,illustration3 ,,first                  
,,direct-,,connected ,,electric         
,,generator ,,unit ,,of  ,,large        
,,capacity ,,ever ,,constructed ,,up    
,,to ,,the ,,time ,,it ,,was ,,made ,,by
 ,,thomas  ,a4 ,,edison ,,in ,,june1    
#ahha4 ,,capacity1 #abjj ,,incandescent 
,,lamps ,,of #af  ,,candle-,,power      
,,each                                  
,a-,b-,c ,,of ,,electricity             
,,by ,,william ,h4 ,,meadowcroft        
,,harper  ,,brothers ,,publishers ,,new 
,,york  ,,london                        
,a-,b-,c of ,electricity                
,,copyright1 #ahhh1 #aiji1 ,,by         
,,william ,h4 ,,meadowcroft             
,,copyright1 #aiae1 ,,by ,,harper       
,,brothers                  ,,printed   
,,in ,,the ,,united ,,states ,,of       
,,america                               
,,published ,,may1 #aiae          ,,from
 ,,the ,,laboratory ,,of ,,thomas ,a4   
,,edison                                
,,orange1 ,n4 ,j4      ,,mr4 ,w4 ,h4    
,,meadowcroft1       ,new ,york ,city4  

,,dear ,,sir3    ,i have read the ,,ms4 
of your ,a-,b-,c of ,electricity1 and   
find that the  statements you have made 
therein are correct4 ,your treatment of 
the  subject1 and arrangement of the    
matter1 have impressed me favorably4    
,yours truly1                           
,,thos4 ,a4 ,,edison          ,,contents
        ,,chap4                         
,,page            ,,introduction ,,to   
,,new ,,edition    viii                 
,,preface                           x   
,i4                                   #a
        ,,ii4 ,,definitions             
#c       ,,iii4 ,,magnetism             
#af       ,,iv4 ,,the ,,telegraph       
#bc         ,v4 ,,wireless ,,telegraphy 
#cc        ,,vi4 ,,the ,,telephone      
#dj       ,,vii4 ,,electric ,,light     
#ed      ,,viii4 ,,electric ,,power     
#hg        ,,ix4 ,,batteries            
#ie         ,x4 ,,conclusion            
#abg          ,,introduction ,,to ,,new 
,,edition      ,the favor with which    
this book has been received has brought 

about the  preparation of this new      
edition4 ,the present volume has been   
enlarged  by the addition of certain new
 material and it has been entirely      
reset4 ,some new illustrations have been
 made1 and in its new dress  the book1  
it is hoped1 will be found to afford an 
even larger measure  of usefulness4 ,the
 principles of the science remain the   
same1 but the  author is glad of the    
opportunity to note certain developments
 in their  application4                 
,w4 ,h4 ,m4    ,,edison ,,laboratory1   
,april1 #aiae4          ,,preface       
,while there is no lack of most         
excellent text-books for the study of   
those branches of ,electricity which are
 above the elementary stage1  there is a
 decided need of text-books which shall 
explain1 in simple  language1 to young  
people of1 say1 fourteen years and      
upward1 a general  outline of the       
science1 as well as the ground-work of  
those electrical  inventions which are  
to-day of such vast commercial          

importance4    ,there is also a need for
 such a book among a large part of the  
adult  population1 for the reason that  
there have been great and radical       
changes in this science since the time  
they completed their studies1  and they 
have not the time to follow up the      
subject in the advanced  books4    ,as  
instances of those changes just spoken  
of1 the electric light1  telephone1 and 
storage batteries may be mentioned1     
which have been  developed during the   
last ten or twelve years1 with the      
result of  adding very many features    
that were entirely new to electricians4 
,with these ideas in view ,i have       
prepared this little volume4 ,it is not 
intended1 in the slightest degree1 to be
 put forward as a scientific  work1 but 
it will probably give to many the       
information they desire  without        
requiring too great a research into     
books which treat more  extensively and 
deeply of this subject4                 
,w4 ,h4 ,m4                             

,a-,b-,c ,,of ,,electricity             
,a-,b-,c ,,of ,,electricity          ,i 
,we now obtain so many of our comforts  
and conveniences by the use of          
electricity that all young people ought 
to learn something of this  wonderful   
force1 in order to understand some of   
the principles which  are brought into  
practice4    ,you all know that we have 
the telegraph1 the telephone1 the       
electric  light1 electric motors on     
street-cars1 electric bells1 etc41      
besides  many other conveniences which  
the use of electricity gives us4        
,every one knows that1 by the laws of   
multiplication1 twice two makes  four1  
and that twice two can never make       
anything but four4 ,well1 these  useful 
inventions have been made by applying   
the laws of electricity  in certain     
ways1 just as well known1 so as to      
enable us to send in a  few moments a   
message to our absent friends at any    
distance1 to speak  with them at a great
 distance1 to light our houses and      

streets with  electric light1 and to do 
many other useful things with quickness 
and  ease4    ,but you must remember    
that we do not know what electricity    
itself  really is4 ,we only know how to 
produce it by certain methods1 and we   
also know what we can do with it when we
 have obtained it4    ,in this little   
book we will try to explain the various 
ways by which  electricity is obtained1 
and how it is applied to produce the    
useful  results that we see around us4  
,we will try and make this explanation  
such that it will encourage many  of you
 to study this very important and       
interesting subject more deeply4    ,in 
the advanced books on electricity there 
are many technical terms  which are     
somewhat difficult to understand1 but in
 this book it will  only be necessary to
 use a few of the more simple ones1     
which it will  be well for you to learn 
and understand before going further4    
,,ii    ,,definitions      ,the three   
measurements most frequently used in    

electricity are      ,the ,volt1    ,the
 ,ampre1    ,the ,ohm4    ,we will      
explain these in their order4           
,illustration3 ,fig4 #a    ,the         
,volt4--,this term may be better        
understood by making a comparison  with 
something you all know of4 ,suppose we  
have a tank containing  one hundred     
gallons of water1 and we want to        
discharge it through a  half-inch pipe  
at the bottom of the tank4 ,suppose1    
further1 that we  wanted to make the    
water spout upward1 and for this purpose
 the pipe  was bent upward as in ,fig4  
#a4    ,if you opened the tap the water 
would spout out and upward as in ,fig4  
#a4    ,illustration3 ,fig4 #b    ,the  
cause of its spouting upward would be   
the weight or pressure of  the water in 
the tank4 ,this pressure is reckoned as 
so many pounds to  the square inch of   
water4    ,now1 if the tank were placed 
on the roof of the house and the pipe   
brought to the ground as shown in ,fig4 
#b1 the water would spout up very  much 

higher1 because there would be many more
 pounds of pressure on  account of the  
height of the pipe4    ,so1 you see1 the
 force or pressure of water is measured 
in pounds1 and1  therefore1 a pound is  
the unit of pressure1 or force1 of      
water4 ,now1 in  electricity the unit of
 pressure1 or force1 is called a volt4  
,this word volt does not mean any       
weight1 as the word pound  weight does4 
,you all know that if you have a pound  
of water you must  have something to    
hold it1 because it has weight1 and1    
consequently1  occupies some space4 ,but
 electricity itself has no weight and   
therefore cannot occupy any space4      
,when we desire to carry water into a   
house or other building we do so  by    
means of hollow pipes1 which are usually
 made of iron4 ,this is the  way that   
water is brought into houses in cities  
and towns1 so that it  may be drawn and 
used in any part of a dwelling4 ,now1   
the principal  supply usually comes from
 a reservoir which is placed up on high 

ground  so as to give the necessary     
pounds of pressure to force the water up
 to  the upper part of the houses4 ,if  
some arrangement of this kind were not  
made we could get no water in our       
bedrooms1 because1 as you know1 water   
will not rise above its own level unless
 by force4    ,the water cannot escape  
as long as there are no holes or leaks  
in the  iron pipes1 but if there should 
be the slightest crevice in them the    
water will run out4    ,in electricity  
we find similar effects4    ,the        
electricity is carried into houses by   
means of wires which are  covered1 or   
insulated1 with various substances1     
such1 for instance1  as rubber4 ,just as
 the iron of the pipes prevents the     
water from  escaping1 the insulation of 
the wire prevents the escape of the     
electricity4    ,now1 if we were to     
cause the pounds of pressure of water1  
in pipes of  ordinary thickness1 to be  
very greatly increased1 the pipes could 
not  stand the strain and would burst   

and the water escape4 ,so it is with    
electricity4 ,if there were too many    
volts of pressure the insulation  would 
not be sufficient to hold it and the    
electricity would escape  through the   
covering1 or insulation1 of the wire4   
,it is a simple and easy matter to stop 
the flow of water from an  ordinary     
faucet by placing your finger over the  
opening4 ,as the water  cannot then     
flow1 your finger is what we will call a
 non-conductor and  the water will be   
retained in the pipe4    ,we have just  
the same effects in electricity4 ,if we 
place some  substance which is          
practically a non-conductor1 or         
insulator1 such as  rubber1 around an   
electric wire1 or in the path of an     
electric current1  the electricity1     
acted upon by the volts of pressure1    
cannot escape1  because the insulation  
keeps it from doing so1 just as the iron
 of the  pipe keeps the water from      
escaping4 ,thus1 you see1 the volt does 
not  itself represent electricity1 but  

only the pressure which forces it       
through the wire4    ,there are other   
words and expressions in electricity    
which are  sometimes used in connection 
with the word volt4 ,these words are    
pressure and intensity4 ,we might say1  
for instance1 that a certain  dynamo    
machine had an electromotive force of   
#aaj volts2 or that the  intensity of a 
cell of a battery was #b volts1 etc4    
,we might mention1 as another analogy1  
the pressure of steam in a  boiler1     
which is measured or calculated in      
pounds1 just as the pressure  of water  
is measured4 ,so1 we might say that #ajj
 pounds steam pressure  used through the
 medium of a steam-engine to drive a    
dynamo could thus  be changed to        
electricity at #ajj volts pressure4     
,the ,ampre4--,now1 in comparing the    
pounds pressure of water with the  volts
 of pressure of electricity we used as  
an illustration a tank of  water        
containing #ajj gallons1 and we saw that
 this water had a downward  force or    

pressure in pounds4 ,let us now see what
 this pressure was  acting upon4    ,it 
was forcing the quantity of water to    
spout upward through the end of  the    
pipe4 ,now1 as the quantity of water was
 #ajj gallons1 it could not  all be     
forced at once out of the end of the    
pipe4 ,the pounds pressure  of water    
acting on the #ajj gallons would force  
it out at a certain  rate1 which1 let us
 say1 would be one gallon per minute4   
,this would be the rate of the flow of  
water out of the tank4    ,thus1 you    
see1 we find a second measurement to be 
considered in  discharging the          
water-tank4 ,the first was the force1 or
 pounds of  pressure1 and the second the
 rate at which the quantity of water was
  being discharged per minute by that   
pressure4    ,this second measurement   
teaches us that a certain quantity will 
pass  out of the pipe in a certain time 
if the pressure is steady1 such         
quantity depending1 of course1 on the   
size or friction resistance of  the     

pipe4    ,in electricity the volts of   
pressure act so as to force the quantity
  of current to flow through the wires  
at a certain rate per second1  and the  
rate at which it flows is measured in   
ampres4 ,for instance1  let us suppose  
that an electric lamp required a        
pressure of #ajj volts  and a current of
 one ampre to light it up1 we should    
have to supply a  current of electricity
 flowing at the rate of one ampre1 acted
 upon by  an electromotive force of #ajj
 volts4    ,you will see1 therefore1    
that while the volt does not represent  
any  electricity1 but only its pressure1
 the ampre represents the rate of  flow 
of the current itself4    ,you should   
remember that there are several words   
sometimes used in  connection with the  
word ampre--for instance1 we might say  
that a  lamp required a current of one  
ampre or that a dynamo would give a     
quantity of #bj ampres4    ,the         
,ohm4--,you have learned that the       
pressure would discharge the  quantity  

of water at a certain rate through the  
pipe4 ,now1 suppose we  were to fix two 
discharge-pipes to the tank1 the water  
would run away  very much quicker1 would
 it not8 ,if we try to find a reason for
 this1  we shall see that a pipe can    
only1 at a given pressure1 admit so much
  water through it at a time4           
,therefore1 you see1 this pipe would    
present a certain amount of  resistance 
to the passage of the total quantity of 
water1 and would  only allow a limited  
quantity at once to go through4 ,but1 if
 we were to  attach two or more pipes to
 the tank1 or one large pipe1 we should 
make  it easier for the water to flow1  
and1 therefore1 the total amount of     
resistance to the passage of the water  
would be very much less1 and the  tank  
would quickly be emptied4    ,now1 as   
you already know1 water has substance   
and weight and therefore  occupies some 
space1 but electricity has neither      
substance nor  weight1 and therefore    
cannot occupy any space2 consequently1  

to carry  electricity from one place to 
another we do not need to use a pipe1   
which is hollow1 but we use a solid     
wire4    ,these solid wires have a      
certain amount of resistance to the     
passage  of the electricity1 just as the
 water-pipe has to the water1 and 7as   
it is in the case of the water7 the     
effect of the resistance to the  passage
 of electricity is greater if you pass a
 larger quantity through  than a smaller
 quantity4    ,if you wanted to carry a 
quantity of electricity to a certain    
distance1  and for that purpose used a  
wire1 there would be a certain amount of
  resistance in that wire to the passage
 of the current through it2 but  if you 
used two or more wires of the same size1
 or one large wire1 the  resistance     
would be very much less and the current 
would flow more  easily4    ,suppose    
that1 instead of emptying the water-tank
 from the roof through  the pipe1 we had
 just turned the tank over and let the  
water all pour  out at once down to the 

ground4 ,that would dispose of the water
 very  quickly and by a short way1 would
 it not8 ,that is very easy to be  seen1
 because there would be no resistance to
 its passage to the  ground4    ,well1  
suppose we had an electric battery      
giving a certain quantity of  current1  
say five ampres1 and we should take a   
large wire that would  offer no         
resistance to that quantity and put it  
from one side of the  battery to the    
other1 a large current would flow at    
once and tend to  exhaust the battery4  
,this is called a short circuit because 
there is  little or no resistance1 and  
it provides the current with an easy    
path  to escape4 ,remember this1 that   
electricity always takes the easiest    
path4 ,it will take as many paths as are
 offered1 but the largest  quantity will
 always take the easiest4    ,as the    
subject of resistance is one of the most
 important in  electricity1 we will give
 you one more example1 because if you   
can  obtain a good understanding of this

 principle it will help you to          
comprehend the whole subject more easily
 in your future studies4    ,we started 
by comparison with a tank holding #ajj  
gallons of water1  discharging through a
 half-inch pipe1 and showed you that the
 pounds  of pressure would force the    
quantity of gallons through the pipe4   
,when  the tap was first opened the     
water would spout up very high1 but as  
the water in the tank became lower the  
pressure would be less1 and1            
consequently1 the water would not spout 
so high4    ,so1 if it were desired to  
keep the water spouting up to the height
  it started with1 we should have to    
keep the tank full1 so as to have  the  
same pounds of pressure all the time4   
,but1 if we wanted the water  to spout  
still higher we should have to use other
 means1 such as a  force-pump1 to obtain
 a greater pressure4    ,now1 if we     
should use too many pounds pressure it  
would force the  quantity of water more 
rapidly through the pipe and would cause

