ELECTRICITY
opposite in direction and cause a repulsion between the
two coils is here utilized to bring about this result. The
secondary coil is movable and its weight is nearly bal-
anced. Any attempt of the current to increase creates a
greater repulsive force between the windings, and the sec-
ondary moves away from the primary so that less flux
from the primary passes through the secondary and the
voltage of the latter is reduced. Such transformers are
now made which produce an almost constant current in arc
lighting circuits. Since 1885 transformers have gradually
developed in size, efficiency, regulation of voltage, and
ability to withstand high voltage. Transformers of 3,000
kilowatts capacity are now quite common. The voltage
regulation is almost one per cent. — i.e., the fall in voltage
from no load to full load is only one per cent. Operation
is successfully carried on at 110,000 volts.
What were some of the details which had to be devel-
oped to produce these large transformers? One of the
first things done was to immerse them in oil. The first
transformers were exposed to the air, from which the
coils absorbed moisture, thus causing them to break down
easily. The oil prevented this absorption, and also acted
to insulate the windings, as it is very much harder for a
spark to pass through oil than through air. In the very
high voltage transformers the oil is exposed to a vacuum,
and the last trace of moisture in it is extracted.
As the size of the transformer increased, greater diffi-
culty was found in keeping it cool, for altho a large
transformer is more efficient than a small one, yet the ac-
tual loss increases with the size, but without a correspond-
ing change in bulk. For example, take the case of a 3,000-
kilowatt transformer. Altho the loss is only about two
per cent., this means an actual loss of 60 kilowatts, or as
much heat as would be developed by 1,000 incandescent
lamps of 16 candle power. To get rid of this heat, cold
water is circulated in pipes through the oil or air is forced
over the transformer.
CHAPTER V
THE DEVELOPMENT OF POWER TRANSMISSION
The location of a convenient spot for the economical
generation of electric power usually does not coincide with
the center of its consumption, so that the connection of
these two points presents a problem which has consumed
the energies of many engineers. Among the natural
available sources of energy to-day which are most promi-
nent are coal and liquid fuels and the fall of water. Coal
and the liquid fuels can, without much expense, be brought
to many industrial centers, and the power plant is then
erected at these points. In many cases, however, as in
the western part of this country, the cost of cartage is
prohibitive. On the other hand, water powers are abun-
dant, but are not usually found at points where manu-
facturing may with profit be carried on.
The power available in such waterfalls, and which has
been wasted for centuries, is at last being utilized through
the medium of electrical transmission and has become an
immense addition to the sources of energy. With the
enormous amounts of power now required, the natural re-
sources of fuel are fast becoming exhausted, and America
would soon be left without the means of carrying on
civilization had not methods of distributing the inexhaus-
tible supply of energy in waterfalls been developed. The
Importance of the work which has been done and is still
being done by those engaged in the design of these power
lines is appreciated by few.
212 ELECTRICITY
Some of the essential parts of such a system of power
distribution need consideration. The power-house must
be located on a stream which has at all times a sufficient
flow to operate the generators at their full capacity. Fail-
ing in this, an artificial lake or "storage resorvoir may be
constructed so that the maximum and minimum flows may
be more nearly equalized. In order that the power may
be economically transmitted, the voltage of the line must
be high, and the higher the better. The loss in the line
varies as the square of the voltage, so that with the same
line loss the power may be transmitted four times as far
by doubling the voltage. It will therefore be seen that
the voltage is one of the important factors in determining
how far power shall be transmitted. There is a limit to
the voltage which a generator may develop on account of
its manner of construction, and at present this seems to be
about 13,000 volts, altho machines of higher voltage have
been built. The next important factor is the transformer,
and in the perfecting of this piece of apparatus a great
deal of attention has been centered. By its means, the
voltage may be raised to almost any degree with a very
slight loss in power, the limit being the ability of its in-
sulating materials to resist breakdown. In the last fifteen
years the advance in the art of constructing transformers
has been such that they may now be built with the same
assurance for 100,000 volts as they were then for 3,000
volts. There is, moreover, prospect of their successful
operation at 500,000 volts.
Why then are lines not yet operating at 500,000 volts?
Now comes the weakest spot of the system, viz., the in-
sulation of the line. The development of insulating ma-
terials has not been able to keep pace with that of the
means for producing high voltages, altho it has been rapid.
Insulators for carrying the lines have increased in size
and cost until they have assumed great importance.
Wooden poles have been replaced by steel towers, and
rights of way have been granted through which the lines
POWER TRANSMISSION 213
may pass. They are regularly patrolled by men whose
business it is to report to the power station immediately
any defects observed.
Operation of these lines in actual practice has not been
as difficult as laboratory experiments tended to prove.
There has been less leakage from the line than was ex-
pected and also fewer breakdowns. One of the main dif-
ficulties in the operation of these long lines has been due
to lightning discharges, but even these are fast being elim-
inated. New lines are usually troubled with malicious per-
sons who delight in shooting off the insulators, but these
have been cured by the severe punishments inflicted.
Large birds have sometimes caused arcs to start between
the line wires by approaching too close.
Each year sees the limit of successful operating voltage
raised. What would have been considered impossible a
few years ago is now an accomplished fact. In 1908 the
highest operating voltage was 110,000 on a line in Michi-
gan about 100 miles in length ; 60,000 is now a standard
voltage. To what distances power may be transmitted in
the future we may only surmise, but it seems assured that
all parts of the world will ultimately be traversed by these
power lines. In reviewing the history of the development
of power transmission, an idea of its rapidity may be
gained by observing the work of the pioneer plants. Altho
much of the work was done in Europe, America has ac-
complished her share and has developed the alternating
current system of power distribution to the point where
it has finally triumphed over the European direct current
system.
During the years from 1880 to 1890 power transmis-
sion was effected almost entirely by direct current. Elec-
tricity for power and lighting was sent out over the same
lines, and the power load usually consisted of a number of
small motors. The generators were wound for low volt-
age so that the lamps could be operated directly from them.
Power stations were erected at the centers of distribution.
214 ELECTRICITY
As the load increased the size of the conductors necessary
to give any kind of regulation became very large and the
cost of the copper was enormous.
Edison was the first to devise a means of effecting an
economy in the weight of copper necessary to transmit a
given amount of power, and brought out the Edison 3-wire
system, by which it was only necessary to use about three-
eighths of the copper employed with the old 2-wire sys-
tem. This system is still used in both direct and alter-
nating current distributions for lighting. Edison made
use of the fact that by doubling the voltage only one-fourth
the weight of copper would be necessary, but he added
a middle or neutral wire, whose voltage was half-way be-
tween the outside wires, so that the voltage between the
outside wires was 240, and between either outside and the
neutral was 120. The lamps were connected between
either outside wire and the neutral, the neutral serving
merely to carry the difference in the currents. If, there-
fore, the number of lamps on each side was the same,
the neutral carried no current. If the lamps were prop-
erly distributed, it was possible to make the unbalancing
current small, so that the neutral wire could be made
smaller than the two outside wires. At the power station
the 120-volt machines were connected in series and the
neutral wire ran from the middle connection.
This was, of course, a great step ahead, as it permitted
the transmission of power to greater distances, but the
main advantage was the improved regulation — i.e., the in-
creased steadiness of the lights. Even this system, how-
ever, was only good for several miles, and therefore did
not enable the power station to be removed to a location
where fuel and water could be more economically obtained.
The system is, however, good for congested districts
where the lines are short.
Upon the introduction of the electric railway, the ne-
cessity for high voltage was forcibly impressed, and 500-
600 volts soon became standard and has remained so un-
POWER TRANSMISSION 215
til the present time. With this increased voltage it be-
came possible to remove the power station to a point of
convenient water and fuel supply. Cars could then be
operated fairly well over a radius of 5 or 6 miles without
expending too much on the feeder cables.
For several years previous to 1890 Nikola Tesla had
experimented with alternating currents with a view to the
production of an alternating current motor, and was at last
successful. About the same time transformers for raising
and lowering the voltage were brought out, and the rotary
converter for changing alternating into direct current was
exhibited in 1893. This completed the steps in the devel-
opment of the present alternating current system. The
high voltage alternating current generator in the railway
power-house gradually displaced the direct-current, and the
power became concentrated in one large station, resulting
in a more economical production of power. During this
evolution the railway lines remained in operation on direct
current at 600 volts.
This radically increased the radius of transmission. Sub-
stations were erected in various parts of the city, and in
these were installed the rotary converters. The power
from the central station was all sent out at high voltage
as alternating current to transformers, from the low volt-
age sides of which it entered the rotary converter, which
changed it into 600-volt direct current. Each sub-station
therefore acted as a supply station, but without the large
cost of a generating station. The lines supplied by each
sub-station were comparatively short and the voltage of
the circuit remained much more nearly constant than be-
fore.
One of the largest and most modern examples of this
system of distribution is that of the Interboro Rapid
Transit Co. of New York City.
Each of the generating units consists of a compound en-
gine and a generator of 3.750 kw. capacity, deliv-
ering 25 cycle alternating current at 11,000 volts. The
216 ELECTRICITY
power is sent out at this voltage directly without the use
of raising transformers and delivered to sub-stations along
the subway lines. At these stations it is then reduced by
means of lowering transformers to such a voltage that
when applied to the rotary converter direct current will
be delivered at 600 volts, which current operates the rail-
way motors.
This system may be said to have become standard for
large cities. Cables for underground use can now be made
which are entirely reliable and satisfactory on 11,000 volts.
This voltage is, however, as high as engineers will will-
ingly guarantee and dispenses with the use of the large
raising transformers necessary with lower voltage gene-
rators.
The first transmission of power to a distance in the
United States was made in the year 1890, one year before
the Frankfort-Lauffen experiment. This station is at the
falls of the Willamette River in Oregon, thirteen miles
from Portland, where water-power estimated at 225,000
horse-power is obtainable.
In 1893 ^ nad been in successful operation for three
years with satisfactory results, both as to the working
of the apparatus and the cost of maintenance, the opera-
tion of the dynamos being described as admirable and the
transformers not having cost a cent for repairs.
The plant, however, to which much of the present
knowledge of conditions affecting high-voltage operation
is due is that of the Telluride Power Co. in Colorado.
This plant operates under particularly severe conditions,
and in the overcoming of the obstacles encountered much
valuable information was gathered. Here, for the first
time, men were systematically trained for operating the
plant, each man receiving a general education in all the
branches of engineering connected with it. Much of its
success was, therefore, due to the knowledge and skill of
its operating force. Here that natural enemy of long-
distance transmission — lightning — was met and conquered.
POWER TRANSMISSION
217
"Near Telluride, Colorado," says Atkinson, "is a water-
power station from which power is electrically transmit-
ted to the Gold King mill, nearly three miles distant, where
it is employed for operating crushers and stamps. It
was equipped, when first constructed, with a Westing-
house alternating-current dynamo of 100 hp., operated by
Fig. 21 — Connections of the Telluride Water-pow^r
Transmisson.
a Pelton turbine wheel driven by water received through
a steel pipe 2 feet in diameter, under a head of 320 feet.
The general construction of this dynamo is the same as
that of the dynamos employed at the Willamette Falls
station, but its field winding is composite, part of the
magnets being excited by the armature current of a sepa-
rate direct-current machine and the others by a current
from its own armature, which is made by an apparatus*
218 ELECTRICITY
equivalent to a two-segment commutator, the adjustment
being such that the e.m.f. of the current delivered through
the mains rises as the current strength increases, compen-
sating for the fall of potential in the line and keeping the
e.m.f. at the motor constant at 3,000 volts. The speed is
83 revolutions per minute, producing 10,000 alternations
of current.
'The main current flows directly to the motor at the
mill without transformation, the only transformers em-
ployed being the small ones connected with the indicators
on the shunt circuits. The motor is the same in size,
horse-power and general construction as the dynamo, and
runs in synchronism with it, but is excited by a current
from its own armature, obtained from a special winding
parallel with the main armature coils, and connected with
the field coils by a circuit in which the current is made*
direct by a commutator. A small Tesla motor of special
construction is employed as a starter for the large motor,
and is connected with the mains by a parallel circuit, as
shown. The armatures of both motors are belted to a
countershaft on which the ratio of size between the pul-
leys is such as to give the armature of the large motor a
little higher speed than that of the small one.
"When the circuit of the small motor is closed its arma-
ture quickly attains its normal speed, putting the arma-
ture of the large one in rotation, at a speed somewhat
higher than that of the dynamo, and causing it to gen-
erate a self-exciting current at the normal e.m.f. of the
circuit. The small motor is then switched off and the
speed of the large one gradually decreases till it is ap-
proximately equal to that of the dynamo, the relative
speed of each machine being indicated by the degree of
illumination in incandescent lamps connected in series
with the secondary coils of two transformers whose pri-
mary coils are connected, respectively, with the circuit
of each machine, as shown; the illumination decreasing,
from decrease of current, as the speeds of the two ma-
POWER TRANSMISSION 219
chines approach equality. When the proper relative speed,
as thus indicated, is attained, the main circuit of the large
motor is closed by its switch and it is connected with the
mill machinery by its friction clutch, the small motor hav-
ing been disconnected by its clutch and brought to rest.
The whole operation of starting is accomplished in about
two minutes by one man.
If the speed of the motor, on starting, should happen
to be a little lower than that of the dynamo it may rise
to the proper speed; but if much lower, it will continue
to decrease, in which case the switch of the large motor
is opened and that of the small one closed, and the speed
thus restored. The field current of the motor, as indicated
by the ammeter, is regulated, on starting, by a rheostat,
and requires no further adjustment for the varying loads.
The line runs across a rough country, ascending a moun-
tain at the power station to a height of 2,500 feet, at an
angle, in some places, of 45 degrees, and parts of it are
practically inaccessible in winter, the snow being some-
times on a level with the tops of the poles. Special pro-
tection is required against lightning, to which this region
is peculiarly liable, 40 discharges through the lightning
arresters having, on one occasion, occurred in 40 minutes.
The successful operation of the plant under these un-
favorable line conditions, and with a comparatively new
type of electric apparatus, since its completion in June,
1891, has inspired such confidence that extensive additions
have been made both for power and lighting, which indi-
cates that for the former purpose as well as the latter
the employment of the alternating current with long-
distance transmission has passed from the experimental
to the practical stage." Since the above writing many
trials of high voltage have been made at this plant, until
it is now operating at 40,000 volts.
The Niagara Falls Power Transmission was one of the
earliest, and is still the largest. The first station was
built on the American side, and contains ten 5,ooo-hp.,
220 ELECTRICITY
two-phase, 25-cycle, 2,200-volt alternating-current genera-
tors. Each of these generators is mounted at the top
of a long, vertical shaft, at the lower end of which is the
turbine. Since the weight of the generator and turbine
is very great, too great to be supported by a bearing, the
turbine is so constructed that the action of the water
tends to balance this weight. The armatures of the gen-
erators are stationary and the field magnets revolve out-
side the armature, being shaped like an umbrella. The
best engineering skill in the world was employed in de-
signing the plant, and its success is largely due to that
fact. Turbine wheels and generators of that size were
practically unknown, and the starting of the plant marked
the beginning of a new era in the development of large
water-powers.
Since the construction of the first plant another similar
one has been built containing eleven units of the same
capacity, making the total output of the two plants 105,000
hp. Two other plants also have been constructed on the
Canadian side of the river, which deliver part of their
power to towns in the United States.
Most of the power from the two American plants is
consumed by local manufactories which have sprung up
there; 30,000 hp. is sent to the city of Buffalo, about 25
miles away. Since power can be transmitted with 25 per
cent, less copper with three-phase than with two-phase
current, the two-phase current, generated at 2,200 volts,
is changed by transformers to three-phase and the voltage
at the same time is raised to 22,000. The distance to
which Niagara Falls is transmitting its power is in-
creasing daily, the greatest distance being to Syracuse,
160 miles away, where power is delivered at 60,000 volts.
A typical water-power station, with a transmission line
which is said to be, at present, the longest in the world,
is that of the Bay Counties Power Co. of California.
"This transmission system," says R. W. Hutchinson, in his
'Long Distance Power Transmission/ "is the longest in
POWER TRANSMISSION 221
existence, and was first put in operation on April 27,
1901. The company supplies power from three plants
operated in parallel. Power is transmitted at 40,000 volts
to Oakland, a distance of 142 miles from the main gen-
erating station, and power is supplied to the Standard
Electric Company for transmission to various points along
San Francisco Bay, the farthest of which is Stockton,
218 miles distant from the main power plant."
Altho long-distance power transmission by continuous
currents is practically unknown in this country, there
are many examples of this type in Europe which have
operated in competition with alternating current, and
which are still being installed. Most of these plants are
located in Switzerland and France, and are in satisfac-
tory operation at present. Much of the development in
continuous current working has been due to M. Thury,
a French engineer, and the originator of the system which
bears his name. In this system a number of series-wound
generators are connected in series, so that their voltages
add together. It is evident, therefore, that any voltage
may be generated by connecting together a sufficient num-
ber of such machines, and 60,000 volts have in this man-
ner been obtained. Direct-current generators of this type
can be built which will operate satisfactorily as high as
4,000 volts. In obtaining the 60,000 volts above men-
tioned sixteen of these generators are connected in series.
Each machine is substantially insulated, both from the
floor and from its driving turbine. The Thury system is
known as a "constant-current" system, because the cur-
rent is held constant no matter what the load may be;
but the voltage is varied, so that at light loads the voltage
is low, and reaches its maximum only at times of full
load.
The line is very simply constructed, consisting of two
wires, and in case of accident to one wire the earth may
be used as a return. The line, therefore, presents a much
simpler construction than that for an alternating-current
222 ELECTRICITY
system requiring three wires. At the receiving end the
electrical power is converted into mechanical power
through a number of series motors connected in series
across the line. A centrifugal governor attached to each
motor holds its speed constant by- varying its field strength.
For this purpose a portion of the current (which is always
the same) is shunted from the field through a resistance.
What are the advantages and disadvantages of this sys-
tem ? The chief advantage claimed for it by its advocates
is the simplicity of its line construction. With direct cur-
rent the insulation of the line is only subjected to the
effective voltage of the line, while in an alternating-
current transmission the voltage which the insulators
must stand is at least 1.4 times the effective line voltage;
and, in addition, surges of waves of voltage are liable to
occur which may double this value. It will therefore be
apparent that the direct-current line has a decided advan-
tage. Another advantage claimed for it is its ability
to operate during lightning discharges, since more effec-
tive arrangements may be made to prevent the lightning
from entering the stations.
Coming to the stations, however, the direct-current
system has serious drawbacks. It has not been found
practicable as yet to build the generators larger than 400
kw. output. To equal one of the Niagara Falls power
stations in output would, therefore, take 125 such gen-
erators. Advocates of the alternating-current system
have always considered these stations too complicated for
satisfactory operation. It must be admitted, however,
that M. Thury, through persistent work, has simplified the
station to such an extent as fully to meet this objection.
On the whole, alternating-current transmissions seem
to be more satisfactory than the direct current, and this
advantage will increase as alternating-current motors
reach the perfection attained by direct-current machines
and line insulation becomes so perfected as easily to
withstand the voltages imposed upon it.
POWER TRANSMISSION 223
Regarding recent developments in high-voltage trans-
mission and its future limits, the 'Engineering Record,'
August 15, 1908, says: "It is just now worthy of special
comment that the record for high voltage has again been
raised, this time to the soaring figure of 110,000 volts.
For once the palm for sensational engineering has left the
Pacific coast, to repose, for a while at least, in the custody
of the Central States. This latest step forward must really
be regarded as epoch-making, since it carries the art of
power transmission from the region of the tried and stand-
ard into the unknown country beyond ; and the best of it is
that the incursion has apparently been a victory. It is
a new proof that all things come to him who dares.
"At last the next great step has been taken, thanks to
the enterprise of the insulator maker, and especially to
the construction of the suspension type of insulator, which
makes relatively easy pressures before difficult. The pin
insulator, when constructed of dimensions adequate for
very high voltage, became unwieldy and mechanically
troublesome; not so the suspension insulator, which actu-
ally leads to improvements in line construction. It will
probably be found, too, as is often the case, that the
precautions now considered necessary in going to very
high voltages will prove to be more than adequate in the
light of practical experience. It is a fact that in Conti-
nental practice surprisingly small and simple insulators
have been found entirely successful for pressures con-
siderably higher than would be attempted with the same
material here. American engineers attach great impor-
tance to preserving a high line insulation, as they should,
but they went through a period in which the size of insu-
lator was all out of proportion to their quality and de-
sign. Now, practice is settling into sounder lines and
will go on to better and better results. The fact is that
at every stage of progress toward high voltage advance
has proved to be easier than seemed at first possible.
Difficulties that seemed insuperable have been, time and
224 ELECTRICITY
again, overcome with comparative ease, so that now one is
not beside the mark in counting upon a very general ad-
vance in the near future. Of course, the plants in which
100,000 volts or more is a figure commercially necessary
are relatively few. As time goes on, however, and the
more remote powers are utilized, high voltage will become
more and more necessary, and will be more generally
employed.
