In admiring the recent developments of electric science as evidenced
by the number of important inventions which have during the past few
years been given to the world, especially in those branches of applied
science which deal more particularly with the generation of
electricity and the production of the electric light, there is often
too great a tendency to forget, or, at least, to pass over in
comparative silence the claims which the great pioneer workers and
discoverers undoubtedly have to a large share of the merit of this
scientific development.
It is, of course, obviously impossible in anything approaching a
retrospect of the science of magneto-electric induction or its
application to illumination to pass slightly over the names of
Oersted, of Ampère, of Davy, and of Faraday, but, in other respects,
their work is too often lost sight of in the splendid modern
developments of their discoveries. Again, there is another group of
discoverer-inventors who occupy an intermediate position between the
abstract discoverers above named and the inventors and adapters of
still more recent times. To this group belong the names of Pixii and
Saxton, Holmes and Nollet, Wilde, Varley, Siemens, Wheatstone, and
Pacinotti, who was the first to discover a means of constructing a
machine capable of giving a continuous current always in the same
direction, and which has since proved itself to be the type of nearly
all the direct current electric machines of the present day, and
especially those such as the Gramme and Brush and De Meritens
machines, in which the rotating armature is of annular form; and when
it is considered what a large number of the well known electric
generators are founded upon this discovery, it must be a matter of
general gratification that the recent International Jury of the Paris
Exhibition of Electricity awarded to Dr. Antonio Pacinotti one of
their highest awards.
The original machine designed by Dr. Pacinotti in the year 1860, and
which we illustrate on the present page, formed one of the most
interesting exhibits in the Paris Exhibition, and conferred upon the
Italian Section a very distinctive feature, and we cannot but think
that while all were interested in examining it, there must have been
many who could not help being impressed with the fact that it took
something away from the originality of design in several of the
machines exhibited in various parts of the building.
This very interesting machine was first illustrated and described by
its inventor in the _Nuovo Cimento_ in the year 1864, under the title
"A Description of a Small Electro-Magnetic Machine," and to this
description we are indebted for the information and diagrams contained
in this notice, but the perspective view is taken from the instrument
itself in the Paris Exhibition.
In this very interesting historical communication the author commences
by describing a new form of electro-magnet, consisting of an iron ring
around which is wound (as in the Gramme machine) a single helix of
insulated copper wire completely covering the ring, and the two ends
of the annular helix being soldered together, an annular magnet is
produced, enveloped in an insulated helix forming a closed circuit,
the convolutions of which are all in the same direction. If in such a
system any two points of the coil situated at opposite ends of the
same diameter of the ring be connected respectively with the two poles
of a voltaic battery, the electric current having two courses open to
it, will divide into two portions traversing the coil around each half
of the ring from one point of contact to the other, and the direction
of the current, in each portion will be such as to magnetize the iron
core, so that its magnetic poles will be situated at the points where
the current enters and leaves the helix, and a straight line joining
these points may be looked upon as the magnetic axis of the system.
From this construction it is clear that, by varying the position of
the points of contact of the battery wires and the coil, the position
of the magnetic axis will be changed accordingly, and can be made to
take up any diametrical position with respect to the ring, of which
the two halves (separated by the diameter joining the points of
contact of the battery wires with the coil) may be regarded as made up
of two semicircular horseshoe electro-magnets having their similar
poles joined. To this form of instrument the name "Transversal electro
magnet" (_Eletro calamita transversale_) was given by its inventor, to
whom is undoubtedly due the merit of having been the first to
construct an electro-magnet the position of whose poles could be
varied at will by means of a circular commutator.
[Illustration: PACINOTTI ELECTRO-MAGNETIC MACHINE.--MADE IN 1860.]
By applying the principle to an electro-magnetic engine, Dr. Pacinotti
produced the machine which we illustrate on the present page. The
armature consists of a turned ring of iron, having around its
circumference sixteen teeth of equal size and at equal angular
distance apart, as shown in Fig. 1, forming between them as many
spaces or notches, which are filled up by coiling within them helices
of insulated copper wire, r r r, in a similar manner to that adopted
in winding the Brush armature, and between them are fixed as many
wooden wedges, m m, by which the helices are firmly held in their
place. All the coils are wound round the ring in the same direction,
and the terminating end of each coil is connected to the commencing
end of the next or succeeding helix, and the junctions so made are
attached to conducting wires which are gathered together close to the
vertical shaft on which the armature ring is fixed, passing through
holes at equal distances apart in a wooden collar fixed to the same
shaft, and being attached at their lower extremities to the metallic
contact pieces of the commutator, c, shown at the lower part of Fig.
3, which is an elevation of the machine, while Fig. 4 is a plan of the
same apparatus.
