IMPROVEMENTS IN DYNAMO-ELECTRIC MACHINES AND APPARATUS CONNECTED THEREWITH
Year: 1881

page_text: LETTERS PATENT to Sir William Thomson, Knight, of Glasgow College, Doctor
of Laws and Professor of Natural Philosophy in the University and College
of Glasgow, in the County of Lanark, North Britain, for an Invention of
PROVISIONAL SPECIFICATION left by the said Sir William Thomson at the
Office of the Commissioners of Patents ou, the 26th December 1881.
Sir WILLIAM THOMSON, Knight, of Glasgow College, Doctor of Laws and
Professor of Natural Philosophy in the University and College of Glasgow, in
the County of Lanark, North Britain. "IMPROVEMENTS IN DYNAMO-ELECTRIC
MACHINES AND APPARATUS CONNECTED THEREWITH."
My Invention consists of improvements in dynamo-electric machines, and which
may be employed either for generating electric currents, or for developing
mechanical energy from electric currents.
One of these improvements consists of a revolving metallic brush to perform the
functions of the fixed metallic brushes or combs which have been hitherto generally
used for making the contacts with the commutator bars.-By means of this brush
the desired effect is produced with but little friction, the mechanical action being
chiefly rolling-The requisite, rigidity or quasi-rigidity of the roller is given
partly by the elasticity of its constituent metallic parts, and partly by centrifugal
force. In some cases I attain similar results by connecting the commutator bars
elastically with the rotating armature, and using either rigid metallic rollers or
rotating brushes to make the contacts upon them.-In some cases I use a single bar
of metal straight or curved, preferentially straight, moving across the lines of force
of a magnetic field instead of a coil of wires or a number of wires connected in
series with one another, as in most of the dynamos hitherto made for producing
the electro-motive force.-One form of apparatus by which this result is attained is
a circular cylinder composed of bars of copper, put together like the staves of a
barrel or vat, and held together against centrifugal force by narrow metallic hoops

page_text: or by a binding of silk or other cord or of fine wire, the bars being insulated from
one another and from any one of these binders which is metallic. I support the
cylinder by letting one or more of its binding hoops roll upon drums preferably
coated with elastic material strongly bound round it.
I sometimes communicate motion by the friction of these rollers or by an
arrangement of toothed wheels fixed on or elastically connected with the shafts
bearing the rollers and gearing into hollows on the hoops; the rollers being free to
rotate relatively to the toothed wheels, to minimize frictional resistance.
I also effect the communication of motion by a very large number of fine silk
threads or other strong cords passing round the copper cylinder and a large light
drum pivoted on an axis parallel or nearly parallel to the axis of the copper
cylinder, this large drum being driven by the motor, or being used itself as a
motor, according as the dynamo is used for generating electricity or developing
mechanical energy from electricity.
I also sometimes use copper bars flexibly connected together so as to constitute,
as it were, an endless web stretched between two revolving drums of insulating
material, or coated with insulating material, by which rapid motion may be com-
municated to it, or taken advantage of to drive machinery where the dynamo is
used as a motor. This arrangement has some peculiar convenience in respect to the
placing of magnets to produce numerous magnetic fields, so as to act properly on
the copper bars; or I make the different electro magnetically effective parts of the
circuit, all in one plane, like spokes of a wheel, connected alternately at their outer
and inner ends.
My Invention includes also arrangements for producing proper fields of force in
dynamos, to allow the use of single bars for the electro-motors,-and-to-be
advantageous.in-some-cases where two or more bars, or portions of wire in series
are used in the same field. To economise the electro-magnetic force and fulfil as
nearly as may be the condition that equal resistances in the different parts of the
conductor constituting the coil contribute equally to the useful electro-magnetic
force of the field I use slips of sheet copper of different breadths or different gauges
or equivalent resistances of the conductor, in different parts of the current.
As part of the circuit of the dynamo and for the purpose of measuring the
currents which it produces I use a tangent galvanometer, in which the box, with
glass cover protecting the needle, is placed on a geometrical slide allowing it to be
moved nearer to, or further from, the coil through which the actuating current
passes.
I sometimes place on this box a steel magnet by which the directive force on the
needle is made considerably larger than the terrestrial magnetic force, an arrangement
particularly useful in a factory or under other circumstances in which there may be
disturbing magnetic forces of considerable magnitude in comparison with the earth's
horizontal force.
I also provide a convenient compensating magnet so placed as to subtract a
known constant from the electro-magnetic force of the coil on the needle, and thus
allow much larger currents to be measured than the largest which, without this
arrangement would let the needle remain within range.
To escape the inconstancies and uncertainties, dependent on the terrestrial
magnetic force and the magnetic force of the steel magnets, to which measurements
by instruments such as the preceding are liable, and at the sametime to obtain a
means for measuring the average of the square of the strength of an alternating
current or of a rapidly varying current whether always in one direction or not
produced by the dynamo, I use a modification of the electro-dynamometer of Weber,
analogous to that of Helmholtz, but differing from the latter in some essential
features, in order to be more convenient for use in connection with dynainos, and
to produce the electro-magnetic force, which is the subject for measurement I use a
fixed coil repelling or attracting a moveable coil above it, or below it.-The
moveable coil is rigidly connected to one arm of a balance.
To gauge the quantity of electricity supplied by the dynamo, I use a moveable