"As to the limits which may be reached one would be
unwise to prophesy. At 100,000, or about there, a condi-
tion is reached where, save for large powers and long
wires, further increase would lead to wires too small to be
desirable mechanically. In addition, it is undesirable, for
electrical reasons, to use anything much below a quarter
inch in diameter at very high pressure, so that there is a
natural limitation to the number of very high voltage plants.
Yet, for the really big work of the future, success depends
on just such bold achievements as the one here considered.
The next step will probably be in the direction of a very
long line at extreme voltage. Here, again, is a debatable
ground, owing to line difficulties. No one has yet oper-
ated a line of such length as to be a material fraction of
the natural wave-length corresponding to the frequency.
There is a possibility of a new class of troubles arising
under such circumstances, and new devices may be re-
quired to meet it. It is on such very long lines that the
use of high-tension continuous current has found some
advocates. Severe requirements as to the use of cables is
a possible source of future trouble, but here also the manu-
facturer may be counted on to push ahead; 20,000-volt
cable is in use in England to the extent of several hundred
miles, and 40,000-volt cable has been successfully worked,
so that if the time should demand underground lines at
100,000 volts or more it is safe to say that they would be
forthcoming."
CHAPTER VI
THE HISTORY OF ELECTRIC LIGHTING
The history of electric lighting begins soon after the
discovery of electric currents. In 1800 Sir Humphry
Davy, while experimenting with the effects of currents,
obtained bright sparks between two charcoal points upon
breaking the contact between them. The number of
cells with which he worked was, however, insufficient to
produce a continuous light. After a few years he in-
creased the number of cells in his battery until it was
composed of 2,000 elements. With this powerful source
of current he was able to obtain a continuous discharge
between carbon points which sustained itself across a gap
of 7 inches and emitted a dazzling light. This light was
exhibited in 1813 at the Royal Institution. Davy found
that the conducting power of the charcoal points was im-
proved by extinguishing the charcoal under mercury. The
consumption of these points was very rapid. The name
"voltaic arc" came from this experiment of Davy's, from
the fact that the stream of vapor formed itself into a
bow, the charcoal points being horizontal.
Owing to the high cost of producing the electric current
no one seems to have cared either to develop a lamp or
to ascertain the properties of the arc itself until 1844,
when Foucault constructed a lamp using carbons from
the retorts of gas works, which were much harder and
more compact than Davy's charcoal points and less easily
consumed.
225
226 ELECTRICITY
Thomas Wright, of London, devised the first apparatus
(1845) in which the adjustment of the carbons is brought
about automatically. W. C. Staite used the electric cur-
rent for the regulation of the carbons in 1848. In 1858
Foucault devised a lamp in which the carbons were made
to approach automatically by means of a clockwork feed,
the clockwork being controlled by an electromagnet. As
the current diminished in strength, due to the increase
in the length of the arc as the carbons burned away, a
magnet in series with the arc weakened and released the
escapement of the clockwork, thus moving the carbons
together. In this lamp both carbons moved, and were
so regulated in their motions as to maintain the arc in
a fixed position. In later lamps, used for general illum-
ination, this was not considered necessary, and the regu-
lating mechanism was considerably simplified. The lamps
were known as "focussing" or "self-centering" lamps,
and are still necessary in some cases, such as stereopti-
con work.
Before proceeding with the history some of the proper-
ties of the arc may be examined. If it is attempted to pro-
duce an arc by means of a few cells of battery the at-
tempt will be unsuccessful. It is necessary that a differ-
ence of potential of about 40 volts should exist between
the carbons before any stream of vapor will be formed.
The longer the arc produced the higher is the voltage
necessary to maintain it. In the ordinary carbon lamp
practically no light comes from the arc itself; it is all
emitted from the white-hot carbon points. If the source
of current is direct or continuous, most of the light is
radiated from the positive carbon, or that by which the
current enters, and this carbon is consumed about twice as
rapidly as the other. From this fact it will be seen that
in such lamps as Foucault's it was necessary to arrange
the mechanism so that the positive carbon should move
at about twice the rate of the negative. Another pecul-
iarity is the manner in which the carbon points burn away.
HISTORY OF ELECTRIC LIGHTING 227
When the combustion takes place in the air the positive
carbon has a depression or "crater" formed in it, and upon
the negative is produced a nib. This seems to be due
entirely to the fact that combustion takes place in air,
as the phenomenon disappears when the arc is enclosed,
and both carbons become blunt. This seemingly slight
difference was, however, a factor of considerable con-
sequence, as the greater part of the light is emitted from
the intensely hot crater of the positive carbon, so that
in the open arc much of the light is cut off from the
horizontal direction by the rim of the crater, which is
removed by enclosing the arc. The temperature of the
arc is the greatest of all earthly temperatures, nearly all
substances volatilizing almost instantly.
Arc-lamp development was stimulated by the construc-
tion of the magneto-electric machine, which greatly de-
creased the cost of power. The introduction of the dy-
namo, however, completely solved the problem of power,
and the field was immediately opened for the electric light.
One of the first successful lights was the electric candle
of Paul Jablochkoff, invented in 1876. This is probably
the simplest of all electric lamps. As shown in Fig. 22, it
consists of two carbon rods placed parallel, and sepa-
rated from each other by plaster of paris, the rods having
brass tubes at their lower ends which make contact with
springs set in the holding device. To start the candle
a thin plate of graphite was laid across the tip, this being
heated by the passage of the current sufficiently to start
the arc. Difficulty was, of course, encountered in oper-
ating these lamps on direct current on account of the
unequal rates of burning of the positive and negative
carbons. It was attempted to overcome this by making
the positive twice as thick as the negative carbon, but the
ratio not being exact, and liable to variation, caused the
failure of this method. They were therefore operated
on alternating current, and over 4,000 were in use in Paris
alone. The lamps, however, were not satisfactory, and
228
ELECTRICITY
inventors gradually reverted to the lamp with the adjust-
ing mechanism.
As soon as arc lamps had to be operated over a consid-
erable territory it was seen that the mode of connection,
known as "series," wherein a single wire is used to con-
nect the lamps together, was preferable to the "parallel''
—The Jablochkoff
Candle.
Fig. 23 — The Starr- King
Incandescent Platinum
Lamp, 1845.
system, which required two wires, both in economy of
wire and in saving of power. This required a special
arrangement of the lamp mechanism. On the series sys-
tem the same current passes through each lamp, and since
it requires about 50 volts to operate a lamp the generator
must develop as many times 50 volts as there are lamps.
This necessitated the construction of a generator which
should develop a high voltage, as there were often as
HISTORY OF ELECTRIC LIGHTING 229
many as 125 lamps on one line, requiring 125 X 5°> or
6,250 volts. Such a suitable generator was devised by
Mr. Charles Brush, and is known as the Brush arc-light-
ing dynamo.
Returning to the mechanism of the lamps suitable for
Fig. 24 — Diagram of Siemens' Differential Lamp.
such a circuit, one of the first of these was constructed
by Hefner Alteneck, and is known as the Siemens differ-
ential lamp. This type of regulator is still in use, altho,
of course, modified and improved. Fig. 24 illustrates the
method of regulating. The lower solenoid R is known as
230 ELECTRICITY
the "series" coil, and carries the same current that passes
through the arc. The upper solenoid T has many turns
of fine wire and is connected across the arc. The two
coils act upon the same core in opposite directions, hence
the name "differential." If the carbons approach too
closely the current in the series coil increases and pulls
them apart, but as the length of the arc is increased*
thereby the voltage across it grows greater and the shunt
coil T receives more current. This prevents the series
coil from producing too great a motion, and the carbons
are held by the balancing action of the two coils. The
upper carbon alone is fed down by the action of gravity,
the lower carbon being fixed. This style of lamp was
also developed by Brush in America, and many thousands
have been used. The combination of the Brush high-
voltage generator and the differential-series lamp was
quite satisfactory as a means of lighting, and many of
these arrangements are in use at the present time, altho
they are fast being replaced by more modern systems.
With the open arc lamp of the Brush type the replace-
ment of the carbons was required daily, and became quite
an item in the total expense of operation. About 15
years ago arcs enclosed by a thin glass were introduced
which required trimming only once in ten or fifteen days.
At first it was thought that the enclosing glass would
cut of! so much of the light as to seriously impair the
efficiency of the lamp. The fact previously mentioned
concerning the flattening of the carbon tips and a con-
sequent better distribution of the light here came to the
aid of the enclosed lamp, so that altho there was some
loss of light due to the glass, the improved distribution
overbalanced that effect. A grave fault, however, was the
deposition of the silicious impurities of the carbons on
the enclosing glass, with a consequent diminution in the
light. Efforts were accordingly directed toward the im-
provement of the carbons, and altho it has not been found
HISTORY OF ELECTRIC LIGHTING 231
possible to produce carbons free from such material, that
fault is not at the present time serious.
Altho the series system of operation is the only prac-
ticable one over long distances, it is often required to
operate arc and incandescent lamps on the same circuit,
as in buildings, etc. For such work the differential mech-
anism of the series system is not suitable. In that sys-
tem the lamps act to steady one another, for with so
many in circuit the fluctuations of one lamp do not ap-
preciably affect the current in the circuit. The operation
of a single lamp requires, therefore, something to replace
the steadying action of the other arcs, and this is accom-
plished by means of a dead resistance. Some energy is,
of course, wasted in this resistance (about 25 per cent.),
but the operation is very satisfactory.
The ordinary carbon arc lamp, altho one of our most
efficient sources of light, is still far from the ideal. Of
the total energy radiated from it only about 10 per cent,
has the proper frequency of vibration to affect the eye
as light. The ideal light would emit rays all of which
would affect the eye. One means of effecting this increase
is to raise the temperature of the heated body; another,
to employ a different material, since all materials do not
emit equal light at the same temperature. Attempts to
utilize the latter principle resulted in the production of
"luminous" and "flaming" arcs. Some of the most prom-
inent workers on this subject are Bremer, Auer, Nernst,
Blondel, Whitney and Steinmetz.
The luminous arc is composed of two electrodes which
supply a stream of light-giving vapor. One of the most
prominent examples of this type is that developed by Mr.
Steinmetz, and known as the magnetic arc. The positive
electrode is a rod of copper, the negative a rod of mag-
netite, or iron ore. The light given off is an intense
greenish white, the efficiency being several times that of
the ordinary arc. They have recently been established
on a commercially operative basis, altho still unsatisfac-
233 ELECTRICITY
tory in some respects. They can operate only on direct
current, which usually involves the rectification of the
alternating current, now almost universally generated.
The flaming arc is almost invariably produced by util-
izing the intense heat of the carbon arc to render incan-
descent various refractory materials. For this purpose
either one or both of the carbons are impregnated with
metallic salts having great light-giving power, as calcium,
titanium, strontium, etc. The most efficient of these are
the salts of calcium, which emit dazzling yellow rays.
For some purposes — as interior lighting — these rays are
objectionable on account of the distortion of color which
they produce, and the salts of titanium are preferred, as
these emit a beautiful white light, altho of less intensity.
The lamps may be operated on either direct or alternating
current. The objectionable features of these lamps are
the increased cost of the carbons and their short life.
For that reason they have not yet come into general use
for street lighting. In respect of life the magnetic arc
has the advantage, its life being about the same as the
enclosed carbon arc — 150 hours.
Developments in arc lighting have followed one another
with such rapidity during the last seven or eight years,
and are still progressing so swiftly, that one hardly knows
where they will stop. The fine organizations of engineer-
ing and scientific skill under the control of large electrical
enterprises have made possible these rapid developments
of the last few years.
"Admirable as is the system of electric-arc lighting for
use in streets and open spaces, and in workshops or large
halls," says Henry Morton in his 'Electricity in Light-
ing/ "it is entirely unfit to take the place of the numerous
lights of moderate intensity employed for general domes-
tic illumination. For this purpose it was at a very early
period perceived that the incandescence, or heating to
luminosity, of a continuous conductor by an electric cur-
rent was the most promising method. It was also at a
HISTORY OF ELECTRIC LIGHTING 233
very early period perceived that the conductor to be used
for this purpose must be one which would admit of being
raised to a very high temperature without being melted
or otherwise destroyed. The first material which was
thought of in this connection was platinum, or one of
its allied metals, such as iridium, which have the highest
melting points among such bodies, and are, besides, en-
tirely unacted upon by the air at all temperatures.
"In 1848 W. E. Staite took out a patent for making
electric lamps of iridium, or iridium alloys, shaped into
an arch or horseshoe form. One of the most serious
difficulties, however, even with these materials, was that
to secure from them an efficient light it was necessary
to bring them so near to their fusing points that a very
minute increase in the current would carry the tempera-
ture beyond this and destroy the lamp by fusing the con-
ductor.
"An escape from the difficulty was offered by the use
of hard carbon, such as that employed for the electrodes
of arc lamps; but here the compensating drawback was
encountered that this substance, when highly heated, was
attacked by the oxygen of the air, or, in other words,
burned. To meet this plans were devised for the replace-
ment of the consumed carbon in a non-active gas or m
a vacuum. Thus, in 1845, a patent was taken out im
England by Augustus King, acting as agent for an Ameri-
can inventor named J. W. Starr, for an incandescent lamp,
the important parts of which are represented in Fig. 23.
Here a platinum wire is sealed through the top of a small
glass chamber constituting the upper end of a barometer
tube. This platinum wire carries at its power end a clamp,
which grasps a thin plate or rod of carbon, and also a non-
conducting vertical rod or support, which helps to sus-
tain another clamp, which grasps the lower end of the
carbon strip and connects it by a wire with the mercury
in the barometer tube below. By passing a current through
the platinum wire, and thence through the upper clamp,
234 ELECTRICITY
carbon strip, lower clamp, wire and mercury, the carbon
strip could be made incandescent, and was to a certain ex-
tent protected by the surrounding vacuum. Tho this lamp
produced a brilliant light, it proved in various respects un-
satisfactory, and was abandoned after numerous trials.
Other inventors, as, for example, Konn, of St. Petersburg,
continued to work with rods or pencils of hard carbon and
achieved a limited success, but the irregularity and brit-
tleness of the material seem to have been an insuperable
objection and drawback, and the problem of commercial
electric lighting by incandescent conductors yet remained
without a solution.
"This was the state of affairs even up to the fall of 1878,
when, as is claimed, William E. Sawyer, in combination
with Albon Man, after many preliminary experiments, pro-
duced their first successful incandescent lamp with an
arch-shaped conductor made of carbonized paper. In
their application for a patent, filed January 8, 1889, these
inventors use the following remarkable language in their
fourth claim: 'An incandescing arc of carbonized fibrous
or textile material.' This indicates that they realized the
importance of what seem to be the common features of the
present electric incandescent lamps, namely, the arc or
arch or bow or loop form, and the carbonized fibrous or
textile material. They also specially refer to carbon in-
candescent conductors made from paper.
"After a long and hotly contested interference, the
United States Patent Office has granted them a patent in
which these points are broadly stated. The lamp brought
out by Messrs. Sawyer and Man, soon after their applica-
tion for a patent, and described and shown in that appli-
cation, was a rather large and complicated structure, and
had no improvement and simplification of this structure
been made the present immense development in electric
lighting would no doubt have been unattained. It is to
T. A. Edison, without doubt, that we owe many of the
simplifications and modifications which, by cheapening the
HISTORY OF ELECTRIC LIGHTING
235
lamp and diminishing its weight, have extended its range
of use and its usefulness to a remarkable degree. On his
return in the fall of 1878 from the far West, where he had
gone in company with Dr. and Mrs. Henry Draper, Dr„
George P. Barker and the present writer, to observe the
total solar eclipse of that year, Mr. Edison visited the
shops and laboratory of William Wallace, at Ansonia,
Conn., where many experiments with electric-arc lights
and dynamo-machines were in progress, and while study-
Fig. 25 — Edison's First Incandescent Platinum Lamp.
ing these was impressed with the desirability of producing
an incandescent electric lamp. Like so many before him,
he first turned to platinum and platinum alloys, and de-
vised a form of lamp admirable for its simplicity, but,
unfortunately, open to a fatal objection. This first lamp
of Edison's is shown in Fig. 25, in which a b is the in-
candescent platinum wire.
"The announcement of a new system of electric light-
ing, made by Mr. Edison and his friends on the foundation
of this device, attracted universal attention, and even
caused a serious fall in the value of 'gas stocks' in this
country and abroad. It is, indeed, amusing now to look
back upon the extravagant assertions and predictions made
at that time and widely circulated when we realize how
236 ELECTRICITY
more than frail was their foundation. In fact, Mr. Edison
very soon found out that this simple device was entirely
insufficient for the purpose proposed, because the heated
platinum wire gradually stretched by its own weight, and
thus was constantly getting out of adjustment, and finally
would become attenuated and break.
"It also happened that, though the secret of this great
invention was carefully guarded, some inkling of it es-
caped, and this enabled those who were familiar with such
subjects to perceive the close similarity between this Edi-
son lamp and a similar device constructed and used by
Dr. J. W. Draper prior to 1847, and described and figured
in articles published by him during that year in the Ameri-
can Journal of Science and Arts, The London, Edinboro
and Dublin Philosophical Magazine, and Harper's New
Monthly Magazine. This apparatus was used by Dr.
Draper as a source of light or lamp with which he deter-
mined the relations between temperature and luminosity.
At the conclusion of his article Dr. Draper says: 'An in-
genious artist would have very little difficulty, by taking
advantage of the movements of the lever, in making a self-
acting apparatus in which the platinum should be main-
tained at a uniform temperature notwithstanding any
change taking place in the voltaic current/
"It also appeared that precisely the same idea had oc-
curred to another inventor, Hiram S. Maxim, who has re-
cently developed such a marvelous improvement in maga-
zine or repeating guns, and who, on December 22, 1879,
filed an application for a patent which, after an interfer-
ence litigation with Edison, was finally issued to Maxim
on September 20, 1881, for the form of electric lamp shown
in Fig. 26. It has also been shown that in 1858 M. G.
Farmer, one of the veteran electricians of America, to
whose work in connection with the dynamo-electric ma-
chine allusion has been made before, lighted a room in his
house at Salem, Mass., for several months with platinum
lamps of similar structure controlled by automatic regula-
HISTORY OF ELECTRIC LIGHTING 23?
tors. During 1878 and 1879, however, Mr. Edison was
most diligently at work, and perceiving the imperfections
of his first ideas, sought in every way to overcome them
It thus came to pass that by December 21, 1879, at which
date he made his first revelation to the public, in the pages
of the New York Herald, he had perfected a platinum
lamp which is shown in outline in Fig. 27, as well as
some other forms substantially like it.
Fig. 26 — Maxim's Incandescent Platinum Lamp.
•"But these platinum conductor lamps were not the only
outcome of Mr. Edison's work between the fall of 1878
and December, 1879. As this Herald article also related,
Mr. Edison, like many before him, having experienced
the insuperable difficulties present in metallic conductors,
had turned his attention to carbon in various forms; and,
like Sawyer and Man, had found fibrous textile materials,
when carbonized, to be most convenient, and paper es-
pecially to be, in the first instance, the most available sub-
stance. Like Sawyer and Man, he had also found the
238
ELECTRICITY
arch, or horseshoe form, to be the most desirable. Tho
working with the same materials and form, Edison pro-
duced a structure very different in appearance from that
of Sawyer and Man, as will be seen by reference to Fig.
28, which represents one of Edison's paper carbon lamps,
which was the first one whose electric properties were ac-
curately measured, these measurements having been made
at the Stevens Institute of Technology, early in 1880, by
Fig. 27 — Eeison's Platinum Lamp on Column Support, 1879.
Fig. 2d, — Edison's Paper Carbon Lamp.
the present writer, acting in his capacity as Chairman of
the Committee on Scientific Tests of the United States
Lighthouse Board, that body desiring information as to this
new light, and deputing the work of investigation to this
committee.
"In this lamp the carbon conductor is supported on plati-
num wires and held in minute platinum clamps at the ends
of these wires, which are sealed through the walls of the
pear-shaped enclosing tube in the manner which has been
HISTORY OF ELECTRIC LIGHTING 239
familiar for twenty years in the construction of the beau-
tiful toys known as 'Geissler tubes/ The interior of this
glass vessel had likewise been exhausted and hermetically
sealed in the manner usual with many Geissler tubes and
with the radiometers of Dr. William Crookes."
Since its invention the Edison lamp has maintained a
practical monopoly, and it is only within the last few years
that other competitors have loomed up which threaten its
supremacy. They still have difficulties to surmount, how-
ever, which have already been overcome in the carbon-fila-
ment lamp.
Edison's first filaments were made of carbonized thread
or paper. It is obvious that such filaments could not be
made with any great uniformity. A great many experi-
ments were made and are still being made to determine the
best method of making them. They are all, however, made
by what is called the "squirting" process, of which an
outline follows.
Pure cellulose, as cotton-wool or blotting-paper, is dis-
solved in a concentrated solution of zinc chloride until a
jelly-like mass is obtained. Great care is required to ob-
tain pure materials, and the various processes must be
closely watched. This mass is filtered by forcing.it through
a suitable filter such as glass-wool, fine wire-gauze, or
flannel. It is then heated under a vacuum to free the vis-
cous material from air carried into it by the cotton-wool
or cellulose. It is then squirted under fairly high pres-
sure through a fine orifice, which just dips below the sur-
face of acidified alcohol contained in a tall glass jar. The
alcohol hardens the cellulose, which forms a fine thread of
a diameter depending on the size of the orifice. By re-
volving the jar, the thread is coiled in it. When hard, it
is removed and washed and wound on drums to dry. When
dry it has the appearance of catgut. It is then given the
desired shape by being wound on molds and baked. Bun-
dles of filaments are then packed in carbon powder in
240 ELECTRICITY
plumbago crucibles which are raised to as high a tempera-
ture as possible.
