John Ambrose Fleming.

Electric lamps and electric lighting, a course of four lectures on electric illumination delivered at the Royal institution of Great Britain online

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J. A. FLEMING, M.A., D.Sc, F.R.S



The Illustrations, Designs, and Text of these Lectures are entered at Stationers
Hall, and are, therefore, copyright.





Alternate-Current Transformer, Vol. I. New Edition.
Alternate-Current Transformer, Vol. II.

Magnets and Electric Currents.

An Elementary Treatise for Electrical Artisans and
Science Teachers.

Electrical Laboratory Notes and Forms.

Consisting of 20 Elementary and 20 Advanced Papers
for the use of Students in Electrical Engineering
Classes. Intended as a help to the Teacher and his
Assistants. A guide to the Student.

Centenary of the Electric Current, 1799-1899.




HE following pages are a tran-
script, with considerable addi-
tions, of a course of Four
Lectures on " Electric Illu-
mination, " delivered by the
Author in 1894 to afternoon
audiences at the Royal Insti-
tution, London. They are in
no sense presented as a com-
plete treatment of a subject
which has long since outgrown
the limits of a single small book

or course of lectures. The original aim was merely
to offer to a general audience such non-technical
explanations of the physical effects and problems
concerned in the modern applications of electricity for
illuminating purposes as might serve to further an
intelligent interest in the subject, and perhaps pave
the way for a more serious study of it. In preparing
a new issue of the book the Author has added to each



chapter paragraphs which serve to bring up the infor-
mation more into line with recent practice, and, with-
out departing from the elementary character of the
work, made the necessary corrections to preserve the
text from being antiquated as to statement.

Many of those who were present at the Lectures
expressed a desire to be again able to refer to the
descriptions and illustrations then given, and at their
request, and in the hope that they may be of use to
others, the lecture notes have been revised and pub-
lished. The aim throughout has been rather to deal
with principles than with details, and to give such
general and guiding explanations of terms and processes
as are essential for a grasp of the outlines of the sub-
ject. For this purpose simple drawings have been
given of as many of the experiments and apparatus
used as possible. For permission to reproduce a set
of photographs of views of the interior of rooms
artistically illuminated with incandescent lamps, and
which are to be found in the second Lecture, the author
is indebted to Mr. A. F. Davies, under whose guidance
these particular instances of electric lighting were

carried out.

J. A. F.

University College, London.
November, 1899.


(For Index to Contents, see pa ye 267.)



14 Illustrations.



ELECTRIC GLOW LAMPS ... ... ... ... 51 137

40 Illustrations.




14 Illustrations.


39 Illustrations.


The reader is requested to make the following corrections :

Page 118, last line

for " Thompson "
read " Thomson."

Page 133, seventh line from bottom

for " slight resistance "
read " slight increase in the resistance."

Page 135, in the table

for "26 and 25"
read " 2-6 and 2-5."

Page 142, seventh line from bottom

for " Thompson "
read " Thomson."



ELECTRIC LIGHTING in Great Britain. A Glance Backward over Twenty
Years. Present Condition of Electric Lighting An Electric Current.
Its Chief Properties. Heating Power. Electrical Resistance.
Names of Electrical Units. Chemical Power of an Electric Current.
Hydraulic Analogies. Electric Pressure. Fall of Electric Pressure
down a Conductor. Ohm's Law. Joule's Law. Units of , Work and
Power. The Watt as a Unit of Power. Incandescence of a Platinum
Wire. Spectroscopic Examination of a Heated Wire. Visible and
Invisible Radiation. Luminous Efficiency. Radiation from Bodies at
Various Temperatures. Efficiency of Various Sources of Light. The
Glow Lamp and Arc Lamp as Illuminants. Colours and Wave-
Lengths of Rays of Light. Similar and Dissimilar Sources of Light.
Colour-distinguishing Power. Causes of Colour. Comparison of
Brightness and Colour. Principles of Photometry. Limitations due
to the Eye. Luminosity and Candle-power. Standards of Light.
Standards of Illumination. The Cand)e-foot. Comparison of Sun-
light and Moonlight. Comparison of Lights. Ritchie's Wedge.
Rumford and Bunsen Photometers. Comparison of Lights of Different
Colours. Spectro-photometers. Results of Investigations.