page_text: coil attached to the beam of a balance, and actuated electro-magnetically by a
powerful steel magnet, or magnets, in its neighbourhood: the balance carries an
arm projecting downwards, as in a part of the apparatus represented in Figures 2.
and 3, of the Drawings attached to the Specification filed in pursuance of my
Patent No. 3032, A.D. 1881. To the lower end of this arm, a fork is attached,
which moves a globe resting between a cylinder and disc, as in Professor James
Thomson's disc-globe and cylinder integrator. The imagnet and moveable coil are
so arranged, that the displacement thus given to the globe from the centre of the
disc is nearly enough in simple proportion to the strength of the current Howing
through the moveable coil at any time. The disc is kept turning uniformly by aid
of clockwork, and the whole amount of angle turned through by the cylinder is
simply proportional to the whole quantity of electricity supplied in a given time,
which is shewn by a counter counting the number of turns and parts of a turn
given to the cylinder.
When the dynamo is driven by water power, or by a steam engine, or gas
engine, with the regulators hitherto in use the machine is caused to run slower
when the current of electricity is augmented: because even with the best ordinary
governors the engine must run somewhat slower before the increased supply of
water, or steam, or gas, required to meet the increased demand for electricity, can
be given.
To remedy this evil I use an electro-magnetic regulator by which increase of
the strength of the current, causes increase of the supply of water, steam, or gas, so
as to fulfil the condition of keeping up a constant difference of potentials between
the mains, or even to somewhat increase the difference of potentials, when increased
current shows need for it.
In some cases I take for the regulating electro-magnetic appliance the dynamo
itself. Increased current through its armature produces increased resistance
against the motor.-I use the effect of this increased resistance in the connecting
machinery between the motor and the dynamo, to regulate the supply of water,
steam, or gas, so as to give increased supply when the resistance increases and
vice versa.
One obvious way of doing this is by a tightening pulley applied to the belt
when the connection between the engine and the dynamo is by belting.
By this or other well known forms of mechanism, some suitable in some cases
and others in others, I cause the motor to run somewhat faster instead of somewhat
slower, when it feels, as it were, more resistance from the dynamo.
For measuring the speed of dynamos I use a spring or a set of springs attached
to a rotating shaft and actuated by centrifugal force, in such a manner that a
marked point on it or marked points on the several springs when there are more
than one, are seen to revolve in a greater or smaller circle according as the speed
is greater or smaller. A conveniently placed scale allows the speed to be read
according to the size of that circle, or I use a liquid not quite filling a rotating glass
tube closed to show the speed by the depression of the lowest point of the
paraboloidal free surface of the liquid.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Sir William Thomson in the Great Seal Patent Office on the
26th June 1882.
Sir WILLIAM THOMSON, Knight, of Glasgow College, Doctor of Laws, and
Professor of Natural Philosophy in the University and College of Glasgow in
the County of Lanark, North Britain. "IMPROVEMENTS IN DYNAMO-ELECTRIC-
MACHINES AND APPARATUS CONNECTED THEREWITH."
My said Invention consists of improvements in dynamo-electric machines and
which may be employed either for generating electric currents or for developing
mechanical energy from electric currents.
One of these improvements consists of revolving metallic brushes for performing
the functions of the fixed metallic brushes or combs which have been hitherto
generally used for making the contacts with the commutator bars.-By means of
these brushes the desired effect is produced with but little friction as compared
with the friction of the fixed brushes hitherto used, the mechanical action being
chiefly rolling. The requisite rigidity, or quasi-rigidity of these rollers or revolving
brushes is given partly by the elasticity of the constituent metallic parts, and
partly by centrifugal force.
In some cases I attain similar results by connecting the commutator bars,
elastically with the rotating armature, and using either rigid metallic rollers or
rotating brushes to make the contacts upon them.
Figures 1 a, to 1 h, Sheets 1, and 2, represent roller brushes adapted to a dynamo
of ordinary type.
Figures 1 a, and 1 b, represent cups of thin sheet copper whose conical portion is
cut radially into a number of divisions as shewn. Before being formed into these
cups these are flat discs which after being thus cut are moulded by pressure to
the shape shewn in the Drawings that is to say a shallow circular cup with
a flat bottom, and divided conical sides with holes in the flat portion for the passing
therethrough of the central shaft or axle and the bolts for holding the same
together.
Figure 1 C,
Sheet 1, represents a similar cup also of thin sheet copper, but whose
conical portion is not cut or divided.-This cup is somewhat less deep than the
cut or divided cups, and is placed when making up a brush, between each pair of
cut or divided cups.
Figure 1 d, Sheet 1, shews, in section, two cups, which may be either of copper
or of brass. They are similar to the cups shewn in Figure 1 c, excepting that they
are much thicker so as to be sufficiently stiff. The cups Figure 1 d, are used as
outside stiffening pieces to hold the thin cups firmly together.-Figure 1 d, also
shews the central shaft and two of three screw bolts of which all three are shewn
in Figures 1e, and 1g, and which are used for bolting the cups together.-The
part marked C, of the axle is thickly covered with copper, and a number of copper
springs (S, S, of Figure 1h, Sheet 2) or a bundle of thin sheet copper strips pressed
against C, by independent springs, serves to connect the brush with the fixed
electrode of the dynamo.-These connections are shewn by the letters C, S, T, in
the before mentioned Figure 1 h.
Figures 1e, 1f, and 1 g, Sheet 1, represent a complete roller brush constituted of
the parts shewn in Figures 1 a, 1 b, 1 c, and 1 d bolted together. After the conical
cups are placed alternately slotted and unslotted on the main shaft, they are then
bolted together by a nut on the main shaft and by the three other screw bolts as
shown.

page_text: Figure 1, Sheet 2, represents a pair of these roller brushes mounted on bearings
proper for application to the commutator burs of a dynamo of the ordinary type.
The pivots P, P, are supported in bushes which are either of lignum vitæ or of
white or other suitable metal insulated by ebonite, wood, or insulite from the
metal fork F, F, which supports them.--This insulation being applied to prevent
any burning away of the pivots or bushes by electric currents crossing the
interspaces between them.-The electric current through the commutator bars and
rolling brushes passes out and in by the connections C, S, T, attached to the main
terminals T, T, of the dynamo, and pressed elastically upon C, (Figures 1 d, 1f,
and 1h Sheets 1 and 2,) the copper circumference of the axle. A, A (Figure 1h,
Sheet 2,) is a slot through which a clamping screw passes to allow the adjustment
of the pair of roller brushes, to proper positions on the circumference of the
commutator bars. B, B', B, B', are clamping nuts and screws, for adjusting and
clamping the forks F, F, bearing the the rolling brushes, so as to produce the
proper pressure on the commutator bars, and to readjust them from time to time as
the commutator bars and brush wear gradually away. In Figure 2a, Sheet 1, is
represented in diagram another form of rolling brush being a bevilled or conical
roller, instead of the cylindrical roller brushes of Figures 1f, and 1 h.
Figure 2a, the elastic constituent parts are thin copper circular dises with radial
cuts like those of Figures 1a, to 1 h, but plain or flat not cupped.-These slotted
discs are bolted together, with smaller unslotted circular discs between every
consecutive two of them, and with thick outside stiff discs E, F, of copper, or of
brass, to keep them all firmly together.-The discs are of graduated diameters so
as when bolted together to constitute a conical surface of the proper angle for any
particular application.-Figure 2a, represents one application of this conical brush
in which the commutator bars represented by B, B, lie in a plane perpendicular to
the main axis of the dynamo-The conical brush may also be applied to any case
in which the commutator bars lie on a cone. To annull slipping as much as
possible of the rolling surfaces of the brush and commutator bars and to make the
motion as near pure rolling as the elasticity of the brush allows of; the bearings of
the brush ought to be so placed that the axis of the conical roller R, R, shall cut
the main axis of the dynamo M, M, at V, the vertex of the conical surface of the
commutator bars.
In
For very high speeds, with which there is liability to severe blows between the
edges of the commutator bars, and the corners of the copper strips constituting the
rolling brushes, I prefer to make the roller solid, and to attach elastic brushes to
the commutator bars as indicated in diagram at Figure 3a, of Sheet 1, in which
B, B, still represent the commutator bars, M, M, the main axis of the dynamo, R, R,
the axis of the roller and V, the point of intersection of the axis which is also, the
common vertex of the cones; E. E, represent elastic slips of copper or pieces of
copper wire attached to the commutator bars, and having their tips T, T, dressed
to the proper conical surface.-S, represents a smooth bevil or smooth conical
surface of thick copper constituting the roller. The metal combs of which one is
indicated by B, E, T, are successively pressed upon by the solid roller S, during
the revolution of the machine.-These combs of which one is drawn on a larger
scale in Figure 4a, may be made up of separate pieces consolidated by solder, or
they be made from solid pieces of thick sheet copper sawn away to constitute the
interstices between the teeth of the comb.
When it is desired to make contact on a greater number of consecutive commu-
tator bars, than is advantageously practicable by the method of rollers, I use the
method shewn in Figure 4 h, Sheet 5, in which a comb A', of the kind represented
in Figure 4a, is fixed and the commutator bars in rotating slip against the ends
of the teeth. In Figure 4 h, the commutator bars are represented in section
by B, B. A copper sheath containing the comb A', is shewn by C, to which is
attached a fixed nut N. A screw S, is provided by which the comb A¹, may be
moved inwards from time to time to keep up the proper pressure thereof, on the
commutator bars B, B, as they and the teeth of the comb A', wear gradually away.--