The carbonized filaments are gauged for diameter and
the legs cut to the required length, after which they are
ready for mounting on to the leading-in wires. There are
two methods for doing this. In one, the ends are laid
against the leading-in wires and a drop of paste composed
of graphite mixed with a binding material is applied, the
paste being afterward dried in an oven; in the other, by
heating the joint red-hot in an atmosphere of benzene, the
benzene having decomposed and carbon deposited.
The filament is then "flashed" in order to make it more
uniform and increase its life. Flashing is accomplished
by placing the filament under a bell-jar filled with hydro-
carbon vapor, and raising it to incandescence by the pass-
age of a current, whereupon the vapor is decomposed and
a firm compact coating of carbon is deposited upon it.
The greatest deposit takes place where the filament is thin-
nest, as the current causes it to heat most in that part.
Flashing, therefore, smoothes out the irregularities of the
filament.
The filaments are next sealed into bulbs and the bulb
exhausted. In the early days, Sprengel mercury pumps
were used, but these were very slow, altho very perfect.
Nowadays, a little phosphorus dissolved in alcohol is intro-
duced into the stem, which is then connected to a mechani-
cal air-pump having oil-sealed valves and exhausted as
far as possible. The stem is then sealed a short distance
below the bulb and the phosphorus vaporized by a little
heat into the bulb, where it combines with the remaining
oxygen and completes the exhaustion. The lamp is then
properly sealed off.
The first patents covering the principle of the Nernst
lamp were taken out by Professor W. Nernst in 1897 and
1898. In its first form it was very crude, serving mainly
to show the fact that the filaments could be produced and
«hat their efficiency was about twice that of the ordinary
HISTORY OF ELECTRIC LIGHTING 241
carbon filament. This was the first incandescent lamp to
threaten the life of the Edison carbon filament lamp. Much
was promised for it at first, and its development was vigor-
ously taken up in this country, England and Germany.
Altho the lamps are still manufactured, very few are in
use, and it is probable that the manufacture of them will
soon cease entirely. The recent introduction of the tung-
sten lamp has made its existence unnecessary, as it is sur-
passed by the tungsten lamp in efficiency, life and first
cost. It contains, however, a very interesting principle,
viz., the employment of an electrolytic conductor as the
incandescent body. This conductor or glower, as it is
called, is practically non-conducting at ordinary tempera-
tures and requires to be heated before it will allow the
passage of current through it. This fact is probably the
principal cause of its failure commercially, as the heating
apparatus is quite complicated, of uncertain life, and the
time consumed in lighting (sometimes half a minute) is
in many cases objectionable. This is the only electric
lamp that can be started with a match and blown out.
The glower of the American form of Nernst lamp is
said to consist of the oxides of several rare metals, such
as yttrium, ytterbium, thorium, etc., altho the true com-
position is known only to a few. The glowers are in the
form of a short, thick filament, cemented to flexible plati-
num terminals by which it is suspended below and close to
heating coils, consisting of porcelain tubes in which are
imbedded resistance wires. These resistance coils are, of
course, necessary to bring the glower up to the tempera-
ture at which it begins to conduct. The heating resistance
is connected in shunt with the glower, which has in its
immediate circuit an electro-magnetic switch for opening
the heater circuit. When the glower becomes sufficiently
heated to conduct, the current in this portion of the circuit
operates the electro-magnetic switch and automatically
cuts out the heating coils.
As the glower conducts electrolytically rather than as a
242 ELECTRICITY
solid, tip to the present it has given a much shorter life
when used on direct or low frequency alternating current
circuits than with higher frequencies. Altho up to the
present time these lamps cannot be called a commercial
success, recent developments and improvements in con-
structional details have made the efficiency of the lamp
equal to that of the tungsten. If a method of producing a
lamp free from the complicated starting apparatus which
now prevails is discovered, these lamps may be heard from
again.
These lamps have followed one another in such rapid
succession that some of them, altho full of promise,
have never been long in the commercial field, having been
succeeded by others still better. Incandescent electric
lamps with metallic filaments are older than carbon-fila-
ment lamps. As long ago as 1840 lamps were constructed
with filaments of platinum, and for thirty years after that
date various attempts were made to construct a practical
lamp, using either platinum or iridium wires for the fila-
ments, the only two metals at all suitable which were ob-
tainable at the time. None of these attempts met with any
commercial success, and the use of metals was finally
abandoned in favor of carbon by the experimenters who
developed the carbon-filament lamp in 1878-1880.
The success attained with carbon caused all considera-
tion of metallic filaments to be put on one side for nearly
twenty years. The introduction of the Nernst lamp ap-
pears to have then stimulated research afresh, and many
inventors turned their attention to the metals, to find the
field greatly widened by the chemical progress which had
been made in the meantime. Instead of only two possible
metals to work with, there were now numbers known with
sufficiently high melting points to suggest great possibili-
ties. After much painstaking effort and laborious work,
carried out by inventors who deserve the highest possible
praise for both their ingenuity and their perseverance,
three commercial metallic-filament lamps have been evolv-
HISTORY OF ELECTRIC LIGHTING 243
ed which have entirely altered the outlook for the future
of the electric lighting industry.
"It is possible," suggests Maurice Solomon in his "Elec-
tric Lamps/ "that these may prove to be only the fore-
runners of further improvements; rumors of fresh de-
velopments are of almost weekly occurrence, and it is dif-
ficult to say at the moment what is likely to be the course
of events during the next few years. Up to the present
none of the rumored improvements have given any evi-
dence of being advanced beyond the laboratory stage, and
many do not appear even to have reached that stage, tho
some have been proved commercial, namely, the osmium,
tantalum, and tungsten (Wolfram or Osram) lamps. The
osmium lamp is the invention of Dr. Auer von Welsbach,
and the earliest patents relating to it were taken out in
1898. The earlier reports in reference to the osmium
lamps appeared in the technical press in 1901, but the lamp
does not appear to have been manufactured commercially
until 1903, and it was not until 1905 that it was introduced
into this country by the General Electric Company.
"The method of manufacture may be gleaned from the
patents and from a paper read by Dr. Fritz Blau before
the Elektrotechnisher Verein in 1905. The process first
tried was that of flashing platinum wire in an atmosphere
of osmium tetroxide (which is volatile). By subsequently
incandescing the alloy in vacuo the platinum can be evap-
orated off, but it was not found possible to produce suffi-
ciently thin filaments in this way. Finally the method
adopted was that of pressing finely-divided osmium, mixed
with an organic binding agent, through small diamond or
sapphire dies. The thread thus formed is carbonized,,
and the carbon is then driven off by incasing the fila-
ment in an atmosphere of steam and hydrogen.
"The filaments have to be raised to a very high tempera-
ture in order to "sinter" together the osmium particles into
a practically homogeneous filament. Sintering may be
described as a sort of modified welding process ; the metal
244 ELECTRICITY
does not fuse, but the particles raised almost to their melt-
ing point bake together and bind very firmly ; as a matter
of fact exactly the same phenomenon occurs with carbon
filaments, which after the first stages of baking are highly
porous, but become dense and homogeneous on further
raising their temperature. The osmium filaments are
mounted in bulbs in the same way as carbon filaments, the
mount being made by fixing together by means of an arc
the end of the osmium filament and the leading-in wire.
The osmium lamp has been described on account of its
interesting position as the first of the new metallic fila-
ment lamps. The lamp must be regarded at present as al-
ready obsolete, having given place to the tungsten lamp,
the filament of which is similar in character to the
osmium filament, but in many respects superior.
"The earliest patents in relation to the tantalun lamp
were taken out by Messrs. Siemens and Halske in 1901
and 1902, but the lamp was not introduced commercially
until 1905. During 1906 and 1907 the lamp has steadily
grown in popularity, and the number now in use is very
large. The tantalum lamp can certainly claim to be the
first metallic filament lamp which proved to the full its
suitability by the development of its formidable rival, the
tungsten lamp, and it will continue to be remembered as
the first lamp to afford solid ground for the hope of a
marked advance in electric incandescent lighting. The
filament of the tantalum lamp is made from pure drawn
tantalum wire, and one of the chief difficulties in its manu-
facture is the preparation of the pure tantalum in a
form suitable for drawing.
"Tantalum metal is obtained in a powdery form by re-
ducing potassium-tantalo-fluoride ; the powder is then
fused electrically in vacuo, the process serving not only to
produce the metal in a coherent form but also to drive off
the occluded gases. The fused ingot is drawn into wire,
the precise method by which this is done not being pub-
lished, but the process must be one of considerable dif-
HISTORY OF ELECTRIC LIGHTING
245
ficulty in view of the extreme hardness of the metal, which
is, however, ductile and the tantalum wires are quite flex-
ible. The metal oxidizes readily, and when heated burns
away completely to oxide; the filament must therefore be
mounted in an exhausted bulb, and the difficulty of dispos-
ing of the necessary length in the bulb has been overcome
in an ingenious manner (rendered possible by the flexibil-
ity of the wire) by winding it on a frame as shown in Fig.
29. In this figure, for the sake of greater clearness, only
Fig. 29 — Method of Suspend
ing Tantalum Filament.
Fig. 30 — Method of Support-
ing Tungsten Filament.
the front half of the frame and filament is shown. This
frame is mounted in a bulb in the usual manner. The
other details of the lamp call for no special mention.
Probably, apart from the difficulty in making the original
tantalum wire, the lamp is one of the easiest of the metal-
lic-filament lamps to manufacture, which leads to the hope
that it may be greatly reduced in price when competition
renders this necessary.
"The earliest patents relating to the production of fila-
246 ELECTRICITY
ments of tungsten appeared in 1904. The most important
are those taken out by Just and Hanaman, Kuzel, and
Welsbach. In 1905 and 1906 many other patentees cov-
ered processes for manufacturing these filaments, but it
must be remembered that by this" time the possibilities of
the metallic-filament lamp were becoming well recognised
and many who patented methods and processes probably
did so only in the hope that their ideas might some day
prove fruitful. The credit for the development of a
commercial lamp rests with the inventors already named,
and lamps are now manufactured by all three of the pro-
cesses which they devised.
"It is too early to say which of these is likely to sur-
vive; possibly some modification combining the advan-
tages of all will prove ultimately the most efficient and re-
liable manufacturing process. The tungsten lamp appears
to have a brilliant future before it. While in its present
form it lacks some of the advantages of the tantalum
lamp, the fact that the consumption of power per candle
is only about half that with tantalum will cover a great
many defects. Unless a new metal filament is brought for-
ward with an efficiency markedly superior, it is difficult to
see what competitor now in the field can stand long against
the tungsten filament."
The commercial development of the tungsten lamp has
been conducted with marvelous rapidity. Everywhere they
are rapidly displacing the carbon filament lamps. Their
fragility, however, restricts their use to places where
they are not subjected to mechanical vibration, altho
by ingenious methods of mounting this defect is fast being-
overcome.
The idea of producing light from incandescent vapors
has always been an attractive one. Theoretically it is pos-
sible to obtain a far more efficient light from these vapors
than from incandescent solids, because the emanations are
more nearly of the same frequency than those from solids.
Discharges in vacuum tubes have been tried for many
HISTORY OF ELECTRIC LIGHTING 247
years and there was developed a form of tubes, known as
Geissler tubes, in which the most beautiful effects were
produced by discharges through rarefied gases, but their
brightness was never sufficient for practical lighting.
About ten years ago Peter Cooper Hewitt, making use
of the fact that a column of mercury vapor is a good con-
ductor, succeeded in constructing a mercury vapor lamp of
great power and efficiency. This lamp consists of a long
glass tube, having two electrodes, the negative of which
is mercury. The arc is formed between these electrodes
and completely fills the tube. This is, therefore, a true
arc lamp. The lamp must be burned in an inclined posi-
tion, the mercury being in constant circulation. It is
vaporized at the lower end, condensed at the upper, and
runs back to the lower again. One feature, which for gen-
eral lighting is objectionable, is the color distortion pro-
duced by this light. Since there are no red rays in it,
red bodies appear black, and all objects have a greenish-
blue appearance. For purposes of photography, for draft-
ing-rooms, etc., it is, however, admirable, being rich in the
upper rays of the spectrum.
Following out the idea of producing light from dis-
charges in a vacuum, MacFarlane Moore has succeeded
in producing a lamp which is extremely ingenious. The
chief advantage claimed is the improved distribution of
the light, the light being nowhere intense. The tubes may
be made an hundred or two feet long and may be fitted to
suit the shape of the room. The discharge is effected by
means of a high-voltage transformer. The tubes give off
a pleasing light of a pink color.
CHAPTER VII
THE DEVELOPMENT OF ELECTRO-CHEMISTRY
The striking effects brought about by electricity formed
the subject of much study about the middle of the eight-
eenth century. At that time friction electrical machines
were in use, and in order to intensify the effects produced,
very large machines were constructed. The most famous
of these is still to be seen in the Teyler Museum in Haar-
lem. Pater Beccaria, some one hundred and thirty years
ago, by using such machines found that metals could be
"revivified" (i.e., reduced) from their calces (oxides)
when the electric spark was passed between two pieces.
In this way he obtained zinc and mercury. Some time
later Priestly investigated the action of the electric
spark on air and observed that an acid was produced; he
mistook this for carbonic acid, until Cavendish recognised
it as nitric acid. Van Marum studied the behavior of sev-
eral other gases in this path of the electric spark (which
led him to notice the formation of ozone), and made ex-
periments also by passing the spark through liquids. Be-
fore him, Priestley had discovered that in oil and ether
the electric spark produces gas, and proved that this gas
contained hydrogen.
The first actual electrolysis was made by Deimann and
Paets van Troostwyk in Haarlem in 1789, in which they
successfully decomposed water into hydrogen and oxygen.
In their experiments the water was contained in a cylin-
drical tube closed at the top, and having a metal wire
248
ELECTRO-CHEMISTRY 249
sealed into its upper end. Another metal wire was intro-
duced into the lower end of the tube, which dipped into
a basin of water. When the sparks struck through the
water, bubbles of gas were disengaged from the metal
wires, and, rising in the tube, gradually displaced the
water. As soon as the column of water sank below the
upper electrode the gas, which was a mixture of hydrogen
and oxygen, exploded. This experiment was later re-
peated by Ritter, using silver wires and a solution of a
silver salt, and he observed that the negative pole became
coated with precipitated silver. On changing the poles,
silver was dissolved from one and deposited on the other
(now the negative pole). In Deimann's experiment, oxy-
gen and hydrogen were simultaneously formed both at the
positive and at the negative poles, so that the process was
not a true electrolytic one like that of Ritter's.
The whole state of the science was changed in a great
degree by the discoveries of Galvani, and particularly by
those of Volta. In 1795, Volta arranged the metals in a
series according to their behavior in galvanic experi-
ments, and in 1798 Ritter showed that the same series is
obtained when the properties of the metals to separate;
other metals from their salt solutions are compared.
"After the introduction of Volta's pile (in 1800) the
physiological and optical phenomena were less studied,"
remarks Sven Arrhenius in his 'Text Book of Electric
Chemistry/ "and more attention was paid to the chemi-
cal actions. As opposed to the electrical machines, these
piles gave large quantities of electricity at a compara-
tively low potential. Nicholson and Carlisle, in 1800, stud-
ied the evolution of oxygen and hydrogen in salt solutions
at immersed gold electrodes which were connected with
the poles of a voltaic pile, and observed that litmus in the
neighborhood of the positive pole was turned red by the
acid produced there.
"Some years later Davy made his brilliant electro-chem-
ical discoveries. He succeeded in decomposing the oxides
250 ELECTRICITY
of the alkali and alkaline earth metals, which had previ-
ously been regarded as elementary substances, and in pre-
paring the pure metals. Further progress in obtaining the
more difficultly reducible metals in this way was later
made by Bunsen and his pupils:"
At the time of Davy's discovery of the alkali metals
Berzelius was just beginning his scientific investigations.
In one of the first of these, carried out jointly with
Hisinger, he studied the action of the electric current
upon solutions of various inorganic substances, resulting
chiefly in the establishment of the first electrochemical
theory. This theory dominated the science of chemistry
for many decades. According to it, each chemical atom,
when in contact with another, possesses, like a magnet,
an electropositive and an electronegative pole. Moreover,
one of these poles is usually much stronger than the other.
Consequently, an atom behaves as if it possessed but one
pole, either electropositive or electronegative, according
as the positive or negative pole, respectively, predominates
in strength. The magnitude and sign of this resultant
polarity upon the atoms of a given element determines its
chemical behavior. If, for instance, the atoms of an ele-
ment are electropositive, it will react with elements whose
atoms are electronegative, and conversely. During this
reaction the two kinds of electricity neutralize each other,
more or less completely according to the degree of in-
equality existing between the positive and negative charges
upon the reacting atoms. If complete neutralization does
not take place the resulting compound itself is electro-
positive or electronegative according as the electropositive
are greater or less than the electronegative charges upon
the component atoms. Compounds which thus possess a
resultant polarity may then enter into further combina-
tions with each other, in such a way as to form a com-
plex compound which is more nearly or quite neutral.
Thus the theory explains not only the formation of sim-
ple compounds from their elements, but also the forma-
ELECTRO-CHEMISTRY 251
tion of complex compounds, such as double salts, from
their component simple compounds. According to this
theory, chemical and electrical processes are closely re-
lated, and all compounds have a dualistic nature, being
formed of an electropositive and an electronegative com-
ponent. This theory is therefore known as the electro-
chemical or dualistic theory. It was applied throughout
the domain of inorganic chemistry, which at that time
was practically the entire science of chemistry, and altho
it contained many arbitrary assumptions it performed a
great service to science because of its systematizing influ-
ence.
For several decades after the establishment of the
dualistic theory no considerable advance was made in
electrochemistry. This lack of progress was soon counter-
balanced by the important discoveries which were made
by Faraday about the year 1835. He was the first to show
that whether electricity is produced by friction or by
means of a voltaic pile it is capable of producing the
same effects. This fact convinced him that there exists
but one kind of positive and one of negative electricity.
He next attempted to discover a relation between the
quantity of electricity flowing through a circuit and the
magnitude of the chemical and magnetic effects which it
could produce. His results may be expressed as follows:
The magnitude of the chemical and magnetic effects
produced in a circuit by an electric current is propor-
tional to the quantity of electricity which passes through
the circuit.
A further discovery was made by Faraday by com-
paring the quantities of different substances in solution
which are decomposed by the same quantity of electricity.
This comparison may be made in a very simple manner
by connecting into one circuit a series of solutions of dif-
ferent substances so that the same quantity of electricity
passes through each solution. The chemical decomposi-
tion produced by the electric current in each solution may
252 ELECTRICITY
then be determined by analysis. The results obtained
may be summarized as follows:
The quantities of the different substances which sep-
arate at the electrodes throughout the circuit are directly
proportional to their equivalent weights, and are inde-
pendent of the concentration and the temperature of the
solutions, the size of the electrodes, and all other circum-
stances.
Those who first recognised the decomposition of water
by the electric current sought an explanation for the sim-
ultaneous appearance of hydrogen at one electrode and
of oxygen at the other. It was not until 1805, however,
that a comprehensive theory for this phenomenon was
put forward. During that year such a theory was pub-
lished by Grotthus. According to this theory the electric
current charges one electrode positively and the other
negatively, and these charged electrodes then exert an
electrical influence upon the water molecules. Under this
influence the water molecules acquire a polarity, the hy-
drogen atom becoming charged with positive and the
oxygen atom with negative electricity. The positive elec-
trode then attracts the negatively charged oxygen atom,
and the negative electrode the positively charged hydro-
gen atom, causing the water molecules to arrange them-
selves in a row or chain.
As science gradually developed, the imperfections of
the theory advanced by Grotthus became more and more
apparent. According to this theory the splitting of the
molecule, which is necessary for the conduction of elec-
tricity, cannot take place until the electromotive force is
sufficiently great to overcome the affinity or cohesion be-
tween the two components of a given compound. As a
matter of fact, however, it was found that, under suitable
conditions of experiment, it is possible to cause an electric
current to pass through a solution even when the electro-
motive force of the current is extremely small.
Clausius was the first to direct attention to the dis-
ELECTRO-CHEMISTRY 253
agreement of the Grotthus theory or conception of elec-
trolysis with facts. Basing his conclusions upon the ex-
perimental results already obtained, he declared "every
assumption to be inadmissible which requires the natural
condition of a solution of an electrolyte to be one of equi-
librium, in which every positive ion is firmly combined
with its negative ion, and which at the same time requires
the action of a definite force in order to change this con-
dition of equilibrium into another differing from it only
in that some of the positive ions have combined with other
negative ions than those with which they were formerly
combined. Every such assumption is in contradiction to
Ohm's law."