^HOEVER undertakes to describe the re-
markable progress during the last twenty
years of the art of electric illumination
must certainly direct attention to three
important dates which, in England at any
rate, formed turning points in the history
of this application of scientific knowledge.
^ In the year 1879 the Government of our

country had its attention directed for the first time to electric
lighting as a possible subject of legislation, and referred the
whole matter to a Select Committee of the House of Commons,
of which Lord Play fair was appointed Chairman. This Com-
mittee met, and took voluminous evidence from numerous and


various experts, but the broad conclusion reached in the report
which it finally presented was generally the expression of
opinion that there was no reasonable scientific ground at that
date for supposing that domestic electric lighting had obtained
a sufficient footing to entitle it to be described as a practical
success, and that, therefore, there seemed no useful result to be
attained by interfering at once, by special legislation, with
electric lighting. Passing over a gap of three years, we find
in the year 1882 the whole aspect of affairs entirely changed
by the completed invention of the electric glow lamp. At
the beginning of that year the first Crystal Palace Electrical
Exhibition enabled the public to properly appreciate the
extent to which the then perfected electric incandescent lamp
had revolutionised artificial lighting, and also the charm
and beauty of that illuminant. Countless details, however,
remained to be perfected, both in the glow lamp and in the
devices for generating, distributing, using and measuring the
electric current required for it. From the commercial point
of view much information had to be slowly accumulated
before even approximately correct opinions could be formed
as to the revenue to be gained from the sale of electric energy
for domestic purposes, and there was at that date but little
information available for enabling an accurate forecast to be
made concerning the probable average annual consumption of
electrical energy by incandescent lamps when used instead of
gas jets in different classes of buildings for illuminating
purposes. There is no doubt, however, that the Electric
Lighting Act of 1882, though much abused at the time,
performed the important function of preventing the survival
of immature schemes.

Between 1882 and 1888 exceedingly important improvements
(some of which it will be necessary later on to examine) were
made, and in 1888 the time seemed ripe for a fresh forward
movement. This was effected by the pressure brought upon


the Legislature to repeal one of the clauses in the Act of 1882,
by which revision much more favourable conditions were
created for inviting the support of capital ; and as soon as the
Electric Lighting Amendment Act of 1888 was an accomplished
fact, a very important inquiry was held by the Board of Trade
in May, 1889, in the Westminster Town Hall, London, under
the chairmanship of Major Marindin. At this inquiry, which
lasted for eighteen days, the whole subject of electric
lighting by public supply, especially with reference to the
needs of London, was carefully debated by many of the
leading scientific and legal experts, and, as a result, the
Metropolis was divided up into certain areas of electric
supply, and conditions were laid down under which the
distribution of current might be undertaken either by Public
Companies or by the Local Authorities. Up to the date of
that inquiry the total amount of electric lighting in London
or in the Provinces had been, comparatively speaking, very
small. From and after that date it has advanced by leaps
and bounds. The progress made in the use of the incandescent
lamp as a means of artificial illumination is shown by the
following figures, and graphically indicated in Fig. 1.