page_text: By means of this screw S, provision is also made for removing a worn comb, and
replacing it with another, while the machine is running, the sheath C, having to
be drawn back for this purpose. In this arrangement the teeth of the comb are
initially dressed to a circular figure corresponding to the circle of the commutator
bars. A large number of such combs, about 16 for example, carried in sheaths C,
all attached to one insulated piece of metal with the corresponding points in lines
parallel to the main axis of the dynamo, and these are used to give contact over a
sufficient length (say four inches for example) of commutator bars, thus causing
every individual tooth of each comb to press by virtue of its own elasticity with as
little as may be of obstruction from neighbouring teeth. Thus I obtain a very
small electric resistance in the sum of the contacts with a very moderate amount
of total pressure.
One form of my improved dynamo is represented in sectional diagrams at
Figures 5 a, and 5 b, Sheet 3, and this consists of a drum or cylinder B, formed of
a sufficient number of insulated copper bars built together like the staves of n
barrel or vat or voussoirs of a circular arch or tunnel.-These bars are bound
together externally by a binding layer of strong silk thread or cord S, or by hoops
of non-magnetic metal. A plug of wood or other insulating material inserted in
one end of the drum serves the purpose of keeping the copper bars in truly circular
figure against the pressures of the roller brushes shewn in position by the dotted
circles C, C, and the anti-friction bearing rollers partly shewn in Figure 5 a, by the
segmental dotted lines A, on both of which the drum B, may be supported. The
transmission of the force to turn the drum, or to take work from it when it is used
as a motor, may be effected by the tangential force of one or more of the bearing
rollers, or it may be effected by means of an axle fixed into the open_mouth of the
_drum_at_the.end-remote-from-the-brushes. When this method is followed the
axle must be hollow to allow a support for the interior part of the electro magnet
to pass through it.
The magnetic fields F, F, I produce by means of an electro-magnet of circular
form in two segments as shown in the Drawing, Figure 5 a. The smaller of these
segments which is suitably supported in the interior of the drum, has its soft iron
core M, wound with copper wire W, W₁, in the ordinary manner, or by strip
copper as described below for the larger segment.-The larger segment of soft iron
which lies wholly without the drum is excited by means of coils of strip
copper W, W, suitably disposed so as to fill the whole available space with copper
conductor and so diminish the resistance in the circuit without losing electro-
magnetic power-This I accomplish as follows:-a coil of flat strip copper of the
required size of aperture, and of the proper number of turns is made. The breadths
of the several layers of this coil are then reduced to such an extent, that the coil is
of the proper shape and size, to be bounded on its two sides by two imaginary planes,
intersecting in the axial line of the inner cylindrical surface of the soft iron core,
and which pass on through each longitudinal edge of the outermost layer of
copper strip. These imaginary planes are shewn in section in the Drawing by the
lines G, H, G, K.
A sufficient number of such insulated coils to entirely cover the soft iron core,
are joined up in series, and constitute the exciting conductor of the exterior
segment of the electro-magnet.-The thickness of the strip copper forming these
coils, is graduated, being thicker in the neighbourhood of the points H, K, and
becoming thinner in the coils whose positions are nearer to the magnetic fields F, F.—
Thus the number of layers in each coil increases as the thickness of the copper
strip diminishes, so that the size of each coil is approximately the same.
In order to minimise loss of energy through the generation of heat by currents
circulating in the individual bars, the thickness of each copper bar in the
revolving drum is small in comparison with the distance it traverses through the
portions of the field in which the magnetic force gradually increases and decreases.
The commutator bars in this form of dynamo are merely prolongations of the
electro-magnetically effective bars or the main bars as I call them for brevity-

page_text: The other ends of the main bars are metallically connected by soldering or other-
wise. The current is induced so as to pass in one direction through one bar, and
through the metal connection at the end to the diametrically opposite bar through
which it passes in the opposite direction. A large number of bars are touched by
each of the collecting brushes which may be a rotating brush as, indicated in
dotted lines C, C, on Sheet 3, at Figure 5 a, or the group of fixed combs described
above with reference to Sheet 5, Figure 4 h..
When it is desired to obtain larger electro-motive force than this mode of con-
nection gives, the two sets of ends may be mutually connected and connected to
commutator bars, according to the Siemens Alteneck method and particularly as
carried into effect by Edison in his large steam-dynamo.
Except for a dynamo drum of very small diameter, it may be advisable to make
the cominutator bars not rectilineal prolongations of the electro-magnetically
efficient bars as shewn in Figures 5 a, and 5 b, Sheet, 3 but to place them on a
cylinder of smaller diameter as in most of the dynamos hitherto made, or to place
them on a conical surface, or to place them radially on a plane perpendicular to the
axis. Considerable latitude of choice in respect to these details, and in the corre-
sponding arrangement of brushes as explained in connection with Figures 1a,
to 1, and Figures 2 a, 3 a, 4 a, Sheets 1, and 2, and 4 h Sheet 5, is admissible with
almost equal advantage.
Another form of dynamo is shewn in part at Figures 7 a, and 7 b, Sheet 5.-This
consists of a wooden dise A, with projecting wooden teeth t, the whole mounted on
an axle B-,A flat slip of copper or a square copper wire C, bent round the teeth t,
to the form shewn in the Drawing is fastened to the edge of the dise A, in the
manner hereinafter described and having its two ends passing in towards the
centre of the disc to two suitably arranged contact pieces. The fastening of the
conductor C, is effected as follows: a sufficient number of notches are cut across
the edge of the disc A, to receive the bends of the conductor C. The conductor C,
being placed in position, wooden pins D, are then laid in the notches over the
conductor, the pins being of such a diameter as to project a little beyond the
surface of each side of the disc A.-A stout steel wire E, is then passed two or
three times round the edge of the disc A, on each side of the square wire C, and so
serves the purpose of pressing each wooden pin into its notch, in that way binding
the conductor wire firmly to the edge of the disc, with strength enough to resist
centrifugal force.
When greater electro-motive force and less resistance are required the zig-zag
may be made inultiple of slip copper as hereinafter described with reference to the
group of electro-inagnets for this form of dynamo represented on. Sheet 6, at
Figures 7 c, and 7 d.
The hereinbefore mentioned form of dynamo, as represented at Figures 7 a,
and 7 b, Sheet 5, is well adapted for an alternating current machine; the magnetic
fields by which the radial portions of the moving conductor are excited being
produced either by fixed steel magnets or by fixed electro-magnets, giving alternate
areas of red and blue (true south and true north) magnetic polarity on the two
sides of the space in which the radial bars move.
When electro magnets are used, I arrange them as shewn in part at Figures 7 c
and 7d, Sheet 6, so that each straight radial part of the conductor W, serves to
excite the soft iron of two contiguous electro-magnets M, M.
A flat circular cast iron ring K, is provided having suitably shaped pieces of soft
iron M, M, bolted or screwed, as shewn, on its surface. A flat strip of sheet copper
or a considerable number of mutually insulated flat strips are then bent, so as to
pass round these soft iron blocks M, M, in a zig-zag manner as shewn in Figures 7 c,
and 7d, (which is a transverse section of Figure 7 c) and with the breadths of the
strips W, everywhere perpendicular to the surface of the ring K.-A sufficient
number of such copper strips W, insulated from each other, and from the iron
blocks M, M, and ring K, and joined in series, form the exciting conductor.—In