At about the same time that Clausius advanced this
theory Hittorf began work upon the migration of the
ions, and a little later Kohlrausch commenced experiments
upon the electrical conductance of solution. The work of
these investigators greatly increased the knowledge of
the process of electrolysis. Making use of their work,
Arrhenius, in 1887, replaced the theory of vibrating ions of
Clausius by the theory of free ions.
According to the material conception of electricity, an
ion may be considered to be a compound of positive or
negative electrons with the element in question. The
formation of an ion is, then, entirely analogous to the
formation of a compound from two ordinary elements.
For instance, in the formation of ions from sodium iodide
the sodium atoms combine with positive and the iodine
atoms with negative electrons. This conception is very
comprehensive, for according to it the law of electro-
chemical change (Faraday's law) appears as a conse-
quence of the laws of definite and multiple proportion.
Altho the theory of electrolytic dissociation was not spared
great opposition in its early years, it has successfully ad-
vanced until at the present time by far the greater num-
ber of investigators accept it and recognise its value.
"It would be impossible to give in a few words a clear
254 ELECTRICITY
conception of all the reasons which led Arrhenius to adopt
his now almost universally accepted views," says Lang-
bein in his 'Electro-Deposition of Metals/ "and a short
statement of these views must, therefore, suffice. He dis-
covered that according to the degree of dilution and the
nature of their combination, salts in aqueous solutions
are to a more or less far-reaching extent decomposed into
independent portions, i.e., the ions, and the term electro-
lytic dissociation is applied to this phenomenon.
"Only combinations which dissociate — are decomposed
and thus form ions — can be conductors of the current, the
progressive motion of the latter being solely taken care of
and effected by the ions. The ions are supposed to be
charged with a certain quantity of electricity — the kath-
ions with positive, the anions with negative, electricity —
and so long as current passes through to the electrolyte,
they move free in the latter. However, when a current is
conducted through the electrolyte, the ions are attracted
by the electrodes, the positively-charged kathions by the.
negatively-charged cathode, and the negatively-charged
anions by the positively-charged anode. By reason of
these movements of the ions to the electrodes this phe-
nomenon is called migration of the ions.
"The ions, on reaching the electrodes, are freed of their
charge, i.e., they yield their electricity to the electrodes.
They lose thereby their ion nature, being transformed by
their separation on the electrodes into the ailotropic or iso-
meric form of the element or combination."
After the true action of Volta's pile had been discov-
ered, the first modification was to immerse the plates of
copper and zinc in the liquid. This arrangement gave
a more powerful and lasting effect than the original pile.
Volta arranged the cells in a circle and called such a
battery a "crown of cups." In 1806, the Royal Institution
of London became possessed of a battery of 2,000 ele-
ments on the trough system. It was with this apparatus
that Davy succeeded in decomposing potash and soda.
ELECTRO-CHEMISTRY 255
This simple type of cell would, however, only work for a
short time on account of the collection of bubbles of gas on
the plates; i.e. the cells became "polarized." Becquerel
studied this effect and succeeded in overcoming it to a
great extent in 1829, by employing two different liquids
separated by a porous partition, each of which enclosed
one of the electrodes. In 1863, Professor Daniell invented
the cell known by his name and which is one of the most
constant current cells ever made, altho not so powerful as
some. The zinc and copper electrodes are here separated
by a jar of porous earthenware, the zinc being surrounded
by dilute sulphuric acid and the copper by a saturated
solution of sulphate of copper. This latter solution is
the "depolarizer," acting to prevent the bubbles of hy-
drogen from collecting on the copper phate, as would be
the case in the simple cell. Instead of hydrogen being
thrown out at the copper pole, copper is deposited from
the sulphate of copper depolarizer so that this solution
becomes constantly weaker and the copper heavier. To
prevent the weakening of the sulphate crystals are added
occasionally. This battery has been much employed in
telegraphic work. A form of this cell, known as the
"gravity" cell, has been much used for this purpose, the
porous partition having here been done away with, and
the separation of the liquids effected by the difference
in their densities.
In 1839, Grove introduced a cell in which the depolar-
izer was strong nitric acid, which surrounded a platinum
plate. This is a much more powerful depolarizer than sul-
phate of copper and the cell was very energetic. It had,
however, the disadvantage of high cost and gave off dis-
agreeable fumes. The first drawback was overcome by
Professor Bunsen, in 1843, wno substituted for the platin-
um plate one of gas-retort carbon. The fumes, however,
still remained. This battery was useful to the early ex-
perimenters, as it furnished a strong and constant current.
Another good depolarizer is chromic acid. This is used
256 ELECTRICITY
in the same manner as nitric acid in the carbon-zinc cell
of Bunsen. It does not, however, give off fumes and yet
is almost as powerful as the Bunsen cell. Various forms
of this cell have been made and they have been extensively
used, especially for telephone ^work. They deteriorate
only slightly on standing.
Perhaps the most extensively used primary cell is the
LeClanche. This is also a zinc-carbon cell, but sal-am-
moniac is used to replace the sulphuric acid of the preced-
ing cells and the depolarizer is the black oxide of man-
ganese. This depolarizer is slow in its action and the cell
is, therefore, not good for constant current work, but it
has a very slow rate of deterioration. This cell is very
extensively manufactured in the "dry" form in which the
exciting fluid is held as a moist paste. The cell is not
entirely dry, however, as is sometimes supposed, for if it
dries out it ceases to work.
One of the most recent primary cells as well as the best
is the zinc-copper-oxide cell of Lalande. In the Edison
form of this cell, the copper oxide is pressed into plates
and mounted in the cell between two zinc plates. The
exciting fluid is caustic potash. The copper oxide acts
as the depolarizer and is reduced to metallic copper. The
cell is very efficient, has a long life, and does not deterio-
rate on standing. Thousands are now in use for such
work as operating railway signals, sparking gas engines,
etc.
The existence of secondary currents was discovered
by Ritter in 1803. Having substituted to the actions of a
Volta's pile another pile formed only of disks of copper,
separated by moist cloth, he remarked that this second
pile, though inactive by itself, gave in its turn an electric
current, in the opposite direction to the current of the
first pile.
This current was of but short duration, and the electro-
motive force was lower than that of the pile used in charg-
ing it. In 1826, De la Rive also found that a secondary
ELECTRO-CHEMISTRY 257
or inverse current could be obtained from plates of plati-
num upon which oxygen and hydrogen had been disen-
gaged in the experiment of the decomposition of water by
a battery. This phenomenon took the name of 'polariza-
tion of the electrodes' and the current itself that of the
'current of polarization.'
After that, secondary currents were the object of many
researches made by physicists, among whom may be men-
tioned Faraday, Grove, Wheatstone, Poggendorff, E. Bec-
querel and Gaugian. In 1859, Gaston Plante studied the
influence of different metals and different liquids on the
production of secondary currents, and on their intensity.
Since that date the question has assumed great import-
ance, having received scientific and practical applications,
due mainly to the researches of this acute observer.
He experimented on voltameters with wires of copper,
silver, tin, aluminum, iron, zinc, gold and platinum, and
for each of them varied the nature of ":he liquid into which
the electrodes were placed. He found that "all the metals
oxidizing at the positive pole of the cell, the secondary
current, obtained after the interruption of the primary
current, was as much more intense as the oxidation was
more complete, if the oxide formed remained adherent and
insoluble in the acidulated liquid of the voltameter." Even
gold and silver did not resist the action of the oxygen of
the pile; they were covered with dark deposits of oxide,
and furnished an energetic secondary current. Platinum
did not oxidize, it is true, in a visible manner, but the
secondary inverse current was of shorter duration than
that of the metals which were covered with a layer of ad-
herent oxide; an effect which was explained by the rapid
decomposition of the oxygenated water produced around
the positive electrode of the voltameter. The action of
the hydrogen was, on the other hand, stronger with plati-
num than with all the other metals, for the electrode
around which this gas was disengaged furnished, with an-
258 ELECTRICITY
other neutral electrode, a more intense secondary current
than when any other metal was employed.
The most important result of these interesting re-
searches is that which assigns the greatest intensity to the
secondary current produced by a voltameter with elec-
trodes of lead, and dilute sulphuric acid as the liquid.
Measuring the electromotive force developed in such a
voltameter, after the rupture of the primary current,
Plante found that it was equal to about one and a half;
times (more exactly, 1.48-1.49) that of the most ener-
getic voltaic element, such as a Grove or Bunsen. This
suggested the idea of constructing secondary cells, and
uniting them in a battery, so as to store up or accumulate
the work of the voltaic pile, in the same way that static
electricity is condensed by the aid of conductors of great
surface separated by an insulating material.
The action in a storage cell is as follows. When the
battery is charged the positive plate consists of lead pe-
roxide and the negative of pure lead in a spongy condi-
tion. When the cell discharges, both plates become a form
of lead sulphate. Upon being charged by having a reverse
current sent through them, they are reformed into lead
peroxide and sponge lead. If the plates were platinum,;
oxygen would be given off where the current enters and
hydrogen where it leaves, but with the lead sulphate plates
the oxygen and hydrogen combine, thus oxidizing one and
reducing the other.
Storage cells have many uses. They are employed in
large sizes in central power stations to equalize the
load on the machinery, serving to help the engines car-
ry the maximum loads so that they are not strained. Elec-
tric automobiles are largely used, but the weight of the
battery seriously handicaps their other excellent qualities.
They also find application in lighting trains, operating in-
dustrial locomotives, supplying telephone lines and ignit-
ing gas engines.
CHAPTER VIII
THE TELEPHONE
In 1854 a Frenchman, Charles Bourseul, predicted the
transmission of speech, and outlined a method correct save
in one particular, but for which error one following his
directions could have produced a speaking telephone. His
words at this date seem almost prophetic :
"I have asked myself, for example, if the spoken word
itself could not be transmitted by electricity; in a word,
if what was spoken in Vienna may not be heard in Paris.
The thing is practicable in this way :
"Suppose that a man speaks near a movable disk, suf-
ficiently flexible to lose none of the vibrations of the voice ;
that this disk alternately makes and breaks the connection
from a battery: you may have at a distance another disk
which will simultaneously execute the same vibrations."
The words "makes and breaks" in Bourseul's quotation
have been italicized by the present writer. They form the
keynote of the failures of those who subsequently followed
Bourseul's directions literally.
Philip Reis, a German inventor, constructed what he
called a telephone in 1861, following implicitly the path
outlined by Bourseul. He mounted a flexible diaphragm
over an opening in a wooden box, and on the center of
the diaphragm fastened a small piece of platinum. Near
this he mounted a heavy brass spring, with which the
platinum alternately made and broke contact when the
diaphragm was caused to vibrate. These contact points
259
260
ELECTRICITY
formed the terminals of a circuit containing a battery and
the receiving instrument. His receiver assumed various
forms, prominent among which was a knitting needle
wrapped with silk-insulated copper wire and mounted on
a cigar box for a sounding board. Its operation was as
follows :
The sound waves set up in the air struck against the
diaphragm of the transmitter, causing it to vibrate in
unison with them. This caused the alternate making and
breaking of the circuit at the point of contact between the
platinum and the spring, and allowed intermittent cur-
V
Fig. 31
-Circuit of Reis Telephone. (From Miller's
American Telephone Practice.)
rents to flow through the receiver. These caused a series
of sounds in the knitting needle by virtue of 'Page's ef-
fect.' The sounding board vibrated in unison with the
molecular vibrations of the needle, and the sound was
thus greatly amplified.
Reis' telephone could be depended upon to transmit
only musical sounds. The question as to whether it
actually did transmit speech has been the subject of much
discussion, but if it did this at all it was very imper-
fectly. "The cause of its failure," says K. B. Miller in
his 'American Telephone Practice,' "to successfully trans-
mit speech will be understood from the following facts :
A simple musical tone is caused by vibrations of very
simple forms, while sound waves produced by the voice in
THE TELEPHONE 261
speaking are very complex in their nature. Sound pos-
sesses three qualities : pitch, depending entirely on the
frequency of the vibrations ; loudness, depending on the
amplitude of the vibrations; and timbre, or quality, de-
pending on the form of the vibration. The tones of a
flute and a violin may be the same as to pitch and loudness
and yet be radically different. This difference is in tim-
bre, or quality."
Reis' transmitter, as he adjusted it, was able only to
make and break the circuit, and a movement of the dia-
phragm barely sufficient to break the circuit produced the
same effect as a much greater movement. The current
Fig. 32 — Sound Waves of Voice and Simple Musical Note.
(From Miller's American Telephone Practice.)
therefore flowed with full strength until the circuit was
broken, when it stopped entirely. The intermediate
strengths needed for reproducing the delicate modulations
of the voice were entirely lacking. This apparatus could
therefore exactly reproduce the pitch of a sound, but not
its timbre and relative loudness. For the next fifteen
years no apparent advance was made in the art of tele-
phony, altho several inventors gave it their attention.
In 1876 Professor Alexander Graham Bell and Pro-
fessor Elisha Gray almost simultaneously invented suc-
cessful speaking telephones. Gray has been one of the
principal claimants for the honor of being the first inven-
tor of the telephone, but Bell has apparently established his
right to it, and has also reaped the profit, for, after long
litigation, the United States Patent Office and the courts
262
ELECTRICITY
have awarded the priority to him as against Gray and
many others.
Bell possessed a greater knowledge of acoustics than of
electrical science, and it was probably this that led him
to appreciate wherein others had failed. His instrument
consisted of a permanent bar magnet having on one end
a coil of fine wire. In front of the pole carrying the coil
a thin diaphragm of soft iron was so mounted as to allow
its free vibration close to the pole.
"Two points will be noticed," says Miller in the work
before cited, "which have heretofore been absent; that no
B
Fig.
33 — Bell Telephone as Transmitter and Receiver.
(From Miller's American Telephone Practice.)
battery is used in the circuit and that the transmitting
and receiving instruments are exactly alike. When the
soft-iron diaphragm of the transmitting instrument is
spoken to, it vibrates in exact accordance with the sound
waves striking against it. The movement of the dia-
phragm causes changes in the magnetic field in which lies
the coil, which changes, as already pointed out, cause cur-
rents to flow in the circuit. These currents flow first in
one direction and then in the other, varying in unison
with the movements of the diaphragm, the waves being
very complex as represented graphically. Passing along
the line wire, these electrical impulses, so feeble that only
the most delicate instruments can detect them, alternately
increase and decrease the strength of the permanent mag-
THE TELEPHONE
263
net of the receiving instrument, and thereby cause it to
exert a varying pull on its soft-iron diaphragm, which, as
a result, takes up the vibrations and reproduces the sound
faithfully."
Fig 34 — Beli/s Centennial Receiver. (From Miller's
American Telephone Practice.)
Bell's earlier instruments were exhibited in 1876 at the
Centennial in Philadelphia. The receiver consisted of a
tubular magnet, composed of a coil of wire, surrounding
a core, and inclosed in an iron tube, which was about i}4
inches in diameter and 3 inches long. This tube was
closed by a thin iron armature, or diaphragm, which rested
264
ELECTRICITY
loosely on the upper face of the iron tube, the length of
the core being such as not quite to touch the diaphragm
when in this position. The whole was mounted on a base,
arrangements being made to .adjust the air gap between
the pole of the core and the diaphragm by means of a
thumbscrew.
The transmitter consisted of an electromagnet in front
of the core, on which was adjustably mounted a diaphragm
of goldbeater's skin carrying a small iron armature at
its center. A long mouthpiece, into which the sounds to
Fig- 35 — Bell's Centennial Transmitter. (From Miller's
American Telephone Practice.)
be transmitted were spoken, served to convey the sound
waves more directly to the diaphragm.
"Nearly all books and articles on telephones," says
Miller, "that treat of Bell's early receiver at all, show and
describe it as having the diaphragm fastened at one edge
by a single small screw to the upper face of the iron tube,
and sprung away from the tube at its opposite side. This
mistake occurred in the first two editions of this work, and
would have been in this one but for Thomas D. Lock-
wood, who was kind enough to call attention to it. The
origin of the error is explained in the following inter-
esting extract from a letter written by Mr. Loekwood to
the writer of this book:
THE TELEPHONE 265
" 'This mistake first appeared in the account given by
Engineering of Sir William Thomson's address to the
British Association in September, 1876, and has been uni-
versally copied. The origin of the mistake is very odd.
The screw of the instrument given to Sir William Thom-
son, and which he exhibited in England on his return, was
put through a hole in the edge of the diaphragm and en-
gaged with a threaded hole of the tube, for the purpose
of attaching the diaphragm while in transit, to prevent it
from getting lost. No one, however, notified Sir William
of this, it probably having been forgotten ; and Sir William
seems to have forgotten what the instrument, as he saw
it in Philadelphia, looked like. Finally, in knocking
about among Sir William's luggage, the free end of the
diaphragm was apparently, and without doubt uninten-
tionally, bent upward, as the picture shows. But when
so bent, being at the same time rigidly fastened at the op-
posite edge, it would not and could not work; and when
Sir William showed it in England he couldn't make it
work.' "
Bell's instrument in a modified form is the standard of
to-day. It is now used as a receiver only, a more efficient
transmitter, depending upon entirely different principles,
having been invented. In speaking of Bell's invention,
Sir William Thomson, Lord Kelvin, said: "Who can but
admire the hardihood of invention which devised such
very slight means to realize the mathematical conception
that if electricity is to convey all the delicacies of quality
which distinguish articulate speech, the strength of its.
current must vary continuously as nearly as may be in
simple proportion to the velocity of a particle of air en-
gaged in constituting the sound?"
Much has been said and books have been written on the?
rights of Reis as the inventor of the speaking telephone.
The validity of Bell's controlling patent was the subject
of many attacks, the litigation finally reaching the Su-
preme Court of the United States. In the opinion of this
266 ELECTRICITY
court (October term, 1887) the following brief but com-
prehensive statement is found:
"We have not had our attention called to a single item
of evidence which tends in any way to show that Reis or
any one who wrote about him had it in his mind that any-
thing else than the intermittent current caused by the
opening and closing of the circuit could be used to do
what was wanted. No one seems to have thought that
there could be another way. All recognised the fact that
the minor differences in the original vibrations had not
been satisfactorily reproduced, but they attributed it to
the imperfect mechanism of the apparatus used, rather
than to any fault in the principle on which the operation
was to depend.
"It was left for Bell to discover that the failure was due
not to workmanship, but to the principle which was
adopted as the basis of what had to be done. He found
that what he called the intermittent current — one caused
by alternately opening and closing the circuit — could not
be made under any circumstances to reproduce the deli-
cate forms of the air vibrations caused by the human
voice in articulate speech, but that the true way was to
operate on an unbroken current by increasing and dimin-
ishing its intensity. , . . Such was his discovery, and
it was new. Reis never thought of it, and he failed to
transmit speech telegraphically. Bell did and he suc-
ceeded. Under such circumstances it is impossible to
hold that what Reis did was an anticipation of the discov-
ery of Bell. To follow Reis is to fail, but to follow Bell
is to succeed. The difference between the two is just the
difference between failure and success."
A very interesting fact, and one which might have
changed the entire commercial status of the telephone in-
dustry, is that in 1868 Royal E. House, of Binghamton,
N. Y., invented and patented an "electro-phonetic tele-
graph," which was capable of operating as a magneto-
telephone, in the same manner as the instruments subse-
THE TELEPHONE 267
quently devised by Bell. House knew nothing of its ca-
pabilities, however, unfortunately for him. The instru-
ment is provided with a sounding diaphragm of pine wood
stiffened with varnish, mounted in one end of a large
sound-amplifying chamber, so formed as to focus the
sound waves at a point near its mouth, where the ear was
to be placed to receive them. The electro-magnet adapted
to be connected in the line circuit had its armature con-
nected by a rod with the center of the wooden diaphragm.
By this means any movements imparted to the armature
by fluctuating currents in the line were transmitted to the
diaphragm, causing it to give out corresponding sounds;
and any movements imparted to the diaphragm by sound
waves were transmitted to the armature, causing its
movements to induce corresponding currents in the line.
Two of these instruments connected in a circuit would
act alternately as transmitters and receivers in the same
manner as Bell's instruments.
It has been shown that in order to transmit speech by
electricity it is necessary to cause an undulatory or al-
ternating current to flow in the circuit over which the
transmission is to be effected, and that the strength of
this current at all times be in exact accordance with the
vibratory movements of the body producing the sound.
Bell's magnetic transmitter was used as the generator
of this current, as a dynamo, in fact, the energy for driv-
ing which was derived from the sound waves set up by the
voice. The amount of energy so derived was, however,
necessarily very small and the current correspondingly
weak, and for this reason this was not a practical form of
transmitter, except for comparatively short lines.
Elisha Gray devised a transmitter which, instead of
generating the undulatory current itself, depended for
its action on causing variation in the strength of a cur-
rent generated by some separate source; this variation in
current strength always being in accordance with the
movements of the diaphragm.
563
ELECTRICITY
He mounted on his horizontal vibrating diaphragm a
metal needle, extending into a fluid of low conductivity,
such as water. The needle formed one terminal of the
circuit, the other terminal being a metal pin extending;
up through the bottom of the containing vessel. The vi-
bration of the diaphragm was supposed to cause changes
in the resistance of the path through the fluid on account
Fig. 36 — Bell's Centennial Fig 37 — Berliner's
Liquid Transmitter. Transmitter.