At the end of 1890 there were probably in use about
200,000 incandescent lamps in London, but at the end
of 1898 rather over two-and-a-quarter million 8 c.p. in-
candescent lamps were in employment. In the Provinces
in 1890 there was hardly any electric lighting worth men-
tioning, whereas at the end of 1898 the total number of
lamps in use in connection with public electric supply
stations was just under three millions, the grand total for
London and the Provinces being 5,206,000 8 c.p. lamps
or their equivalent. There are at the present time (July,
1899) thirty-six electric lighting undertakings in and
around London, including London proper and Greater
London, These are in the hands of either public Limited


Liability Companies or of the Local Authorities. In the
Provinces there are, at the same date, completed, or being
completed, 150 electric lighting stations in as many towns
and cities. In these the electric supply is likewise given
either by the Local Authority or by a Limited Company.
Whereas, however, in London the majority of the lamps in
use are supplied by Companies, in the Provinces it is the
reverse. The Local Authorities, in the provincial towns to a

3,000,000 8 c.p. Lamps


a.000,000 8 c.p. Lamps


1,000,000 8 c.p. Lamps





1830 1891








Fia. 1. Diagram showing the Progress of Electric Lighting in London
and the Provinces in Nine Years. The altitude of the vertical black lines
represents to scale the number, from year to year, of 8 c.p. lamps installed.
The firm lines are lamps in London and suburbs, and the dotted lines are
lamps in the Provinces.

considerable extent, have assumed the position of " under-
takers," as they are called in the Acts, but in a few cases
have allowed the Provisional Order to be possessed by Public
Companies. Hence in the Provinces of the United Kingdom


electric lighting has largely become municipalised, and in
many cities (such as Liverpool, Sheffield and others) where
the public electric lighting has been originated by a Limited
Company, the Corporation has ultimately purchased the
undertaking, often for much more than its original cost.

In the ten years between 1888 and 1898 it may be said
that the business side of public electric supply and the art of
management and control of public electric generating stations
became a specialised industry. The causes contributing to
financial success or failure in this new industry were carefully
studied, and, side by side with this attention to the com-
mercial questions involved, steady progress in the mechanical
and electrical improvements of the machinery of generation
and distribution took place. Hence, at the close of the
nineteenth century, we find a large number of new industries
created by the demand for electric current for lighting. An
assistance also has been given to pure science by the necessity
for more exact knowledge on the electrical and magnetic
qualities of the materials employed in the construction of
electrical appliances. Collaterally, a strong impetus was
given to the improvement of other mechanical machines,
such as the steam engine. Engineers directed attention to
the improvement of the dynamo in regard to its mechanical
construction, and electricians provided new information, not
only on the electrical theory of the dynamo, but on the
principles affording a means for predetermining the results
of operation for any particular design.

The result has been the evolution of a new machine viz.,
the combined high-speed steam engine and dynamo which
places in our possession a most perfect and highly-efficient
device for converting the energy 01 high-pressure steam into
electric energy in the form of an electric current ; the total
loss in conversion not exceeding 10 per cent, in large plants.


Simultaneously with these improvements in the generating
appliances proceeded others for effecting the distribution and
use of electric currents, particularly in incandescent and arc
lamps. Moreover, it was soon found that incandescent electric
lighting lent itself very readily to decorative purposes in a
manner impossible for the older illuminants. Hence the
subject of "Electric Lamps and Electric Lighting" has not
only a scientific and commercial, but also an artistic side, and
has considerable practical interest for every householder.

Accordingly, in the following short treatise attention will
be directed to the elucidation of facts which ought to be
known by every user of the electric light, and the knowledge
of which will enable him to understand something of the
principles which underlie the art of electric illumination, and
to comprehend as well the aid which it can render, when
properly applied, to beautify and please.

