IMPROVEMENTS IN ELECTRIC LIGHTING, HEATING, AND MOTIVE-POWER APPARATUS.
Year: 1878

page_text: PROVISIONAL SPECIFICATION left by John Munro at the Office of the
Commissioners of Patents on the 11th October 1878.
JOHN MUNRO, of 4, Montague Road, West Croydon, in the County of Surrey.
"IMPROVEMENTS IN ELECTRIC LIGHTING, HEATING, AND MOTIVE-POWER APPARATUS.'
"
In employing electricity from dynamo-electric machines, voltaic batteries, or other
sources, for lighting, heating, or motive purposes it is often necessary to divide up
the current in a convenient manner, so as to make the current from a single source
feed a number of electrical lamps, heating, or motive apparatus. And it is
important that each of these lamps, &c., should be fed so independently of the others
that when any one or a number of the lamps, &c., are lit, and the rest unlit, there
should not be an unusual divergence of the current to the particular lamp which is
lit; nor should the extinction of the light of any one of the lamps, &c., effect the
rest which are lit. To effect this several devices have been resorted to, such as
placing the lamps in subsidiary circuits derived from the main circuit through
which the current flows, so as to divide the current between them in such a manner
as to provide that should any one of these branch circuits fail, there would be no
interruption of the others. Condensers have also been inserted in these circuits for
the purpose of storing up the electricity, whereby a greater number of lamps may
be fed from one source. All these arrangements however are capable of feeding a
very limited number of lamps; they are more or less complicated; and by them
the extinction of any one light is either attended by a sudden increase of the
remaining lights, or electricity is uselessly spent and wasted.
My improvement consists of a divider and distributor of the electric current
which will allow of a large number of separate lainps, heating, and motive apparatus,
say a hundred, or less or more, being fed from the same current, and this with no

page_text: interference of one light with the others. All the lights may be of equal size and
brilliance if desired, each lamp and lamp circuit being independent of the rest, so
that one, or a number of the lamps in the system may be extinguished without
affecting the illuminating power of the others, and without any waste of the
current.
My divider is based upon the principle that if the current supplying an electric
lamp be a discontinuous or intermittent one whose pulsations occur a sufficient
number of times per second, the practical effect is the same as if it were a
continuous current. This is a result of the fact that the image of light lingers for
a certain space of time (about one-tenth of a second) on the retina before it
disappears. I therefore construct an apparatus for breaking up the current from
the machine or other source, and distributing portions of it to the different lamps
to be fed in such a manner that a quickly intermittent current shall flow to each
and produce the effect of a continuous current. For this purpose I cause a shaft to
revolve with great rapidity round its axis, and I cause the near ends of all the
separate lamp circuits to centralize themselves radially round this shaft. The shaft
is connected to one pole of the dynamo-electric machine or other source, and a
brush contact is so fitted to it as to sweep the ends of the circuits round the shaft
as the latter revolves. The circuits are insulated from one another, and
consequently each one gets a share of the current which the brush deals out. The
far ends of the lamp circuits are of course connected to the other pole of the
dynamo-electric machine or other electric source. The number and breadth of the
contact pieces, and the angular velocity of the shaft, determine the duration of the
pulse of current, and the number of pulses entering a particular circuit in a second.
Practically to produce a good continuous light the number of turns made by the
shaft should be from 600 to 1,800 per minute. I sometimes also cause the contacts
to be distributed alongside the shaft itself, so that cams or other projecting contacts
arranged helically on the shaft may make contact with the former contacts as the
shaft revolves, or I employ other similar devices for effecting the required sub-
.division and distribution of the current. Sometimes I fix two or more distributing
brushes or helical contacts, &c., on the same shaft so as to distribute two or more
separate currents from separate sources to separate systems of lainps, &c. The
shaft may be made to rotate by any convenient source of power, such as a gas,
steam, water, or electric motor. I also employ clockwork, especially for domestic
purposes, to drive the distributing shaft. When an electric motor is employed for
this purpose it may be driven by the current or part of the current coming from
the machine or other source.
Instead of a revolving shaft, I sometimes also employ an oscillating shaft, lever,
or other body to effect the same purpose; and besides these rotating and oscillating
levers, I sometimes employ vibrating bodies, such as tuning forks, to vibrate
between the contacts of the lamp circuits and distribute currents to these circuits.
The divider may be placed beside the electric machine or source of power itself, or
it may be placed at some distance from it in any convenient situation, such as the
room of a building, to the other rooms of which it may distribute the electricity
necessary to light them. In such a case the current from the machine has to bo
brought to the divider by a conductor.
In order to render the current from certain dynamo-electric machines more
continuous, I employ, if necessary, the device of causing it to pass through the
circuit of a special form of condenser, known as Muirhead's artificial cable, or a
condenser formed on the principle of a submarine cable, or in circuit through an
ordinary telegraphic condenser. This has the effect of retarding the current and
blending its inequalities into a uniform current. I also employ this or other
similar device, such as an induction coil, or a secondary battery to blend the inter-
mittent currents from the divider into a continuous current when required.
It will be seen from the above description that my improvement principally
consists in dividing and moderating the intensity of the electric light by

page_text: breaking up the current and mechanically distributing pulses of it to separate
lamps, these pulses so rapidly succeeding each other that the effect of a continuous
current and a continuous light is produced. The Invention is also applicable to
the distribution of the current for heating and motive purposes, but it is specially
intended for the electric light.