(From Miller's American Telephone Practice.)
of the varying distance between the points of the elec-
trodes and therefore corresponding changes in the
strength of the current.
Bell also used a liquid transmitter in which a conduct-
ing liquid was held in a conducting vessel, forming one
terminal of the circuit. The other terminal was a short
THE TELEPHONE 269
metallic needle, carried on the diaphragm, and projecting
slightly into the liquid, so that the area of contact between
the liquid and the needle would be varied to better advan-
tage by the vibration of the diaphragm than if the needle
were immersed a greater distance into the fluid.
Bell's liquid transmitter depended on variation in the
extent of immersion of the electrode, while Gray's in-
strument, owing to the great extent to which the pin was
immersed, depended rather on the variation in the length
of the conducting path through the liquid itself, a faulty
principle for this purpose.
Bell's liquid transmitter was also exhibited at the
Philadelphia Centennial in 1876, and, unlike that of Reis,
simply caused variations in the resistance of the circuit,
and thereby allowed a continuous but undulatory current
to pass over the line, the variations in which were able to
reproduce all the delicate shades of timbre, loudness and
pitch necessary in articulate speech.
Gray and Bell embodied, or attempted to embody, in
these instruments the main principle upon which all suc-
cessful battery transmitters are based. A battery fur-
nished the current, and the transmitter, actuated by the
voice, served to modulate it. It was not long, however,
before a much better means was devised for putting this
principle into practice.
In 1877 Emile Berliner, of Washington, D. C., filed a
caveat, and later in the same year applied for a patent
on a transmitter depending upon a principle pointed out
in articles published in 1856, 1864 and 1874 by the French
scientist Du Moncel, that if the pressure between two
conducting bodies forming part of an electric circuit be
increased, the resistance of the path between them will be
diminished, and conversely, if the pressure between them.
be decreased, a corresponding increase of resistance wilJ.
result.
Berliner's transmitter is shown in principle in Fig. 37,,
which is a reproduction of the principal figure in his now
270 ELECTRICITY
famous patent. In this A is the vibratory diaphragm of
metal, against the center of which rests the metal ball, C,
carried on a thumbscrew, B, which is mounted in the
standard, d. The pressure of .the ball, C, against the
plate, A, can be regulated by turning the thumbscrew.
The diaphragm and ball form the terminals or electrodes
of a circuit, including a battery and receiving instrument.
The action of this instrument (which at best has never
been satisfactory or commercial) is as follows: When the
diaphragm vibrates, the pressure at the point of contact,
a, becomes greater or less, thus varying the resistance
of the contact and causing corresponding undulations in
the current flowing.
Soon after this Edison devised an instrument using
carbon as the medium for varying the resistance of the
circuit with changes of pressure. Edison's first type of
carbon transmitter consisted simply of a button of com-
pressed plumbago bearing against a small platinum disk
secured to the diaphragm. The plumbago button was
held against the diaphragm by a spring, the tension of
which could be adjusted by a thumbscrew.
A form of Edison's transmitter, devised by George M.
Phelps in 1878, is shown in Fig. 38. The transmitting
device proper is shown in the small cut at the right of
this figure, and is inclosed in a cup-shaped case formed
of the two pieces, A and B, as shown. Secured to the
front of the enlarged head, e, of the adjustment screw,
E is a thin platinum disk, F, against which rests a cylin-
drical button, G, of compressed lampblack. A plate of
glass, I, carrying a hemispherical button, K, has at-
tached to its rear face another platinum disk, H. This
second platinum disk rests against the front face of the
lampblack disk, G, and the button, K, presses firmly
against the center of the diaphragm, D. The plates, F and
H, form the terminals of the transmitter, and as the dia-
phragm, D, vibrates, it causes variations in the pressure
THE TELEPHONE
271
and corresponding changes in the resistance of the cir-
cuit, thus producing the desired undulations of current.
Professor David B. Hughes made a most valuable con-
tribution tending toward the perfection of the battery-
transmitter. By a series of interesting experiments he
demonstrated conclusively that a loose contact between
the electrodes, no matter of what substance they are com-
posed, is far preferable to a firm, strong current. The
apparatus used in one of his earlier experiments, made in
1878, is shown in Fig. 39, and consists simply of three
wire nails, of which A and B form the terminals of the
Fig. 38 — Phei. ps-Edison Transmitter. (From Miller's
American Telephone Practice.)
circuit containing a battery and a receiving instrument.
The circuit was completed by a third nail, C, which was
laid loosely across the other two. Any vibrations in the
air in the vicinity caused variations in the intimacy of
contact between the nails, and corresponding variations
in the resistance of the circuit. This was a very ineffi-
cient form of transmitter, but it demonstrated the princi-
ple of loose contact very cleverly.
It was found that carbon was, for various reasons, by
far the most desirable substance for electrodes in the
loose-contact transmitter, and nothing has ever been found
to approach it in efficiency and desirability.
272
ELECTRICITY
Another form of transmitter devised by Hughes, and
called by him the microphone, is shown in Fig. 39. This
consists of a small pencil of gas carbon, A, pointed at
each end, and two blocks, B, B, of carbon fastened to a
diaphragm or sounding board, C. These blocks are hol-
lowed out in such a manner as to loosely hold between
them the pencil, A. The blocks, B, B, form the terminals
of the circuit. This instrument, tho crude in form,
Fig- 39 — Hughes' Carbon and Nail Microphones. (From
Miller's American Telephone Practice.)
is of marvelous delicacy and is well termed microphone.
The slightest noises in its vicinity, and even those incapa-
ble of being heard by the ear alone, produce surprising
effects in the receiving instrument. This particular form
of instrument is, in fact, too delicate for ordinary use,
as any jar or loud noise will cause the electrodes to break
contact and produce deafening noises in the receiver.
Nearly all carbon transmitters of to-day are of the loose-
contact type, this having entirely superseded the first form
devised by Edison, which was then supposed to depend
THE TELEPHONE 273
on the actual resistance of a carbon block being changed
under varying pressure.
In speaking of Professor Hughes' work on loose con-
tacts and the microphone, the Telegraph Journal and
Electrical Review, an English electrical paper, says in
its issue of July 1, 1878: "The microphone is a striking
illustration of the truth that in science any phenomenon
whatever may be turned to account. The trouble of one
generation of scientists may be turned to the honor and
service of the next. Electricians have long had sore
reasons for regarding a 'bad contact' as an unmitigated
nuisance, the instrument of the evil one, with no con-
ceivable good in it, and no conceivable purpose except
to annoy and tempt them into wickedness and an ex-
pression of hearty but ignominious emotion. Professor
Hughes, however, has, with a wizard's power, trans-
formed this electrician's bane into a professional glory
and a public boon. Verily, there is a soul of virtue in
things evil."
Professor Hughes, in an article in Nature, June 27,
1878, thus describes the conditions necessary for micro-
phonic action: "If the pressure on the materials is not
sufficient, we shall have a constant succession of inter-
ruptions of contact, and the galvanometer needle will in-
dicate the fact. If the pressure on the materials is grad-
ually increased the tones will be loud but wanting in
distinctness, the galvanometer indicating interruptions;
as the pressure is still increased, the tone becomes clearer,
and the galvanometer will be stationary when a maximum
of loudness and clearness is attained. If the pressure
be further increased, the sounds become weaker, tho very
clear, and, as the pressure is still further augmented, the
sounds die out (as if the speaker was talking and walk-
ing away at the same time) until a point is arrived at
where there is complete silence."
Only one radical improvement now remains to be re-
corded. In 1 881 Henry Hunnings devised a transmitter
274
ELECTRICITY
wherein the variable resistance medium consisted of a
mass of finely divided carbon granules held between two
conducting plates. His transmitter is shown in Fig. 40.
Between the metal diaphragm, A, and a parallel conduct-
ing plate, B, both of which are securely mounted in a
case formed by the block, D, and a mouthpiece, F, is a
Fig. 40 — Hunntng's Granular Carbon Transmitter. (From-
Miller's American Telephone Practice.)
chamber filled with fine granules of carbon, C. The dia-
phragm, A, and the plate, B, form the terminals of the
transmitter, and the current from the battery must there-
fore flow through the mass of granular carbon, C. When
the diaphragm is caused to vibrate by sound waves, it is
brought into more or less intimate contact with the car-
bon granules and causes a varying pressure between them.
The resistance offered by them to the current is thus
varied, and the desired undulations in the current pro-
duced. This transmitter, instead of having one or a few
points of variable contact, is seen to have a multitude of
THE TELEPHONE 275
them. It can carry a larger current without heating, and
at the same time produce greater changes in its resistance, .
than the forms previously devised, and no ordinary sound
can cause a total break between the electrodes. These
and other advantages have caused this type in one form
or another to largely displace all others.
At first the practice was to put the transmitter, together
with the receiver and battery, directly in circuit with the
line wire. With this arrangement the changes produced
in the resistance by the transmitter were small in com-
parison with the total resistance of the circuit, especially
in the case of a long line, and the changes in current were
therefore small. Edison remedied this difficulty by using
an induction coil in connection with the transmitter.
The induction coil used then and now is made as fol-
lows: Around a core formed of a bundle of soft-iron'
wires is wound a few turns of comparatively heavy in-
sulated copper wire. Outside of this, and entirely sep-
arate from it, is wound another coil consisting of a great
number of turns of fine wire, also of copper, and insulated.
The transmitter, together with the battery, is placed in a
closed circuit with the coarse winding of a few turns,
while the fine winding of many turns is included directly
in circuit with the line wire and the receiving instrument.
The coarse winding is usually termed the primary wind-
ing, because it is associated with the primary source of
current, the battery; while the fine winding is usually
termed the secondary winding, because the currents flow-
ing in it at the transmitting station are secondary, or
induced currents. In coils of this kind the coarse wind-
ing is almost invariably termed the primary for the above
reason, altho many conditions exist in electrical work and
in telephone work where the high-resistance winding is
in reality the primary coil.
The circuit arrangement spoken of is shown in Fig. 41,
in which T is a transmitter, B a battery, P and S primary
and secondary windings, respectively, of an induction coil,
276 ELECTRICITY
L', L' the line wires, and R the receiving instrument. It is
well to state here that the usual way of indicating the
primary and secondary of an induction coil in diagraphic
representation of electrical circuits is by an arrangement
of two adjacent zigzag lines, as shown in Fig. 41. A
current flowing in the primary winding of the induction
coil produces a field of force in the surrounding space,
and any changes caused by the transmitter in the strength
of the current produce changes in the intensity of this
Fig. 41 — Transmitter With Induction Coil. (From Miller's
American Telephone Practice.)
field. As the secondary winding lies in this field, these
changes will, by the laws of Faraday and Henry, cause
currents to flow in the secondary winding and through
the line wire to the receiving instrument. In good induc-
tion coils the electro-motive forces up in the secondary
coil bear nearly the same ratio to the changes in electro-
motive force in the primary coil as the number of turns
in the secondary bears to the number of turns in the
primary.
The use of the induction coil with the transmitter ac-
complishes two very important results: First, it enables
the transmitter to operate in a circuit of very low re-
THE TELEPHONE 277
sistance, so that the changes in the resistance produced by
the transmitter bear a very large ratio to the total re-
sistance of the circuit. This advantage is well illustrated
by contrasting the two following cases :
Suppose a transmitter capable of producing a change
of resistance of one ohm be placed directly in a line cir-
cuit whose total resistance is 1,000 ohms; a change in
the resistance of the transmitter of one ohm will then
change the total resistance of the circuit one one-thou-
sandth of its value, and the resulting change in the cur-
rent flowing will be but one one-thousandth of its value.
On the other hand, suppose the same transmitter to be
placed in a local circuit, as above described, the total re-
sistance of which circuit is five ohms; the change of one
ohm in the transmitter will now produce a change of
resistance of one-fifth of the total resistance of the cir-
cuit, and cause a change of one-fifth of the total current
flowing. It is thus seen that fluctuations in the current
can be produced by a transmitter with the aid of an in-
duction coil which are many times greater than those
produced by the same transmitter without the coil.
The second advantage is that by virtue of the small
number of turns in the primary winding and the large
number in the secondary winding of the induction coil,
the currents generated in the secondary are of a very
high voltage as compared with those in the primary, thus
enabling transmission to be effected over much greater
length of line, and over vastly higher resistances than
would be possible if the transmitter were forced to vary
the current flowing through the entire length of the line.
Neither the telephone receiver nor the transmitter have
undergone any radical changes since their early days.
Various minor details have received the attention of en-
gineers and inventors, but the magneto-telephone is still
the receiver and the variable resistances of the carbon
contacts the means of transmission.
The principal developments have been in the means
THE TELEPHONE
279
of intercommunication. The growth of the telephone
industry has been very rapid, and from being a luxury
the telephone has become a business necessity. The ten-
dency has been toward the simplification of the sub-
scriber's station and the improvement of the central office.
The battery current for talking is now supplied in concen-
trated communities from the central station. Consider-
able trouble formerly was experienced through the de-
terioration of the battery at the subscriber's station.
The telegraphone or telephonograph is an instrument
which records magnetically sounds produced at a distance
^Quesc/r/ee/i* xep/ioduciho MAGN£rs
Fig. 43 — Poulsen's Telegraphone. (From Standard Handbook
for Electrical Engineers.)
It was originated by Mr. Poulsen, a Danish inventor.
Fig. 43 shows the essential parts. Either a steel band is
used or a long steel wire rolled from one drum to the
other under the recording magnet, which receives the talk-
ing currents and engraves them magnetically upon the
steel wire. To reproduce the message it is only necessary
to pass the steel wire under a reproducing magnet con-
nected to a telephone receiver, the reproduction being
very perfect. The message may be erased from the wire
by means of the obliterating magnet supplied with an
alternating current.
CHAPTER IX
ELECTRIC RAILWAYS
Altho the earliest recorded experiments date back
three-quarters of a century, the electric railway is essen-
tially of modern development, for it achieved a recognised
position less than twenty years ago, long after the tele-
phone, the arc and incandescent lamp, and the stationary
electric motor had been thoroly established. This is but
natural, for it is the logical outcome of the establishment
of certain cardinal principles and practices in the kindred
arts.
The first roads to carry passengers commercially were
built in Europe, but the first railway experiments and
the modern commercial impetus, as well as most of the
essential and distinctive features of the art as it stands
to-day, an example of almost unprecedented industrial
development, are distinctively American, as Frank J.
Sprague pointed out in his paper before the Electrical
Congress of 1904, from which much of the following mat-
ter is taken.
Brandon, Vt., birthplace, and Thomas Davenport, black-
smith, father, are the names first on the genealogical tree
of the electric railway, in the year 1834. A toy motor,
mounted on wheels, propelled on a few feet of circular
railway by a primary battery, exhibited a year later at
Springfield, and again at Boston, is the infant's photo-
graph. This was only three years after Henry's inven-
tion of the motor, following Faraday's discovery, ten
280
ELECTRIC RAILWAYS 281
years earlier, that electricity could be used to produce
continuous motion.
The records of Davenport's career, unearthed by the
late Franklin Leonard Pope, show this early inventor
a man of genius, deserving a high place in the niche of
fame, for in a period of six years he built more than a
hundred operative electric motors of various designs, many
of which were put into actual service, an achievement,
taking into account the times, well nigh incredible.
For nearly two score years various inventors, handi-
capped with the limitations of the primary battery, and
in utter ignorance of the principles of modern dynamo
and motor construction, labored with small result. The
invention by Pacinotti in 1861 of the continuous current
dynamo may properly be said to date all modern electric
machines. These were developed in their earliest forms
by Gramme and Siemens, Wheatstone and Varley, Farmer
and Rowland, Hefner-Alteneck and others, and brought
into existence the elements essential to any possible com-
mercial success. Yet notwithstanding that the principle of
the reversibility of the dynamo-electric machine and the
transmission of energy to a distance by the use of two
similar machines, said to have been discovered and
described by Pacinotti in 1867 — the same year in which
Prof. Farmer described the principle of the modern
dynamo in a letter to Henry Wilde — and demonstrated in-
dependently at the Vienna Exposition by Fontaine and
Gramme in 1873, many years more passed before the im-
portance and availability of this principle were generally
recognised.
From 1850 to 1875 is a long period relatively, and yet
there seemed to have been practically an entire cessation
of experimental electric railway work until in the latter
year George F. Greene, a poor mechanic of Kalamazoo,
Mich., built a small model motor which was supplied from
a battery through an overhead line, with track return, and
three years later he constructed another model on a larger
282 ELECTRICITY
scale. Greene seemed to have realized that a dynamo was
essential to success, but he did not know how to make one
and did not have the means to buy it.
Shortly afterward, in 1879, at tne Berlin Exposition,
Messrs. Siemens and Halske constructed a short line about
a third of a mile in length, which was the beginning of
much active work by this firm. The dynamo and motor
were of the now well-known Siemens type, and the current
was supplied through a central rail, with the running rails
as a return, to a small locomotive on which the motor was
carried longitudinally, motion being transmitted through
spur and beveled gears to a central shaft from which con-
nection was made to the wheels. The locomotive drew
three small cars having a capacity of about 20 people and
attained the speed of about eight miles an hour.
Perhaps more than to any other the credit for the first
serious proposal in the United States should be awarded
to Field. Curiously enough, patent papers were filed by
Field, Siemens and Edison, all within three months of
each other, in the spring and summer of 1880. Priority of
invention was finally awarded to Field, he having filed a
caveat a year before. He had been actively interested in
electric telegraphs, and in an account of his work pub-
lished some 20 years ago, it is stated that he early con-
structed two electric motors and had in mind the opera-
tion of street cars in San Francisco, but had not been able
to do anything in the matter because of a realization that
a dynamo must be used instead of a battery. In 1877
while in Europe he saw some Gramme machines, and on
his return two of them were ordered but not delivered.
Later a dynamo was ordered from Siemens Brothers in
London which was lost, and this was replaced by another
which arrived in the fall of 1878. Meanwhile two Gramme
machines were placed at his disposal, and shortly after-
ward an electric elevator was operated. In February,
1879, he made plans for an electric railway, the current to
be delivered from a stationary source of power through a
ELECTRIC RAILWAYS 283
wire enclosed in a conduit, with rail return, and in 1880-
81 he constructed and put in operation an experimental
electric locomotive in Stockbridge, Mass.
Pending the settlement of patent interferences between
Edison and Field (the Siemens application being late was.
rejected), the two interests were combined in a corpora-
tion known as "The Electric Railway Company of the
United States," and the first work of the company was the
operation of an electric locomotive at the Chicago Railway
Exposition in 1883. This locomotive, called "The Judge,'*
after the late Chief Justice Field, ran around the gallery
of the main exposition building on a track of about one-
third of a mile in length.
The motor used was a Weston dynamo mounted on the
car and connected by beveled gear to a shaft from which
power was transmitted by belts to one of the wheels. The
current was taken from a center rail, with track return.
A lever operated clutches on the driving shaft, and the
speed was varied by resistance. The reversing mechanism
consisted of two movable brushholders geared to a disk
operated by a lever, each arm carrying a pair of brushes,
one of which only could be thrown into circuit at a time,
to give the proper direction of movement.
Meanwhile several other inventors were getting actively
into the field of transmission of power and electric rail-
ways. In the summer of 1882 Dr. Joseph R. Finney oper-
ated in Allegheny, Pa., a car for which current was sup-
plied through an overhead wire on which traveled a small
trolley connected to the car with a flexible cable, and about
the same time in England Dr. Fleming Jenkin, following a
paper by Messrs. Ayrton and Perry before the Royal In-
stitution on an automatic railway, proposed a scheme of
telpherage which was developed by those gentlemen.
In the early part of the same year the writer, Mr.
Sprague, then a midshipman in the United States Navy,
who had in 1879 and 1880 begun the designing of motors,
was ordered on duty at the Crystal Palace Electrical Ex-
284 ELECTRICITY
hibition then being held at Sydenham, England. While
in London he became impressed with a belief in the possi-
bility of operating the underground railway electrically.
He first considered the use of main and working conduc-
tors, the latter being carried between the tracks, with rail
return, but noting the complication of switches on certain
sections of the road, conceived the idea of a car moving
between two planes, traveling on one and making upper
pressure contact with the other, those planes being the
terminals of a constant potential system. For practical
application the lower of the two planes was to be replaced
by the running track and all switches and sidings, and the
upper plane by rigid conductors supported by the roof of
the tunnel, and following the center lines of all tracks
and switches, contact to be made therewith by a self-
adjusting device carried on the car roof over the center
of the truck and pressed upward by springs.
In 1882 he applied for a patent on the first idea, which
was but a variation from that shown in other patents, but
the second laid dormant for nearly three years because of
central station work and the development of the applica-
tion of stationary motors.
Meanwhile in the United States Charles J. van Depoele,
a Belgian by birth and a sculptor by original trade and an
indefatigable worker, had become interested in electric
manufacture and soon energetically attacked the railway
problem. His first railway was a small experimental line
constructed in Chicago in the winter of 1882-83, the cur-
rent supplied from an overhead wire. In the fall of 1883
a car was also run at the Industrial Exposition at Chicago.
A year later a train pulled by a locomotive and taking
current from an underground conduit was successfully
operated at the Toronto Exhibition to carry passengers
from the street car system, and again in the year follow-
ing Van Depoele operated another train at the same place,
using on this occasion an overhead wire and a weighted
arm pressing a contact up against it.
