Scientific American Supplement, No. 417
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[Illustration]
SCIENTIFIC AMERICAN SUPPLEMENT NO. 417
NEW YORK, DECEMBER 29, 1883
Scientific American Supplement. Vol. XVI, No. 417.
Scientific American established 1845
Scientific American Supplement, $5 a year.
Scientific American and Supplement, $7 a year.
* * * * *
TABLE OF CONTENTS
I. ENGINEERING AND MECHANICS.--Machine for Making Electric
Light Carbons.--2 figures
The Earliest Gas Engine
The Moving of Large Masses.--With engravings of the removal
of a belfry at Cresentino in 1776, and of the winged bulls from
Nineveh to Mosul in 1854
Science and Engineering.--The relation they bear to one another.
By WALTER R. BROWNE
Hydraulic Plate Press.--With engraving
Fast Printing Press for Engravings.--With engraving
French Cannon
Apparatus for Heating by Gas.--5 figures
Improved Gas Burner for Singeing Machines.--1 figure
II. TECHNOLOGY.--China Grass, or Rhea.--Different processes and
apparatus used in preparing the fiber for commerce
III. ARCHITECTURE.--Woodlands, Stoke Pogis, Bucks.--With engraving.
IV. ELECTRICITY, LIGHT, ETC.--Volta Electric Induction as Demonstrated
by Experiment.--Paper read by WILLOUGHBY SMITH before the Society
of Telegraph Engineers and Electricians.--Numerous figures
On Telpherage.--The Transmission of vehicles by electricity to a
distance.--By Prof. FLEEMING JENKIN
New Electric Battery Lights
The Siemens Electric Railway at Zankeroda Mines.--3 figures
Silas' Chronophore.--3 figures
V. NATURAL HISTORY.--A New Enemy of the Bee
Crystallization of Honey
An Extensive Sheep Range
VI. HORTICULTURE, ETC.--The Zelkowas.--With full description
of the tree, manner of identification, etc., and several
engravings showing the tree as a whole, and the leaves,
fruit, and flowers in detail
VII. MEDICINE, HYGIENE, ETC.-The Disinfection of the Atmosphere.
--Extract from a lecture by Dr. R.J. LEE, delivered at the
Parkes Museum of Hygiene. London
A New Method of Staining Bacillus Tuberculosis
Cure for Hemorrhoids
* * * * *
VOLTA-ELECTRIC INDUCTION.
[Footnote: A paper read at the Society of Telegraph Engineers and
Electricians on the 8th November, 1883]
By WILLOUGHBY SMITH.
In my presidential address, which I had the pleasure of reading before
this society at our first meeting this year, I called attention,
somewhat hurriedly, to the results of a few of my experiments on
induction, and at the same time expressed a hope that at a future date I
might be able to bring them more prominently before you. That date has
now arrived, and my endeavor this evening will be to demonstrate to you
by actual experiment some of what I consider the most important results
obtained. My desire is that all present should see these results, and
with that view I will try when practicable to use a mirror reflecting
galvanometer instead of a telephone. All who have been accustomed to the
use of reflecting galvanometers will readily understand the difficulty,
on account of its delicacy, of doing so where no special arrangements
are provided for its use; but perhaps with a little indulgence on your
part and patience on mine the experiments may be brought to a successful
issue.
[Illustration: VOLTA-ELECTRIC INDUCTION.]
Reliable records extending over hundreds of years show clearly with what
energy and perseverance scientific men in every civilized part of the
world have endeavored to wrest from nature the secret of what is termed
her "phenomena of magnetism," and, as is invariably the case under
similar circumstances, the results of the experiments and reasoning of
some have far surpassed those of others in advancing our knowledge. For
instance, the experimental philosophers in many branches of science were
groping as it were in darkness until the brilliant light of Newton's
genius illumined their path. Although, perhaps, I should not be
justified in comparing Oersted with Newton, yet he also discovered what
are termed "new" laws of nature, in a manner at once precise, profound,
and amazing, and which opened a new field of research to many of the
most distinguished philosophers of that time, who were soon engaged in
experimenting in the same direction, and from whose investigations arose
a new science, which was called "electro-dynamics." Oersted demonstrated
from inductive reasoning that every conductor of electricity possessed
all the known properties of a magnet while a current of electricity was
passing through it. If you earnestly contemplate the important adjuncts
to applied science which have sprung from that apparently simple fact,
you will not fail to see the importance of the discovery; for it was
while working in this new field of electro-magnetism that Sturgeon made
the first electro-magnet, and Faraday many of his discoveries relating
to induction.