page_text: this form of dynamo, a separate exciter must be used, and any convenient form of
brush may be adopted.
The arrangement or construction of dynamo described with reference to
Figures 5 a, and 5 b, has this advantage that in it there is no moving iron and no
change in the magnetism of iron during the running of the machine.-The alter-
native plan represented in Figures 6 a, and 6b, Sheet 4, loses something of this
advantage, but the consequent loss of energy through heat generated by changes in
the magnetization of soft iron is in many applications more than compensated by
the superior solidity and strength of the drum, and the simpler and less expensive
form of magnet which it admits. In the arrangement in Figures 6 a, and 6b, the
bars are bound together not by silk cords as in the arrangement shewn in
Figures 5, and 5 b, Sheet 3, but by a composite cylinder formed of thin flat iron
rings, insulated from each other. These flat rings are of very soft iron, and the
thinner they are the better, in respect to avoidance of loss of energy by induced
currents through them.-I at present make the thickness perpendicular to the
plane of the ring, about a quarter of the breadth of the ring in this plane.-A
large number of these rings are put together with insulating material such as
varnish or thin paper between them, and they are bolted together by a large
number of long iron bolts.-These bolts are coated with insulating material, and
to minimise loss of energy through currents circulating in each bolt, they are
placed as near the outer circumference of the composite cylinder, as is consistent
with strength. To allow the transmission of torque (or turning power) along the
cylinder for very heavy work, numerous radial holes are bored in the spaces
between the rings into which iron keying pins coated with insulating material are
inserted. To insert these pins the screws holding the rings together are first cased
_ sufficiently-to-allow-the-pins-to-be-pressed-in-by-moderate-enough-pressure not to
injure the insulating coats.-When all the pins are inserted, the screws
tightened so as to press the rings together against the keying pins with very great
force..
are
In Figure 6a, Sheet 4, M, represents the interior magnet which may be a
permanent steel magnet or may be of soft iron or steel kept magnetic by a current
through an insulated conductor wound longitudinally over it (the direction of its
length being perpendicular to the plane of the diagram), K, represents a continuous
massive bearing frame of iron, serving also as second keeper or armature for the
magnet M; the first or chief keeper being the cylinder of iron rings I, K, may be
of cast iron for economy and it may be independently magnetised with as much
magnetism as it can retain so that its poles R', B', inay be of the opposite polarities
to the neighbouring poles B, and R, of M.-The electro-magnetically effective bars
are shewn at E, E. The middle bars of the two groups simultaneously touched by
the collecting brushes are approximately at P, P.-The dotted circles J, J, indicate
the positions of these brushes when they are made as described above, with
reference to Figures 1 a, to 1 h, Sheets 1 and 2 and when the commutator bars are
prolongations of the main bars.
For a large and powerful dynamo the main drum may be four metres long and
one metre in diameter the main bars may be strips of sheet copper, each, one
centimetre broad and one millimetre thick and the iron may be of two centimetres
breadth. These numbers are only given by way of example. The same arrange-
ment or construction may be utilised for dynamos of much smaller diameter.-
When great length is given to the drum with moderate diameter and thickness, it
may be necessary or advantageous to introduce antifriction rollers under its middle
or at several points along its length, to bear its weight or part of its weight.-In
such cases 1 prefer to bear part of this weight by means of the driving beit, which
I then apply to a crown pulley fixed to the druin round its middle. This crown
pulley consists merely of a certain number of the flat constituent rings of the drum
made of larger exterior diameters than that of the other rings.-The external
diameters of those special rings must be large enough to give sufficient rigidity of

page_text: circular figure to the pulley, and they must be graded so as to give the proper
degree of crowning to the pulley. In these circumstances the driving shaft, or the
first driven shaft, when the dynamo is used as a motor, is placed above the dynamo
drum, and in such a position, that with or without the aid of a tightening pulley,
the two parts of the belt, where they leave the drum are nearly vertical-I prefer
for this purpose to use a belt consisting of a number of endless cords, which may
be made by cutting the proper lengths from a strong hemp cord, and splicing its
ends with an ordinary long splice; these cords being consolidated by india-rubber,
after the manner of the ordinary india-rubber belt. An ordinary india-rubber
belt, preferably endless, or an ordinary leather belt may however be used.-It is
advisable (though not absolutely necessary) to use an automatic tightening pulley,
not only for the ordinary reasons in favor of this arrangement but, because, to give
good results for many purposes, very high speeds, such as 3,000 centimetres per
second or more, may be required, and the consequent centrifugal force would stretch
the belt considerably, entailing an inconveniently great preliminary static tension,
if there is no automatic tightening pulley.
This form of drum with the iron outside the main bars is adapted to utilise
rather an interior than an exterior electro-magnet, I therefore in it dispense
with the large exterior electro-magnet of Figures 5 a, and 5 b, Sheet 3, and make
the interior electro-magnet M, in the form of a flat slab of soft iron or steel, which,
when its permanently retained magnetism does not suffice, is to be kept excited by
an electric current through insulated copper wire, or strips of copper laid on
parallel to the axis of the drum and bent round the ends of the slab as in the
electro-magnet described in connection with Figures 5 a, and 5 b, Sheet 3. The
electro-magnet M is encased in and supported by a strong brass casing E', with
strongly attached brass ends carrying round steel shafts, projecting outwards from
the two ends of the main drum.-The main drum is pivoted on these shafts by
hollow bearings fixed in two strong wooden discs by which the two ends of the
hollow drum are closed.-Perforations or canals are made in the steel shaft for the
electrodes of the electro-magnet.-Or I support the cylinder by letting one or more
of its binding hoops roll upon drums preferably coated with elastic material strongly
bound round it.
When convenient in respect to locality and other circumstances I prefer to make
the axis of the drum vertical. In such cases I support its weight on a horizontal
wheel pivoted on a vertical shaft below it, which for brevity I call a turn-table.
The lower ends of the copper bars of the drum are metallically connected together
and may or may not be insulated from the turn-table.-The collecting brushes are
applied to the upper ends or to commutator bars connected with the upper ends
of the main bars. These brushes may be attached to anti-friction rollers serving
to keep the drum steadily in proper position.-Or they may be fixed brushes or
groups of adjustable combs, made and arranged as described above with reference
to Figure 4h Sheet 5.-The exterior secondary fixed keeper or armature may now
be a, (as shewn in plan by K, K, Figure 6 b, Sheet +,) cylinder of cast iron, of either
one casting, or made up of rings of cast iron laid one over the other instead of
being of the shape represented by K, K, in Figure 6a. This cylinder should have
bars of soft iron B', R, screwed to it to serve the purpose of the polar parts B', R',
of the keeper K K of Figure Ga.-The fixed magnet M, is now supported from a
plate, or horizontal bars above it resting on the top of the iron cylinder.―The
central vertical bar bearing its weight may serve as a shaft to steady the main
drum by means of a disc of wood or other insulating material fixed in the upper
open mouth of the drum with a hole in its middle carrying a proper collar.
As part of the circuit of the dynamo, and for the purpose of measuring the
currents which it produces, I use a tangent galvanometer in which the box, with
glass cover protecting the needle, is placed on a geometrical slide allowing it to be
inoved nearer to, or further from, the coil through which the actuating current passes.
I sometimes place on this box a steel magnet by which the directive force
on the needle is made considerably larger than the terrestrial magnetic force, an