ELECTRIC RAILWAYS 285
Experiments were also carried on by him on the South
Bend Railway in the fall of 1885, where several cars were
equipped with small motors, and also in Minneapolis,
where an electric car took the place of a steam locomotive.
Other equipments were operated at the New Orleans Ex-
hibition and at Montgomery, Ala., where the current was
at first taken from a single overhead wire which carried a
traveling trolley connected to the car by a flexible con-
ductor.
Other equipments were put in operation at Windsor,
Ont. ; Detroit, Mich.; Appleton, Wis., and Scranton, Pa.
In these several equipments the motors were placed on
the front platforms of the cars and connected to the wheels
by belts or chains. The cars were headed in one direc-
tion and operated from one end only.
In 1888 the Van Depoele Company was absorbed by the
Thomson-Houston, which had recently entered the railway
field, and Van Depoele continued in its active development
until his death in 1892.
Among the early American workers of this period none
was for a time more prominent than Leo Daft, who after
considerable development in motors for stationary work
took up their application to electric railways, making the
first experiments toward the close of 1883 at his company's
works at Greenville, N. J., these being sufficiently success-
ful to be repeated in November of that year on the Sara-
toga and Mt. McGregor road. The locomotive used there
was called "The Ampere," and pulled a full-sized car. The
motor was mounted on a platform and connected by belts
to an intermediate shaft carried between the wheels, from
which another set of belts led to pulleys on the driving
axles. A center rail and the running rails formed the
working conductors. Variation of speed was accomplished
by variation of field resistance, this being accentuated by
the use of iron instead of copper in some of the coils.
In the following year Daft equipped a small car on one
of the piers at a New York seaside resort, and a little
286 ELECTRICITY
later another one at the Mechanics' Fair in Boston, the
motor for this last being subsequently put on duty at
the New Orleans Exposition. In 1885 work was begun
hy the Daft Company on the Hampton branch of the Bal-
timore Union Passenger Railway Company, where in
August of that year operations were begun, at first with
two and a year later with two more small electric loco-
motives which did not carry passengers themselves, but
pulled regular street cars. A center and the running rail
were used for the normal distribution, but at crossings an
overhead conductor was installed and connection made to
it by an arm carried on the car and pressed up against it.
The driving was by a pinion operating on an internal gear
on one of the axles.
Daft's most ambitious work followed when a section of
the Ninth Avenue Elevated Road was equipped for a dis-
tance of two miles, on which a series of experiments were
carried on during the latter part of 1885, with a locomotive
called "The Benjamin Franklin." The motor was mounted
on a platform pivoted at one end, and motion was com-
municated from the armature to the driving wheel through
grooved gears held in close contact partly by the weight
of the machine and partly by an adjustable screw device.
This locomotive, pulling a train of cars, made several trips,
but the experiments were soon suspended. This work was
followed by street railway equipments at Los Angeles and
elsewhere, using double overhead wires carrying a trolley
carriage.
Meanwhile Bentley and Knight, after some experiments
in the yards of the Brush Electric Company at Cleveland
in the fall of 1883, installed a conduit system in August,
1884, on the tracks of the East Cleveland Horse Railway
Company. The equipped section of the road was 2 miles
long, the conduits were of wood laid between the tracks,
and two cars were employed which were each equipped
with a motor carried under the car body and transmitting
power to the axle by wire cables.
ELECTRIC RAILWAYS 287
These equipments were operated with varying degrees
of success during the winter of 1884-85, but were aban-
doned later. This work was followed by a double over-
head trolley road at Woonsocket, the motors being sup-
plied by the Thomson-Houston Company, and later by a
combined double trolley and conduit road at Allegheny, Pa.
In 1884-85 J. C. Henry installed and operated in Kansas
City a railway supplied by two overhead conductors, on
each of which traveled a small trolley connected to the car
by a flexible cable. The motor was mounted on a frame
supported on the car axle, and the power was transmitted
through a clutch and a nest of gears giving five speeds.
In the following year a portion of another road was
equipped. A number of experiments seem to have been
conducted there and on some the rails were used as a re-
turn. The collectors were of different types, and it is
said that among others there was one carried on the car.
The final selection was a trolley having four wheels dis-
posed in pairs in a horizontal plane, carried by and grip-
ping the sides of the wires ; this feature, but using one
wire and rail return, characterized a road installed by
Henry in San Diego, Cal., opened in November, 1887.
Meanwhile work had begun in Great Britain, where the
first regular road to be put in operation was that known
as the Portrush Electric Railway, in Ireland, installed in
1883 by Siemens Brothers, of London. Power was gener-
ated by turbines, and the current was transmitted by a
third rail supported on wooden posts alongside of the
track, the running rails constituting the return. The pres-
sure used was about 250 volts.
This was followed in the same year by a successful short
road at Brighton, installed by Magnus Volk, the current
being transmitted through the running rails. Then came
the railway installed at Bessbrook, Newry, in 1885, under
the direction of the Messrs. Hopkinson, and at Ryde in
1886, in which latter year was also installed the Blackpool
road by Holroyd Smith. In this latter case the conduit
288 ELECTRICITY
system was used with complete metallic circuit. The mo-
tor was carried underneath the car between the axles and
connected by chain gearing. Fixed brushes with end con-
tact were used for both directions of running.
Reverting to work in the United States, Sprague again
took up the electric railway problem, and in 1885, before
the Society of Arts, Boston, advocated the equipment of
the New York Elevated Railway with motors carried on
the trucks of the regular cars, and work was actually
begun on the construction of experimental motors.
Shortly afterward a regular truck was equipped and a
long series of tests made on a private track in New York
City. In May, 1886, an elevated car was equipped with
these motors and a series of tests begun on the Thirty-
fourth Street branch of the road.
These motors may be considered the parent models of
the modern railway motor. They were centered through
the brackets on the driving axles, connected to them by
single reduction gears, and the free end of the motor was
carried by springs from the transom, the truck elliptics
being interposed between this support and the car body.
The truck had two motors; they were run open; had one
set of brushes and were used not only for propelling the
car but for braking it. The motors were at first shunt
wound, but later had a correcting coil in series with the
armature at right angles to the normal field to prevent
shifting of the neutral point. The car was operated from
each end by similar switches, current at 600 volts was
used, and increase of speed was effected by cutting out re-
sistance in the armature circuit and then by reducing the
field strength. This enabled energy to be returned to the
line when decreasing from high speed. It being impossible
to interest the railway management, the experiments were
finally suspended. Soon afterward a locomotive designed
by Field had a short trial on the same section of the
elevated.
Sprague then turned his attention to building a loco-
ELECTRIC RAILWAYS 289
motive car of 300 hp. capacity, each truck to be equipped
with two motors, each having a pair of armatures geared
to the axle, but this evidently being ahead of the times,
and the possibilities of street tramway traction becoming
evident, these equipments were abandoned, and he began
the development of the type of motor finally used in Rich-
mond, one crude form of which was first used in storage
battery experiments in Philadelphia and others in New
York and Boston in 1886.
Reviewing the conditions at the beginning of 1887, statis-
tics compiled by T. Commerford Martin show that, in-
cluding every kind of equipment, even those a fraction
of a mile long and operated in mines, there were but nine
installations in Europe, aggregating about 20 miles of
track, with a total equipment of 52 motors and motor
cars, none operated with the present overhead line or con-
duit, and seven cars operated by storage batteries, while
in the United States there were only ten installations, with
an aggregate of less than 40 miles of track and 50 motors
and motor cars, operated mostly from overhead lines with
traveling trolleys flexibly connected to the cars. These
were partly Daft, but principally Van Depoele roads. Al-
most every inventor who had taken part in active work
was still alive. The roads, however, were limited in char-
acter, varied in equipment and presented nothing sufficient
to overcome the prejudices of those interested in transpor-
tation and command the confidence of capital.
As a result of all these experiments the series wound
motor soon became universal because of its ability to start
a car with the least expenditure of energy, and has held
its place to the present time with minor improvements in
its structure and method of gearing; 550-600 volts has
become standard for the operation of the motors, this
value having been found the most satisfactory. Altho
higher voltages are desirable for economy of transmission,
the difficulties encountered in the construction of the
motors offset any advantages gained thereby.
290 ELECTRICITY
As previously explained, the higher the voltage used,
the further may the power be economically distributed.
In the direct current system the voltage is limited to about
600. With this comparatively low voltage, cars could be
economically operated only within a few miles of the gen-
erating station. The development of the alternating cur-
rent transformer, by means of which the voltage could be
raised or lowered without mechanism, showed the way to
new developments. The direct current generators in the
power stations were gradually removed and alternators
substituted. Power could be generated at either low or
high voltages, stepped up by means of transformers sent
over the line at a high voltage to a sub-station, dropped
to a lower voltage again by the transformers, and changed
to direct current by means of rotary converters, from
which the car lines were fed. This is the system at present
in use in all the large cities. The most unsatisfactory part
of this system is the sub-station with its rotary converter,
which increases the cost of the sub-station itself and re-
quires considerable attention.
One unfamiliar with the development of motors might
ask why the cars were not equipped with alternating cur-
rent motors. Motors of this class are, however, of quite
recent origin, and their application to the severe strains
of railway work has only been accomplished in the last
four or five years. One of the most successful of these
is the alternating current series motor developed by the
Westinghouse Company and it promises soon to be very
widely applied. The outlook for equipping long railway
lines heretofore operated by steam is very promising and
in fact has already begun.
In May, 1905, the Westinghouse Company completed the
first heavy locomotive to be operated by single-phase
alternating current. This locomotive complete weighs 136
tons. It was built in two halves, each having three axles,
each axle driven by a 225-hp. single-phase series motor
having single reduction gears with a ratio of 18: 95. The
292 ELECTRICITY
current required to operate this locomotive (6,600 volts, 25
cycles) is collected from the trolley wire by means of a
pneumatically operated pantagraph trolley, with sliding
contact, and carried through an oil switch and circuit
breaker to an auto transformer. In this transformer it
is reduced to 325 volts, at which pressure it is used in the
motors. This locomotive, being designed for heavy
freight service, develops a draw-bar pull of 50,000 pounds
at speed of from 10 to 12 miles per hour.
Following several other successful applications of these
motors, the New York, New Haven & Hartford Railroad
decided to equip its road as far as Stamford, Conn., a dis-
tance of 22 miles, with the Westinghouse system. The
locomotives used weigh 70 tons and are each equipped with
four gearless motors of 250 hp. each. These locomotives
operate over 12 miles of track in the city of New York
by means of 600-volt direct current and over 22 miles of
track supplied with alternating current at 11,000 volts, 25
cycles. Each locomotive is capable of hauling a 200-ton
passenger train in accommodation service, requiring one
stop every two miles, at a schedule speed of 26 miles per
hour and a maximum speed of 45 miles per hour. In ex-
press service a maximum speed of 60 to 75 miles per hour
can be attained. Perhaps the longest line yet equipped is
that of the Spokane and Inland Railroad, having a total
length of track of 146 miles.
It has been attempted to apply other forms of alternat-
ing current motors to railway propulsion. One of these is
known as the "repulsion" motor, and altho it has been tried
on short lines, it does not as yet appear to have been so
successful as the "series" type. This form has also been
used in Germany, where some interesting tests on high
speed lines have been made during which speeds of 140
miles per hour have been recorded and 126 miles per hour
with a car carrying passengers.
CHAPTER X
THE ELECTRO-MAGNETIC TELEGRAPH
As early as 1774, Lesage constructed an electric tele-
graph consisting of twenty-four wires, at the end of each
of which was a pith-ball electroscope; and in 1816 Ron-
alds constructed a line of one wire, using pith-balls and
two synchronous wheels. He endeavored to bring the
matter to the attention of the British government, and
received the really exquisite reply that "telegraphs of any
kind are now wholly unnecessary, and no other than the
one now in use will be adopted." A very important step
was taken in 1828 by Harrison Gray Dyar, of New York,
who invented a method of recording in which a discharge
was made to pass through a sheet of moistened litmus
paper moving at a uniform rate. A line was actually set
up and experimented upon in the same year. In all of
these systems it was proposed to use frictional electricity;
but, even with the present vastly increased power of pro-
duction and control of this species of electricity, a suc-
cessfully operating telegraph would hardly be possible.
The real electric telegraph began with Galvani and
Volta, and, as already intimated, more than one system
has been fairly successful, the fundamental principles of
which were understood before the close of the first decade
of the present century. The complete solution of the
problem, however, would unquestionably have been post-
poned for many years but for the discovery of Oersted
in 1820. Immediately on its announcement, the telegraph
293
294 ELECTRICITY
became the dream of many men in many countries. "Con-
cerning its origin and growth," says T. C. Mendenhall
in his 'Century of Electricity,' "the great majority of
Americans have been singularly mistaken. The popu-
lar impression seems to be that it. is exclusively an Ameri-
can invention, and that in America it was almost exclu-
sively the product of the genius of one man. It hardly
need be said that these impressions are extremely erro-
neous.
"Ampere, whose genius had accomplished so much in
the early development of the theory of electro-magnetism,
was probably the first to suggest its use in telegraphy.
His method was founded on Oersted's experiment. If a
needle could be deflected by an electric current, if this
could be accomplished by a wire or wires of great length,
and if these movements of the needle could be converted
into a code by means of which letters or words could be
expressed, then the electro-magnetic telegraph was pos-
sible. Ampere's suggestion was to employ a number of
wires and to deflect a number of needles. Considerable
attention was given to the development of this idea for
a number of years following the discovery of its funda-
mental principle. The progress of the invention was
seriously retarded by the publication of an inves-
tigation by Barlow, of the Woolwich Military Acad-
emy, in 1825, in the course of which he discovered that
there was an enormous diminution in the power of a cur-
rent to produce effects with an increase of distance, and
which led him to declare that the project of an electro-
magnetic telegraph could not possibly be successful."
The invention of the electro-magnet by Sturgeon ap-
parently offered a new solution of the problem ; but, owing
to the imperfect construction of his magnets, the difficulty
of overcoming distance was not diminished. This ob-
stacle, which seemed for a time to be insurmountable, was
conquered by Joseph Henry in the manner already de-
scribed. Out of Oersted's experiment grew the needle-
ELECTRO-MAGNETIC TELEGRAPH 295
telegraph — a form which prevailed for several years in
Europe, until it gave way before the evident superiority of
that founded on the electro-magnet, which grew out of
the researches of Henry, and which is generally known
as the Morse or American system.
The needle-telegraph was first in the field, and its work-
ing will first be considered. Many of its earlier forms
appear as suggestions only, no attempt having been made
to put them in practical operation. In 1832, however,
Baron Schilling, a Russian counselor of state, had a
working system in which thirty-six needles were used,
and which included an ingenious alarm for calling the
attention of the receiving operator. It consisted of a
device by means of which the movement of one of the
needles released a small ball of lead, which, by dropping
upon the mechanism of the alarm, set it in operation. A
model of this system was exhibited before the emperors
Alexander and Nicholas.
A little later the two illustrious German philosophers,
Gauss and Weber, established a successfully operating
line at Gottingen. It was two or three miles long, and a
double wire was used. Magnetic needles or bars, freely
suspended, were used as receiving instruments, and the
arrangement included a device for setting off an alarm-
clock. The current from a battery was first used, but
afterward the secondary or induced current was sub-
stituted. This line was in working order in 1833, ano^
was established mainly for experimental purposes. The
practical development of the scheme was given over to
Steinheil, in whose hands it grew with rapidity. In 1837
he had constructed several miles of telegraph, extending
from Munich to various points in the vicinity. His work
appears to have been officially sanctioned by the govern-
ment, and his wires doubtless constituted the first electric
telegraph ever erected for commercial purposes. The
system included a method of recording the message as
received, which might also be read by sound, the signals
296 ELECTRICITY
being distinguished from each other by the use of bells
differing in pitch.
"But altogether the most valuable contribution made
by Steinheil," says Mendenhall, "was the discovery that
the use of a double wire was unnecessary, it being possible
to establish electric communication between two points
by the use of one wire, whose terminals were joined to the
earth through plates of metal, or other conductors ex-
posing considerable surface. As it largely reduced the
cost of construction, this discovery was of prime impor-
tance. It was really a repetition of what Franklin had
long before accomplished when he stretched his wire
across the Schuylkill River, but the relation between the
two experiments was not at the time appreciated or fully
understood."
Both the science of electricity and the art of telegraphy
owe much to the genius of Sir Charles Wheatstone, whose
interest in and connection with telegraph enterprises be-
gan in 1835, in which year he exhibited one of Schilling's
telegraphs in his lectures, and in the year 1837, when he
formed a copartnership with W. F. Cooke, for the pur-
pose of introducing the electric telegraph into England.
Their first patent was taken out in 1837; and the system
required five needles, with as many wires for their manipu-
lation, and a sixth wire for the "return current." Wheat-
stone developed numerous improvements during the next
few years, and as early as 1840 a dial instrument show-
ing the letters of the alphabet was patented. Numerous
difficulties were encountered and overcome, and by 1844
the enterprise was on a sound financial basis.
The operation of working a telegraph was at first nat-
urally regarded by most people as a mystery and by many
as a fraud. When communication was established be-
tween Paddington and Slough, a distance of about twenty
miles, the wires were insulated partly by silk and were
suspended through goose-quills attached to posts along
the Great Western Railway. The telegraph company not
ELECTRO-MAGNETIC TELEGRAPH 297
only invited the patronage of the public in a legitimate
business way, but it also exhibited its apparatus as a nov-
elty. This short line speedily established itself in the
good graces of the people through its instrumentality in
securing the arrest of a criminal.
The construction expenses incident to the use of a large
number of wires, to say nothing of other difficulties, led
to the reduction of the number of needles employed to
two, and one in which a single wire was sufficient. A
single needle is now almost universally employed wher-
ever the needle system has survived competition with
other forms. The movements of the needle are readily
applied to signaling the alphabet by combinations of
swings to the right and to the left. It will be remembered
that in Oersted's experiment a reversal of the current
through the wire reversed the direction of the deflection
of the needle. The operating key is so arranged that
when its handle is turned to the right a current is sent
through the line which deflects the needle in the same
direction; and when the opposite movement is made the
current is reversed and the needle swings to the left.
The alphabet may and generally does correspond with
what is known as the "Morse Code." A swing to the
right is interpreted as a long signal or dash, and one to the
left as the short or "dot" signal of the Morse system.
For many years the needle system of telegraph was
used almost exclusively in Great Britain, altho it never
succeeded in gaining a foothold on the continent of Eu-
rope or in any other part of the world. Its principal
advantage is the comparatively feeble current required to
work it; but it is slower than the Morse system, and does
not lend itself to sound-reading, or to methods of secur-
ing written records of the messages which it transmits.
It has therefore almost entirely given way to other sys-
tems, even in Great Britain, altho, as will be seen, it is
retained in connection with long ocean-cables, and within
298 ELECTRICITY
a few years a self-recording device has been successfully-
applied to it.
The system of telegraphy now almost universally in
use is one which originated in America, and whose de-
velopment was nearly contemporaneous with that of the
needle system. In England the fundamental experiment
about which the telegraph grew was that of Oersted;
while in America the electro-magnet, as constructed by
Sturgeon and improved by Henry, was made the basis of
the invention. As there has been much misunderstanding
concerning the distribution of credit for the evolution
of this system of telegraphy, it may not be out of the
way to consider at some length its more important phases.
Much credit must always be accorded Professor S. F. B.
Morse, through whose indefatigable labors and persistent
faith the commercial value of the enterprise was first
established. Born in the last century, he reached the age
of forty years before having apparently given a single
thought to what was to be the great work of his life.
His early training was that of an artist, altho he was
always fond of scientific pursuits. He studied in London
under the best masters, and was highly successful in his
chosen profession, some of his works bringing him great
renown. His first conception of an electro-magnetic tele-
graph seems to have arisen out of a conversation with a
friend on board the packet ship Sully, on a voyage from
Havre to New York in 1832. In this conversation some
experiments of the French were described, in which elec-
tricity had been transmitted through long distances. Some
one remarked, "It would be well if we could send news
in this rapid manner"; to which Morse at once replied,
"Why can't we?" And from that moment he devoted his
energies to accomplishing the desired end.
During the remainder of the voyage he made drawings
of forms of apparatus and considered the transmission of
signals into an alphabet. He does not appear to have
been familiar with the principles of electro-magnetism at
ELECTRO-MAGNETIC TELEGRAPH 299
that time, and it is affirmed that the use of an electro-
magnet was suggested to him by the gentleman with whom
this first discussion was held. On reaching New York,
he began experimenting upon the subject, and in 1835
he had completed a working model of his recording in-
strument. It was not until 1837, however, that he was
able to put two of them in operation at the extremities of
a short line, so as to be able to both receive and send sig-
nals. In that year his apparatus was exhibited to many
people in the University of New York. In the following
year he made an unsuccessful effort to secure aid from
Congress to establish an experimental line between Wash-
ington and Baltimore. He then visited Europe, but failed
to secure patents for his inventions. During the session
of Congress of 1842-43 he again struggled to secure
recognition and an appropriation to enable him to build
his experimental line. The scheme was considered
quixotic by many members of Congress, and at the last
moment he despaired of success; but during the midnight
hour of the last night of the session, March 3, 1843, a bill
was passed appropriating thirty thousand dollars for the
line from Washington to Baltimore.