 the  water to become heated because of 
the resistance of the pipe to the       
passage of that quantity acted upon by  
so great a pressure4    ,this is just   
the same in electricity1 except that the
 wire itself would  become heated1 some 
of the electricity being turned into    
heat and lost4  ,if a wire were too     
small for the volts pressure and ampres 
of current  of electricity the          
resistance of such wire would be        
overcome1 and it  would become red-hot  
and perhaps melt4 ,electricians are     
therefore  very careful to calculate the
 resistance of the wires they use before
  putting them up1 especially when they 
are for electric lighting1 in  order to 
make allowances for the ampres of       
current to flow through  them1 so that  
but little of the electricity will be   
turned into heat  and thus rendered     
useless for their purpose4    ,the unit 
of resistance is called the ohm         
7pronounced like home  without the h74  
,all wires have a certain resistance per

 foot1 according to the nature  of the  
metal used and the size of the          
wire--that is to say1 the finer  the    
wire the greater number of ohms         
resistance it has to the foot4    ,water
 and electricity flow under very similar
 conditions--that is  to say1 each of   
them must have a channel1 or conductor1 
and each of  them requires pressure to  
force it onward4 ,water1 however1 being 
a  tangible substance1 requires a hollow
 conductor2 while electricity1  being   
intangible1 will flow through a solid   
conductor4 ,the iron of  the water-pipe 
and the insulation of the electric wire 
serve the same  purpose--namely1 that of
 serving to prevent escape by reason of 
the  pressure exerted4    ,there is     
another term which should be mentioned  
in connection with  resistance1 as they 
are closely related1 and that is        
opposition4  ,there is no general       
electrical term of this name1 but1 as it
 will be  most easily understood from   
the meaning of the word itself1 we have 

used it4    ,let us give an example of  
what opposition would mean if applied to
  water4 ,probably every one knows that 
a water-wheel is a wheel having  large  
blades1 or paddles1 around its          
circumference4    ,when the water1 in   
trying to force its passage1 rushes     
against one of  these paddles it meets  
with its opposition1 but overcomes it by
 pushing  the paddle away4 ,this brings 
around more opposition in the shape of  
another paddle1 which the water also    
pushes away4 ,and so this goes on1  the 
water overcoming this opposition and    
turning the wheel around1 by  which     
means we can get water to do useful work
 for us4    ,you must remember1 however1
 that it is only by putting opposition  
in  the path of a pressure and quantity 
of water that we can get this work4     
,the same principle holds good in       
electricity4 ,we make electricity in    
different ways1 and in order to obtain  
useful work we put in its path  the     
instruments1 lamps1 or machines which   

offer the proper amount of  resistance1 
or opposition1 to its passage1 and thus 
obtain from this  wonderful agent the   
work we desire to have done4    ,you    
have learned that three important       
measurements in electricity are  as     
follows3    ,the volt is the practical  
unit of measurement of pressure2    ,the
 ampre is the practical unit of         
measurement of the rate of  flow2 and   
,the ohm is the practical unit of       
measurement of resistance4              
,,iii    ,,magnetism      ,now we will  
try to explain to you something about   
magnets and  magnetism4 ,there are very 
few boys who have not seen and played   
with  the ordinary magnets1 shaped like 
a horseshoe1 which are sold in all      
toy-stores as well as by those who sell 
electrical goods4    ,well1 you know    
that these magnets will attract and hold
 fast anything  that is made of iron or 
steel1 but they have no effect on brass1
  copper1 zinc1 gold1 or silver1 yet    
there is nothing that you can  see which

 should cause any such effect4 ,you will
 notice1 then1 that  magnetism is like  
electricity2 we cannot see it1 but we   
can tell that  it exists1 because it    
produces certain effects4 ,and here is  
another  curious thing--magnetism       
produces electricity1 and electricity   
produces  magnetism4 ,this seems to be a
 very convenient sort of a family       
affair1  and it is owing to this close  
relation that we are able to obtain so  
many wonderful things by the use of     
electricity4    ,we shall now show you  
how electricity produces magnetism1 and1
 when we  come to the subject of        
electric lighting we will explain how   
magnetism  produces electricity4        
,illustration3 ,fig4 #c    ,the easiest 
way to show how electricity makes       
magnetism is to find out  how magnets   
are made4 ,suppose we wanted to make a  
horseshoe magnet1  just mentioned above2
 we would take a piece of steel and wind
 around  it some fine copper wire1      
commencing on one leg of the horseshoe  

and  winding around until we came to the
 end of the other leg4 ,then we  should 
have two ends of wire left1 as shown in 
the sketch4 7,fig4 #c47    ,we connect  
these two ends with an electric battery1
 giving1 say1 two  volts1 and then the  
ampres of current of electricity will   
travel  through the wire1 and in doing  
so has such an influence on the steel   
that it is converted into a magnet1 such
 as you have played with4 ,the  current 
is broken--that is to say1 it is shut   
off several times in  making a magnet of
 this kind1 and then the wire is taken  
away from the  battery and is unwound   
from the steel horseshoe1 leaving it    
free from  wire1 just as you have seen  
it4 ,this horseshoe is now a permanent  
magnet--that is1 it will always attract 
and hold pieces of iron and  steel4     
,now1 if you were to do the same thing  
with a horseshoe made of soft  iron     
instead of steel it would not be a      
magnet after you stopped the  current of
 electricity from going through the     

wires1 although the piece  of iron would
 be a stronger magnet while the         
electricity was going  through the wire 
around it4    ,the steel magnet is      
called a permanent magnet1 and its ends1
 or  poles1 are named ,north and ,south4
 ,there is usually a loose piece of     
steel or iron1 called an armature1 put  
across the ends1 which has the  peculiar
 property of keeping the magnetism from 
becoming weaker1 and  thereby retaining 
the strength of the magnet4 ,the        
strongest part of the  magnet is at the 
poles1 while1 at the point marked       
7which is called  the neutral point7    
there is scarcely any magnetism4    ,it 
will be well to remember the object of  
the armature as we shall  meet it again 
in describing dynamo machines4    ,the  
magnets made of iron are called         
electromagnets because they exhibit     
magnetism only when the ampres of       
current of electricity are flowing      
around them4 ,they also have two poles1 
north and south1 as have  permanent     

magnets4 ,electromagnets are used in    
nearly all electrical  instruments1 not 
only because they are stronger than     
permanent magnets1  but because they can
 be made to act instantly by passing a  
current of  electricity through them at 
the most convenient moment1 as you will 
see  when we explain some of the        
electrical instruments which are used to
  produce certain effects4 7,fig4 #d47  
,illustration3 ,fig4 #d    ,of course   
there are a great many different shapes 
in which magnets  are made4 ,the        
simplest is the bar magnet1 which is    
simply a flat or  round piece of iron or
 steel4 ,suppose you made a magnet of a 
flat piece  of steel and put on top of  
it a sheet of paper1 and then threw on  
the  paper some iron filings1 you would 
see them arrange themselves as is  shown
 in the following sketch4 7,fig4 #e47   
,the filings would always arrange       
themselves in this shape1 no matter  how
 large or small the magnets were4 ,and1 
if you were to cut it into  two or half 

a dozen pieces1 each piece would have   
the same effect4 ,this  shows you that  
each piece would itself become a magnet 
and would have  its poles exactly as the
 large one had4    ,illustration3 ,fig4 
#e    ,now1 we have another curious     
thing to tell you about magnets4 ,if you
  present the north pole of a magnet to 
the south pole of another magnet1  they 
will attract and hold fast to each      
other1 but if you present a  south pole 
to another south pole1 or a north pole  
to a north pole1 they  will repel each  
other1 and there will be no attraction4 
,you can perform  some interesting      
experiments by reason of this fact4 ,we 
will give you  one of them4    ,take1   
say1 a dozen needles and draw them      
several times in the same  direction    
across the ends of a magnet so that they
 become magnetized4  ,now stick each    
needle half-way through a piece of cork1
 and put the  corks1 with the needles   
sticking through them1 into a bowl of   
water4  ,then take a bar magnet and     

bring it gradually toward the middle of 
the  bowl and you will see the corks    
advance or back away from the magnet4   
,if the ends of the needles sticking up 
out of the water are south poles  and   
the end of the magnet you present is a  
north pole1 the needles will  come to   
the center2 but will go to the side of  
the bowl if you present  the south pole4
 ,you can vary this pretty experiment by
 turning up the  other ends of part of  
the needles4    ,you will remember that 
when we explained what resistance meant1
 we  told you that electricity would    
always take the easiest path1 and while 
part of it will flow in a small wire1   
the largest portion will take  an easier
 path if it can get to something larger 
that is a metallic  substance4          
,electricity will only flow easily      
through anything that  is made of metal4
 ,you will also remember that you       
learned that when  electricity took a   
short cut to get away from its proper   
path it was  called a short circuit4    

,all this must be taken into            
consideration when magnets are being    
made4  ,in the first place1 the wire we 
wind around steel or iron to make       
magnets must always be covered with an  
insulator of electricity4 ,magnet  wire 
is usually covered with cotton or silk4 
,if it were left bare1  each turn of the
 wire would touch the next turn1 and so 
we should make  such an easy path for   
the electricity that it would all go    
back to the  battery by a short circuit1
 and then we would get no magnetic      
effect in  the steel or iron4 ,the only 
way we can get electricity to do useful 
work for us is to put some resistance or
 opposition in its way4 ,so  you see    
that if we make it travel through the   
wire around the iron or  steel1 there is
 just enough resistance or opposition in
 its way to give  it work to get through
 the wire1 and this work produces the   
peculiar  effect of making the iron or  
steel magnetic4    ,the covering on the 
wire1 as you will remember1 is called   

insulation4          ,,iv    ,,the      
,,telegraph      ,every one knows how   
very convenient the telegraph is1 but   
there are  not many who think how       
wonderful it is that we can send a      
message in a  few seconds of time to a  
distant place1 even though it were      
thousands  of miles away4 ,and yet1     
though the present system of            
telegraphing is a  wonderful one1 the   
method of sending a telegram is simple  
enough4 ,the  apparatus that is used in 
sending a telegram is as follows3       
,the ,battery4                ,the      
,wire4                ,the ,telegraph   
,key4                ,the ,sounder4     
,the different kinds of electric        
batteries will be mentioned afterward1  
so we will not stop now to describe     
them1 but simply state that a  battery  
is used to produce the necessary        
electricity4 ,as you all know  what wire
 is1 there is no necessity of describing
 it further4    ,the telegraph key is   
shown in the sketch below4 7,fig4 #f47  

,illustration3 ,fig4 #f    ,this        
instrument is usually made of brass1    
except that upon the handle  there is   
the little knob which is of hard rubber4
 ,the handle1 or lever1  moves down when
 this knob is pressed1 and a little     
spring beneath  pushes it up again when 
let go4 ,you will see a second smaller  
knob1 the  use of which we will explain 
later4    ,the sounder is shown on the  
following page4 7,fig4 #g47    ,the part
 consisting of the two black pillars is 
an electromagnet1  and across the top of
 these pillars is a piece of iron called
 the  armature1 which is held up by a   
spring4    ,illustration3 ,fig4 #g      
,now let us see how the battery and wire
 are placed in connection with  these   
instruments4 ,you have seen that we     
usually have two wires for  the         
electricity to travel in1 one wire for  
it to leave the battery1  and the other 
to return on4 ,but you will easily see  
that if two wires  had to be used in    
telegraphing it would be a very         

expensive matter1  especially when they 
had to be carried thousands of miles4   
,so1 instead  of using a second wire1 we
 use the earth to carry back the        
electricity  to the battery1 because the
 earth is a better conductor even than  
wire4  ,although a quantity of ground   
equal in size to the wire would offer   
thousands of times greater resistance   
than the wire1 yet1 owing to the  great 
body of our earth1 its total resistance 
is even less than any  telegraph wire   
used4    ,when two electric wires are   
run from a battery and connected        
together  through some instrument1 this 
is called a circuit1 because the        
electricity has a path in which it can  
travel back to the battery4 ,this  would
 be a metallic circuit2 but when one    
wire only is used1 and  the other side  
of the battery is connected with the    
earth1 it is called  a ground or earth  
circuit1 because the electricity returns
 through  the earth4    ,illustration3  
,fig4 #h    ,if you look at this sketch 

7,fig4 #h7 you will see how the         
telegraph  instruments are connected and
 will then be able to understand how a  
message can be sent4    ,here we have   
two sets of telegraph apparatus1 one of 
which1 let us  say1 is in ,new ,york and
 the other in ,philadelphia4    ,you    
will see that one wire from the battery 
is connected with the  earth1 and the   
other wire with the sounder4 ,another   
wire goes from the  sounder to one leg  
of the key so as to make the brass base 
of the key  part of the circuit4 ,the   
other leg of the key is insulated from  
the  brass base by being separated      
therefrom with some substance which will
  not carry electricity1 such1 for      
instance1 as hard rubber4    ,we will   
suppose that there is already a wire    
strung up on poles between  ,new ,york  
and ,philadelphia1 and that the key1    
sounder1 and battery in  the latter city
 are connected in the same way as those 
in ,new ,york4    ,now1 to enable us to 
send a message from one city to the     

other we must  connect the ends of the  
wires to the instruments in each city2  
so we  connect one end to the insulated 
leg of the key in ,new ,york1 and the   
other end to the insulated leg of the   
key in ,philadelphia4    ,everything is 
now completed1 and1 as soon as we find  
out what is the  use of that part of the
 key that has a little round1 black     
handle1 we  shall be ready to start4    
,this is called the switch4    ,if you  
will look once more at the picture of   
the key you will see  under the long    
handle 7or lever7 a little point which  
the lever will  touch when it is pressed
 down4 ,now this little point is part of
 that  insulated leg1 and1 therefore1   
this point is also insulated from the   
base4 ,if a current of electricity were 
sent along the wire it could not  get   
any farther than this point unless we   
put in some arrangement to  complete the
 path1 or circuit1 for it to travel in4 
,we therefore put in  the switch4       
,one end of the switch 7which is made of

 brass with a rubber handle7  is        
fastened on the base of the key1 so that
 it may be moved to the  right or left4 
,the other end1 when the switch is moved
 to the left  7or closed71 touches a    
piece of brass fastened to the little   
point  we have mentioned1 and so makes a
 free path for the electricity to go    
through the base of the key and through 
the wire to the sounder1 and  from there
 to the battery1 and so back to the     
earth4 ,this switch must  be opened     
before the sounder near it will respond 
to its neighboring  key4    ,now we are 
ready to send a message4 ,suppose we    
want to send a telegram  from ,new ,york
 to ,philadelphia4 ,the operator in ,new
 ,york opens his  switch and presses    
down his key several times4 ,the switch 
on the  ,philadelphia key being closed1 
the electricity goes through to the     
sounder1 and1 this being made an        
electromagnet by the current passing    
through the wire1 the iron armature is  
attracted by the magnetism and  drawn   

down to the magnet with a snap4 ,it will
 stay there as long as the  ,new ,york  
operator keeps his lever pressed down1  
but1 when he allows  it to spring up1   
there is no current passing through the 
,philadelphia  sounder and there is no  
magnetism1 consequently the armature    
springs up  again with a click4    ,as  
often as the operator presses down his  
key lever and lets it spring  up again1 
the same action takes place in the      
sounder1 and it makes that  click1      
click1 which you have heard if you have 
ever seen telegraph  instruments in     
operation4    ,let us continue1 however1
 to send our message4 ,the ,new ,york   
operator1  having pressed down his key  
several times to signal the             
,philadelphia  operator1 closes his     
switch to receive the answer from       
,philadelphia4  ,the operator in the    
latter city then opens his switch and   
presses down  his key several times1    
which makes the ,new ,york sounder      
click1 in the  same way1 to let the     