Soon after the discovery by Oersted just referred to, Faraday, with the
care and ability manifest in all his experiments, showed that when an
intermittent current of electricity is passing along a wire it induces
a current in any wire forming a complete circuit and placed parallel
to it, and that if the two wires were made into two helices and placed
parallel to each other the effect was more marked. This Faraday
designated "Volta-electric induction," and it is with this kind of
induction I wish to engage your attention this evening; for it is a
phenomenon which presents some of the most interesting and important
facts in electrical science.
Here are two flat spirals of silk-covered copper wire suspended
separately, spider-web fashion, in wooden frames marked respectively A
and B. The one marked A is so connected that reversals at any desired
speed per minute from a battery of one or more cells can be passed
through it. The one marked B is so connected to the galvanometer and a
reverser as to show the deflection caused by the induced currents, which
are momentary in duration, and in the galvanometer circuit all on the
same side of zero, for as the battery current on making contact produces
an induced current in the reverse direction to itself, but in the same
direction on breaking the contact, of course the one would neutralize
the other, and the galvanometer would not be affected; the galvanometer
connections are therefore reversed with each reversal of the battery
current, and by that means the induced currents are, as you perceive,
all in the same direction and produce a steady deflection. The
connections are as shown on the sheet before you marked 1, which I think
requires no further explanation.
Before proceeding, please to bear in mind the fact that the inductive
effects vary inversely as the square of the distance between the two
spirals, when parallel to each other; and that the induced current in
B is proportional to the number of reversals of the battery current
passing through spiral A, and also to the strength of the current so
passing. Faraday's fertile imagination would naturally suggest the
question, "Is this lateral action, which we call magnetism, extended to
a distance by the action of intermediate particles?" If so, then it is
reasonable to expect that all substances would not be affected in the
same way, and therefore different results would be obtained if different
media were interposed between the inductor and what I will merely call,
for distinction, the inductometer.
With a view to proving this experimentally, Faraday constructed three
flat helices and placed them parallel to each other a convenient
distance apart. The middle helix was so arranged that a voltaic current
could be sent through it at pleasure. A differential galvanometer was
connected with the other helices in such a manner that when a voltaic
current was sent through the middle helix its inductive action on
the lateral helices should cause currents in them, having contrary
directions in the coils of the galvanometer. This was a very prettily
arranged electric balance, and by placing plates of different substances
between the inductor and one of the inductometers Faraday expected to
see the balance destroyed to an extent which would be indicated by the
deflection of the needle of the galvanometer. To his surprise he found
that it made not the least difference whether the intervening space was
occupied by such insulating bodies as air, sulphur, and shellac, or such
conducting bodies as copper and the other non-magnetic metals. These
results, however, did not satisfy him, as he was convinced that the
interposition of the non-magnetic metals, especially of copper, did
have an effect, but that his apparatus was not suitable for making it
visible. It is to be regretted that so sound a reasoner and so careful
an experimenter had not the great advantage of the assistance of
such suitable instruments for this class of research as the
mirror-galvanometer and the telephone. But, although he could not
practically demonstrate the effects which by him could be so clearly
seen, it redounds to his credit that, as the improvement in instruments
for this kind of research has advanced, the results he sought for have
been found in the direction in which he predicted.