page_text: arrangement particularly useful in a factory or under other circumstances in which
there may be disturbing magnetic forces of considerable magnitude in comparison
with the earth's horizontal force.
I also provide a convenient compensating magnet so placed as to subtract a
known constant from the electro-magnetic force of the coil on the needle and thus
allow much larger currents to be measured than the largest which without this
arrangement would let the needle remain within range.
For measuring the difference of potential between any two points in a circuit in
which a current is flowing continuously in one direction, 1 use the instrument shewn
in Figures 1, Sheets 7, 8, 9, and 10, and substantially as hereinafter described.
The instrument shewn in elevation in Figures 1, Sheets 8, and 9, and in plan
in Figure 1, Sheet 7 and in section in Figure 1, Sheet 10, I call a potential
galvanometer.
It consists of a coil C, of fine German silver, copper or other suitable wire,
insulated by a covering of suitable insulating material such as silk, and a system of
magnetic needle or needles properly supported by a jewelled cap resting on a hard
point as described in the Specification of my Patent of 1876 No. 1339, and carried
by a suitable frame f, which also carries a light index i, the whole being suitably
supported or suspended in such a manner, that the point of support is in the centre
from which the circular scale S, has been described.
The coil of this instrument is made of so high a resistance that when its terminals
are attached to two points of an electric circuit of moderate resistance, no material
diminution of the difference of potentials between those two points, is produced. I
generally use a coil of upwards of 5,000 ohms resistance.
This system of needles and index is enclosed in a box A, with a glass cover,
which box shields it from currents of air.-This box A, is supported on three feet
and a spring, two of which feet slide in a V groove cut in a slip of hard wood such
as box wood, let into the platform P, and in a direction at right angles to the plane
of the coil C, and in such a position that the centre of the magnotic axis of the
needles moves nearly enough along a line at right angles to the plane of the coil,
and passing through its centre.-The sensibility of the instrument can by this means
be altered at pleasure to suit greater or smaller strengths of current.
The index i, attached to the needle frame f, ranges round the circular scale S,
the centre of which is as aforesaid immediately under the point of support of the
needles, and which scale is divided into parts subtending angles at the centre
corresponding to equal differences measured along a tangent to the arc at O.—Thus
the numbers read on the scale are proportional to the tangents of the angles of
deflection. To facilitate the accurate reading off of the position of the index, a
mirror m, is placed in the bottom of the box A.-This system of needles, index i,
and scale S, enclosed in a box A, as described, is referred to hereinafter as the
'magnetometer" of the instrument.
"
To prevent damage to the supporting point or suspension the needles and index,
when the instrument is not in use are lifted off the support by means of a suitable
mechanism. A nechanism which I find convenient for this purpose is represented
in the Drawings Figures 1, Sheets 7, 8, and 10.-It consists of a small collar
piece f¹, having a conical edge, against which the conical point of the screw's, can
be brought to bear so as to lift the collar piece fl, and raise the system of needles
and index from its support.
In order to render the indications of the instrument more accurate, when it is
used in the vicinity of large masses of iron or in the neighbourhood of dynamos or
of conductors carrying currents, I place a semicircular permanent magnet M, (which
I call a field magnet) of suitable strength over the box of the magnetometer, in
such a position that the line joining its poles is horizontal and parallel to the plane
of the coil, and passes through and is bisected by the centre of the magnetic axis
of the needles. One end of this magnet bears a cross piece p, Figures 1, Sheets 7,
and 9, furnished with two knobs or feet, one of which rests on a conical hollow,
the other on a plane surface.-The other end of the magnet M, is formed into a

page_text: rounded point which rests in the circular V groove g, Figures 1, Sheets 7, and 8,
carried by the screw s¹. By turning this screw sl, forwards or backwards, the line
joining the poles can be brought into accurate parallelism with the coil C, which
is the case when the index i, points to the division marked O, on the circular
scale S.
On the platform of the instrument, and along the side of the V groove, a scale
which for brevity I call the axial scale, is marked the divisions in which represent
the deflection, which corresponds when the front of the magnetometer box A, is
opposite this mark, to one volt. of difference of potentials between the two ends of
the coil in the case in which the intensity of the magnetic field is one centimetre-
gramme-second, that is to say the unity of the centimetre-gramme-second system.
One end of the wire composing the coil C, is connected to one contact piece of a
key K, Figures 1, Sheets 7, and 8, the other contact piece of which is connected to
one of two terminal strips of copper T, and the other ond of the wire is connected
to the other terminal strip T.
When a measurement is not being made with the instrument the key K, is out of
contact and consequently no current flows through the coil. Thus heating of the
coil except during the time of actual observation is prevented.
When the current in the coil would produce a deflection of the needle greater
than the range of motion provided for a counteracting force is applied by means of
a bar-magnet resting in the above mentioned V groove, and shewn in dotted
lines B, R, in Figures 1, Sheets 7, 8, 9, and 10, so that its magnetic axis is in the
same vertical plane as the axis of the coil.
For the purpose of indicating approximately the temperature of the coil, a
thermometer t, (whose position is shewn in dotted lines in Figures 1, Sheets 7, 8, 9
and 10,) is provided with the instrument and should be placed when the instrument
is in use, with its bulb in the centre of the coil C.-The instrument is given out
for use with the values of the deflections for different positions of the magneto-
meters determined by experiment.-When it is about to be used the plane of the
coil C, is so adjusted, by means of the magnetometer, the levelling screws L, L,
Figures 1 Sheets 7, 8, 9, and 10, and the spirit level 1, that the plane of the
coil C, is approximately in the magnetic meridian and the platform of the instrument
is level.
Figures 2, and 3 of Sheets 9, and 10, show what I call a current-galvanometer,
on the same plan, with just this difference, that a coil C, of small resistance
consisting of one turn, or of several turns of thick copper wire, or of stout strip
copper as shewn is used instead of the high resistance coil of the potential
galvanometer. The temperature of the coil need not be noticed generally in the
current galvanometer as its resistance is so small as to be generally of no
moment.
The number of divisions of deflection produced, on the index i, by a current of
one Ampère when the magnetic field in which the magnetometer system of
needles is situated, has an intensity of one centimetre-gramme-second unit is
marked on the axial scale.
In Figures 2, and 3, Sheets 9, and 10, the coil C, of the current-galvano-meter or
meter is provided with the terminal strips T, which when used in connection with
the spring contact piece, Figures 4, and 5, Sheet 9, allows the instrument to be
introduced into or taken out of a circuit without interrupting the current in that
circuit. The terminal T, consists of two thin strips of copper connected with the
ends of the coil laid parallel to one another with their flat surfaces facing, and kept
apart by a thin sheet of insulating material. The adjustment of the instrument
for use is the same as that described above in the case of the potential galvan-
ometer Figures 1, Sheets 7, 8, 9, and 10.
A form of needle which I find convenient for the magnetometer above described
is shewn in Figures 7, to 10, Sheet 5.-The index a, consists of two strips of
aluminium which are bent and placed side by side with their planes vertical so as
to form a needle of the shape shewn in the Drawing. They are rivetted together