It will be necessary to open the whole of our discussion by
some simple iliustrations of the meaning of fundamental terms.
Every science as well as every art has its necessary technical
terms, and even if these words at first sound strangely, they are
not therefore necessarily difficult to understand. We are all
familiar with the fact that electric illumination depends upon
the utilisation of something which we call the electric current.
Little by little scientific research may open up a pathway
towards a fuller understanding of the true nature of an electric
current, but at the present moment all that we are able to
say of it is, that we know what it can do, how it is produced,
and the manner in which it can properly be measured. Two
principal facts connected with it are, that when a conductor,
such as a metallic wire or a carbon filament, or any other
material which is capable of being employed as a conductor,
is traversed by an electric current, heat is generated in the
conductor, and the space round the conductor becomes capable
of influencing a magnetic needle. These facts can be simply


illustrated by passing an electric current through an iron wire
(sec- Fig. 2). You will notice that as the current is gradually-
increased the iron wire is brought up from a condition in
which it is only slightly warm to one in which it becomes
visibly red hot in the dark, and finally brilliantly incandescent.
At the same time if we explore the region round about the wire
with a suspended compass needle, we find that at every point
in the neighbourhood of the wire the magnetic needle places
itself, or tries to place itself, in a position perpendicular to the

FIG. 2. An iron wire W is rendered incandescent by an electric current
sent through it from a battery B. The magnetic needle N S held near it
sets itself across the wire.

wire. This fact, of capital importance, was discovered by
H. C. Oersted in 1820, and in the Latin memoir in which he
describes his epoch-making discovery he employs the following
striking phrase to express the behaviour of a magnetic needle
to the wire conveying the current. He says, "The electric
conflict performs circles round the wire." That state which
he called the electric conflict round the wire, we now in more
modern language call the magnetic field embracing the con-
ductor. We shall return in a later lecture to this last fact.


Meanwhile I wish at present to fasten your attention on the
heating qualities of an electric current, and the laws of that
heat production and radiation. The same electric current
produces heat at very different rates in different conductors,
and the quality of a body in virtue of which the electric current
produces heat in passing through it is called its electric
resistance. If the same electric current is passed through con-
ducting wires of similar dimensions, but of different materials,
it produces in them different quantities of heat in the same
time. Before you (Fig. 3) is a chain composed of spirals
of iron and copper wire. These wires are each of the same
length and of the same diameter. Sending through this com-

FIG. 3. A chain W composed of alternate spirals of copper C and iron I
is traversed by an electric current sent through it by a battery B. The
iron links become red hot, the copper links only slightly warm.

pound chain an electric current, we notice that the iron wire
links are very soon brought up to a bright red heat, whilst the
copper links, though slightly warm, are not visibly hot. We
have, therefore, before us an illustration of the fact that a
current heats the conductor, but that each conductor has a
specific quality called its electrical resistance, in virtue of which
the same strength of current produces heat in it at a rate
depending on the nature of the material. Other things being
equal, the bodies which are most heated are said to have
the highest resistance.


It is now necessary to notice the units in which these two
quantities, namely, electric current and electric resistance, are
measured. For the sake of distinction, units of electric
quantities are named after distinguished men. We follow a
similar custom in some respects in common life, as when we
speak of a " Gladstone " bag or a " Hansom " cab, and
abbreviate these terms into a gladstone and a hansom.
Primarily the distinctive words here used are the names of
persons, but by application and abbreviation they become the
names of things. An electric current is measured in terms of
a unit current which is called an ampere, and electrical
resistance is measured in terms of a unit which is called an
ohm, these being respectively named after two great investi-

FIG. 4. Glass lantern trough containing two lead plates n p, and a
solution of sugar of lead. When a current from a battery B is sent through
the cell it deposits the lead in tufts on the negative plate n.

gators, Andre Marie Ampere and Georg Simon Ohm. In
order to understand the mode in which an electric current
can thus be defined, we must direct attention to another
property of electric currents, namely, their power of decom-
posing solutions of metallic salts. You are all familiar with
the substance which is called sugar of lead, or, in chemical
language, acetate of lead. Placing in a small glass trough
a solution of acetate of lead and two lead plates (see Fig. 4), I
place the cell in the electric lantern and project the image
upon the screen. If an electric current is passed through
the solution from one lead plate to the other it decomposes