A and B will now be placed a definite distance apart, and comparatively
slow reversals from ten Leclanche cells sent through spiral A; you will
observe the amount of the induced current in B, as shown on the scale of
the galvanometer in circuit with that spiral. Now midway between the two
spirals will be placed a plate of iron, as shown in Plate 2, and at once
you observe the deflection of the galvanometer is reduced by less than
one half, showing clearly that the presence of the iron plate is in some
way influencing the previous effects. The iron will now be removed, but
the spirals left in the same position as before, and by increasing the
speed of the reversals you see a higher deflection is given on the
galvanometer. Now, on again interposing the iron plate the deflection
falls to a little less than one-half, as before. I wish this fact to be
carefully noted.
The experiment will be repeated with a plate of copper of precisely the
same dimensions as the iron plate, and you observe that, although the
conditions are exactly alike in both cases, the interposition of the
copper plate has apparently no effect at the present speed of the
reversals, although the interposition of the iron plate under the same
conditions reduced the deflection about fifty per cent. We will now
remove the copper plate, as we did the iron one, and increase the speed
of the reversals to the same as in the experiment with the iron, and you
observe the deflection on the galvanometer is about the same as it was
on that occasion. Now, by replacing the copper plate to its former
position you will note how rapidly the deflection falls. We will now
repeat the experiment with a plate of lead; you will see that, like the
copper, it is unaffected at the low speed, but there the resemblance
ceases; for at the high speed it has but very slight effect. Thus these
metals, iron, copper, and lead, appear to differ as widely in their
electrical as they do in their mechanical properties. Of course it would
be impossible to obtain accurate measurements on an occasion like the
present, but careful and reliable measurements have been made, the
results of which are shown on the sheet before you, marked 3.
It will be seen by reference to these results that the percentage of
inductive energy intercepted does not increase for different speeds of
the reverser in the same rate with different metals, the increase with
iron being very slight, while with tin it is comparatively enormous. It
was observed that time was an important element to be taken into account
while testing the above metals, that is to say, the lines of force took
an appreciable time to polarize the particles of the metal placed in
their path, but having accomplished this, they passed more freely
through it.
Now let us go more minutely into the subject by the aid of Plate IV.,
Figs. 1 and 2. In Fig. 1 let A and B represent two flat spirals, spiral
A being connected to a battery with a key in circuit and spiral B
connected to a galvanometer; then, on closing the battery circuit, an
instantaneous current is induced in spiral B. If a non-magnetic metal
plate half an inch thick be placed midway between the spirals, and the
experiment repeated, it will be found that the induced current received
by B is the same in amount as in the first case. This does not prove,
as would at first appear, that the metal plate fails to intercept the
inductive radiant energy; and it can scarcely be so, for if the plate is
replaced by a coil of wire, it is found that induced currents are set
up therein, and therefore inductive radiant energy must have been
intercepted. This apparent contradiction may be explained as follows:
In Fig. 2 let D represent a source of heat (a vessel of boiling water
for instance) and E a sensitive thermometer receiving and measuring the
radiant heat. Now, if for instance a plate of vulcanite is interposed,
it cuts off and absorbs a part of the radiant heat emitted by D, and
thus a fall is produced in the thermometer reading. But the vulcanite,
soon becoming heated by the radiant heat cut off and absorbed by itself,
radiates that heat and causes the thermometer reading to return to about
its original amount. The false impression is thus produced that the
original radiated heat was unaffected by the vulcanite plate; instead of
which, as a matter of fact, the vulcanite plate had cut off the radiant
heat, becoming heated itself by so doing, and was consequently then the
radiating body affecting the thermometer.
The effect is similar in the case of induction between the two spirals.
Spiral A induces and spiral B receives the induced effect. The metal
plate being then interposed, cuts off and absorbs either all or part of
the inductive radiant energy emitted by A. The inductive radiant energy
thus cut off, however, is not lost, but is converted into electrical
energy in the metal plate, thereby causing it to become, as in the case
of the vulcanite in the heat experiment, a source of radiation which
compensates as far as spiral B is concerned for the original inductive
radiant energy cut off. The only material difference noticeable in
the two experiments is that in the case of heat the time that elapses
between the momentary fall in the thermometer reading (due to the
interception by the vulcanite plate of the radiant beat) and the
subsequent rise (due to the interposing plate, itself radiating that
heat) is long enough to render the effect clearly manifest; whereas in
the case of induction the time that elapses is so exceedingly short
that, unless special precautions are taken, the radiant energy emitted
by the metal plate is liable to be mistaken for the primary energy
emitted by the inducing spiral.