page_text: so as to form a thin tapering point at one end and an open frame at the other.
An aluminium strip forms a bridge b, over this frame and is bent down the two
sides of this frame so as to strengthen it, and carry the needles and sapphire cap c,
as shewn in the drawing.
:
Figures 3 to 7, Sheet 11, represent views of an alternative form for either the
potential or the current galvanometer which may be used in a fixed installation
when portability and the gradations of sensibility given by the sliding magnet-
ometer are not required.-N, denotes a needle or a group of needles hung by a
single silk fibre from a bar H, fixed across the tops of two fixed coils C, C¹-The
tangents of the angles of deflection of N, produced by the electro-magnetic force of
the current through these coils are indicated by a pointer P, attached to N,
pointing to numbers on a scale S, S, graduated according to tangents as described
above with reference to the magnetometer represented in Figure 1, Sheets 7, 8, 9,
and 10, and Figures 7 to 10, Sheet 5, and the accuracy of the reading is facilitated
by the aid of a horizontal mirror under the pointer also as described above.
The instrument shewn in Figures 2, 3, and 4, Sheet 8, is an alternative instrument
for the measurement of currents. It consists of two rectangular coils c, c², of thick
copper strip or wire, one of which c, is fixed in an inclined position to a frame or
sole plate P, so that the two longer edges E, E¹, are horizontal.-The coil c¹ rests
on two knife edges K, K, of hardened steel which are in one and the same hori-
zontal-line-parallel to E, E, and passing through the centres of inertia of the coil c
and coinciding with the line in which two diagonal planes are drawn from the
upper edge of E, and the lower edge of E¹, the other drawn through the lower
edge of E, and the upper edge of E', would intersect. The knife edges K, K, rest
on the bottoms of flat V grooves cut in hard steel or other suitable substance. The
balanced coil e', is made smaller than the fixed coil so as to move altogether
within the latter; and its breadth, in the direction at right angles to the line of
the knife edges K, K, is shorter than the corresponding diameter of the fixed coil,
by an amount equal to the height of one side of the fixed coil above the other, so
that when the movable coil is horizonal, the plane of either of its long sides, and
the contiguous side of the fixed coil is at 45° to the horizon.
The ends of the moveable coil c¹, are connected with mercury placed in cups
M, M, the surface of the mercury being nearly on a level with the knife edges.
One terminal of the fixed coil is in connection with the mercury, in one of the
cups M, and the other cup is in connection with one of the terminals T, of the
instrument while the remaining end of the fixed coil is fixed coil is in connection
with the other terminal T
By this arrangement the whole current flows in succession through both coils.
According to the arrangement of the mercury cups, the current may be made to
flow in the same or in opposite directions round the two coils, which will therefore
in the former case attract, in the latter repel one another.-The movable coil c¹,
will, because of this action, turn on its knife edges, in one direction or the other,
according to the force acting on it, is attractive or repulsive.-The amount of the
force in different cases is measured by a micrometer screw AL, applied to pull up
the upper end of a spiral spring S, of which the lower end pulls the movable coil
and balances the electro-magnetic force.-The screw m, is furnished with a head p,
graduated to show the one-hundredths of a turn, and works through a nut n,
to which is attached a cross-arm, carrying an index mark, which when the screw
is turned, is moved along the scale s, the space between two divisions, of which is
equal to the pitch of the screw. Thus by means of the graduated head p, of the
screw and the scale 8, the number of complete turns, and portion of a turn of
the screw necessary to produce any required change of the force of the spring is
registered.
When the instrument is being used the line of knife edges is set approximately
in the magnetic meridian at the place as indicated by the direction which the
needle of the small compass u, attached to the sole-plate of the instrument assumes
when no current is flowing through the coils.

page_text: In Figures 1 and 2 Sheet 11 is shewn another alternative form of my current
meter which has the advantage of being not sensibly affected by the magnetic
forces such as are experienced in as close propinquity to the dynamo as it may bo
in some cases convenient to choose for the meter. It consists of two rectangular
frames of copper wire or strip, one of which is fixed with its longer sides vertical.―
The other frame is hung from a torsion head H, by a suspension wire w, made up
of two wires of different thicknesses, the upper part being the thinner. The copper
frame is thus hung in a vertical plane with its two longer sides vertical and at the
middle points of the two horizontal edges are fixed two copper points made of two
very short pieces of copper wire with one end of each shaped to a blunt cone.―
These conical ends point downwards into two large shallow mercury cups, one
just above the middle of the upper horizontal side of the fixed frame, the
other just above the middle of the lower horizontal side of the fixed frame-The
mercury in the lower cup is in contact with one of the terminals T, of the
instrument, and the middle point of the lower horizontal side of the fixed wire
frame is in contact with the other terminal, the mercury in the upper mercury
cup is in contact with the middle point of the upper horizontal side of the fixed
frame. Thus the course of the current, if we suppose it to enter by the terminal
attached to the fixed frame, is up the two sides of that frame to the upper mercury
cup, then down the two sides of the movable frame to the mercury cup, and
thence to the other terminal of the instrument.-The zero position chosen for the
movable coil is that in which the moment round the vertical axis of the electro-
magnetic force experienced by the movable coil is a maximum. It is easily found
by experiment The upper or thinner part of the suspension wire is attached to
the torsion head H, by means of which the wire can be turned round, and the
angle through which the upper end has been turned relatively to the lower end of
the suspension wire (when by the torsional elastic force of the wire, the moveable
frame is brought to its zero position) can be read off. The thicker wire at its
junction with the thinner wire carries rigidly fixed to it, a cross-bar n, which can
be turned round 'by means of two pins f, f, fixed. in the lower graduated torsion
head H¹.
In the actual use of the instrument the upper torsion head is first turned so as
to tend to bring the movable frame back to its zero position while the action of
the current flowing through it tends to deflect it from that position.-This serves
to twist both wires, and if the torsional couplo required is not one which would
twist the upper wire beyond its elastic limits, this head only may be turned.-If
when the upper torsion head has been turned through the range allowed for it, it
is found that the couple given by the twist thus applied to the compound wire
is not sufficient to bring the movable frame back to its zero position, the lower
torsion head is turned until the two stops are brought up to the cross-bar, and as
much further as suffices to bring the movable frame back to the zero position.--
The whole angle thus turned through by the lower torsion head will be pro-
portional by Coulomb's law to the couple required to keep the movable frame in
the zero position against electrical forces.
For the purpose of introducing into or withdrawing the current-meter from the
dynamo circuit, I use one or more of the appliances shewn in Figures 4, to 13,
Sheet 9. Figures 4, and 5, represent a side view and plan of spring contact pieces
consisting of a pair of stout strips of copper c, c, bent into the form shewn in the
Drawing, and held in position by having placed between them in such a position
that their points project beyond it and come into contact with one another, a pieco
of insulating material I, and served round with cord or otherwise securely fixed.-
The projecting points of the copper strips are kept pressed together by means of a
strong elastic band 8 passed round two semi-circular pieces, one soldered to the
back of each strip as shewn in the Drawing. The spring contact piece, shewn in
Figures 4, and 5, is placed permanently in the circuit; but when it is not being
used to include the current-meter, it forms part simply of that circuit, the current
flowing from a, through the strips of copper c, c, to b, or in the opposite direction.―