operator there know that he is ready to 
receive  the message4 ,he then closes   
his switch and receives the telegram    
which  the ,new ,york operator sends    
after opening his key4    ,telegraphic  
messages are sent and received in this  
way and are read by  the sound of the   
clicks4    ,these sounds may be         
represented on paper by dots1 dashes1   
and spaces4  ,for instance1 if you press
 down the key and let it spring back    
quickly1  that would represent a dot4   
,if you press down the key and hold it a
  little longer before letting it spring
 up again1 it would represent a  dash4  
,a space would be represented by waiting
 a little while before  pressing down   
the key again4    ,we show you below the
 alphabet in these dots1 dashes1 and    
spaces1 and  these are the ones now used
 in sending all telegraphic messages4   
,illustration    ,thus1 you see1 if you 
were telegraphing the word and you would
 press  down your key and let it return 
quickly1 then press down again and      

return after a longer pause1 which would
 give the letter ,a2 then slowly  and   
quickly1 which would be ,n2 then slowly 
and twice quickly1 which  would be ,d4  
,any persevering boy can learn to       
operate a telegraph instrument by a     
little study and regular practice2 and1 
as complete learner's sets  can be      
purchased very cheaply1 this affords a  
pleasant and useful  recreation for     
boys4    ,there are many cases where two
 boys living near each other have a set 
of telegraph instruments in their homes 
and run a wire from one house  to the   
other1 thus affording many hours of     
pleasant and profitable  amusement4     
,in giving the above explanation of     
telegraphing we have described only  the
 simple and elementary form4 ,in large  
telegraph lines1 such as  those of the  
,western ,union1 there are many more    
additional instruments  used1 which are 
very complicated and difficult to       
understand2 such1  for instance1 as the 
quadruplex1 by which four distinct      

messages can  be sent over the same wire
 at the same time4 ,we have1 therefore1 
described only the simplest form in     
order to give the general idea  of the  
working of the telegraph by             
electromagnetism1 which is the          
principle of all telegraphing4    ,when 
you study electricity more deeply you   
will find this subject and  the many    
different instruments very interesting  
and wonderful4          ,v    ,,wireless
 ,,telegraphy      ,if it has seemed    
extraordinary to you that only one wire 
should be  necessary for sending a      
message by the electric telegraph1 and  
that our  earth can be used instead of a
 second wire1 how much more wonderful it
  is to realize that in these days we   
can exchange telegraphic messages  with 
different points without any connecting 
wires at all between them1  even though 
the places be many hundred miles apart4 
,thus1 two ships on  the ocean1 entirely
 out of sight of each other1 may        
intercommunicate1  or may telegraph to  

or receive despatches from a far-distant
 shore2  indeed1 telegraphy without     
wires has been accomplished across the  
,atlantic ,ocean4 ,in the language of   
the day1 this is called wireless        
telegraphy1 although it is more correct 
to think of it as aerial1 or  space1    
telegraphy4 ,as you will naturally want 
to know how this is  effected1 we will  
try to explain the main principles in a 
simple manner4    ,if you drop a stone  
into a quiet pond1 you will see the     
water form into  ring-like waves1 or    
ripples1 which travel on and on until   
they die away  in the far distance4     
,these waves are caused1 as we have     
seen1 by a  disturbance of the body of  
water4    ,probably you have already    
learned in school that all known space  
is  said to be filled with a medium     
called ether1 and that this medium is   
so exceedingly thin that it penetrates1 
or permeates1 everything1 so  that it   
exists in the densest bodies as well as 
in free space4 ,for the  sake of        

obtaining a clear idea of this theory we
 may imagine that the  ether envelops   
and permeates every thing in the entire 
universe4 ,hence  we can easily realize 
that1 although we cannot see or feel the
 ether1  any disturbance of it will set 
it in wavelike motion4    ,modern       
science accounts for light1 radiant     
heat1 and electrical  phenomena by      
reason of wavelike disturbances1        
vibrations1 or pulsations  of this      
ether4 ,thus1 if you should strike a    
light1 the ether would be  disturbed1   
causing waves to form1 which1 like the  
waves in the water1  would travel in    
every direction4 ,when these waves      
reached the eyes of  another person     
within seeing distance1 that person's   
eyes would be so  acted upon by the     
waves that he would see the light which 
you had made1  and would see it         
instantly1 for light waves travel about 
#ahf1jjj miles  per second4    ,so1 if  
you create an electrical disturbance1   
the same kind of an effect  will be     

produced2 that is to say1 waves in the  
ether will be created1  or propagated1  
and will travel on and on in every      
direction4 ,now1 if  some form of       
electrical appliance can be made that   
will be of the right  kind to respond to
 them 7as the eye responds to light     
rays71 these  electric waves can be made
 practically useful for transmitting    
messages  through space4 ,this is just  
what has been done1 and we will now give
  you a brief general description of one
 kind of apparatus used4    ,for        
sending1 or transmitting1 as it is      
usually termed1 there  is used an       
induction-coil1 having rather large     
brass balls on the  secondary terminals2
 suitable batteries1 a condenser1 a     
,morse telegraph  key1 and an aerial1 or
 wire which is carried away up into the 
air  vertically1 and is made fast to a  
pole or special tower4 ,when these are  
connected properly1 the closing of the  
circuit with the key will cause  sparks 
to jump between the brass balls4 ,this  

electrical discharge1  or oscillation1  
is carried by the aerial into the upper 
air and  causes intense pulsations in   
the ether1 which set up waves as already
  mentioned4 ,if the circuit is opened  
again the disturbance ceases4 ,so1  by  
alternately closing and opening the     
circuit1 the ,morse characters  can be  
imitated4    ,but how can these signals 
be received by the man for whom they are
  intended1 who may be a hundred miles  
or more away8 ,he has a receiving  set1 
consisting of a sensitive relay1        
batteries1 resistance-coils1 a  ,morse  
register1 an aerial1 and a special      
device called a coherer4  ,this is the  
important part of the whole set1 because
 it is sensitive  to the electrical     
waves4 ,it consists of a little glass   
tube about as  large around as an       
ordinary lead-pencil1 and perhaps two   
inches long4  ,in the tube are two      
metallic plugs1 each having a wire      
attached so that  one wire projects from
 each end of the tube4 ,the plugs are   

separated  inside the tube by a very    
small space1 and in this space are some 
metal filings4 ,one wire from the       
coherer is connected to the aerial  and 
the other to the ground4 ,when there are
 no electrical ether waves  to influence
 them1 these filings1 being loosely     
separated1 are at  rest and offer high  
resistance2 but when the ether is       
disturbed by  electrical vibrations and 
the waves arrive at the coherer 7through
 the  aerial71 these filings are drawn  
together1 or cohere4 ,this lowers their 
resistance and they become a better     
conductor4 ,now1 the coherer wires  are 
also connected through a battery to the 
relay1 which in turn is  connected      
through another battery to a ,morse     
register4 ,therefore1 when  the filings 
become a conductor1 the current flows   
through them and the  circuit to the    
relay is closed4 ,that attracts an      
armature which closes  the circuit of   
the ,morse register and thus marks the  
electrical impulse  on a strip of paper 

tape4 ,in the mean time1 a restoring    
device1 called  a decoherer1 operated   
also by the relay circuit1 has tapped   
upon the  coherer1 thus shaking the     
filings loose again1 so that they are   
ready  to cohere again and register     
another impulse1 or character4 ,thus1 by
  pressing the key at the transmitting  
end for long or short periods1 to       
represent ,morse characters1 long and   
short waves are propagated in the  ether
 and are received and recorded at the   
receiving end through the  coherer and  
other parts of the receiving set4 ,in   
this way telegraphic  messages are sent 
and received through space1 between     
points separated  by hundreds or        
thousands of miles4    ,we have tried to
 describe to you the general principles 
underlying  the art of wireless         
telegraphy as plainly as possible1 using
 for  illustration the simplest kind of 
apparatus employed for the practical    
sending and receiving of messages4 ,at  
the present day there are  several      

systems in actual practice1 and with the
 growth of the art  there have been many
 elaborations of apparatus that have    
come into  use4 ,for instance1 the      
coherer is not as much used as formerly4
 ,in its  place there are employed      
several kinds of wave-detectors as they 
are now termed1 and in many of the      
systems the electrical pulsations  are  
generated by a dynamo-machine instead of
 batteries4 ,then1 again1  instead of   
the messages being recorded by a ,morse 
register at the  receiving end1 the     
operator receives them by means of a    
telephone  receiver1 through which he   
hears the ,morse characters and writes  
them  down in words as he hears them4   
,generally the aerial1 or antenn1 as  it
 is sometimes named1 consists of several
 wires1 sometimes a large  number1      
carried to a considerable height4       
,there are a great many other details   
which might be written to explain  all  
the complicated apparatus which is used 
in some of the systems1  but it is not  

intended in this book to offer more than
 a general  explanation of main         
principles4 ,we must leave it to you to 
study the  details elsewhere if you so  
desire after you have read these pages4 
,,vi    ,,the ,,telephone      ,you     
probably all know that the telephone is 
an electrical instrument by  which one  
person may talk to another who is at a  
distance4 ,not only can  we talk to a   
person who is in a different part of the
 city1 but such  great improvements have
 been made in these instruments that we 
can talk  through the telephone to a    
person in another city1 even though it  
be  hundreds of miles away4    ,the main
 principle of the telephone is          
electromagnetism1 as in the  telegraph1 
but there are other important points in 
addition to those we  mentioned in      
describing the latter4    ,let us take  
first the      ,,induction-,,coil       
,you will remember that an electromagnet
 is made by winding many turns  of wire 
around a piece of iron and sending a    

current of electricity  through this    
wire4    ,now1 suppose this current of  
electricity was being supplied by two   
cells of a battery4 ,if you took in your
 hands the wires coming from  these two 
cells1 giving1 say1 four volts1 you     
could not feel any  shock2 but if you   
were to take hold of the ends of the    
wires on the  electromagnet and separate
 them while this same current was going 
through1 you would get a decided shock4 
,this separation would break the        
circuit1 and the reason you would get  a
 shock is that1 while the electricity is
 acting on the wire1 the iron  itself is
 magnetized1 and on breaking the circuit
 reacts upon the wire1  producing for a 
moment more volts of pressure in every  
turn of it4  ,thus1 you see1 this weak  
pressure of electricity as it travels   
through  the wire can yet produce1      
through its magnetism1 strong momentary 
effects1 but you cannot feel it unless  
you break the circuit4      ,,how ,,the 
,,induction-,,coil ,,is ,,made    ,the  

object of the induction-coil is to      
produce high intensity1 or  pressure1   
from a comparatively weak pressure and  
large current of  electricity2 so1 if we
 add still more wire1 the magnet has a  
larger  number of turns to act upon and 
thus makes a very strong pressure1 or   
large number of volts1 but a lesser     
number of ampres4    ,instead of taking 
one piece of iron1 as we would for an   
ordinary  electromagnet1 we take a      
bundle of iron wires in making an       
induction-coil1 as these give a stronger
 effect4 ,around this bundle of  wires  
we wrap many turns of insulated copper  
wire4 ,this is called the  primary coil1
 and the ends of this wire are to be    
attached to the  battery4               
,illustration3 ,fig4 #i    ,on top of1  
or over1 this primary coil we wrap a    
great many turns of  very fine wire1 of 
which1 as it is so fine1 a great length 
can be used4  ,this is called the       
secondary coil1 and it is in this coil  
that the  volts1 or pressure1 of        

electricity become strongest4    ,above 
we show you a sketch of an              
induction-coil4 7,fig4 #i47    ,at the  
left-hand side of the cut is a          
circuit-breaker1 which is  simply a     
piece of iron 7armature7 on a spring    
placed opposite the iron  core4 ,this   
armature is made a part of the wire     
leading to the primary  coil4 ,when the 
current from the battery is sent through
 the wires1  the core becomes magnetized
 and draws this armature away from a    
fixed  contact point1 thus breaking the 
circuit1 but the spring pulls it back1  
again completing the circuit1 and so it 
keeps going back and forth very  rapidly
 with a br-r-r-ing sound4    ,if you    
were now to take hold of the ends of the
 secondary coil you  would get a        
continuous series of quick shocks which 
would feel like  pins and needles       
running into you4    ,perhaps most of   
you have taken hold of the handles of a 
medical battery  and have had shocks    
therefrom4 ,in so doing1 you have simply

 had the  current from the secondary of 
an induction-coil4 ,the current may be  
made weaker by sliding a metallic cover 
over part of the iron core and  so      
shutting off part of the magnetic       
effect4      ,,sparking ,,coils         
,while on this subject we may add that  
these coils will produce sparks  from   
the two ends of the wire of the         
secondary coil4 ,these sparks vary  in  
length according to the amount of wire  
in the coil4 ,small ones are  made which
 give a spark a quarter of an inch in   
length1 while others  are made which    
will give sparks #aj1 #ab1 and #af      
inches in length4 ,in the  latter1      
however1 there are many miles of wire in
 the secondary coil4    ,the largest    
induction-coil known is one which was   
made for an ,english  scientist4 ,there 
are #cda1hej turns1 or #bhj miles1 of   
wire in the  secondary coil4 ,with #cj  
cells of ,grove battery this coil will  
give a  spark #db inches in length4 ,you
 may form some idea of the effect of    

this  induction-coil when we state that 
if we desired to produce the same       
length of spark direct from batteries1  
without using an induction-coil1  we    
should require the combined volts of    
pressure of #fj1jjj to #ajj1jjj  cells  
of battery4    ,having explained to you 
briefly the induction-coil--how it is   
made  and its action--we must ask you to
 bear these principles in mind1 and     
presently we will tell you how it is    
used in the telephone4    ,the next     
thing we shall try to explain will be   
,,the ,,vibrating ,,diaphragm    ,did   
you ever take the end of a cane in your 
hand1 raise it up over your  head1 and  
then bring it down suddenly and sharply1
 so that it nearly  touched the ground1 
as though you were about to strike      
something8 ,if  not1 try it now with a  
thin walking-cane or with a pine stick  
about  three feet long and one-half inch
 thick1 and you will find that there  is
 a peculiar sound given out4 ,it is not 
the stick that makes this  sound1 but it

 is owing to the fact that you have     
caused the air to  vibrate1 or tremble1 
and thus give out a sound4              
,illustration3 ,fig4 #aj    ,if you     
strike a tuning-fork sharply you will   
see the ends vibrate and a  sound will  
be given4 ,if you put your fingers on   
top of a silk hat and  speak near it you
 will feel vibrations of your voice4    
,every time you speak you cause         
vibrations of the air2 and the louder   
and higher you speak the greater the    
number of vibrations4    ,suppose you   
take a thin piece of wood in your hands 
7say1 for instance1  the lid of a       
cigar-box cut in the shape shown in the 
picture1 ,fig4 #aj7  and hold it about  
two inches from your mouth and then     
speak4 ,you will  feel the wood tremble 
in your hand4 ,this is because the      
vibrations of  the air cause the wood to
 vibrate in the same manner4 ,these     
vibrations  are very minute and cannot  
be seen with the naked eye1 but they    
actually take place1 and could be       