The current induced in the receiving spiral by the inducing one is
practically instantaneous; but on the interposition of a metal plate
the induced current which, as before described, is set up by the plate
itself has a perceptible duration depending upon the nature and mass of
metal thus interposed. Copper and zinc produce in this manner an induced
current of greater length than metals of lower conductivity, with the
exception of iron, which gives an induced current of extremely short
duration. It will therefore be seen that in endeavoring to ascertain
what I term the specific inductive resistance of different metals by
the means described, notice must be taken of and allowance made for
two points. First, that the metal plate not only cuts off, but itself
radiates; and secondly, that the duration of the induced currents
radiated by the plates varies with each different metal under
experiment.
This explains the fact before pointed out that the apparent percentage
of inductive radiant energy intercepted by metal plates varies with the
speed of the reversals; for in the case of copper the induced current
set up by such a plate has so long a duration that if the speed of the
reverser is at all rapid the induced current has not time to exhaust
itself before the galvanometer is reversed, and thus the current being
on the opposite side of the galvanometer tends to produce a lower
deflection. If the speed of the reverser be further increased, the
greater part of the induced current is received on the opposite terminal
of the galvanometer, so that a negative result is obtained.
We know that it was the strong analogies which exist between electricity
and magnetism that led experimentalists to seek for proofs that would
identify them as one and the same thing, and it was the result of
Professor Oersted's experiment to which I have already referred that
first identified them.
Probably the time is not far distant when it will be possible to
demonstrate clearly that heat and electricity are as closely allied;
then, knowing the great analogies existing between heat and light, may
we not find that heat, light, and electricity are modifications of
the same force or property, susceptible under varying conditions of
producing the phenomena now designated by those terms? For instance,
friction will first produce electricity, then heat, and lastly light.
As is well known, heat and light are reflected by metals; I was
therefore anxious to learn whether electricity could be reflected in
the same way. In order to ascertain this, spiral B was placed in this
position, which you will observe is parallel to the lines of force
emitted by spiral A. In this position no induced current is set up
therein, so the galvanometer is not affected; but when this plate of
metal is placed at this angle it intercepts the lines of force, which
cause it to radiate, and the secondary lines of force are intercepted
and converted into induced currents by spiral B to the power indicated
by the galvanometer. Thus the phenomenon of reflection appears to be
produced in a somewhat similar manner to reflection of heat and light.
The whole arrangement of this experiment is as shown on the sheet before
you numbered 5, which I need not, I think, more fully explain to you
than by saying that the secondary lines of force are represented by the
dotted lines.
Supported in this wooden frame marked C is a spiral similar in
construction to the one marked B, but in this case the copper wire is
0.044 inch in diameter, silk-covered, and consists of 365 turns, with
a total length of 605 yards; its resistance is 10.2 ohms, the whole is
inclosed between two thick sheets of card paper. The two ends of the
spiral are attached to two terminals placed one on either side of the
frame, a wire from one of the terminals is connected to one pole of a
battery of 25 Leclanche cells, the other pole being connected with one
terminal of a reverser, the second terminal of which is connected to the
other terminal of the spiral.
Now, if this very small spiral which is in circuit with the galvanometer
and a reverser be placed parallel to the center of spiral C, a very
large deflection will be seen on the galvanometer scale; this will
gradually diminish as the smaller spiral is passed slowly over the face
of the larger, until on nearing the edge of the latter the smaller
spiral will cease to be affected by the inductive lines of force from
spiral C, and consequently the galvanometer indicates no deflection. But
if this smaller spiral be placed at a different angle to the larger
one, it is, as you observe by the deflection of the galvanometer, again
affected. This experiment is analogous to the one illustrated by diagram
6, which represents the result of an experiment made to ascertain the
relative strength of capability or producing inductive effects of
different parts of a straight electro-magnet.