In the meantime many apparently insuperable obstacles
had been encountered in the attempt to secure the suc-
cessful working of the apparatus. In the beginnings
Morse used a magnet with a few turns of wire, as Stur-
geon had done, and a single cell of battery. With this his
instrument failed to work through more than a few feet
of wire. This difficulty was surmounted by taking ad-
vantage of the researches of Henry, using what he called
an "intensity" magnet and many cells of battery instead
of one. Altho by this method signals could be trans-
mitted through a comparatively long distance, they were
still too feeble to print themselves upon the moving strip
of paper. To overcome this difficulty it was only neces-
sary to introduce the device known as the 'relay,' by
means of which the work on the main circuit was reduced
300 ELECTRICITY
to making and breaking the current of a local battery, on
the circuit of which was the recording machine. In this
short circuit the current was easily made strong enough
to operate the registering instrument. This method of
working had been devised nearly ten years before by
Henry, and it had also been used by Wheatstone in his
needle system.
In Morse's first attempt to build his experimental line
from Washington to Baltimore in 1844, the wires were
^placed underground instead of upon poles ; but the former
method was soon abandoned for the latter, which had
already been in use for several years in Europe and else-
where. In Morse's first instrument the 'transmitter' was
mechanical ; that is to say, the message to be sent was
first "set up" in "dots and dashes" by arranging long and
short type in proper order in a line, and by the regular
movement of this line of type the circuit was closed for
periods of time necessary to the reproduction of the dots
and dashes at the other end. Morse did not imagine that
signals could be made by the hand with sufficient regular-
ity to produce legible records. This was soon discovered
to be possible, however, and for the clumsy mechanical
transmitter the simple key in use to-day was substituted,
by the skilful manipulation of which the operator pro-
duces dots and dashes with such regularity and rapidity
as to leave nothing to be desired.
The statements made above, derived from papers of
an official character, may be summarized as follows : In
the Morse telegraph are found the battery, for which
credit must be given primarily to Volta, and then to
Daniell, who in 1836 devised a battery nearly constant in
its strength — an essential requisite to its application to the
telegraph ; the key, or transmitter, which, except in de-
tails of construction, is practically that in use since ex-
periments on electricity were begun; the receiving instru-
ment, of which the essential feature is the electro-magnet,
due primarily to Sturgeon, but modified and improved so
ELECTRO-MAGNETIC TELEGRAPH 301
as to be available for this work by Henry; the relay, by
means of which the local current is put in operation, which
was used by Henry and also by Wheatstone ; the line wire
suspended on poles — a method first practically used by
Dr. W. O'Shaughnessy at Calcutta in 1839.
While it appears, therefore, that Morse cannot justly
claim priority in the discovery of a single scientific prin-
ciple involved in the telegraph, it must be admitted on all
hands that he played a most important part in its develop-
ment. In Europe all effort had been in the direction of
the use of the needle system. Morse was quick to see the
advantages of the electro-magnet, and especially the ease
with which it could be made to leave a permanent record
of the message. His use of a simple armature with to-
and-fro motion, armed with a style, or pencil, which
marked long or short lines upon a moving slip of paper,
and his alphabet made up of these dots and dashes, show
great ingenuity and mechanical judgment. As a measure
of the value of his system, compared with the English,
it is sufficient to repeat that to-day it has driven nearly
every other from the field.
As the popularity of the telegraph increased and the
number of line wires grew large, attempts were made to
make one line wire transmit more than one message at
the same time. Various schemes have been tried, most
of which have failed by reason of the complications of the
apparatus and the consequent troubles attending them.
The step in the direction of utilizing the line wire more
fully was the invention of the duplex system by Dr. Wil-
helm Gintl in 1853. This system was improved by Carl
Frischen, of Hanover, until it lacked only one essential
element — means to overcome the condenser-like action
of the long line wire. It was not until 1872 that this was
supplied by Joseph B. Stearns,, of Boston, who introduced
a condenser into the artificial line of the duplex system
and, by adjusting it, made the artificial line behave like
the line wire itself. This important addition made the
302 ELECTRICITY
system entirely successful, so that it became possible to
transmit two messages in opposite directions at the same
time.
Following the success of the_ duplex system, there was
developed a method by which two messages could be sent
simultaneously in the same direction, and it was but a
step to combine these two systems so that two messages
could be sent each way simultaneously. This last is known
as the quadruplex system, and was immediately success-
ful because there were no delicate adjustments to be made
and no rotating parts as in some of the synchronous tele-
graphs which have been tried from time to time.
As early as 1852 Moses G. Farmer, of Salem, Mass.,
devised a synchronous-multiple telegraph in which he
proposed to employ two rotating switches, one at each
end of the line, to successively and simultaneously join
the several operators at one station with those of another.
The idea was to connect two operators for an instant, pass
on to the next two, and so on, returning to the first two
operators so quickly that the relay of the receiving opera-
tor would not have had time to change nor the key of the
sender to make a dot. The impulses of the current had
therefore to be made with great frequency, and the control
of this impulsive current was the principal cause of fail-
ure. Another difficulty was the maintenance of the ro-
tating switches in synchronism.
The public is occasionally startled with an announce-
ment that some one has invented a telegraph by which a
wire may be utilized for twenty or perhaps forty trans-
missions, but usually it is the old wanderer in a new
garb. Speed by this method, however, is limited far
within the bounds of these statements. It might seem
that it would only be necessary to multiply the number of
contacts and to increase the velocity of the rotating arms ;
but the limit in this direction is soon reached, for only
a certain number of impulses can be transmitted over a
line within a certain period with force sufficient to pro-
ELECTRO-MAGNETIC TELEGRAPH 303
duce signals. Many valuable improvements have been
made in recent years in this class of telegraphy, but large
as the art has grown, the great object of all has been
to obtain more perfect synchronism — that is to say, to
cause two mechanically independent arms to rotate at the
same speed.
One of the most recent of these synchronous telegraphs
and which is now being exploited is that invented by Mr.
Delaney. The principle is that of Farmer, but the method
used to hold the rotating switches in synchronism is ex-
tremely ingenious. It is stated that 1,000 words per min-
ute may be transmitted over a single wire. The messages
■are prepared on a tape by a punching machine and re-
ceived on a chemically prepared strip of paper.
The idea of printing the despatch is not new. In the
early days of the electric telegraph (1841) Wheatstone
took out a patent for printing the message in ordinary
letters upon a strip of paper. Since then many inventors
have followed out the same idea, with more or less suc-
cess. The most perfect of all these systems, however, is
that invented by Professor David E. Hughes, which, in a
modified form, is now very generally used as a news or
stock ticker. Fig. 45 shows the connections for such a
telegraph.
The sending station is at A and one of the receiving
stations at B. The line is fed with an alternating current
produced by reversing commutator, 4. This alternating
current does not affect printing relay 5, but does operate
polar relay 6, which in turn operates the escapement. Re-
verser 4 is driven by constant-speed motor 1 and has as
many segments as there are characters on the type wheel.
The escape wheel 10 is provided with an equal number of
teeth, so that each revolution of reverser 4 will produce
one revolution of type wheel 7. On the shaft with the
reverser is rigidly mounted a cylinder provided with a
number of pins arranged spirally as shown ; each pin is in.
304
ELECTRICITY
line with a segment of the reverser and also in line with
a pin fastened to the keyboard.
Depressing a given key will always stop the cylinder
and therefore type wheel 7 in the same place. The con-
nection to the motor 1 is made with friction clutch 2,,
which slips when cylinder 3 is stopped. Now it is evident
Fig. 45 — Arrangement of a Printing Telegraph or "News
Ticker." (From Standard Handbook for Electrical Engi-
neers.)
if type wheel 7 is started with its characters in certain
position and is rotated by a motor through gear 11 and
controlled by escapement magnet 6, that it will always
remain in the same relative position with cylinder 3, and
that the operator can stop the type wheel in any desired
position.
ELECTRO-MAGNETIC TELEGRAPH 305
If the type wheel stops because of the arrest of the
cylinder 3 by depression of a key, the current ceases to
alternate and magnet 5 has time to draw up its armature,
8, and press the tape against the type wheel, thus printing
the character which corresponds to key depressed at the
sending station.
These are ingenious arrangements for reproducing at
a distant point handwriting, drawings, etc. One of the
[Vmwu
T
I
. line
HI
_ line
springs
springs I
Fig. 46 — Denison Electrochemical Facsimile Telegraph.
(From Standard Handbook for Electrical Engineers.)
first of these is known as Casselli's pantelegraph, because
the reproduction may be of the same size or even larger
than the original. The message to be sent is written
with an insulating ink on a piece of tinfoil and received
on a sheet of chemically prepared paper upon which a
blue dot is left at each current impulse. The motions of
the marking style at the two stations are controlled by
similar pendulums. In the Denison system these pendu-
lums are forced to vibrate together through the control of
electro-magnets operated by the same alternating current.
306
ELECTRICITY
The most recent and useful of these arrangements is
the telautograph. The message is reproduced as fast as
it is written. Drawings or sketches are transmitted with
great accuracy; in fact, every motion of the sending pen
is instantly followed by the receiver. Some of these are
in use in the United States army.
The insulation of conductors for use under water was
made possible by the discovery of gutta-percha by an Eng-
lish surgeon in India in 1842. It is extremely probable
that the widespread use of submarine cables would have
been postponed many years had this substance remained
///?e
3L.
"1
j
a
Sfe'
=?
/'
Fig. 47 — Electromagnetic Facsimile Telegraph. (From
Standard Handbook for Electrical Engineers.)
unknown. One of the first cables insulated by this ma-
terial, and possibly the very first, was laid in 1848 across
the Hudson River, from Jersey City to New York. In
1850 a cable was laid across the channel, from Dover to
Calais, but it was unprotected by any sheathing or armor,
and it lasted but a single day.
In the following year the experiment was repeated,
this time with a cable protected by a number of heavy
iron wires. The operation was successful, and permanent
telegraph communication was established. During the
next few years the number of submarine cables increased
rapidly, as did also their length, altho, on account of ig-
norance in regard to many conditions necessary to insure
the best success, failures were numerous. Many people
began to consider the feasibility of a line connecting the
ELECTRO-MAGNETIC TELEGRAPH 307
continents across the Atlantic Ocean. A few sanguine
capitalists combined to further the enterprise, and through
the undaunted courage and faith of an American, Mr.
Cyrus W. Field, the purely financial obstacles were sur-
mounted. Unfortunately, the electrical and engineering
problems to be met with were not understood; and the
first cable of 1858, after gasping for breath for a few
short weeks, lay dumb forever at the bottom of the sea.
Something of the character of this cable may be learned
from the following brief description by Sir William
Thomson, to whom, more than to any other one man,
the world is indebted for the success of submarine tele-
graphy : "In the year 1857 as much iron as would make a
cube twenty feet wide was drawn into wire long enough
to extend from the earth to the moon, and bind several
times around each globe. This wire was made into 126
lengths of 2,500 miles, and spun into 18 strands of 7 wires
each. A single strand of 7 copper wires of the same
length, weighing in all no grains per foot, was three times
coated with gutta-percha, to an entire outer thickness of
.4 of an inch; and this was 'served' outside with 240 tons
of tarred yarn, and then laid over with the 18 strands of
iron wire in long, contiguous spirals and passed through
a bath of melted pitch."
An attempt to lay this cable in 1857 resulted in the loss
of 400 or 500 miles by breaking from the stern of the ship
from which it was run. After some further experimenta-
tion, it was determined to employ two ships to lay it in
the following year; and accordingly, on the 29th of July,
1858, the Niagara and the Agamemnon, each loaded with
half the cable, met in mid ocean, joined the ends, and
started, the Niagara for the west and the Agamemnon
for the east. On the 5th of August the ends were suc-
cessfully landed on the opposite shores of the Atlantic.
The cable was known to be in bad condition before the
laying was completed, and the earnest but ill-advised ef-
forts which were made to force it to work during its brief
308 , ELECTRICITY
period of activity only tended to shorten its life. Com-
munication of a very irregular and unsatisfactory charac-
ter was maintained for several weeks. The admirable
mirror galvanometer, which had just been devised by Sir
William Thomson, was for the first time in use at the
Valentia end, while for a time the attempt was made to
use the ordinary receiving apparatus which had been pro-
vided by the company at Newfoundland. Later the gal-
vanometer was put in use on this side, but not before very
powerful currents had been used on the cable. In fact,
Sir William Thomson has declared his belief that, if
proper methods of handling the cable electrically had
been in use from the beginning, its performance would
have been lasting and in the main satisfactory.
Owing to the fragmentary character of many of the
messages transmitted, a single sentence from that of the
Queen to the President having been received on August
16, and the remainder twenty-four hours later, many per-
sons in both Europe and America became skeptical as to
the transmission of signals, and not a few even doubted
that the cable had been laid. As a matter of fact, four
hundred messages, containing over four thousand words,
were sent. On September i interchange of messages
ceased ; but on October 20 the cable spoke its last words —
"two hundred and forty" — which were read at Valentia,
being part of a message giving the number of battery-
cells then on the line. From that date the "splendid com-
bination of matter lay at the bottom of the sea, forever
useless." But it had not lived in vain; the possibility of
the thing was demonstrated, and it only remained to sur-
mount the obstacles which this trial had shown.
During a few years succeeding this first attempt, the
problem was studied in the light of the experience which
it had afforded. Another trial was made in 1865, this
time by the Great Eastern, a vessel which offered many
advantages for cable-laying. After about two-thirds of
the distance was run the cable broke, and further opera-
ELECTRO-MAGNETIC TELEGRAPH 3°9
tions were postponed until the following year, when a
complete cable was successfully laid, and that of 1865
pickecl up, spliced and finished. Since then other lines
have been placed across the Atlantic; and now the opera-
tions of laying an ocean cable attracts no attention.
One of the difficulties encountered in attempting to send
messages through such a long cable was that due to the
electrostatic capacity of the cable. The cable acts like a
very large condenser, so that when the voltage is applied
at one end the current does not instantly rise to its steady
value, but takes several seconds, and when the supply
of voltage is disconnected the current continues to flow.
In order to signal rapidly, therefore, it was necessary to
overcome this action and to use very delicate receiving
instruments. For this purpose Sir William Thomson,
Lord Kelvin, devised the well-known siphon recorder,
which is really a sensitive galvanometer whose moving
coil carries a siphon tube filled with ink, the ink being
ejected from it in fine drops on a strip of paper. To pro-
duce these fine drops the siphon tube is connected to a
small electrostatic machine, so that the tube is electrified.
Altho the telephone has made such rapid advances as
a means of communication, the telegraph still holds its
own field. The greater simplicity of the latter, the less
expensive lines, the greater distances to which messages
can be transmitted, all combine for its preservation. The
flattening out of the waves on a telephone line due to the
condenser-like action of the line has not yet been over-
come. The difference between the telephonic waves at the
beginning and end of a line may be compared to that be-
tween the noisy exhaust of an automobile motor without
and with a muffler. In the case of the transmission of
telephone waves it is, therefore, a problem of how to rid
the line of its muffler.
CHAPTER XI
WIRELESS TELEGRAPHY
Professor Henry, of Princeton University, was the
first to show the oscillatory character of the discharge of
a Leyden jar. This single loud spark, which to the eye
seems to pass in one direction across the gap, is really a
quick succession of current surges, first one way and then
the other, and has its mechanical analogy in the pendu-
lum.
At the outset it may be well to analyze this spark dis-
charge, as it is still the most prominent means of ra-
diating the electric waves used to transmit signals. Sup-
pose this pendulum analogy of the spark discharge be-
tween two spheres be taken and the similarity of the two
actions noted. If a heavy pendulum be drawn back
by means of a light fiber, it will finally strain the fiber to
such an extent as to cause it to break. The pendulum
being suddenly released gradually acquires motion, which
is accelerated until its lowest position is reached, after
which it is retarded just as it was accelerated and stops
at about the same height at which it started. The process
is then repeated, but in the opposite direction. Now com-
pare the action on the two charged spheres. The pressure
in the dielectric surrounding the spheres is gradually
raised until it suddenly gives way, there being a flow of
current from the positive to the negative sphere, which
current gradually increases and is greatest at the instant
when both dielectrics are at the same potential, just as the
310
WIRELESS TELEGRAPHY 311
motion of the pendulum was greatest at its lowest position.
The current then begins to decrease and finally stops when
the dielectric is again strained to about the same potential
it had at first but reversed in direction. The current then
starts back again just as the pendulum again acquired mo-
tion.
Now let it be considered what goes on in the space sur-
rounding this action. A current is always surrounded by
a field of magnetic force, which field is proportional to
the strength of the current. As this current between the
two spheres increases there is, therefore, sent out an in-
creasing magnetic field which is radiated into space, reach-
ing a maximum and again decreasing with the current.
But while the current increases the electrostatic strain
about the sphere decreases, thus sending out an electro-
static wave which again increases as the current de-
creases. It will thus be seen that as these surges take
place alternate electromagnetic and electrostatic waves
are radiated into space.
Why do not these surges keep on forever? Mainly be-
cause the current in its flow across the gap encounters a
resistance, and instead of converting all its energy into
magnetic waves loses a portion as heat at each surge.
This corresponds to oscillating the pendulum in a liquid
or viscous material, the energy of its motion soon being
converted into heat.
So much for the creation of these waves. But how may
their passage through space be detected? One way is by
catching them on a wire. What is the manner of the
catching? If a wire be placed so that it cuts the wave
transversely to its line of motion, it is clear that the mov-
ing magnetic wave will induce in it an electromotive force.
As these waves follow in rapid succession, a series of al-
ternating electromotive forces is set up in the wire. These
oscillatory currents are sometimes called "jigs." How
these jig currents make their presence known varies with
the style of wave detector used.
312 ELECTRICITY
Before entering upon the history of this "spark tele-
graphy," as the Germans call it, it may be well to review
some of the experiments which preceded this system. In
1838 Professor Joseph Henry, of Princeton, making with
an electrical machine and Leyden jar a one-inch spark in
the top room of his residence, set up induced currents in
the cellar of the same building. Professor Morse, how-
ever, was probably the first to successfully transmit sig-
nals without wire. On December 16, 1842, he sent a wire-
less telegram across a canal eighty feet wide; and in No-
vember, 1844, L. D. Gale, acting under instructions
from Professor Morse, made wireless signals across the
Susquehanna River at Havre de Grace, a distance of
nearly one mile. In the latter experiment Mr. Gale used
as a source of energy six pairs of plates in the form of
a galvanic battery. He found that the best results were
obtained when on each side of the river two plates were
immersed near its bank and were connected by an insulated
wire stretched along each shore for a distance three times
as great as that which measured either path of the cross-
ing signals. A few years later James Lindsay, a Scotch-
man, repeated Morse's experiments, but without knowing
of them. In 1859 he read a paper before the British Asso-
ciation on the subject of "Telegraphing without Wires,'*
and among his hearers were Faraday and Lord Kelvin.
A method of signaling without wires by means of the
inductive effect of two parallel circuits was successfully
used by Sir William Preece in 1882. The principle of
this method is as follows : If two loops of wire are placed
parallel to each other and an intermittent current is passed
through one of them, waves of magnetic flux are sent out,
portions of which thread the second loop and by their
fluctuations produce currents in it which may be detected
by a telephone or other device. The strength of such
signals falls off very rapidly from the source, and such a
system can only be made to operate over short distances.
Preece constructed two parallel lines, one on the Eng-
WIRELESS TELEGRAPHY
3*3
lish coast and one on the Isle of Wight, the arrange-
ment of which is shown in Fig. 48. It will be seen that
the loop from which the waves emanate is formed by the
line wire and the earth.
The crowning achievement, however, was the work of
Hertz, whose early death deprived the world of the aid
of a most powerful brain. In 1886 Hertz discovered that
if a loop of wire having a small air-gap left in it were
Fig. 48
-Preece's Apparatus for Signaling by Electro-
magnetic Induction.
placed at a distance from a spark discharge of a Leyden
jar, minute sparks would pass across the air-gap of the
loop, thus indicating the presence of electric waves. He
subsequently made a very complete study of the behavior
of these waves and thus gave a tremendous impetus to
the development of wireless telegraphy.
Second to the work of Hertz is that of Sir Oliver
Lodge, who in 1889 discovered the effect of electric waves
on the breaking down of the electrical resistance of two
knobs barely in contact, which discovery resulted in the
first means used to detect the presence of electrical waves,
viz., the coherer.
314 ELECTRICITY
The development of wave detectors is an important
chapter. For these instruments Professor Fleming has
suggested the use of the word cymoscope as a general
term including all classes of wave detectors. A great
number of these have been -invented, but they may all
be included under the following classes: i, spark cymo-
scopes; 2, contact cymoscopes; 3, thermal cymoscopes;
4, magnetic cymoscopes; 5, electrolytic cymoscopes; 6,
electrodynamic cymoscopes; 7, vacuum tube cymoscopes.