measured with a delicately balanced     
instrument4    ,illustration3 ,fig4 #aa 
,now let us try another experiment in   
further illustration of this  principle4
 ,we will take a tube about three inches
 long and one and  one-half or two      
inches in diameter4 ,this tube may be   
made of cardboard4  ,now cut out a piece
 of thin cardboard which will just fit  
over one  end of the tube4 ,this piece  
we will call the diaphragm4 ,fasten the 
diaphragm by pasting it with two strips 
of thin paper to the tube4  ,these      
strips of paper should be fastened only 
on the ends1 and the  middle of the     
paper allowed to be slack1 as shown in  
the picture1 so  that the diaphragm may 
work backward and forward easily4 ,take 
a small  shot about the size seen in the
 sketch and tie it to a single thread of
  fine silk1 then let it hang as shown  
in the sketch 7,fig4 #aa71 so that  it  
will only just touch the diaphragm4     
,now1 if you speak into the open  end of
 the tube the diaphragm will vibrate and

 the shot will be seen  to move to and  
from it according to the strength of the
 vibrations4 ,if  we could by any means 
make a diaphragm in another tube        
reproduce these  same vibrations1 we    
should hear the same words respoken1 if 
the tube  were held to the ear4         
,illustration3 ,fig4 #ab    ,while the  
vibrations caused by the human voice are
 too minute to be  seen1 it may seem    
surprising that they can be made to     
produce power4  ,this is done by an     
ingenious mechanism called a            
,phonomotor1 perfected  by the great    
inventor ,thomas ,a4 ,edison1 of whom   
every one has probably  heard4 ,this    
mechanism1 when spoken or sung at 7or   
into7 immediately  responds by causing a
 wheel to revolve4 ,no amount of blowing
 will start  the wheel1 but it can      
instantly be set in motion by the       
vibrations  caused by sound4    ,the    
,phonomotor 7which is shown in the      
engraving ,fig4 #ab7 has a  diaphragm   
and mouthpiece4 ,a spring1 which is     

secured to the bedpiece1  rests on a    
piece of rubber tubing placed against   
the diaphragm4 ,this  spring carries a  
pawl that acts on a ratchet or roughened
 wheel on the  fly-wheel shaft4 ,a sound
 made in the mouthpiece creates         
vibrations in  the diaphragm2 the       
vibrations of the diaphragm move the    
spring and pawl  with the same impulses1
 and as the pawl thus moves back and    
forth on  the ratchet-wheel it is made  
to revolve4    ,the instrument1         
therefore1 is of great value for        
measuring the  mechanical force of sound
 waves1 or vibrations1 produced by the  
human  voice4      ,,the ,,transmitter  
,that part of the telephone into which  
we speak is called the  transmitter4    
,this is usually a piece of hard rubber 
having a round  mouthpiece cut through  
it4 ,at the other side of this          
mouthpiece is  placed a diaphragm made  
of a thin piece of metal1 which is held 
m  place by a light spring4 ,behind this
 diaphragm1 and very close to  it1 is   

placed a carbon button4 ,between this   
carbon button and the  diaphragm is a   
small piece of platinum1 which is placed
 so as to touch  both the button and    
diaphragm very lightly4 ,this platinum  
contact  piece is connected with one of 
the wires running to the primary of  the
 induction-coil1 and the spring attached
 to the carbon button is  connected with
 the battery to which the other wire of 
the primary is  connected4 ,this is all 
shown in the sketch of a transmitter4   
7,fig4 #ac47    ,illustration3 ,fig4 #ac
    ,a is the mouthpiece2 ,b1 the       
diaphragm2 ,c1 the carbon button2 ,d1   
the  wire at the end of which is the    
platinum contact2 ,e1 the battery2 and  
,f1 the induction-coil2 ,p1 ,p are the  
wires to the primary1 and ,s1 ,s to  the
 secondary wires4    ,we will now say a 
few words about the receiver1 and then  
describe the  manner in which the       
telephone works4      ,,the ,,receiver  
,this is that part of the telephone     
which is held to the ear1 and  by which 

we can hear the words spoken into the   
transmitter of the  telephone at the    
other end of the line4    ,illustration3
 ,fig4 #ad    ,the receiver is made of  
hard rubber1 and contains a permanent   
bar  magnet1 which is wound with wire so
 as to make it also an electromagnet    
when desired4 ,in front of this magnet  
is placed loosely a diaphragm  of thin  
sheet iron4 ,this diaphragm is placed so
 as to be within the  influence of the  
magnet1 but just so that neither one can
 touch the  other4    ,fig4 #ad is a    
sketch of the receiver4 ,a and ,b are   
the wires leading to  the magnet1 ,c1   
and ,d is the diaphragm4 ,e and ,f are  
where the wires  connect1 one from the  
secondary of the induction-coil in the  
other  telephone1 and the other         
connected with the earth4      ,,the    
,,carbon ,,button    ,the little carbon 
button plays an important part in the   
telephone4  ,you will see from the      
sketch of the transmitter that the      
current of  electricity will flow       

through the carbon button to the contact
 point  and through the wire to the     
primary of the induction-coil4    ,now1 
carbon has a peculiarity1 which is this1
 that if we press this  carbon button1  
ever so slightly1 against the platinum  
contact1 there  would be less resistance
 to the flow of the electricity through 
the  wire to the primary1 and the more  
we press it the less the resistance     
becomes4 ,the consequence of this would 
be that more current would go to  the   
primary1 and the secondary would become 
correspondingly stronger4  ,if the      
carbon button were left untouched1 and  
nothing pressed against  it1 the flow of
 current through it would be perfectly  
even4    ,having examined the inside of 
the transmitter and receiver1 and       
understanding the effect of pressure on 
the carbon button1 let us now  see      
,,how ,,the ,,telephone ,,works    ,when
 we speak into the mouthpiece of the    
transmitter1 the vibrations of  the air 
cause the diaphragm to vibrate very     

rapidly1 and1 of course1  every movement
 of the diaphragm presses more or less  
against the  carbon button1 in          
consequence of which the currents       
passing through the  primary of the     
induction-coil are constantly increased 
or diminished  and thus produce similar 
effects1 but magnified1 in the          
secondary4    ,the effect of this is    
that the magnet in the receiver of the  
other  telephone is receiving a rapidly 
changing current1 which1 producing      
corresponding magnetic changes1 makes   
the magnet alternately weaker  or       
stronger4 ,this influences1 by          
magnetism1 the iron diaphragm           
accordingly1 and makes it reproduce the 
same vibrations that were  caused by the
 speech at the transmitter of the       
sending telephone4 ,thus1  the same     
vibrations being reproduced1 the        
original sounds are given  out1 and we  
can hear what the person at the sending 
telephone is saying4    ,the action of  
the telephone illustrates well the      

wonderfully quick  action of the        
electric current by the reproduction of 
these sound  waves1 or air vibrations1  
for they number many thousands in one   
minute's speech4          ,,vii         
,,electric ,,light      ,we have now    
arrived at a very interesting part of   
the study of  electricity1 as well as a 
more difficult part than we have yet    
told you  of1 but one which you can     
easily understand if you read carefully4
    ,you must all have seen electric    
lights1 either in the streets or in     
some large buildings1 for so many       
electric lights are now used that  there
 are very few people who have not seen  
them4 ,but perhaps some of  you have    
only seen the large1 dazzling lights    
that are used in the  streets1 and do   
not know that there is another kind of  
electric light  which is in a globe     
about the size and shape of a large     
pear1 and gives  about the same light as
 a good gas-jet4    ,these two kinds of 
electric lights have different names4   

,the large1 dazzling lights which you   
see in the streets are called           
arc-lights1 and the small1 pear-shaped  
lamps1 which give a soft1  steady light1
 are called incandescent lights4 ,we    
will tell you later  why these names are
 given to them4    ,illustration3 ,fig4 
#ae    ,the incandescent lights are     
generally used in houses1 stores1       
theaters1  factories1 steamboats1 and   
other places where a number of small    
lights  are more pleasant to the eyes4  
,the arc-lights 7,fig4 #ae7 are used to 
light streets and large spaces where a  
great quantity of light is  wanted4     
,it would not be pleasant to have one of
 these dazzling arc-lamps in  your      
parlor--although it would give a great  
deal of light--because  your eyes would 
soon become tired4 ,but two or three of 
the small  incandescent lights 7,fig4   
#af7 would be very agreeable1 because   
they  would give you a nice1 soft light 
to read or work by1 and would not  tire 
your eyes4 ,so1 you see1 these two      

different kinds of lamps are  very      
useful in their proper places4    ,now1 
if you will read patiently and          
carefully1 we will try and explain  how 
both these lights are made4             
,illustration3 ,fig4 #af    ,you have   
seen that the telegraph1 telephone1     
electric bells1 etc41 are  worked by    
batteries4 ,electric lights1 however1   
require such a large  amount of current 
that it is too expensive to produce them
 in large  quantities by batteries4 ,a  
small number of lamps could be lighted  
by  batteries1 but if we were to attempt
 to use them to light #ejj or #a1jjj    
lamps together1 the expense would be so 
enormous as to make it entirely  out of 
the question4    ,there are many        
millions of incandescent lamps in use in
 the ,united  ,states1 but you will     
easily see that there could not be that 
number  used if we had to depend on     
batteries to light them4 ,you will      
understand this more thoroughly when you
 have finished reading this  little     

book4    ,well1 you will ask1 if we     
cannot use batteries1 what is used to   
produce  these electric lights8         
,machines called dynamo-electric        
machines1 or generators1 which  are     
driven by steam-engines or water-power1 
are used to produce the  electricity    
which makes these lamps give us light4  
,you will remember that in the chapter  
on ,magnetism we explained to you  how  
electricity makes magnetism1 and now we 
will explain how1 in the  dynamo1       
magnetism makes electricity4            
,illustration3 ,fig4 #ag    ,it has been
 found that the influence of a magnet is
 very strong at  its poles1 and that    
this influence is always in the same    
lines4 ,this  influence has been        
described as lines of force1 which you  
will see  represented in the sketch     
above by the dotted lines 7,fig4 #ag74  
,of  course1 these lines of force are   
only imaginary and cannot be seen  in   
any magnet1 but they are always present4
 ,the meaning of this term  lines of    

force1 then1 is used to designate the   
strength of the magnet4    ,many years  
ago the great scientist ,faraday made   
the discovery that1  by passing a closed
 loop of wire through the magnetic lines
 of force  existing between the poles of
 a magnet1 the magnetism produced the   
peculiar effect of creating a current of
 electricity in the wire4 ,if  the      
closed loop of wire were passed down1   
say from ,u to ,d1 the current  flowed  
in the wire in one direction1 and if it 
were passed upward1  from ,d to ,u1 the 
current flowed in the other direction4  
,thus1 you see1  magnetism produces     
electricity in the closed loop of wire  
as it cuts  through the magnetic lines  
of force4 ,just why or how1 nobody      
knows2  we only know that electricity is
 produced in that way1 and to-day we    
make practical use of this method of    
producing it by embodying this          
principle in dynamo-machines1 as we will
 shortly explain4    ,in carrying this  
discovery into practice in making       

dynamo-machines  we use copper wire4 ,if
 iron were used1 there would be a       
current of  electricity generated1 but  
it would be much less in quantity1      
because  iron wire has much greater     
resistance to the passage of electricity
  than the same size of copper wire4    
,perhaps you can understand it more     
thoroughly if we state that when a      
closed loop of wire is passed up and    
down between the poles of a strong      
magnet there is a very perceptible      
opposition felt to the passage of  the  
wire to and fro4    ,this is due to the 
influence of the magnetism upon the     
current produced  in the wire as it cuts
 through the lines of force1 and1       
inasmuch as  these lines of force are   
always present at the poles of a magnet1
 you  will see that1 no matter how many 
times you pass the loop of wire up  and 
down1 there will be created in it a     
current of electricity by its  passage  
through the lines of force4             
,illustration3 ,fig4 #ah    ,suppose    

that1 instead of using one single loop  
of copper wire1 you  wound upon a spool 
a long piece of wire like that in ,fig4 
#ah1 and that  you turned this spool    
around rapidly between the poles of the 
magnet1  you would thus be cutting the  
lines of force by the same wire a great 
many times1 and every time one length of
 the wire cut through the lines  of     
force some electricity would be         
generated in it1 and this would         
continue as long as the spool was       
revolved4 ,but1 as each length would    
only be a part of the one piece of wire1
 you will easily see that there  would  
be a great deal of electricity generated
 in the whole piece of  wire4           
,illustration3 ,fig4 #ai    ,all we have
 to do1 then1 is to collect this        
electricity from the two  ends of the   
wire1 and use it4 ,if we should attach  
two wires to the  two ends of this wire 
on the spool1 they would be broken off  
when it  turned around1 so we must use  
some other method4 ,we fix on the end of

  the spool 7which is called an         
armature7 two pieces of copper1 so that 
they will not touch each other 7as in   
,fig4 #ai71 and fasten the ends  of the 
wire to these pieces of copper4 ,this is
 called a commutator1  and1 as you see1 
is really the ends of the wire on the   
spool4 ,now we  get two thin1 flat      
pieces of copper and fix them so that   
they will  rest upon the copper bars of 
the commutator1 but will not go round   
with  it4 ,these two flat pieces of     
copper are called the brushes1 and they 
will collect from the commutator the    
electricity which is gathered in  the   
wire around the spool4 ,as the brushes  
stand still1 two wires can  be fastened 
to them1 and thus the ampres of current 
of electricity1  acted upon by the volts
 pressure1 can be carried away to be    
used in the  lamps1 for you must        
remember that as long as the spool turns
 around it  gathers more electricity    
while there is any magnetism for the    
wire on  the spool to pass through4 ,the

 constant revolving of the spool creates
  so much electricity that it is driven 
out from the wire on the spool1  through
 the commutator to the brushes1 and     
there it finds a path to  travel away   
from the pressure of the new electricity
 which is all the  time being made4     
,in this way we get a continuous current
 of electricity in the two wires        
leading from the commutator1 and can use
 it to light electric lamps or  for     
other useful purposes4    ,in explaining
 this to you1 so far1 we have used as an
 illustration  of the magnet one of the 
steel permanent magnets in order to make
  the explanation more simple1 but now  
that you understand how the  electricity
 is made1 we must explain to you        
something about the magnets  that are   
used in dynamo-machines4 ,we can perhaps
 make this more clear  by giving another
 example4    ,suppose you had a dynamo  
which was lighting up #ajj of the       
incandescent  lamps1 each of #bjj ohms  
resistance and each requiring #ajj volts

  pressure4 ,now each lamp would take   
just a certain quantity of  electricity1
 say half an ampre2 so1 the #ajj lamps  
would require one  hundred times that   
quantity4 ,but1 if you turned off #ej of
 these lamps  at once1 the tendency     
would be for the pressure to rise above 
the  #ajj volts required for the other  
#ej1 and they would be apt to burn  out 
quicker4 ,it is plainly to be seen1     
then1 that we must have some  means of  
regulating the magnetism so as to       
regulate the lines of force  for the    
wire on the armature to cut through4 ,we
 can do this with an  electromagnet1 but
 not with a permanent magnet1 because we
 cannot  easily regulate the amount of  
magnetism which a permanent magnet will 
give4    ,there is another reason why we
 cannot use permanent magnets in a      
dynamo1 and that is because they cannot 
be made to give as much  magnetism as an
 electromagnet will give4    ,thus you  
will see that there are very good       
reasons for using  electromagnets in    