A, Fig. 1, represents the iron core, PP the primary coil, connected
at pleasure to one Grove cell, B, by means of the key, K; S, a small
secondary coil free to move along the primary coil while in circuit with
the galvanometer, G. The relative strength of any particular spot can be
obtained by moving the coil, S, exactly over the required position. The
small secondary coil is only cut at right angles when it is placed in
the center of the magnet, and as it is moved toward either pole so the
lines of force cut it more and more obliquely. From this it would appear
that the results obtained are not purely dependent upon the strength of
the portion of the magnet over which the secondary coil is placed, but
principally upon the angle at which the lines of force cut the coil so
placed. It does not follow, therefore, that the center of the magnet is
its strongest part, as the results of the experiments at first sight
appear to show.
It was while engaged on those experiments that I discovered that a
telephone was affected when not in any way connected with the spiral,
but simply placed so that the lines of force proceeding from the spiral
impinged upon the iron diaphragm of the telephone. Please to bear in
mind that the direction of the lines of force emitted from the spiral
is such that, starting from any point on one of its faces, a circle
is described extending to a similar point on the opposite side. The
diameter of the circles described decreases from infinity as the points
from which they start recede from the center toward the circumference.
From points near the circumference these circles or curves are very
small. To illustrate this to you, the reverser now in circuit with
spiral C will be replaced by a simple make and break arrangement,
consisting on a small electro-magnet fixed between the prongs of a
tuning-fork, and so connected that electro-magnet influences the arms of
the fork, causing them to vibrate to a certain pitch. The apparatus is
placed in a distant room to prevent the sound being heard here, as I
wish to make it inductively audible to you. For that purpose I have here
a light spiral which is in circuit with this telephone. Now, by placing
the spiral in front of spiral C, the telephone reproduces the sound
given out by the tuning-fork so loudly that I have no doubt all of you
can hear it. Here is another spiral similar in every respect to spiral
C. This is in circuit with a battery and an ordinary mechanical make and
break arrangement, the sound given off by which I will now make audible
to you in the same way that I did the sound of the tuning-fork. Now you
hear it. I will change from the one spiral to the other several times,
as I want to make you acquainted with the sounds of both, so that you
will have no difficulty in distinguishing them, the one from the other.
There are suspended in this room self-luminous bodies which enable us by
their rays or lines of force to see the non-luminous bodies with which
we are surrounded. There are also radiating in all directions from me
while speaking lines of force or sound waves which affect more or
less each one of you. But there are also in addition to, and quite
independent of, the lines of force just mentioned, magnetic lines
of force which are too subtle to be recognized by human beings,
consequently, figuratively, we are both blind and deaf to them. However,
they can be made manifest either by their notion on a suspended magnet
or on a conducting body moving across them; the former showing its
results by attraction and repulsion, the latter by the production of an
electric current. For instance, by connecting the small flat spiral of
copper wire in direct circuit with the galvanometer, you will perceive
that the slightest movement of the spiral generates a current of
sufficient strength to very sensibly affect the galvanometer; and as
you observe, the amplitude of the deflection depends upon the speed
and direction in which the spiral is moved. We know that by moving a
conductor of electricity in a magnetic field we are able to produce an
electric current of sufficient intensity to produce light resembling
in all its phases that of solar light; but to produce these strong
currents, very powerful artificial magnetic fields have to be generated,
and the conductor has to be moved therein at a great expenditure of heat
energy. May not the time arrive when we shall no longer require these
artificial and costly means, but have learned how to adopt those forces
of nature which we now so much neglect? One ampere of current passing
through an ordinary incandescent lamp will produce a light equal to ten
candles, and I have shown that by simply moving this small flat spiral a
current is induced in it from the earth's magnetic field equal to 0.0007
ampere. With these facts before us, surely it would not be boldness to
predict that a time may arrive when the energy of the wind or tide will
be employed to produce from the magnetic lines of force given out by the
earth's magnetism electrical currents far surpassing anything we have
yet seen or of which we have heard. Therefore let us not despise the
smallness of the force, but rather consider it an element of power from
which might arise conditions far higher in degree, and which we might
not recognize as the same as this developed in its incipient stage.
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