the solution of acetate of lead, extricating from the solution
molecules of lead and depositing them on one of the lead
plates, and you see the tufted crystals of lead being built up
in frond-like form on the negative pole in the cell. We might
employ, in preference to a solution of acetate of lead, a solution
of nitrate of silver, which is the basis of most marking inks,
and the same effect would be seen. It was definitely proved
by Faraday that we might define the strength of an electric
current by the amount of metal which it extricates from the
solution of a metallic salt in one second, minute, or hour. The
Board of Trade Committee on Electrical Standards have now
given a definition of what is to be understood by an electric
current of one ampere in the following terms : An electric
current of one ampere is a current which will in one hour
extricate from a solution of nitrate of silver 4-025 grammes
of silver.* Otherwise we might put it in this manner : A
current of electricity is said to have a strength of one ampere
if, when passed through a solution of nitrate of silver, it
decomposes it and deposits on the negative plate one ounce of
silver in very nearly seven hours. We are acquainted in the
laboratory with currents of electricity so small that they
would take 100,000 years of continuous action to deposit
one ounce of silver, and we are familiar in electric lighting
practice with currents great enough to deposit one hundred-
weight of silver in thirty minutes. The simple experiment
just shown is the basis of the whole art of electro-plating.
Hence, when we speak later of a current of one ampere, or ten
amperes you will be able to realise in thought precisely what
such a current is able to achieve in chemical decomposition.
It may be convenient at this stage to bring to your notice the
fact that an 8 candle-power incandescent lamp working at 100
volts usually takes a current of about one-third of an ampere,
a current which would deposit by electro -plating action one
ounce of silver in about twenty-one hours.

* 28'3495 grammes = 1 ounce avoirdupois.



We pass next to consider another important matter, viz.,
that of electric pressure or potential ; and we shall be helped
in grasping this idea by considering the corresponding concep-
tion in the case of the flow of fluids. When a fluid such as
water flows along a pipe it does so in virtue of the fact that
there is a difference of pressure between different points in
the pip9, and the water flows in the pipe from the place where
the pressure is greatest to the place where the pressure is
least. On the table before you is a horizontal pipe (Fig. 5)
which is connected with a cistern of water, and which delivers

FIG. 5. Horizontal pipe P, having six vertical gauge tubes attached to
it. The pipe P is in connection with a water cistern C, and when the tap
T is shut the water stands up at the same level, A B, ia all the tubes.

water to another receptacle at a lower level. In that pipe are
placed a number of vertical glass tubes to enable us to measure
the pressure in the pipe at any instant. The pressure at the
foot of each gauge glass is exactly measured by the head or
elevation of the water in the vertical gauge glass, and at the
present moment, when the outlet from the horizontal pipe is
closed, you will notice that the water in all the gauge glasses
stands up to the same height as the water in the cistern., In
other words > the pressure in the pipe is everywhere the same.


Opening the outlet tap we allow the water to flow out from
the pipe, and you will then observe that the water sinks (see
Fig. 6) in each gauge glass, and, so far from being noTV uniform
in height, there is seen to be a regular fall in pressure
along the pipe, the gauge glass nearest the cistern showing
the greatest pressure, the next one less, the next one less
still, and so on, the pressure in the horizontal pipe gradually
diminishing as we proceed along towards the tap by which
the water is flowing out. This fall in pressure along the pipe
takes place in every gas and water pipe, and is called the

FIG. 6. Horizontal pipe P, through which water is flowing from a
cistern C to a reservoir R. When the tap T is open the water stands at
gradually decreasing heights in the pressure tubes. The dotted line A B
shows the hydraulic gradient.

hydraulic gradient in the pipe. The flow of water takes
place in virtue of this gradient of pressure. It will be next
necessary to explain to you that there is an exactly similar
phenomenon in the case of an electric current in a wire, and
that there is a quantity which we may call the electric pres-

Online LibraryJohn Ambrose FlemingElectric lamps and electric lighting, a course of four lectures on electric illumination delivered at the Royal institution of Great Britain → online text (page 1 of 24)