The first cymoscope invented was that used by Hertz
in his investigation of electric waves, and belongs to the
first class. It consisted merely of a ring broken at one
point and arranged so that the gap might be adjusted
M
Fig. 49 — The Branley Filings Coherer.
by means of a micrometer screw. Tiny sparks across this
gap indicated the presence of waves. Since the electro-
motive force required to produce a spark across even a
small gap is very considerable, it will be obvious that
such a detector could only operate at a short distance,
and would, therefore, be useless for the purpose of sig-
naling.
The next invention, made in 1890, was the Bramly
coherer, Fig. 49, which consisted of a small glass tube
containing two metallic plugs and separated by a gap par-
tially filled with metallic filings. This is an example of
the second class. The metallic filings, when loosely
packed, offer a very high resistance to the passage of cur-
rent through them, but the presence of waves breaks
down their contact resistance, which continues after the
waves have ceased. In order to again restore their re-
WIRELESS TELEGRAPHY
315
sistance they must be tapped or shaken, an operation
known as decoherence. It is obvious that such an appa-
ratus may be used like a key in a telegraphic circuit —
a key operated by electric waves — and may therefore be
used to operate a telegraphic instrument. Such was the
first device used. It was defective, however, in that it
was necessary to tap it after each signal, decoherence
was not certain, it required frequent adjustment, and the
result was often a confused lot of signals.
Many arrangements of loose contacts were tried, and
Fig. 50 — The Lodge-Muirhead Coherer.
the coherer was improved by Marconi, Lodge, Braun, and
others. One of the principal troubles being the opera-
tion of decoherence, most of the inventors sought to de-
velop a coherer which should be self-restoring, and a
number of successful types were invented. One of these
was the Hughes coherer, employing carbon granules
placed between iron plugs. The most perfect and suc-
cessful of all these is, however, that devised by Sir Oliver
Lodge and Dr. Muirhead, and used in the Lodge-Muirhead
system. As shown in Fig. 50, it consists of a steel disk,
slightly separated from a globule of mercury by a film
of oil, the disk being arranged to rotate slowly. The
316 ELECTRICITY
presence of waves breaks down the oil film and estab-
lishes contact with the mercury, which contact immedi-
ately breaks upon the cessation of the waves. A siphon
recorder, placed in series with the cymoscope, is used to
record the message.
Altho a number of forms of the magnetic style of detector
were devised, it was not until 1902 that a successful work-
ing apparatus was produced. For some time before that
it was known that the oscillating currents received would
annul wholly or in part the magnetic hysteresis of iron
when passed through a coil surrounding the iron. Hys-
teresis acts like molecular friction, so that when a mag-
netizing current is passed through a coil surrounding an
iron core, the magnetization does not increase and de-
crease with the current in the coil, but lags behind it. If
another coil be placed around this same core and the
oscillating currents passed through it, this hysteresis will
be suddenly removed and the magnetism in the core will
suddenly change in value. This sudden change could be
detected by a third coil surrounding the core and con-
nected to a telephone receiver, resulting in a sudden click.
This was the principle of which Marconi made use in
his magnetic detector, and which he has used in his long-
distance experiments. The arrangement is shown in Fig.
18. It consists of a band of iron wires passing through
two coils, one carrying the jig currents and one con-
nected to the telephone. The wires are magnetized by
two permanent magnets, and as they move under that
portion where the two poles meet, the magnetic flux in
them undergoes a reversal, which reversal, however, al-
ways takes place at the same point until the jig currents
pass, when the flux is suddenly shifted backward, causing
a sound in the telephone.
These detectors have come into very general use on ac-
count of their convenience, sensitiveness, and adaptation
to rapid signaling. In 1901, Dr. Lee de Forest patented
a detector which depends for its operation on the dis-
WIRELESS TELEGRAPHY
317
ruption of the minute metallic bridges or 'trees' which
form, under suitable conditions, between the electrodes
of an electrolytic cell. The apparatus, called a 'respond-
er,' consists in a glass tube similar to that of a coherer,,
in which are fitted two electrodes, preferably of tin, The
space between the electrodes — about y«* inch — is filled with
a viscuous, semiconducting liquid, such as glycerin with
a small admixture of water, together with some peroxide
of lead as a depolarizer, to prevent the excessive evolu-
Fig. 51 — The Marconi Magnetic Detector.
tion of gas. When a cell of suitable voltage is connected
across this "responder," metallic "trees" or bridges are
formed, which make a path of low resistance; but upon
the passage of the jig currents these "trees" are broken
down and the circuit broken, producing a sound in a tele-
phone receiver. Immediately upon the cessation of the
jig currents, however, these "trees" again establish them-
selves.
Another very successful and extremely sensitive de-
tector was invented by Fessenden and Vreeland, and
consists of a small platinum cathode containing nitric
acid, with a minute anode of platinum wire Yioooo inch
318 ELECTRICITY
in diameter. This little electrolytic cell, when polarized
to the critical point by being connected to a battery, is
remarkably sensitive to jig currents. It has been em-
ployed by Fessenden in his transatlantic experiments.
Many other detectors have "been developed which have
operated successfully, but those described are used most
generally.
It would not be possible in a few words to give a com- -
prehensive idea of the various systems in use, as many
important improvements which have been made in the last
ten years. Those systems which have attained commercial
importance are the Marconi, the Fessenden, the De For-
est, the Slaby-Arco, and the Lodge-Muirhead. The great-
est differences are usually found in the receiving appa-
ratus.
The first system used by Marconi employed the coherer
as a wave detector and the Ruhmhorff coil to produce the
sparks from which the waves were radiated. The dia-
grammatic arrangement of the sending and receiving ap-
paratus is shown in Fig. 52, T being the coherer and
L the telegraphic relay. Experiments with this form of
apparatus were first made in 1896 in England, where Mar-
coni went to obtain the assistance of Sir William Preece.
These experiments were so successful that trials were
made during the next year, at each of which something
new was learned whereby the distance of transmission
was increased. From some of these experiments Marconi
worked out the effect of the height of the antenna, or
aerial wire, on the distance of transmission.
In August, 1897, Marconi organized a company known
as the Wireless Telegraph and Signal Co., with a capital
of $5,000,000. In June, 1897, Marconi went to Rome, and
after having undertaken in this city, at the instigation
of the Minister of Marine, several experiments from one
floor to another with a conductor three yards in height,
was invited by the Hon. Brin, Minister of Marine, to
undertake, in the presence of a select commission com-
WIRELESS TELEGRAPHY
319
posed of officers who were specialists belonging to the
royal marines, some fresh experiments. The place chosen
was the Gulf of Spezzia. The experiments took place
between the nth and the 18th of July, 1897. The appa-
ratus made use of for transmitting and receiving was
similar to those employed on the Bristol Channel; that
is to say, aerial wires ending above in metallic sheets.
The coil was less powerful than that used in the former
case, giving sparks 10 inches in length only.
The apparatus was located, during the entire series of
Fig- 52 — Rudimentary Transmitting and Receiving Apparatus*
experiments, in the electrical laboratory of St. Bartholo-
mew, and bore an aerial line about 75 feet in height, which
was afterward prolonged to 90, terminating in a square
metal sheet of about 8 feet in the side.
On the first three days, viz., nth, 12th and 13th of July,
the experiments were executed on land, which gave very
good results up to a distance of 3^ kilometers, or say
2 miles; on the 14th of July the receiver was set up on.
board a tug, having a mast about 50 feet in height, which
bore an aerial wire of equal length ending in a sheet about
8 feet in the side.
The transmitting station was bound to carry out the
following instructions: Ten minutes after the start of
320 ELECTRICITY
the tug it was to send for 15 minutes dots and dashes at
intervals of 10 seconds; then transmit a phrase, maintain-
ing between each signal an interval of 10 seconds; then
to suspend transmission for an interval of 5 minutes, after
which it should go through the same round, but with in-
tervals of 5 seconds instead of 10 between each signal.
The tug having started from the little port of St. Bar-
tholomew, the receiver registered some signs even before
transmission had begun on land, a fact due doubtless to
extraneous causes. She directed her course toward the
western mouth of the mole, and continued to receive sig-
nals, not, however, in the order and in the intervals that
had been prearranged, but much more frequently. The
zlzy was covered with stormy clouds and in the distance
lightning was frequent, hence it was surmised that be-
sides the signals that were really transmitted, others, due
to atmospheric influence, were impressing themselves,
which rendered the strip of paper on which they were
registered illegible.
On again repeating these experiments after the storm
clouds had disappeared, correspondence came out very
clearly up to a distance of 5,500 meters (nearly 3 miles),
with the tug stationary. The tug was again put in mo-
tion, so as to interpose between itself and the station
at St. Bartholomew the point called Le Castagne, in order
to ascertain what effect such a screen would have on sig-
naling.
The signals ceased as soon as the obstacle intervened,
to recommence on the tug being moved from its influ-
ence. On the return journey the messages continued to
come out clear and exact.
On the 17th of July trials were made from the same
stations of St. Bartholomew to the armored ship San
Martino, anchored at a distance of about i}i miles from
the transmitting station, the aerial conductor of which
had been carried to a height of about 40 yards, while the
WIRELESS TELEGRAPHY 321
ship bore at the receiver an aerial line, first of 20, and
then of 30 yards in height.
Transmission succeeded perfectly, independent of the
position of the coherer and the receiver; that is to say,
even if they were screened at the sending station and
surrounded by metallic masses under cover or placed
below the water-line in the ship.
It was at once foreseen by many experimenters, among
them Sir Oliver Lodge, that with the old forms of appa-
ratus there would be interference between wireless sta-
tions, as the receivers would respond to all wave lengths.
To understand how it is possible to make a sending or a
receiving circuit which will send out or respond to only
one kind of electric wave, let the pendulum analogy again
be used. In order to set a pendulum in motion it is neces-
sary that the impulsive force should be imparted to it the
same number of times per second in which the pendulum
naturally oscillates. Even if stray forces are applied, but
are not properly timed, the effect on the pendulum will
be small, whereas a very minute but properly timed force,
acting for some time, will produce considerable motion
in a large pendulum. All these characteristics of the
pendulum may be applied to the electric circuit — the natu-
ral period of vibration, the small effect of a lot of waves
differing in length, and the large effect of a succession of
feeble but similar waves.
Sir Oliver Lodge, in 1897, took out a patent for a
'syntonic* system of wireless telegraphy, based directly
on his own work on the discharge of Leyden jars and on
Hertz's experimental results. The transmitter consisted
of two large cones of sheet metal placed with their axes
in a vertical line, and having a spark-gap between their
apices. In another form of transmitter a single metal
sphere, separated by small spark-gaps from the terminals
of an induction coil, was used as a radiator. Both types
produced direct Hertzian radiation, the latter giving
waves of very high frequency. The spherical oscillator
322
ELECTRICITY
was partially enclosed in a copper cylinder, open at one
end in order that the rays might be condensed in one
direction. The receiver, for use in connection with the
large cones, consisted of two similar cones connected
through the primary of a smalftransformer, the secondary
of which was connected to the coherer circuit. The di-
mensions of the transmitter and receiver were adjusted to
give equifrequent natural vibrations and therefore res-
onance. No earth connection was made, as it was de-
sired that the transmission should be purely by means of
Fig- S3 — Lodge's Syntonic Method of Signaling.
free radiations. The early conical form of radiator has
now given place to the horizontal conductors. Stations
in which this latter arrangement has been adopted are
now working in various parts of the world.
As soon as Marconi had modified his system of telegraphy
he applied it immediately to the conquest of record dis-
tances in radiotelegraphic transmission. To this end he
set up a station at the Lizard (Cornwall), which was
immediately put into communication with Marconi's ex-
perimental station at St. Katherine's, Isle of Wight, at
a distance of 300 kilometers (about 200 miles), in which
he used an aerial conductor consisting of four vertical
wires standing about 5 feet from one another, about 144
WIRELESS TELEGRAPHY 323
feet in height, along with a strip of wire netting of the
same length.
Under the new system the energy required to telegraph
to a given distance was very much diminished, so that
150 watts sufficed to communicate to the 300-kilometec
distance. 1
Encouraged by the results of the experiments in com-
munication between St. Katherine's and the Lizard, Mar-
coni put his whole heart into the attempt to resolve the
arduous problem of establishing transatlantic radiotele-
graphic communication. Repeated experiments had shown
that long waves, either by successive reflection or dif-
fraction, could turn round the v surface of the earth, so
that their transmission to very great distances resolved
itself only into a question of sufficient power in the trans-
mitting apparatus and sufficient sensibility in the receiv-
ing; but these necessitated large financial means, which
would, however, not be wanting in a man whose business
acumen was not less surprising than his experimental abil-
ity.
Being largely subsidized by the Marconi Wireless Tele-
graph Company, Marconi began, early in 1901, unknown
to every one, his trials, by establishing two specially pow-
erful stations at Poldhu, near Cape Lizard, in Cornwall,
on one side of the ocean, and at Cape Cod, in Massachu-
setts, on the other side. The results of these first trials
are not known, and judging by the silence maintained
in this regard they were probably negative. The two
stations, that had cost the sum of more than £15,000,
were destroyed by storms in September of the same year.
Marconi caused the station at Poldhu to be rebuilt, fur-
nishing it with powerful machines and radiators, and
decided to attempt communication with St. Johns, New-
foundland; that is to say, to a lesser distance than that
previously chosen, viz., of about 1,500 miles. At St.
Johns, Newfoundland, where Marconi had obtained from
the Government every facility for making the trials, the
324 ELECTRICITY
installation was of the simplest character, consisting of
a receiving station only. The aerial line was maintained
at a height of about 400 feet by means of a kite.
Marconi had already agreed with the station at Poldhu
that every day, at six o'clock in- the evening, a long series
of letter S should be sent. This letter, in the Morse al-
phabet, consists of three dots.
The message was received telephonically. On the 12th
of December, 1901, Marconi announced that he had re-
ceived the different S's at equal and determinate inter-
vals, and he proclaimed that it was practically, physically
and mathematically impossible that the signals could have
come from any other place but Cape Lizard.
In the summer of 1902 Mr. Marconi made an interesting
comparative test of his first (coherer) system and his
second (magnetic detector) system. The ship "Carlo
Alberto" was fitted out with both sets of receiving appa-
ratus. By previous arrangement a set of signals from
the Poldhu station was to be sent out at certain hours
of the day. As the voyage toward Kronstadt proceeded
the signals diminished in strength, and at a distance of
900 kilometers were not perceptible during the day. At
night, however, they continued to be received by both
systems until the port of Kronstadt was reached, when
only the magnetic detector responded, and that only
feebly. The disturbing action of daylight was very
marked in these tests.
Having received an invitation from the Canadian Gov-
ernment to continue his experiments in Canada, Marconi
erected a large station at Table Head, on the island of
Cape Breton, at the mouth of Glace Bay, and 3,800 kilo-
meters from Poldhu. On Dec. 20, 1902, Mr. Marconi
sent the first radiograms across the Atlantic to the Kings
of England and Italy. Shortly afterward another station
was erected at Cape Cod, in Massachusetts, the distance to
the Poldhu station being 3,200 miles, or 660 miles further
than the Glace Bay station. On Jan. 16, 1903, a complete
WIRELESS TELEGRAPHY 325
radiogram was sent by President Roosevelt to the King of
England.
Professor Fessenden commenced in 1897 the develop-
ment of the system which is now the property of the
National Electric Signaling Company. For two years he
was engaged by the United States Government for special
research in the subject, and had the advantages of all
the resources of a government department at his com-
mand. His inventions are very numerous, and in many
respects original, and his results show a precision and
practicality not attained by many other experimenters in
the same field.
Magnetic, thermal and electrolytic detectors, methods
of exact tuning, and even wireless telephony, are covered
by Fessenden's patents. Among these, perhaps that which
has contributed most to the success of the system is
the barretter. In its original form this was a thermal
receiver, depending for its action on the change of re-
sistance in a very fine platinum wire when carrying the
jig current. Latterly the continuous wire has been dis-
carded in favor of an electrolytic coil, one electrode of
which is an extremely fine point. The apparatus has been
described more fully under wave detectors. An impor-
tant feature of this system, which greatly aids secrecy
of transmission, is the arrangement of the sending key,
which does not break the circuit, but merely alters the
wave length of the waves given out, by cutting out some
inductance. Thus, unless a receiving station is tuned
with extreme accuracy to the transmitter, it will receive,
instead of signals, only a long, continuous dash; hence
only a very sharply tuned receiver will receive a mes->
sage at all. In the latest forms of apparatus the differ-
ence in frequency between the waves sent out during"
spaces and those sent as signals is only *4 Per cent.;
interception by rivals is, therefore, almost impossible.
Fessenden is apparently the first to use an aerial consist-
326 ELECTRICITY
ing of a steel tube standing on an insulating foundation,
and held in position by insulated stays.
The following guarantees are made for the Fessenden
system by the holding company. Guarantee for distance :
I kw. sets, 250 miles; 5 kw. sets, 400 miles; 20 kw. sets,
700 to 750 miles. Guarantee for the preventer, used to
prevent other sending stations from interfering with the
receipt of messages.
"Where the distance of the interfering station from
the receiving station is more than 1 per cent, of the dis-
tance between the sending and receiving stations, a dif-
ference in wave length of 3 per cent, is sufficient to cut
out the interference without the signals being appreci-
ably weakened, interfering and sending stations being of
equal power."
Guarantee for the secrecy sender: "With our latest
form of secrecy sender the variation in wave length is
guaranteed to be only % per cent, between space and
dots. We guarantee that no other system can read the
messages."
Guarantee for wave measurer: "We guarantee this
device to be capable of detecting difference of wave
length of 34 Per cent., and to be capable of measuring*
wave lengths at a distance from the sending station."
There are also devices whereby atmospheric discharges
will not interfere with reception, and a device for modify-
ing the intensity of emitted waves without altering their
length communicate with near-by stations.
A report giving a description of the Fessenden system,
as applied to transatlantic signaling between Massachu-
setts and Scotland may be of interest here:
"The power is developed by a boiler-engine-alternator
equipment having a maximum capacity of 25 kw., 60 cycles
current. A transformer steps up the voltage to about
25,000, thus charging the condensers, which are discharged
by means of a gap adjustable so as to effect the discharge
at any desired point of the cycle.
WIRELESS TELEGRAPHY 327
"The receiver used is the liquid barretter in its latest
form. The aerial is formed by a tower extending to a
height of 415 feet above the ground-level, and supporting
a sort of umbrella formed of wires at its top. The tower
is essentially a steel tube 3 feet in diameter, supported
1 every 100 feet of its height by a set of four steel guys,
there being thus sixteen guys in all. The tower is piv-
oted at its base on a ball-and-socket joint, and is insu-
lated from the ground for a voltage of 150,000. The
guys are insulated from the tower as well as from the
ground; besides, they are divided into 50-foot sections
by means of strain insulators. One of the most serious
problems to be solved was the construction of these strain
insulators, which, while capable of safely transmitting
the maximum stress of about 20,000 pounds, also resist
an electrical tension of 15,000 volts each. The maximum
deflection of the top of the tower in a 90-mile hurricane
is computed to be l$% inches. A wave chute containing
over 100 miles of wire, and extending over six acres, is
a very essential feature of the installation.
"On January 3, 1906, the first signals were received
from the American side, and shortly afterward commu-
nication was established, so that messages were freely
exchanged at night. The intensity of the signals re-
ceived by telephone was at times so great that the mes-
sages could easily be read with the diaphragm three inches
from the ears of the operator. A station twenty miles
distant from Brant Rock, using about 30 kw., and send-
ing on a wave length differing not much more than 3
per cent, from that of the Scottish station, was cut out
while messages were received from Machrihanish."
A system differing in many respects from the other
systems has been devised by Sir Oliver Lodge and Dr.
Muirhead. The rotating steel disk coherer described un-
der wave detectors is used by them. Another feature is
the use of two capacity areas at both sending and receiv-
328 ELECTRICITY
ing stations, by the adjustment of which they may be
brought into tune.
This system has been installed in many places with
great success, and altho it has not yet operated over such
distances as the Marconi and Fessenden systems, it com-
pares favorably with them in syntonizing power, and
has the advantage of using the siphon recorder.
The Telefunken System is based on the patents of
Professors Slaby and Braun and of Count von Arco. It
may be considered as striking a mean between the earlier
systems of Marconi and Lodge-Muirhead, tho of course
with many variations and elaborations in detail. A system
of wires, similar to those used by Marconi, forms the
aerial, and the earth connection is given by a large ca-
pacity, as in the Lodge-Muirhead apparatus. A coherer
and receiving circuit in many respects similar to the Mar-
coni arrangement is employed.
The De Forest system has had quite an extended com-
mercial application, especially in the United States. It
has the advantage of very rapid signaling, 25 to 30 words
per minute having been reached. Communication by this
system has been established between Manhattan Beach,
New York, and Colon, Panama, a distance of 2,170 miles.
The extension of wireless telegraphy and the study of
the relations of electrical discharges in radio-active bodies
bids fair to be the most fruitful of the fields of the im-
mediate future. The Age has been well called the Age
of Electricity, and much amazement ever is expressed
that Man should utilize so well a force concerning which
he knows so little. The complete understanding of the
phenomena of atomic force and of radio-activity may go
far to unlock many of the closed doors of Nature, and the
electrical scientist of to-day is steadily approaching that
understanding.
)oA o<$V. /o7