The commutator consists of a small boxwood cylinder, carrying around
its cylindrical surface two rows of eight holes, one above the other,
in which are fitted sixteen contact pieces of brass which slightly
project above the surface of the wood, the positions of those in the
upper circle alternating or "breaking joint" with those in the lower,
and each contact piece is in metallic connection with its
corresponding conducting wire, and, therefore, with the junction of
two of the helices on the armature. Against the edge of the commutator
are pressed by means of adjustable levers two small brass contact
rollers, k k, which are respectively connected with the positive and
negative poles of the voltaic battery (either through or independent
of the coils of a fixed electro-magnet, to which we shall presently
refer), and the magnetic axis of the ring will lie in the same plane
as the line joining the points of contact of the battery and rotating
helix, this axis remaining nearly fixed notwithstanding the rotation
of the iron ring in which the magnetism is induced.
In the apparatus figured in Figs. 3 and 4, the armature rotates
between the two vertical limbs, A B, of a fixed electro-magnet
furnished with extended pole pieces, A A, B B (Fig. 4), each of which
embraces about six of the armature coils. The fixed electro-magnet is
constructed of two vertical iron cylindrical bars, A and B, united at
their lower extremities by a horizontal iron bar, F F, the one being
rigidly and permanently attached to it, while the other is fastened to
it by a screw, G, passing through a slot so that the distance of the
pole pieces from one another and from the armature ring is capable of
adjustment.
The connections of the machine, which are shown in Fig. 3, are made as
follows: The positive current, entering by the attachment screw, h,
passes by a wire to the right hand commutator screw, l, to the
right-hand roller, k, through the commutator to the ring, around
which it traverses to the left-hand roller, k¹, and screw, l¹, to
the magnet coil, A, and thence through the coil of the magnet, B, to
the terminal screw, h, on the right hand of the figure. This method
of coupling up is of very great historical interest, for it is the
first instance on record of the magnet coils and armature of a machine
being included in one circuit, giving to it the principle of
construction of a dynamo-electric machine, and antedating in
publication, by two years, the interesting machines of Siemens,
Wheatstone, and Varley, and preceding them in construction by a still
longer period.
With this apparatus Dr. Pacinotti made the following interesting
experiments with the object of determining the amount of mechanical
work produced by the machine (when worked as an electro-magnetic
engine), and the corresponding consumption of the elements of the
battery: Attached to the spindle of the machine was a small pulley, Q
Q (Fig. 3), for the purpose of driving, by means of a cord, another
pulley on a horizontal spindle carrying a drum on which was wound a
cord carrying a weight, and on the same spindle was also a brake and
brake-wheel, the lever of which was loaded so as just to prevent the
weight setting into motion the whole system, consisting of the two
machines, when no current was flowing. In this condition, when the
machine was set in motion by connecting the battery, the mechanical
work expended in overcoming the friction of the brake was equal to
that required to raise the weight; and, in order to obtain the total
work done, all that was necessary was to multiply the weight lifted by
the distance through which it was raised. The consumption of the
battery was estimated at the same time by interposing in the circuit a
sulphate of copper voltameter, of which the copper plate was weighed
before and after the experiment. The following are some of the results
obtained by Dr. Pacinotti in experimenting after the manner just
described. With the current from a battery of four small Bunsen
elements, the machine raised a weight of 3.2812 kilos to a height of
8.66 m. (allowing for friction), so that the mechanical work was
represented by 28.45 m. During the experiment the positive plate of
the voltameter lost in weight 0.224 gramme, the negative gaining 0.235
gramme, giving an average of chemical work performed in the voltameter
of 0.229 gramme, and multiplying this figure by the ratio between the
equivalent of zinc to that of copper, and by the number of the
elements of the battery, the weight of zinc consumed in the battery
was computed at 0.951 gramme, so that to produce one kilogrammeter of
mechanical work 33 milligrammes of zinc would be consumed in the
battery. In another experiment, made with five elements, the
consumption of zinc was found to be 36 milligrammes for every
kilogrammeter of mechanical work performed. In recording these
experiments, Dr. Pacinotti points out that although these results do
not show any special advantage in his machine over those of other
construction, still they are very encouraging, when it is considered
that the apparatus with which the experiments were made were full of
defects of workmanship, the commutator, being eccentric to the axis,
causing the contacts between it and the rollers to be very imperfect
and unequal.
In his communication to the _Nuovo Cimento_, Dr. Pacinotti states that
the reasons which induced him to construct the apparatus on the
principle which we have just described, were: (1) That according to
this system the electric current is continuously traversing the coils
of the armature, and the machine is kept in motion not by a series of
intermittent impulses succeeding one another with greater or less
rapidity, but by a constantly acting force producing a more uniform
effect. (2) The annular form of the revolving armature contributes
(together with the preceding method of continuous magnetization) to
give regularity to its motion and at the same time reduces the loss of
motive power, through mechanical shocks and friction, to a minimum.