making dynamo-machines4 ,let us see now 
how these  electromagnets and dynamos   
are made1 and then examine the methods  
which  are followed to operate and use  
them4    ,you must remember1 to begin   
with1 that in referring to wire used  on
 magnets and armatures and for carrying 
the electricity away to  the lamps1 we  
always mean wire that is covered or     
insulated4 ,in  electric lighting1      
insulated wire is always used1 except at
 the  points where it is connected with1
 the dynamo1 the lamps1 a switch1 or    
any point where we make what is called a
 connection4    ,as the shape of the    
magnets is different in the dynamos of  
various  inventors1 we will take for    
illustration the one that is nearest    
the shape of the horseshoe and the shape
 that is generally used in  illustrating
 the principle of the dynamo4 ,this is  
the form used by ,mr4  ,edison1 whom we 
have previously mentioned4 ,this form is
 shown in ,fig4  #bj4    ,now1 although 
this magnet appears to be in one piece1 

it really  consists of five parts       
screwed together so as to make1         
practically1  one piece4 ,the names of  
the parts are as follows3 ,f1 ,f are the
 cores2  ,c the yoke1 which binds them  
together2 and ,p1 ,p the pole pieces1   
where the magnetism is the strongest4   
,these pole pieces are rounded out  to  
receive the armature1 which1 as you will
 remember1 is the part  that turns      
around4    ,illustration3 ,fig4 #bj     
,the cores1 ,f1 ,f1 are first wound with
 a certain amount of wire1 which        
depends upon the use the dynamo is to be
 made for4 ,thus1 you will see1  there  
will be on each core two loose ends of  
the wire that is wound  around          
it--namely1 the beginning of the wire   
and the end where we leave  off winding1
 which on the two cores together will   
make four ends of  wire4 ,we will tell  
you presently what is done with them4   
,after the cores are wound1 they are    
screwed firmly to the yoke and to  the  
pole pieces1 so as to make1 for all     

practical purposes1 one whole  piece    
pretty nearly the shape of a horseshoe  
magnet4    ,illustration3 ,fig4 #ba     
,now1 to make the dynamo complete1 we   
must put in the armature between  the   
poles1 which are rounded off1 as you    
will see1 to accommodate it4  ,the      
armature is held up by two bearings1    
which you will see in the  sketch of the
 complete dynamo above4 7,fig4 #ba47    
,the armature in a practical            
dynamo-machine consists of a large spool
  made of thin sheets of iron firmly    
fastened together and having a steel    
shaft run through the center1 upon which
 it revolves4    ,this spool1 or        
armature1 is wound with a number of     
strands of copper  wire4 ,the           
commutator1 instead of consisting of two
 bars1 is made in  many dynamos with as 
many bars as there are strands of wire1 
and the  ends of these wires are        
fastened to the bars of the commutator  
so as  to make1 practically1 one long   
piece of wire1 just as we showed you in 

explaining how the electricity was      
produced4    ,the brushes1 resting upon 
the commutator1 carry away the          
electricity  from it into the wires with
 which they are connected4    ,now we   
have our dynamo all put together and    
ready to start as soon as  we properly  
connect these four loose ends of wire on
 the cores4    ,if you will turn back to
 ,fig4 #bj you will see that two of the 
wires are  marked ,i1 and the other two 
,o4 ,the letter ,i means the inside     
wire1 or  where the winding began1 and  
the letter ,o means the outside wire1 or
  where we left off winding4    ,now1 if
 we fasten together 7or connect7 the two
 ends of wires1 ,i and  ,o1 near the top
 of the magnet1 we make the two wires   
round the cores  into one wire1 which   
starts1 say1 at ,i near the poles1 goes 
all around  one core1 crosses over and  
around the other core down to the other 
end  of the wire to ,o1 near the poles4 
,so far we have called the iron a       
magnet1 although it is not a magnet     

until electricity is put into it2 so1   
when the dynamo is started  for the     
first time1 these two ends of wire1 ,i  
and ,o1 are connected  to a battery or  
other source of current for the purpose 
of sending  electricity through the wire
 on the cores4 ,when the electricity    
goes  into this wire the iron           
immediately becomes a magnet1 and the   
lines of  force are present at the      
poles4    ,now1 the armature is turned  
around rapidly by a steam-engine1 and1  
as  the wire on the armature cuts the   
lines of force with great rapidity  and 
so frequently1 there is quickly         
generated a large quantity of           
electricity1 which passes out as fast as
 it is made through the  commutator and 
the brushes to the lamp4 ,and so long as
 the armature is  revolved and the      
battery attached1 the electricity will  
be made1 or1 as  it is usually termed1  
generated4    ,as we stated above1 a    
battery is used the first time the      
dynamo is  run1 and now we will explain 

why it is not needed afterward4         
,although iron will not become a        
permanent magnet1 like steel1 it does   
not lose all its magnetism after it has 
been once thoroughly charged4  ,when the
 dynamo is stopped1 after the first     
trial1 and the battery is  taken away1  
you will discover only traces of        
magnetism about the poles4  ,they will  
not readily attract even a needle or    
iron filings2 but there  is1            
nevertheless1 a very small amount of    
magnetism left in the iron4  ,small as  
this magnetism is1 however1 it is enough
 to make very faint  and weak lines of  
force at the poles of the magnet4       
,after the battery is taken away1 the   
ends of the wire on the cores1  which   
were connected to the battery1 are      
connected1 instead1 to the  wires which 
carry away the electricity from the     
brushes to the lamps4  ,thus1 you will  
see1 if any electricity goes from the   
dynamo to the  lamps1 part of it must   
also find its way through the wires     

which are  around the cores4    ,we will
 now start up the dynamo without having 
any battery attached and  see what      
happens4 ,the armature turns around and 
the wires upon it cut  through those    
very faint lines of force which are     
always at the poles4  ,this1 as you     
know1 makes some electricity2 very      
little1 to be sure1 but  it comes out   
through the brushes to the wires leading
 to the lamps1  and there it finds the  
wires leading back to the cores4 ,well1 
part of  this weak current of           
electricity goes into these wires and   
travels back  round the cores and so    
makes the magnetism stronger4 ,the      
consequence of  this is that the lines  
of force become stronger and1 as the    
armature  keeps turning around1 the     
electricity naturally becomes stronger1 
and  so there is more of it going       
through the wires back to the cores and 
increasing the strength of the magnet   
all the time1 until the dynamo  becomes 
strong enough to generate all the       

current it was intended to  give for the
 lamps4    ,of course1 you understand   
that the stronger the magnet becomes1   
the greater will be the lines of force  
and the greater the amount  of          
electricity made by the turning of the  
armature4 ,now1 there is  naturally a   
limit to what can be done with any      
particular dynamo2 so1  while the       
electricity continues to strengthen the 
magnetism and the  magnetism increases  
the electricity1 this cannot go beyond  
what is  called the saturation point of 
the magnet4    ,saturation means that   
the iron is full of magnetism1 and will 
hold  that much but no more4 ,you will  
learn more as to the saturation of      
magnets when you study electricity more 
deeply1 and we therefore do not  intend 
to enter into that subject in this book4
 ,we will only state1  however1 that the
 magnets of dynamos are not always      
charged up to their  saturation point4  
,,the ,,lamps    ,so far you have       
learned how the current of electricity  

is produced1 and  now we will follow    
along the wires to find out how it makes
 the lamps  give out both strong lights 
and the smaller1 pleasant ones4         
,suppose we take first the large1       
dazzling lights we see in the streets1  
which1 as you know1 are called          
,,arc-,,lights    ,those who have seen  
the arc-lamps will readily recognize    
them from the  picture in ,fig4 #bb4    
,you will see that there are two sticks1
 or pencils1 of carbon4 ,now  you will  
remember that in the chapter on         
,magnetism we told you that in  order to
 have electricity do work for us we must
 put some resistance or  opposition in  
its way4 ,when we get light from an     
electric lamp it is  because we make the
 electricity do some work in the lamp1  
and this work  is in pushing its way    
through a resistance or opposition which
 is in  the lamp4    ,illustration3     
,fig4 #bb    ,when we generate          
electricity in the dynamo and put two   
wires for it to  travel in1 the current 

goes away from the dynamo through one of
 the  wires and will go back to the     
dynamo through the other one if it can  
possibly get a chance to get to this    
other one4 ,now1 the electricity  which 
is constantly being made fills the wires
 and acts as a pressure  to force the   
current through the wires back to the   
dynamo1 and1 if we  put no resistance or
 opposition in the way1 it would have a 
very easy  path to travel in and would  
do no work at all4 ,the wires leading to
 an  electric lamp should have very     
little resistance1 not sufficient to    
require any work from the current in    
passing through4    ,so1 if we bring the
 two carbons in an arc-lamp together    
they really  form part of the wire1 and 
do not interrupt the current in its     
travels1 but1 if we separate the        
carbons1 we make a gap which the        
current must jump across if it wants to 
go on4 ,as the volts1 or  pressure1 is  
so great1 the current must jump1 and    
this against the  resistance or         

opposition in an arc-lamp is that which 
gives the  current so much work to do4  
,indeed1 so hard is it for the current  
to  jump across this gap that it breaks 
off from one carbon a shower of  tiny   
particles as fine as the finest dust1   
and makes them white hot in  passing to 
the other4 ,this shower of fine carbon  
dust1 together with  the ends of the    
carbons1 being white hot1 of course     
makes a light1 and  this is the dazzling
 light which you see in the arc-lamp4   
,of course1 when the electricity has    
jumped over from one carbon to the      
other1 it goes through it to the wire1  
and so passes on to the next  lamp1     
where it has to jump again1 and so on   
until it has gone through  the last     
lamp1 then it has an easy path to get   
back to the dynamo4    ,now1 we want you
 to understand more thoroughly how that 
much resistance  or opposition will     
cause heat1 so we will try to give you a
 simple  example4    ,most of you know  
that if you were holding a rope tightly 

in your hands  and some one pulled it   
through them quickly and suddenly1 it   
would get  very hot and your hands would
 feel as though they were being burned4 
,this is heat caused by your hands      
resisting or opposing the passage of    
the rope through them1 and if you could 
hold on tightly enough and the  rope was
 drawn through quickly enough1 it would 
take fire4 ,this fire  would1 therefore1
 cause heat and light4    ,it is just   
this principle of resistance to the     
passage of the current  which causes the
 light in an arc-lamp1 as we have shown 
you4      ,,incandescent ,,lamps    ,you
 have just learned that the light in an 
arc-lamp is caused by the  current      
forcing off from the carbon sticks tiny 
particles and heating  them up until    
they give a brilliant light4 ,so1 you   
see1 in an arc-light  there is a wearing
 away of carbon by electricity1 and     
therefore these  sticks1 or pencils1 of 
carbon in time are all burned away4 ,in 
practice  the carbon pencils last about 

eight or ten hours1 and then new ones   
must be put in4    ,now1 in the         
incandescent lamp there is also carbon  
used1 but the light  is not produced by 
the combustion or wasting away of the   
carbon1 as we  will show you4    ,the   
picture below will show you the         
appearance of an incandescent lamp4     
7,fig4 #bc47    ,illustration3 ,fig4 #bc
    ,you will see that this lamp        
consists of a pear-shaped globe1 and    
inside  is a long ,u-shaped strip of    
carbon no thicker than an ordinary      
thread4  ,this is a strip of bamboo     
cane#a which has been carbonized to a   
thread  of charcoal4 ,it is joined to   
two wires which come through the glass4 
,these two wires come down through the  
bottom of the globe1 and one is         
fastened to a brass screw-ring1 while   
the other wire is fastened to a  brass  
button at the bottom of the lamp4 ,these
 two 7the ring and button7  must1 as you
 know1 be separated from each other by  
something which  will not carry         

electricity1 or they would make a short 
circuit when the  electricity was       
applied4 ,we separate the ring and the  
button in various  ways4    ,now1 if we 
took the ends of two wires which were   
charged with the  proper amount of      
electricity and put one wire on the     
screw-ring and the  other on the button1
 the lamp would light up1 because there 
would be a  complete path for the       
current to travel in4    ,illustration3 
,fig4 #bd    ,it will1 however1 be plain
 to you that it would be awkward to     
light the  lamps in this way1 so we use 
a socket into which the lamp is screwed4
  7,fig4 #bd47    ,the wires from the   
dynamo carrying the electricity are     
connected in the  socket1 one wire with 
the screw thread into which the         
screw-ring fits1  and the other with a  
button which the button on the lamp     
touches when  the lamp is screwed into  
the socket4 ,thus we have a connected   
path for  the current to travel in1 or1 
as it is termed1 a complete circuit4    

,you will notice that in the            
incandescent lamp the electricity does  
not need to jump1 as it does in the     
arc-light1 because we give it one       
continuous line to travel in4    ,in    
order1 however1 to get the current to do
 work for us1 we put some  resistance in
 its path1 which it must overcome in    
order to travel back  to the dynamo4    
,the resistance in an incandescent lamp 
is the ,u-shaped  carbon strip 7or1 as  
it is called1 filament74 ,this charcoal 
filament  has so much greater resistance
 than the wires that it opposes1 or     
resists1 the passage of the electricity 
through it2 but the electricity  must go
 through1 and1 as it is strong enough to
 force its way1 it  overcomes this      
resistance and passes on through the    
carbon to the wire  at the other end4   
,you see it is a struggle between the   
carbon and the  electricity1 the current
 being determined to go on and the      
carbon  trying to keep it back2 and1 in 
the end1 the electricity1 being the     

stronger1 gets the best of it2 but the  
struggle has been so hard that  the     
carbon has been raised to a white heat1 
or incandescence1 and so  gives out a   
beautiful light1 which continues as long
 as the current of  electricity flows4  
,you will remember that in the arc-light
 the carbons are slowly consumed  and   
new ones must be put in4 ,if the carbon 
in the incandescent light  were         
consumed1 it would not last many        
minutes1 because it is only about  the  
size of a horsehair4 ,now1 you will     
naturally inquire why this fine  strip  
is not burned up when it is raised to so
 high a heat4 ,well1 we  will tell you4 
,you know that if you light a match and 
let it burn the wood will all be        
consumed4 ,but did you ever light a     
match1 put it into a small bottle1  and 
put the cork in8 ,if you never did1 do  
so now as an experiment1 and  you will  
see that the match will keep lighted for
 an instant and then  go out without    
consuming the wood4    ,the reasons for 

this are very simple4 ,in order to burn 
anything up  entirely it is absolutely  
necessary to have the gas called oxygen 
present1 and1 as the air you live in    
contains a very large amount of  oxygen1
 there is more than sufficient in your  
room to cause the wood  of the match to 
be entirely consumed after it is        
lighted4 ,but there is  such a small    
quantity of oxygen in the bottle that it
 is not enough to  keep the fire going  
in the match1 and1 consequently1 it will
 not burn  up the wood4    ,the reason  
the filament in an incandescent lamp is 
not burned up is  because there is no   
oxygen inside the globe4 ,after the     
carbon is  put in its place all the     
oxygen is drawn out through a tube1 and 
the  glass is sealed up so that no more 
oxygen can get in4 ,this is called      
obtaining a vacuum1 and vacuum means a  
space without air4    ,there being no   
oxygen in the globe1 it is impossible   
for the carbon to  burn up2 so the      
incandescent lamp will continue to give 