page_text: When it is desired to introduce the current-meter into the circuit, the contact piece
of Figures 4, and 5, Sheet 9, which is connected by flexible electrodes with the
main circuit, is slipped on the terminals T, T¹, of the current-meter. Thus the new
circuit through the current-meter is completed before the old circuit through c, c, is
broken. Figures 6, and 7, represent in side view and plan, an auxiliary pair of
terminals to be used when the flexible electrodes require eking out to reach the
meter. Then the two strips c', c¹, being pushed in further between the spring
contact pieces c, c, separate them, thus formning one circuit from a, through the
meter to b. The Figures 8, and 9, represent in plan and side view a form of
contact piece, which I find convenient for use in connection with my potential
galvanometer hereinbefore described. It consists of two copper strips a, a', bent
into the form shewn in Figure 9, and insulated from each other by a strip of
insulating material b, the whole being bound tightly together by a serving of cord
or other suitable material.-In use, the extremity of the contact piece is pressed in
between the two strips of copper T, Figures 1, Sheets 7, and 10, which form the
electrodes of the instrument.
Figures 10, to 13, represent a form of spring contact which I find convenient for
applying the flexible electrodes of the potential galvanometer to the parts of the
dynamo circuit of which the difference of potentials is to be measured. It consists
of a wooden piece W, of the form shewn in the Drawing and of flat copper strips
or round rods c, c, pressed by a strong india-rubber band S, against the wood on
which it pivots at P.
The instrument shewn in Figures 1, 2, and 3, Sheet 12, I use to determine the
total quantity of electricity which has flown during a known interval of time
-through-a-circuit-of-which-this-instrument-forms-a-part-Figure 1-is-a-side
elevation, Figure 2, a front elevation, and Figure 3, another side elevation, namely
of the side opposite to that shewn by Figure 1.-The instrument consists of a coil C,
of rectangular form, similar to the movable coil of the current-meter described
above, pivoted so as to turn round knife edges as does the beam of an ordinary
balance. The line of knife edges is so placed as to give a sufficient amount of
stability to the pivoted mass. Attached to one end of the coil C, opposite to the
line of knife edges is a lever 1, which is at right angles to the plane of the coil, and
is adjusted in any particular case so as to be nearly vertical when the nominal
amount of current is flowing through the coil. The lower end of this lever l, carries
a fork f, between the prongs of which a globe G is placed. The globe G rests
between an inclined plane disc D, and a cylinder K, the axis of which is hori-
zontal and parallel to the plane of the disc and at right angles to the line of
knife edges. The disc is thus so placed that its horizontal diameter is at right
angles to the line of knife-edges; and the cylinder is placed at such a distance from
the disc that the point of contact of the globe with the disc in any position, is in
the horizontal diameter of the disc.-The disc, globe, and cylinder, thus form a
disc-globe, and cylinder-integrator precisely of the form known as Professor James
Thomson's disc-globe and cylinder-integrator. The alternative method by cone and
cylinder of his Invention may be used instead of the disc and cylinder.
The disc D, is kept moving with uniform angular velocity round an axis
through its centre, and at right angles to its plane by means of a train of clock
work W, driven by a weight or spring and regulated by any of the well known
methods. This train of clock work may be either kept continuously in motion or
may be automatically started and stopped by means of an electro-magnetic
appliance actuated by the current itself.
The coil C, is placed between the poles of a series of horse-shoe permanent
magnets M, made of steel, glass hard, placed with their planes at right angles to
the line of knife edges, and their like poles turned in similar directions, so that
the whole series of magnets forms a long-polc horseshoe magnet, with its
poles in a horizontal plane, and between the poles of which the coil C is
placed.
By means of the three dials d, Figure 3, and the scale on the end of the

page_text: cylinder K, the number of turns and fractions of a turn of the cylinder, produced
in any time are registered and since this is proportional to the total amount of
electricity, which has passed through the coil C, the total number of Coulombs used
in that time can be obtained by multiplying this number by a factor depending on
the constants of the instrument, or the registering apparatus of the instrument
may be made to register the total number of Coulombs directly.-The ends of the
coil C, dip in the line of knife-edges into two mercury cups, to which the
terminals T, are connected.
It may be convenient in some applications of the instrument that it should be
capable of registering continuous currents flowing in either direction. It may be
made to do this by prolonging the cylinder past the centre of the disc, that is to
the left in Figure 2, and furnishing the instrument with proper counting apparatus,
which shall register the motion of the cylinder in each direction.
When the dynamo is driven by water power, or by a steam engine or gas engine,
with the regulators hitherto in use, the machine is caused to run slower, when the
current of electricity is augmented, because even with the best ordinary governors,
the engine must run somewhat slower before the increased supply of water or
steam or gas required to meet the increased demand for electricity, can be
given.
To remedy this evil I use an electro-magnetic regulator by which increase of the
strength of the current, causes increase of the supply of water, steam, or gas, 80 as
to fulfil the condition of keeping up between the mains a constant difference of
potentials, or even to somewhat increase the difference of potentials, when increased
current shews need for it.
In some cases I take for the regulating electro-magnetic appliance the dynamo
itself. Increased current through its armature produces increased resistance
against the motor. I use the effect of this increased resistance in the connecting
machinery between the motor and the dynamo to regulate the supply of water,
steam, or gas, so as to give increased supply, when the resistance increases, and
vice versa.
One obvious way of doing this is by tightening pulleys applied to the belt, when
the connection between the engine and the dynamo is by belting. This is
illustrated in the Drawing, Figure 1 i, Sheet 2, which shews an arrangement which
in many cases is convenient for this purpose.-W, represents the driving pulley of
the motor; w, the belt pulley of the dynamo; B, the driving belt; P1, P2, a pair
of tightening pulleys, on the two parts of the belt. Each pulley is placed within
a frame, hinged so as to turn round a horizontal axis A, and the pulley P, is made
to bear upon the belt by means of a spring S.-If we suppose the tension of the
upper part of the belt to be increased, the pulley P¹, with its frame will be raised,
elongating the spring S, thus bringing greater pressure to bear on the belt. The
slack of the lower part of the belt, is at the same time taken up by the pulley P²,
near the spring S, is attached to the frame carrying the pulley P', a crank K,
actuating a stop-cock by which the supply of steam, or water, or gas, may be
regulated. Figure 5, Sheet 13, shews an alternative arrangement of pulleys which
produces the same result, with the advantage that it makes the belt tighter in each
part instead of only in the working part, when the work done is greater.―
E, represents the driving pulley of the engine; R, represents a light wooden pulley
riding on the belt; C, F, represents a stiff fork hanging on the axle of R, and
carrying a heavy weight W; D, represents the driving pulley of the dynamo;
S, represents a slack-lifting pulley pivoted on a triangular frame K, H, A, which is
finely-pivoted by knife-edges on a horizontal axis A; w, is a weight fixed at H,
heavy enough to bring the centre of gravity of itself and the frame and pulley to
a position g, a little to the left (in the Drawing) of the vertical A, V.-When the
resisting force of D, increases, R, is raised and the weight of w, and its connections
ideally collected at g, lifts the slack of the belt by the pulley S, increasing the
tension in this part of the belt in virtue of the augmented distance of g, from A, V,
The upward motion of C, admits more water, steam, or gas, or otherwise
-