(3) In the annular system no attempt is made suddenly to magnetize and
demagnetize the iron core of the rotating armature, as such changes of
magnetization would be retarded by the setting up of extra currents,
and also by the permanent residual magnetism which cannot be entirely
eliminated from the iron; and with this annular construction such
charges are not required, all that is necessary being that each
portion of the iron of the ring should pass, in its rotation, through
the various degrees of magnetization in succession, being subjected
thereby to the influence of the electro-dynamic forces by which its
motion is produced. (4) The polar extension pieces of the fixed
electro-magnet, by embracing a sufficiently large number of the iron
projecting pieces on the armature ring, continue to exercise an
influence upon them almost up to the point at which their
magnetization ceases when passing the neutral axis. (5) By the method
of construction adopted, sparks, while being increased in number, are
diminished in intensity, there being no powerful extra currents
produced at the breaking of the circuit, and Dr. Pacinotti points out
that when the machine is in rotation a continuous current is induced
in the circuit which is opposed to that of the battery; and this leads
to what, looked at by the light of the present state of electric
science, is by far the most interesting part of Dr. Pacinotti's paper,
published, as it was, more than seventeen years ago.
In the part to which we refer, Dr. Pacinotti states that it occurred
to him that the value of the apparatus would be greatly increased if
it could be altered from an electro-magnetic to a magneto-electric
machine, so as to produce a continuous current. Thus, if the
electro-magnet, A B (Figs. 3 and 4), be replaced by a permanent
magnet, and the annular armature were made to revolve, the apparatus
would become a magneto-electric generator, which would produce a
continuous induced current always in the same direction, and in
analyzing the action of such a machine Dr. Pacinotti observes that, as
the position of the magnetic field is fixed, and the iron armature
with its coils rotates within it, the action may be regarded as the
same as if the iron ring were made up of two fixed semicircular
horseshoe magnets with their similar poles joined, and the coils were
loose upon it and were caused to rotate over it, and this mode of
expressing the phenomenon was exactly what we adopted when describing
the Gramme machine, without having at that time seen what Dr.
Pacinotti had written fifteen years before.
In explanation of the physical phenomena involved in the induction of
the electric currents in the armature when the machine is in action as
a generator, Dr. Pacinotti makes the following remarks: Let us trace
the action of one of the coils in the various positions that it can
assume in one complete revolution; starting from the position marked
N, Fig. 2, and moving toward S, an electric current will be developed
in it in one direction while moving through the portion of the circle,
N a, and after passing the point, a, and while passing through the
arc, a S, the induced current will be in the opposite direction,
which direction will be maintained until the point, b, is reached,
after which the currents will be in the same direction as between N
and a; and as all the coils are connected together, all the currents
in a given direction will unite and give the combined current a
direction indicated by the arrows in Fig. 2, and in order to collect
it (so as to transmit it into the external circuit), the most eminent
position for the collectors will be at points on the commutator at
opposite ends of a diameter which is perpendicular to the magnetic
axis of the magnetic field. With reference to Fig. 2, we imagine
either that the two arrows to the right of the figure are incorrectly
placed by the engraver, or that Dr. Pacinotti intended this diagram to
express the direction of the current throughout the whole circuit, as
if it started from a, and after traversing the external circuit
entered again at b, thus completing the whole cycle made up of the
external and internal circuits.
Dr. Pacinotti calls attention to the fact that the direction of the
current generated by the machine is reversed by a reversal of the
direction of rotation, as well as by a shifting of the position of the
collectors from one side to the other of their neutral point, and
concludes his most interesting communication by describing experiments
made with it in order to convert it into a magneto-electric machine.
"I brought," he says, "near to the coiled armature the opposite poles
of two permanent magnets, and I also excited by the current from a
battery the fixed electro-magnets (see Figs. 3 and 4), and by
mechanical means I rotated the annular armature on its axis. By both
methods I obtained an induced electric current, which was continuous
and always in the same direction, and which, as was indicated by a
galvanometer, proved to be of considerable intensity, although it had
traversed the sulphate of copper voltameter which was included in the
circuit."
Dr. Pacinotti goes on to show that there would be an obvious advantage
in constructing electric generating machines upon this principle, for
by such a system electric currents can be produced which are
continuous and in one direction without the necessity of the
inconvenient and more or less inefficient mechanical arrangements for
commutating the currents and sorting them, so as to collect and
combine those in one direction, separating them from those which are
in the opposite; and he also points our the reversibility of the
apparatus, showing that as an electro-magnetic engine it is capable of
converting a current of electricity into mechanical motion capable of
performing work, while as a magneto-electric machine it is made to
transform mechanical energy into an electric current, which in other
apparatus, forming part of its external circuit, is capable of
performing electric, chemical, or mechanical work.
All these statements are matters of everyday familiarity at the
present day, but it must be remembered that they are records of
experiments made twenty years ago, and as such they entitle their
author to a very distinguished place among the pioneers of electric
science, and it is somewhat remarkable that they did not lead him
straight to the discovery of the "action and reaction" principle of
dynamo-electric magnetic induction to which he approached so closely,
and it is also a curious fact that so suggestive and remarkable a
paper should have been written and published as far back as 1864, and
that it should not have produced sooner than it did a revolution in
electric science.--_Engineering._
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