its light for a  very long time1 some of
 them lasting for thousands of hours4   
,some day1  however1 from a great       
variety of obscure causes1 the filament 
becomes  weak in some particular spot   
and breaks1 and the light ceases4 ,when 
this happens1 we unscrew the lamp and   
put another one in1 and the light  goes 
on as usual4    ,now you have learned   
how the incandescent lamp is made to    
give light4  ,we will add that it is a  
beautiful1 soft1 white light1 almost    
without  heat1 it will not explode1     
throws off no poisonous fumes like gas  
or  oil lamps1 and has many other points
 of comfort and convenience which  make 
it very desirable4                      
,,electric-,,light ,,wires    ,before   
closing the subject of electric light   
you would perhaps like to  know         
something about the way in which we     
place the wires leading to  the lamps4  
,illustration3 ,fig4 #be    ,if you     
remember what we told you about         
measurements in the beginning of  this  

book1 it will be easy to understand what
 follows3    ,you know that if you have 
a very great pressure you can force a   
quantity through a small conductor4     
,this is the principle upon which  the  
arc-lamps are run4 ,every arc-lamp takes
 about #dj to #ej volts and  from #e to 
#aj ampres to produce the light1 and    
they are connected with  the wires as   
shown in ,fig4 #be4    ,this is called  
running lamps in series1 and1 as you    
will see from  the sketch1 the wire     
starts out from the dynamo and connects 
with one  carbon of the first arc-lamp1 
and to the other carbon is connected    
another wire which goes on to the next  
lamp1 and so on until the last  lamp is 
reached1 and then the wire goes back to 
the dynamo4 ,this forms1  practically1  
one continuous loop from one brush to   
the other of the  dynamo4    ,the       
current starts out1 makes its way       
through the first lamp1 goes on  to the 
next1 makes its way through that1 and so
 on till it has jumped  the last one2   

then it goes back to the dynamo4        
,now1 as each of these jumps requires a 
pressure of #dj or #ej volts1 you  will 
easily see that the total pressure1 in  
volts1 of the electricity  must be as   
many times #dj or #ej volts as there are
 lamps to be lighted2  so1 if there were
 #fj lamps in circuit1 there would be   
#b1djj to #c1jjj  volts pressure1 which1
 while it gives very fine lights1 might 
cause  instant death to any one touching
 the wires4    ,suppose anything        
happened to the first lamp1 which       
stopped the current  from jumping       
through it4 ,there would be no path for 
the current to  travel farther1 and1    
consequently1 all the lights would go   
out4 ,to get  over this difficulty there
 is sometimes used what is called a     
shunt1  which only acts when the lamp   
will not light4 ,this shunt carries the 
current round the lamp to the other     
wire1 so that it may travel on and      
light up the other lamps4      ,,wires  
,,for ,,incandescent ,,lamps    ,the    

wiring for incandescent lamps is carried
 out in an entirely  different way1     
which you can see by comparing ,fig4 #be
 ,a with ,fig4 #be  which shows the     
wiring for arc-lamps4    ,illustration3 
,fig4 #be ,a    ,this is called         
connecting in multiple arc4    ,you will
 notice that the two wires running out  
from the dynamo 7which  are called the  
main wires7 do not form one continuous  
loop as in the  arc-light system1 but   
that a smaller wire is attached to one  
of the  main wires and then connected   
with the screw-ring in the lamp-socket2 
then another wire is connected with the 
button in the socket and  afterward to  
the other main wire4 ,every lamp forms  
an independent path  through which the  
current can travel back to the dynamo4  
,now1 if we turn one of these           
incandescent lamps out1 we simply shut  
off  one of these paths and the         
electricity travels through the other   
lamps1  and1 if we wish1 we can turn out
 all the lamps but one and there will   

still be a way for the electricity to go
 back to the dynamo4    ,in the         
arc-lamps we must have a very high      
number of volts pressure1  because the  
electricity has only one path1 and it   
all has to pass  through the first and  
other lamps till it comes to the last   
one4 ,in  the incandescent light the    
electricity has as many paths as there  
are  lamps1 so we only need to keep one 
certain pressure in volts in the  main  
wires all the time4 ,this pressure is   
even all the way through  the main      
wires1 and1 therefore1 it is ready to   
light a lamp the instant  it is turned  
on1 because1 as you have seen1          
electricity will always get  back to the
 dynamo if there is a possible chance1  
and the lamp opens a  path4    ,the     
volts pressure used to operate any      
number of incandescent lamps is         
altogether very much less than for a    
number of arc-lights4 ,for example1  in 
the ,edison system the pressure         
7sometimes called electromotive  force7 

is only about #aaj volts1 which is very 
mild and not at all  dangerous4 ,this   
electromotive force would be the same if
 there were  one lamp or ten thousand   
lighted4    ,while this ,edison current 
would not hurt any one1 you should      
remember  that it is much the better    
plan not to touch any electric-light    
wires  until you have learned a great   
deal more on this subject4    ,we may   
add that each of the standard           
incandescent lamps requires only  about 
one-quarter of an ampre of current to   
make them give a light of  #af          
candle-power1 which is about the light  
given by a very good gas-jet1  and while
 the electromotive force1 or pressure1  
would only be about  #aaj volts1 whether
 there were one lamp or ten thousand    
lighted1 there  must be sufficient      
ampres in the wires to give each lamp   
its proper  quantity4      ,,switches   
,we have made mention several times of  
turning on or off one or more  lights1  
and now1 perhaps1 you would like to know

 how this is done4    ,suppose the      
electricity was traveling through wires 
to one or several  lamps1 it would light
 up those lamps as long as the wires    
provided  a path to travel in1 but if   
you were to cut out one of them1 which  
is called breaking the circuit1 there   
would be no road for the  electricity to
 follow1 and1 consequently1 its course  
would be stopped  short and the lamps   
would go out4 ,you will remember that   
electricity  must have a complete       
circuit or it can do no work1 and in    
electric  lighting it is always a       
metallic circuit that is used4    ,now1 
the switch is simply a device which is  
used to break the circuit  so that the  
current cannot pass on4 ,the simplest   
form of switch is seen  in the sketch4  
7,fig4 #bf47    ,illustration3 ,fig4 #bf
    ,you will see that there is a wire  
cut in two1 and to one piece is         
attached a metallic piece1 ,a1 which    
turns one way or the other1 and  when it
 is turned so as to touch the other part

 of the wire the circuit  is closed and 
the electricity goes from the lower part
 of the wire  through the metallic piece
 ,a to the other part of the wire1 thus 
making  a complete circuit or path for  
the electricity to travel in4    ,if we 
turn the piece ,a away from the upper   
wire this breaks the circuit  and cuts  
off the path1 and1 of course1 the lamps 
would go out4    ,this is the principle 
of the switch1 and1 although they are   
made in  thousands of ways1 switches all
 have the same object--namely1 the      
closing and breaking of the circuit1    
whether it is for one or a hundred      
lamps4      ,,wire ,,on ,,dynamos    ,in
 explaining to you the construction and 
working of dynamo-machines1  we did not 
state anything about the amounts of wire
 used in winding the  machine4    ,it is
 not our intention to say exactly how   
much is used on any one  dynamo1 because
 that is among the things you will have 
to learn when  you come to study the    
subject of electricity more deeply4     

,we simply want to have you understand  
that upon the number of turns of  wire  
on any one machine depends the effect   
that that amount of wire1  carrying     
electricity1 will have upon a certain   
weight of iron when the  armature is    
revolved a certain number of turns per  
minute4    ,a certain number of strands 
of wire on an armature will only do a   
certain amount of work at the most1 so  
you will see that a small dynamo  will  
not produce as much electricity as a    
larger one containing more  iron and    
wire4 ,for high pressure there must be  
more strands of wire  cutting the lines 
of force more frequently than would be  
required for  low pressure2 and1 to     
produce a great many ampres1 the        
armature must  be larger and the wire   
upon it thicker than it would need to be
 if only  a small number of ampres were 
wanted4    ,this of itself is a very    
deep and complicated subject1 and many  
books  have been written upon it alone4 
,we shall1 therefore1 not attempt to go 

more deeply into it in this little book1
 but simply content ourselves  with     
giving you the general idea1 which will 
be sufficient until you  make a thorough
 study of the subject4          ,,viii  
,,electric ,,power      ,one of the most
 convenient uses to which electricity is
 put is in  producing motive power for  
driving all kinds of machines1 from a   
sewing-machine to a railway train1 and  
we will now try to explain how  we can  
get this kind of work from electricity4 
,to begin with1 you all know that a     
piece of machinery is usually made  to  
work by revolving a wheel which is part 
of the machine1 either by  means of a   
steam-engine or by water-power1 or1 as a
 sewing-machine1 by  foot-power4 ,now1  
when we work a piece of machinery by    
electricity we do  just the same thing  
by using1 instead of the steam-engine or
 water or  foot power1 an               
electric-engine called an electromotor1 
which operates  in the same way--namely1
 by turning the wheel of the machine it 

is  applied to4    ,foot-power is hard  
work for the person who is applying the 
power1 and1  as you can easily see1 one 
person can make only a very little power
 by  use of the feet4 ,steam and water  
power can be used for any large amount  
of work1 but the work must be within a  
few hundred feet of the engine  or the  
power cannot be used4    ,if there were 
a factory using steam-power a block or  
two away from  where you lived1 and you 
had a lathe in your house which you     
would like  to have run by the          
steam-power in the factory1 it would be 
practically  impossible to do this4     
,now1 if the factory were still farther 
away from  your house1 it would be still
 more impossible1 and if it were a mile 
away it would be foolish to dream of    
taking steam-power from a place so  far 
away4    ,suppose1 however1 that this   
factory was lighted by electric lights1 
it would be a very easy matter to take  
some of the power over to your  house4  
,this could be done1 even if the factory

 were miles away1 by  taking two wires  
from their electric-light wires and     
running them  into your house to an     
electromotor connected with your lathe4 
,this  electromotor would then run your 
lathe just as well as if it were  belted
 to a steam-engine4    ,so1 you see1    
power can be carried in the form of     
electricity through  two wires over very
 great distances and made to do work at 
a long way  from the engine which is    
turning the dynamo to make the          
electricity4  ,thus1 you may have       
brought into your house wires which will
 give lights  and1 at the same time1    
power to run a sewing-machine1 a lathe1 
or any  other piece of machinery4       
,having learned so far that a dynamo    
will make a continuous current of       
electricity1 and that two wires will    
carry this current to any place  where  
it is wanted1 let us now see what takes 
place in the electromotor  to transform 
the electricity into power4    ,an      
electromotor 7which we will now call by 

its short name1 motor7 is  simply a     
machine made like a dynamo4 ,curious as 
it may seem to you1 it  is a fact that  
if you take two dynamo-machines exactly 
alike1 and run  one with the            
steam-engine so as to produce           
electricity1 and then take  the two main
 wires and attach them to the brushes of
 the other dynamo1  the electricity will
 drive this other dynamo so as to       
produce a great  deal of power which    
could be used for driving other         
machines4 ,thus1 the  second dynamo     
would become a motor4    ,in the chapter
 on dynamos we explained something about
 the way they  were made and how the    
electricity was produced4      ,,the    
,,motor    ,you will remember that the  
armature consists of a spool wound with 
wire4 ,this spool is made of iron plates
 fastened together so as to form  one   
solid piece4 ,the armature of a motor   
may be made in the same way2  in fact1  
the whole motor is practically a        
dynamo-machine4    ,there is something  

more about magnetism which we will tell 
you of  here1 because you will more     
easily understand it in its relation to 
an  electromotor4    ,if we take an     
ordinary piece of iron and bring one end
 of it near to  7but not touching7 one  
pole of a magnet1 this piece of iron    
will itself  become a weaker magnet as  
long as it remains in this position4    
,this  is said to be magnetism by       
induction4 ,the end of the piece of iron
  nearest to the magnet will be of the  
opposite polarity4 ,for instance1  if   
the pole of the magnet were north1 the  
end of the iron which was  nearest to   
this north pole would be south1 and1 of 
course1 the other  end would be north4  
,to make this more plain we show it in  
the following  sketch4 7,fig4 #bg47     
,this would be the same whether the     
magnet were a permanent or an           
electromagnet4    ,you will remember    
also that the north pole of one magnet  
will attract  the south pole of another 
magnet1 but will repel a north pole4    

,these are the principles made use of in
 an electromotor1 and we will  now try  
to show you how this is carried into    
practice4    ,illustration3 ,,steel     
,,permanent ,,magnet    ,,iron    ,fig4 
#bg    ,although a motor is made like a 
dynamo1 we will show a different form   
of machine from the dynamo already      
illustrated1 because it will help  you  
to understand more easily4 7,fig4 #bh47 
,here we have an electromagnet with its 
poles1 and an iron armature  wound with 
wire1 just as in the dynamo we have     
described1 except that  its form is     
different4    ,illustration3 ,fig4 #bh  
,a commutator and brushes are also used1
 but the electricity1 instead  of being 
taken away from the brushes1 is taken to
 them by the wires  connected with them4
 ,two wires are also connected which    
take part of  the electricity around the
 magnet1 just as in the dynamo4    ,now1
 when the volts pressure and ampres of  
electricity coming from a  dynamo or    
battery are turned into the wires       

leading to the brushes of  the motor1   
they go through the commutator into the 
armature and round  the magnet1 and so  
create the lines of force at the poles  
and magnetize  the iron of the armature4
    ,let us see what the effect of this 
is4    ,the poles of the magnet become  
north and south1 and the four ends on   
the armature also become north and      
south1 two of each4    ,by referring to 
,fig4 #bh again we shall see what takes 
place4    ,the north pole of the magnet 
is doing two things3 it is repelling1 or
  forcing away1 the upper north pole of 
the armature and at the same time       
drawing toward itself the lower south   
pole of the armature4    ,in the mean   
time the south pole of the magnet is    
repelling the south  pole of the        
armature and at the same time drawing   
toward itself the  north pole of the    
armature4    ,this1 of course1 makes the
 armature turn around1 and the same     
poles  are again presented to the       
magnet1 when they are acted upon in the 

same manner1 which makes the armature   
revolve again1 and this action          
continues as long as electricity is     
brought through the wires to the        
brushes4 ,thus1 the armature turns      
around with great speed and strength1   
and will then drive a machine to which  
it is attached4    ,the speed and       
strength of the motor are regulated by  
the amount of iron  and wire upon it1   
and by the volts pressure and ampres of 
electricity  supplied to the brushes4   
,motors are made from a small size that 
will  run a sewing-machine up to a size 
large enough to run a railway train1    
and are often operated through wires at 
a great distance from the place  where  
the electricity is being made1 sometimes
 miles away4    ,they are also made in a
 great many different forms1 but the    
principle  is practically the same as we
 have just described to you4            
,,ix    ,,batteries      ,so far we have
 only described one way of producing    
electricity--namely1  by means of a     

dynamo-machine driven by steam or water 
power4 ,the supply  of electricity so   
obtained is regular and constant as long
 as the steam  or water power is applied
 to the dynamo4    ,there is another and
 very different way of producing        
electricity1 and  this is by means of a 
chemical process in what is called a    
battery4    ,to obtain electricity from 
the dynamo we must spend money for the  
coal  to make the steam which operates  
the steam-engine1 or for the water      
which turns the water-wheel1 as well as 
for an engineer in both cases4  ,when we
 obtain electricity from a battery we   
must spend money for the  chemicals and 
metals which are constantly consumed in 
the battery4      ,,primary ,,batteries 
,an electrical battery is a device in   
which one or more chemical  substances  
act upon a metal and a carbon1 or upon  
two different metals1  producing thereby
 a current of electricity1 which will   
continue as long  as there is any action
 of the chemicals upon the metal and    