page_text: augments the motive power, by means of a cord, connecting-rod, or lever
moved by C.
By either of the above described, or by other well known forms of mechanism,
some suitable in some cases, and others in other cases, I cause the motor to run
somewhat faster, instead of somewhat slower, when it feels as it were more
resistance from the dynamo.
For measuring the speed of dynamos, I use a spring or a set of springs; as shewn
in Figures 3, and 4, Sheet 13, attached to a rotating shaft and actuated by
centrifugal force in such a manner that a marked point on it, or marked points on
the several springs, when there are more than one are seen to revolve in greater or
smaller circles according as the speed is greater or smaller. -A conveniently placed
scale (which is not shewn in the Drawing, but which may be either fixed or
rotating), allows the speed to be read according to the size of that circle, Figures 3,
and 4, Sheet 13, represent the ends of a shaft A, with six springs 8, 8, 8, 8, 8, 8, loaded
at their ends with little masses which also serve for stops.-The springs are in
three pairs held on to the shaft by collars R, R, R-T, T are two stops carried by
the shaft. When the shaft revolves, the springs tend to fly out by centrifugal
force. At a certain speed the outermost springs fly out at a higher speed the
middle pair of springs and at a still higher speed the innermost. The scale for
each spring is to be graduated by trial-Or I use a liquid not quite filling a
rotating glass tube or three or more such tubes closed to shew the speed by the
depression of the lowest point of the paraboloidal free surface of the liquid.―
Figures-1,and-2, Sheet-13, shew-three-glass-tubes-each-about-half-filled-with-
alcohol or sulphuric ether, chosen because the disturbing effect of capillary
attraction on the vertex of the figure which would be a true paraboloid were there
no capillary attraction is less for these liquids than for water or other liquid which
in other respects might be convenient. These tubes are mounted on brass pieces
supported on pivots and geared together so that the speed of the third is twice
that of the second, and four times that of the first.-S, represents a shaft for com-
municating motion from the shaft whose speed is to be indicated.-The numbers
2.5, 5, 10, 20, and 40 marked on three scales, fixed beside the three tubes, show
approximately the positions of the lowest points of the surfaces of the liquids in
the three tubes when the speed of the middle tube is 25, or 5, or 10, or 20, turns
per second, supposing the apparatus to be made on the actual scale of the Drawing.
The actual graduation, of each of the three speed scales is to be done by trial
because uncertainty as to the accurate diameters of the tubes and want of rigourous,
physical, and mathematical investigations of the effects of capillarity make it
impossible to graduate them accurately enough by theory. When the speed is
between 25, and 10, or something more than 10, turns of the central tube per
second, it is read on No. 3 scale. When it is between 10, and 20, it may be read
on No. 2 scale, but for part of the range it may be also read on No. 3.-From 20,
to 40, or something more than 40, it may be read on No. 1 scale. When the speeds
to be measured do not differ more than in the ratio of 2, to 1, a single rotating
tube with single scale suffices, or by using a single tube of larger diameter and
greater length than those shewn in the Drawing, a good single scale may be
obtained for a larger range of speeds.
Having now described, and particularly ascertained the nature of my said
Invention and the system, mode, or manner, in or under which the same is or may
be used or practically carried into effect, I would observe in conclusion that what I
consider to be novel and original and therefore claim as the Invention secured to
me by the herein before in part recited Letters Patent is :-
First. The rotating Brushes for dynamos constructed and operated substantially
as herein before described with reference to Sheet 1, and Figure 1, h, Sheet 2, of the
accompanying Drawings.
Second. The elastic combs attached to the commutator bars of dynamos to make
multiple contacts on a fixed or rotating smooth metal surface, or on a rotating

page_text: brush substantially as hereinbefore described with reference to Figures 2 a, and 3 a
Sheet 1, of the accompanying Drawings.
Third. The fixed brush consisting of a group of combs each separately adjusted
to press on the surface of the commutator bars so that each tooth shall be kept in
contact by its own elasticity, substantially as herein before described with reference
to Figure 4 h, Sheet 5, of the accompanying Drawings.
Fourth. The cylinder composed of flat straight bars of copper, separated by thin
slips of insulating material such as paper or mica, the lengths of the bars being
parallel to the axis of the cylinder and their flat sides directed radially towards the
said axis, the same being held together by cord, or wire binding, or by hoops of
non-magnetic material, and stiffened by rings, which may be of iron, or of non-
magnetic material; the said cylinder so constructed to serve for the main moving
part of a dynamo, or electric machine having fixed magnets, either inside the said
cylinder or outside it, or both inside and outside the said cylinder substantially as
herein before described with reference to Sheet 3, and Figure 6 a, Sheet 4, of the
accompanying Drawings.
Fifth. The same structure of cylinder as that of Claim Four, but with soft iron
outside the cylinder of copper bars whether in the shape of varnished or otherwise
insulated wire serving to bind the same together, or flat insulated rings serving as
stiffeners, and in some cases as driving pulleys the iron also serving to lead the
lines of magnetic force out from an interior magnet or magnets across the electro-
magnetically effective copper bars, and thence round the outside or to fixed iron
outside.
Sixth Supporting or carrying the aforesaid rotating cylinder with its axis
horizontal entirely or partially. on its stiffening rings by anti-friction rollers as
hereinbefore described with reference to Figure 6b, Sheet 4, of the accompanying
Drawings.
Seventh Supporting the said cylinder on what I have for brevity called a
turn-table, and using anti-friction rollers near the upper edge of the said cylinder
to inaintain it in position whilst rotating on a vertical axis substantially as herein-
before described.
Eighth Employing elastic metal brushes or springs carried by these anti-friction
rollers to collect the electric currents from the main bars of the said cylinder or from
commutator bars connected to these main bars substantially as hereinbefore
described.
Ninth. Pivotting the said cylinder on fixed shafts rigidly connected with
interior electro-magnet-frame, and in cases when the axis is horizontal bearing the
weight of the whole machine and resisting the tendency of the interior electro-
magnet to turn, by prolongations of the shafts which need not be so massive or so
arranged as to give absolute fixity relatively to the earth, as herein before described.
Tenth Supporting, when the axis is vertical, the interior electro-magnet-frame
from above by a fixed bar or bars coming through the upper open mouth of the
cylinder, or through a collar in a disc fixed to and closing the mouth of the
cylinder, and steadying the lower part of the electro-magnet against lateral dis-
placement by a pin projecting from it downwards into a hole in the centre of the
turn-table as hereinbefore described.
Eleventh. The alternate current machine constructed with magnets arranged
radially as herein before described with reference to Figures 7 c, and 7 d, Sheet 6,
of the accompanying Drawings.
Twelfth. The current and potential galvanometer substantially as hereinbefore
described with reference to Figures 1, Sheets 8, 9, and 10, and Figures 2, and 3,
Sheets 9, and 10, and Sheet 11, Figures 3, to 7, of the accompanying Drawings.
Thirteenth. The two alternative forms of current-meter substantially as herein-
before described with reference to Figures 2, 3, and 4, Sheet 8, and Figures 1, and 2,
Sheet 11, of the accompanying Drawings.
Fourteenth. The meter for measuring and recording the whole quantity of
lectricity which flows through the circuit in any time, substantially as herein-

page_text: before described with reference to Figures 1, 2, and 3, Sheet 12, of the accompanying
Drawings.
Fifteenth. The governor for speed founded on amount of force worked against,
substantially as hereinbefore described, with reference to Figure 5, Sheet 13, and
Figure 1, Sheet 2, of the accompanying Drawings.
Sixteenth. The speed indicator showing speed by paraboloidial depression of
liquid surface in a rotating tube substantially as hereinbefore described with
reference to Figures 1, and 2, Sheet 13, of the accompanying Drawings.
Seventeenth. The elastic speed indicator substantially as herein before described
with reference to Figures 3, and 4, Sheet 13, of the accompanying Drawings.
In witness whereof I the said Sir William Thomson have hereunto set my
hand and seal this Fifteenth day of June in the year of our Lord, One
thousand eight hundred and eighty two.