carbon1 or  upon the two metals4        
,batteries for producing electricity may
 be divided into two classes1  called   
open circuit batteries and closed       
circuit batteries4    ,open-circuit     
batteries are those which are used where
 the electricity  is not required       
constantly without intermission--for    
instance1 in  telephones1 electric      
bells1 burglar alarms1 gas-lighting1    
annunciators1  etc4    ,closed-circuit  
batteries are those which are used where
 the effect  produced must be continuous
 every moment1 as1 for instance1 in     
electric  lights and motors4    ,the    
open-circuit battery is made in many    
different ways1 so we only  describe two
 of the principal ones4    ,as we told  
you in an early part of this book1 we do
 not know just what  electricity is1 nor
 why it is produced under the conditions
 existing  in a battery4 ,but we do know
 that by following certain processes and
  making certain chemical combinations  
we can make as much electricity  and in 

such proportions as we want4    ,the two
 metals1 or the metal and carbon1 in a  
battery are called the  elements1 and to
 these are connected the wires which    
lead from the  battery to the           
instruments to be worked by it4    ,the 
,leclanch ,battery4--,this form of      
open-circuit battery consists of  a     
glass jar in which is placed the        
elements4 ,one element consists of a    
rod of zinc1 and the other element is   
carbon and powdered black oxide  of     
manganese4 ,these two 7the carbon and   
black oxide of manganese7 are  placed in
 an earthenware vessel called a porous  
cup4 ,this is simply a  small jar made  
of clay which is not glazed4 ,thus1 the 
liquid which is  in the glass jar       
penetrates through the porous cup to the
 carbon and  manganese which it         
contains1 and so the chemicals affect   
both these  and the zinc at once1 for1  
in order to obtain electricity1 you will
  remember that the chemical action must
 take place at the same time upon  both 

the elements in the same vessel4 7,fig4 
#bi47    ,the chemical substance used in
 this battery is sal-ammoniac1 or salts 
of ammonia4 ,a certain quantity of this 
salt is dissolved in water1  and this   
solution is poured into the glass jar4  
,when this is done the  battery will    
generate electricity at once4           
,illustration3 ,fig4 #bi    ,it should  
be remembered that the proper term for  
the chemical mixture  which acts upon   
the elements in any battery is          
electrolyte4    ,the ,dry               
,battery4--,the cleanliness1            
convenience1 high efficiency1 and       
comparatively low internal resistance of
 the dry cell has brought it  into great
 favor in the last few years4 ,it is now
 extensively used in  preference to the 
,leclanch and other open-circuit        
batteries having  liquid electrolyte for
 light work1 such as bells1             
gas-lighting1 burglar  alarms1 ignition 
on motor-boats1 automobiles1 etc4       
,the dry cell is also used in great     

numbers for pocket flash-lamps1  and in 
other ways where it would be impossible 
to employ batteries  containing liquids4
    ,a dry cell consists of zinc1       
carbon1 and the electrolyte1 which is a 
mixture so made that it is in the form  
of a gelatinous or semi-solid  mass1 so 
that it will not run or slop over4    ,a
 piece of sheet zinc is formed into a   
long tube1 and a round1 flat  piece of  
zinc is soldered at one end1 thus making
 a cup open at one  end4 ,this forms the
 cell itself1 and at the same time      
becomes one of  the elements4 ,the other
 element is a piece of battery carbon   
which is  long enough to project out of 
the top of the cell about half an inch  
or  more4 ,while the cell is being      
filled with the electrolyte the carbon  
is  held up by a support so that it does
 not touch the zinc at the bottom  of   
the cup4 ,of course1 the zinc cup and   
the carbon are provided with  proper    
binding-posts or other attachments1 so  
that conducting wires can  be connected4

    ,the electrolyte is packed into the 
cup and around the carbon in such  a way
 that the cup is entirely filled within 
about half an inch from  the top1 and   
then some melted tar or pitch is poured 
over the top of  the electrolyte4 ,this 
seals the cell and binds the contents   
solidly  together4 ,just before the     
sealing compound hardens1 one or two    
holes  are made in it so that the gases 
may escape4    ,the composition of the  
electrolyte itself is not exactly alike 
in all  dry cells1 as the various       
manufacturers follow their own          
particular  formulas4 ,however1 as you  
may be curious to know something about  
it1 we  would state that one formula    
embraces flour1 water1 plaster of       
,paris1  granulated carbon1 zinc        
chloride1 ammonium chloride1 and        
manganese  binoxide4    ,you will       
remember that the ,leclanch and the dry 
batteries are purely  open-circuit      
cells1 and that they can be used to     
advantage for electric  bells1          

annunciators1 burglar alarms1 gas       
ignition1 etc41 where the  current of   
electricity is not doing continuous     
work1 but only for a  few seconds at a  
time4 ,consequently1 the batteries have 
a little rest  in between1 if only for a
 few seconds4    ,now1 if we were to    
attempt to use open-circuit batteries   
for electric  lights or motors1 where   
the electricity must work constantly    
every  second1 the batteries would      
polarize--that is to say1 they would    
only  work a few minutes and then stop1 
because the chemicals used in them  are 
of that kind that they will only allow  
the battery to do a little  work at a   
time4    ,the batteries we have been    
describing will do the ordinary work for
  which they are intended for sometimes 
a year without requiring any  attention1
 but if we try to make them do work for 
which they were not  intended1 they     
would only last a few days4    ,if we   
should want to operate electric lights  
or motors continuously  from a battery  

we must1 therefore1 use                 
,,closed-,,circuit ,,batteries    ,there
 is a great variety of ways in which    
closed-circuit batteries  are made1 but1
 as the main principles are very much   
alike1 we will  only describe two       
general kinds1 those with and those     
without a porous  cup4#b    ,in the     
first place1 we must state that         
closed-circuit batteries proper  usually
 consist of a glass jar and two         
elements--carbon and zinc4  ,sometimes a
 porous cup is used2 for what reason you
 will soon learn4    ,the chemicals that
 are used are usually different from    
those used in  the open-circuit         
batteries and are much stronger4 ,these 
chemicals are  usually sulphuric acid   
and bichromate of potash 7or chromic    
acid71  which are mixed with water4     
,we will now examine two of the types of
 closed-circuit batteries1  taking first
 the one without the porous cup1 of     
which the ,grenet is a  good example4   
,illustration3 ,fig4 #cj    ,this       

battery1 as you see1 consists of a glass
 jar1 in which are placed  two plates of
 carbon and one of zinc4 7,fig4 #cj47   
,the latter is between  the two carbon  
plates and is movable up and down1 so   
that it may be  drawn up out of the     
solution when it is not desired to use  
the battery4  ,when the zinc is in the  
solution there is a steady and          
continuous  current of electricity      
developed1 which can be taken away by   
wires from  the connections on top of   
the battery4    ,if the zinc were left  
in the solution when the battery was not
 in use1  the acid would act upon it    
almost as much as though the electricity
  were not being used1 and thus the zinc
 would be eaten away and the acid  would
 be neutralized1 so that no more action 
could be had when we  wanted more       
electricity4    ,now1 in the ,grenet    
battery we can light a lamp or run a    
motor for  several hours continuously1  
but at the end of that time the solution
  would become black and it would do no 

more work4 ,then we must throw out  that
 solution and put in fresh1 and the     
battery will do the same work  again1   
and so on4    ,if you should only want  
to light your lamp or run your motor for
 a few  minutes1 you could pull the zinc
 up from the solution and put it down   
again when you wanted the electricity   
once more4 ,the carbon element in  the  
battery is not consumed by the acid1    
although the zinc is4    ,illustration3 
,fig4 #ca    ,now you will see the use  
of the porous cup4 ,we will take as an  
illustration of this type an ordinary   
battery in which a porous cup is  used4 
7,fig4 #ca47    ,here1 you will see1 the
 carbon is placed in the porous cup1    
while the  zinc is outside in the glass 
jar4 ,in the glass cell with the zinc   
is usually used water made slightly     
acid1 and the strong solution of        
sulphuric acid and bichromate of potash 
7or chromic acid7 is poured in  the     
porous cup1 where the carbon is placed4 
,the strong solution penetrates the     

porous cup very slowly and gets to  the 
zinc1 when it immediately produces a    
current of electricity4 ,but  the acid  
does not get at the zinc so freely as it
 does in the battery  without a porous  
cup1 and1 consequently1 neither the acid
 nor the zinc  is so rapidly used up4   
,where porous cups are used1 the        
batteries will give a continuous        
current for a very much longer time than
 without them1 and will1  sometimes1    
give many hours' work every day for     
several months without  requiring any   
change of solution4                     
,polarization4--,there is one other     
reason why a longer working time  can be
 had from a battery with a porous cup1  
and that is1 in a battery  without a    
porous cup the action of the acid upon  
the zinc is so rapid  that the carbon   
plates become covered with gas1 and1    
therefore1 the  proper action by the    
acid cannot take place upon them4 ,thus1
 the  battery ceases to work1 and is    
said to be polarized4 ,when a porous    

cup is used1 the action of the acid upon
 the zinc is slow enough to  give off   
only a small amount of gas1 and thus the
 acid has a chance to  act upon the     
carbon plates and develop a steady      
current of electricity4      ,,the      
,,work ,,done ,,by ,,batteries    ,the  
pressure and quantity of electricity    
given off continuously by open  and     
closed circuit batteries is very        
different4    ,the pressure 7or         
electromotive force7 of one cell of an  
ordinary  open-circuit battery is only  
about one volt1 and the current is      
usually  very much less than one ampre1 
except in a dry cell1 which may give    
more4    ,in the closed-circuit         
batteries described1 the electromotive  
force  of each cell is about two volts1 
while the current varies from #a to     
perhaps #ej ampres1 according to the    
size of the zinc and carbon plates4     
,it would not matter if you made one    
cell as big as a barrel1 nor if you  put
 in a dozen carbons and zincs1 the      

electromotive force would not  exceed   
the volts mentioned for each type of    
battery1 but the ampre  capacity would  
be greater than in a smaller cell on    
account of the  larger size of the      
carbon and zinc plates4    ,internal    
,resistance4--,there is one other point 
which affects the  number of ampres     
which can be obtained from a            
closed-circuit battery1  and that is    
whether there is a large or small       
internal resistance in  the battery     
itself4    ,this depends upon the       
solution which is used and the          
arrangement of the  plates4    ,if there
 is a high resistance in the battery    
itself 7called internal  resistance71   
the electricity must do work to overcome
 this resistance  before it can get out 
of the battery to do useful work through
 the  wires1 and1 consequently1 the     
capacity in ampres is limited4    ,if1  
on the other hand1 there is very little 
resistance in the battery1  the current 
has very little work to flow to the     

wires leading from the  battery1 and we 
can get a larger quantity1 or greater   
number of ampres4    ,thus1 you will see
 that while the closed-circuit battery  
is the  stronger1 and will do all that  
the open-circuit battery will do1 and   
even more1 in a short time the latter1  
though weaker1 will do about as  much   
work for the same amount of zinc and    
carbon as the former1 but  takes a much 
longer time4      ,,batteries ,,for     
,,electric ,,light    ,as we have       
explained to you1 closed-circuit        
batteries are used for  producing       
incandescent electric lights in small   
numbers1 as well as  for running motors4
    ,to operate incandescent lights1 a  
number of batteries connected  together 
are used4 ,the number used depends upon 
the pressure which the  lamps require to
 make them give the required light4 ,we 
will now explain  how the batteries are 
connected together for this purpose4    
,illustration3 ,fig4 #cb    ,suppose you
 wished to light an incandescent lamp   

of1 say1 three  candle-power1 which     
required six volts4 ,we would take three
  closed-circuit batteries which would  
each give two volts1 and connect  by a  
piece of wire the zinc of the first to  
the carbon of the second1  and the zinc 
of the second to the carbon of the      
third1 as shown in the  sketch4 7,fig4  
#cb47    ,we would then attach a wire to
 the carbon of the first and one to the 
zinc of the third1 and there would be   
six volts in these two wires1  which    
would light up one six-volt lamp nicely4
    ,this is called connecting in       
series1 or for intensity4    ,now if    
each of these cells gave ten ampres     
alone1 the three will only  give ten    
ampres together when they are connected 
in series4    ,if our lamp only required
 one ampre1 you would naturally think   
that  ten similar lamps put on the wires
 would give as good light as the one1   
but that is not so4    ,although you    
might light up two lamps1 the pressure  
would drop and the  lights would become 

less brilliant if you put on the whole  
number4 ,so1  if we wished to put on the
 whole ten lights we would connect      
another  battery and thus increase the  
pressure1 which would probably make     
these  ten lamps burn brightly4         
,these rules hold good for connecting   
any number of batteries for lamps  of   
any number of volts--that is to say1    
there should be calculated  about two   
volts for each cell and an allowance    
made for drop in  pressure4             
,,connecting ,,in ,,multiple    ,there  
is another way of connecting batteries1 
and that is to obtain a  larger number  
of ampres4 ,this is called connecting in
 multiple arc1  or for quantity4        
,illustration3 ,fig4 #cc    ,let us take
 again for an illustration the three    
cells giving each #b  volts and #aj     
ampres4 ,this time we connect the carbon
 of the first to  the carbon of the     
second1 and the carbon of the second to 
that of the  third2 then we connect the 
zinc of the first to that of the second1

 and  the zinc of the second to that of 
the third1 as shown in the sketch4      
7,fig4 #cc47    ,we then attach a wire  
to the zinc and one to the carbon in the
 third  cell1 and we then can obtain    
from these two wires only #b volts1 but 
#cj ampres4    ,there are1 again1 many  
ways of connecting several of these sets
  together1 but it is not intended in   
this book to go into these  at length1  
for the reason that we only set out to  
give a simple  explanation of the first 
principles of this subject4    ,we shall
 therefore only give an illustration of 
one more method of  connecting batteries
 which will be easy to understand4 ,this
 is called      ,,multiple ,,series     
,the sketch we have last given shows    
three batteries connected in  multiple4 
,these we will call set ,no4 #a4        
,now1 suppose we take three more        
batteries exactly similar and connect   
them together just in the same manner4  
,let us call this set ,no4 #b4 ,now     
take the wire leading from the carbon of

 set ,no4 #b and connect it with  the   
wire leading from the zinc of set ,no4  
#a4 ,then take a wire leading  from the 
zinc of set ,no4 #b1 and a wire leading 
from the carbon of set  ,no4 #a1 and    
connect them with the lamps or motors4  
,these two sets being  connected in     
multiple series1 we shall get #d volts  
and #cj ampres4    ,this is called      
connecting in multiple series1 and may  
be extended  indefinitely with any      
number of batteries4    ,we should add  
that one of the elements in a battery is
 called  positive1 and the other        
negative4      ,,the ,,edison ,,primary 
,,battery    ,as this type of battery   
will work efficiently on either open or 
closed circuit1 we have thought best to 
describe it separately at this  place1  
in order not to confuse your ideas while
 reading about batteries  generally4    
,the type of cell we will now describe  
was originated by an inventor  named    
,lalande1 and was known by that name2   
but it has been greatly  improved and   

rendered more efficient by ,edison1 and 
is now manufactured  and sold by him    
under the name of the ,edison ,primary  
,battery4    ,before describing the cell
 itself1 let us consider the action that
  takes place in a battery of this kind4
    ,if certain metals are placed in a  
suitable solution1 and are connected    
together1 outside of the solution1 by   
wires1 vigorous chemical action  will   
take place at the surfaces of the       
metals1 and electrical energy  will be  
produced4 ,the plates must be of        
different metals1 and the  solution     
should be one that will dissolve neither
 of them except when  an electric       
current is allowed to flow4    ,one of  
the metals is usually zinc1 which is    
gradually eaten away or  dissolved by   
the solution while the battery is       
delivering electrical  energy4 ,it is   
the chemical combination of the zinc and
 the solution  that produces this       
energy1 which leaves the zinc in the    
form of an  electric current1 and passes

 through the solution to the other      
metal1  out of the cell to the wire1 and
 thence back by another wire to the     
zinc1 where it is once more started on  
its circuit4    ,at the surface of the  
other metal1 which may be1 and          
frequently is1  copper1 small bubbles of
 the gas called hydrogen are produced4  
,this gas  rises to the surface of the  
liquid and gradually passes off into the
  air4 ,but its presence offers         
resistance to the passage of the        
current2  so that generally there is    
associated with the copper a supply of  
the  gas oxygen4 ,oxygen and hydrogen   
are always very eager to mix with  each 
other1 and1 therefore1 when the hydrogen
 bubbles appear they are  quickly taken 
up by the oxygen near by4 ,the mixture  
of these two gases  forms water1 which  
becomes part of the solution4 ,all of   
this happens so  quickly that the       
hydrogen cannot be perceived so long as 
there is any  oxygen left in the        
copper-oxide plate4    ,illustration3   

,fig4 #cd    ,in the ,edison ,primary   
,battery 7,fig4 #cd7 the plates are     
zinc1 known as  the negative1 and copper
 oxide 7copper and oxygen71 or the      
positive4  ,these are suspended in a    
solution of caustic soda and water1 the 
plates  and solution being contained in 
jars of glass or porcelain4 ,the plates 
are provided with suitable wires for    
connecting the cells with one  another  
and with the lamps1 motors1 or other    
devices which they are to  operate4     
,there are usually two zinc plates and  
one copper-oxide plate1  or multiples   
thereof4 ,the quantity of current that  
may be withdrawn  depends on the size   
and number of the plates1 as well as    
upon their  construction and            
arrangement4    ,the voltage of these   
cells is low1 being about #j4fe volt    
each2 but this  is more than compensated
 for by the fact that the internal      
resistance  of the battery is so low    
that the voltage is not perceptibly     
affected  even at continuous            

high-discharge rates1 and that the      
voltage remains  practically constant   
throughout the life of the cell4        
,furthermore1 when the battery is not in
 use there is practically no  local     
action4 ,consequently1 the cells may    
remain on open circuit 7that  is1 doing 
no work7 for years and there will be no 
loss of energy4 ,the  cell will then    
operate with the same practical         
efficiency as if it were  new4 ,in some 
classes of work this battery remains in 
service from four  to six years without 
attention4    ,another peculiar         
advantage of this battery lies in the   
fact that the  plates and the           
electrolyte are so well proportioned    
that they are all  exhausted at the same
 time1 and then new plates and solution 
can be put  in the jar1 restoring it to 
its original condition4 ,these batteries
 are  used in great numbers for railway 
signal work and for other purposes1     
such as fire and burglar alarm systems1 
various telephone functions1  operation 

of electric self-winding and programme  
clock systems1 small  electric-motor    
work1 for low candle-power electric     
lamps1 gas-engine  ignition1            
electro-plating1 telegraph systems1     
chemical analysis1 and  other           
experimental work where batteries are   
required that will remain  in use for   
long periods of time without requiring  
any attention or  renewal4    ,the      
remarks that have been made on previous 
pages about connecting up  batteries in 
series1 multiple1 and multiple series   
apply also to these  ,edison ,primary   
,cells4 ,fig4 #ce shows a battery of    
four of these cells  connected in       
series4      ,,secondary1 ,,or          
,,storage1 ,,batteries    ,the open and 
closed circuit batteries we have so far 
described are used  to produce          
electricity by the action of the        
chemicals upon the elements  contained  
in them4 ,they are called primary       
batteries4    ,illustration3 ,fig4 #ce  
,the batteries which we will now tell   

you of are called secondary1 or         
storage1 batteries1 and do not of       
themselves make any primary current1    
but simply act as reservoirs1 so to     
speak1 to hold the energy of the        
electric current which is led into them 
from a dynamo or primary  battery4 ,at  
the proper time and under proper        
conditions these secondary  batteries   
will give back a large percentage of the
 energy of the  electric current which  
has been stored in them4    ,this class 
of battery has been called by these     
three names3 secondary  battery1        
accumulator1 and storage battery2 but as
 the latter name  is used almost        
exclusively in this country1 we shall   
use it in the  following description4   
,,two ,,types    ,there are two distinct
 types of storage battery4 ,one is      
called the  lead or acid storage        
battery1 and the other the alkaline or  
nickel-iron storage battery4 ,each of   
them simply acts as a reservoir  to hold
 the energy of the electric current     

which is led into it1 and  each of them1
 under proper conditions1 will give back
 that energy4  ,as the lead storage     
battery is the oldest in point of       
discovery and  invention1 we will       
describe it first4      ,,the ,,lead    
,,storage ,,battery    ,a lead storage  
battery usually consists of a glass or  
hard-rubber jar  containing lead plates 
and a solution consisting of water and  
sulphuric  acid4 ,a single unit is      
usually called a cell4 7,fig4 #cf47     
,there are always at least two lead     
plates in a storage-battery cell of     
this kind1 although there may be any    
number above that4 ,for the sake of     
making a clearer explanation to you1 we 
will take as an illustration a  cell    
containing only two plates4#c           
,illustration3 ,fig4 #cf    ,we have1   
then1 a glass or hard-rubber jar        
containing two lead plates  and a       
solution consisting of water and        
sulphuric acid4 ,these plates are       
called the elements1 and one is called  

the positive and the other the  negative
 element4 ,the solution is called the   
electrolyte4    ,the positive element is
 a sheet of lead upon which is spread a 
paste  made of red-lead4 ,the negative  
element is a similar sheet of lead upon 
which is spread a paste made of         
litharge4    ,now1 when these plates are
 thus prepared1 they are put into the   
acid  solution in the jar1 and a wire   
attached to each plate is connected     
with the two wires from a dynamo or     
other source of electric current1  just 
as a lamp would be connected4    ,the   
electric current then goes into the     
storage-battery cell1 entering  by the  
positive plate and coming out by the    
negative4 ,these plates  and the paste  
upon them offer some resistance1 or     
opposition1 to the  passage of the      
current1 so the electricity must do some
 work to get  from one to the other4    
,the work it does in this case is to so 
act upon  the paste that its chemical   
nature is changed4    ,so1 after the    

primary current has been passed from one
 plate to the  other for some time1 and 
after several discharges1 the storage   
battery may be disconnected1 being now  
formed4    ,the paste on the lead plates
 is now found to have changed its       
chemical  nature1 the paste on the      
positive plate having been transformed  
into  peroxide of lead1 and that on the 
negative plate into spongy lead4 ,on    
arriving at this condition1 the paste on
 the plates is called active  material4 
,this process of formation is absolutely
 essential before the lead  storage     
battery is ready to be used for actual  
work4 ,so1 when the  plates have been   
fully formed1 the storage battery may be
 again  connected with a source of      
electric current which again enters by  
the  positive plate and leaves by the   
negative4 ,this current so acts on the  
active material that it combines with   
the acid solution and1 through  the     
energy of the charging current1 forms   
other chemical compounds  which may for 

convenience be called sulphates4 ,when  
the charging  current has flowed through
 the battery long enough to produce     
these  changes in the active material   
the battery is said to be charged1 and  
is ready for useful work4    ,if the two
 wires attached to the plates are now   
connected with electric  lamps1 or a    
motor1 or other device1 the active      
material will develop  energy in the    
effort to again change its nature4 ,this
 energy takes  the form of an electric  
current1 which leaves the battery and   
passes  through the conductors and      
operates the lamps1 motors1 or other    
devices  in its passage4    ,in this way
 the battery is said to be discharged1  
and at the end  of its discharge it can 
again be charged and discharged in a    
similar  manner for a long time1 until  
the active material is either used up or
  drops off the plates4    ,so far as   
the actual details of construction are  
concerned1 lead  storage batteries are  
made in a great many different ways1 but

 the  materials are1 in general1 of the 
same nature as those we have  mentioned 
above4      ,,the ,,alkaline ,,storage  
,,battery    ,we shall now describe an  
entirely different type of storage      
battery1  which contains neither lead   
nor acid4 ,it is one of the many        
inventions  of ,thomas ,a4 ,edison4     
,in the alkaline storage battery the gas
 called oxygen plays a very  important  
part1 and we will try to make it clear  
to you what this part  is4    ,you are  
well aware of the fact that if you leave
 your pocket-knife  out in the air it   
will get rusty4 ,the reason for this is 
that iron or  steel quickly tends to    
combine with the oxygen of the air1 and 
this  combination of oxygen and iron is 
rust1 otherwise called oxide of iron1   
or iron oxide4    ,this iron oxide1 or  
rust1 is therefore the result of a      
chemical action  between the iron and   
the oxygen4    ,now as all chemical     
actions require the expenditure of      
energy1 there  has been developed either

 heat or electricity in the process4    
,the  oxygen may be taken away from the 
iron oxide1 chemically2 but here  again 
would be another chemical action which  
would require energy to be  once more   
expended4    ,iron oxide may be made    
chemically in many different ways4 ,it  
is  frequently made in the form of a    
powder4 ,therefore1 we do not have to   
depend upon iron rust for a supply of   
this material4    ,before going further 
we must consider another oxide--namely1 
nickel  oxide4 ,it is characteristic of 
nickel that when it is combined with    
oxygen to a certain degree so as to form
 the compound known as nickel  oxide1 it
 will receive still more oxygen4        
,now1 if under proper conditions we     
compel iron oxide to give up its  oxygen
 to some other kind of chemical         
compound1 such as nickel oxide1  we must
 expend energy4 ,but1 on the other hand1
 if this nickel oxide  gives back the   
oxygen to the iron--which it will do if 
opportunity is  given--there is energy  

produced again in receiving the oxygen4 
,in other  words1 the energy previously 
expended1 or part of it1 is now         
returned4    ,this action and reaction  
are practically those that take place in
 the  ,edison alkaline storage battery4 
,for simplicity of illustration we  will
 consider a cell containing only two    
plates1 one positive and one  negative4 
,the negative plate is made up of a     
number of small1 flat1 perforated       
pockets containing iron oxide in the    
form of a fine powder4 ,the  positive   
plate is made up of small1 perforated   
tubes containing  nickel oxide mixed    
with very thin flakes of metallic       
nickel4 7,fig4 #cg  illustrates these   
plates1 the positive being in front47   
,illustration3 ,fig4 #cg    ,these two  
elements1 positive and negative1 having 
wires or conductors  attached1 are      
placed in a nickeled-steel can          
containing the  electrolyte1 which      
consists of a potash solution4 ,you will
 see that  this differs from a lead     

storage battery1 in which the           
electrolyte is  sulphuric acid and      
water4 ,if we were to put this acid     
solution into a  metallic can 7except   
one made of lead7 the can would not last
 long1 as  the acid would quickly eat   
holes through it4    ,now let us see    
what takes place in the ,edison alkaline
 storage  battery4 ,if an electric      
current from a dynamo or other source of
  electricity is caused to pass through 
the positive to the negative  plate the 
oxygen present in the iron oxide passes 
to and remains with  the nickel oxide4  
,during all the time this is going on   
the battery is  said to be charging1 and
 when all the oxygen has been removed   
from  the iron oxide and is taken up by 
the nickel oxide1 then the battery  is  
said to be charged1 and the flow of     
current into the battery is  stopped4   
,a change has now taken place4 ,the     
powder in the negative plate is no      
longer iron oxide1 but has been reduced 
to metallic iron1 because the  oxygen   

has been removed4 ,the powder in the    
positive plate is now raised  to a      
higher or super oxide of nickel1 because
 it has taken the oxygen  that was in   
the iron4    ,but the nickel oxide will 
readily give up its excess of oxygen1   
and the  iron will receive it back      
freely if permitted4 ,if the proper     
conditions  are established1 this       
transfer of oxygen will take place1 but 
the iron  cannot receive it without     
delivering energy4    ,illustration3    
,fig4 #ch    ,the proper conditions are 
established by providing a conducting   
circuit between the two elements1 in    
which lamps1 motors1 or other           
electrical devices are placed4 ,as soon 
as this circuit is provided1 the        
opportunity is given to the iron to     
receive the oxygen4 ,this it does1  and 
in so doing develops electrical energy4 
,this energy is in the form of electric 
current which is then delivered  by the 
battery on what is called the discharge1
 and this current may  be used for      

lighting lamps or for operating motors  
or other electrical  devices4    ,the   
battery is said to be discharging as    
long as the iron is receiving  oxygen   
from the nickel oxide4 ,as soon as it   
becomes iron oxide once  more1 the      
giving out of energy ceases and the     
battery is said to be  discharged1 and  
must again be charged to obtain further 
work from it4  ,such a battery can be   
charged and discharged an indefinite    
number of  times4    ,this type of      
battery is very rugged1 and its         
combinations are not  self-destructive4 
,it is very simple1 as it provides      
chiefly for the  movement of the oxygen 
back and forth2 besides1 it gives much  
more  current for its weight than the   
lead type of storage battery4 7,fig4 #ch
  shows the plates of a standard ,edison
 cell removed from container47          
,,connecting ,,storage ,,batteries      
,on the discharge1 one cell of a lead   
storage battery gives an average  of    
about #b volts1 and a cell of alkaline  

storage battery about #a4b  volts1 no   
matter what its size or the number of   
plates may be4 ,when  there are more    
than two plates in one cell1 all the    
positives in that  cell are connected   
together by metallic strips or bands1   
and all  negatives in the cell are      
connected together in a similar way4    
,although we cannot obtain more than the
 above-named electromotive  force from  
one cell of either type of storage      
battery1 we can obtain a  greater ampre 
capacity by using large plates instead  
of small ones1 or  by using a larger    
number of small size4    ,the same      
effects are produced by connecting the  
cells in series1 or  multiple1 or       
multiple series1 as we showed you in    
regard to primary  batteries2 and the   
storage batteries may be charged as well
 as  discharged when connected in any   
one of these ways4      ,,charging      
,,current    ,the current which is used 
for charging must always be greater in  
pressure than that of the storage       

batteries which are being charged4 ,if  
it is not1 the storage batteries will be
 the stronger of the two and  will      
overpower the charging current and so   
discharge themselves4          ,x       
,,conclusion      ,we will now bring    
this little volume to a close1 having   
given you a  brief outline of the       
simplest rudiments of that wonderful    
power of  nature1 ,electricity4    ,we  
may compare this subject to a beautiful 
house the inside of which  you would    
like to examine from top to bottom4 ,we 
have opened the door  for you2 now walk 
in and examine everything4 ,there may be
 a great many  stairs to climb1 but what
 you see and learn will repay for all   
the  trouble4      ,,the ,,end          
,,footnotes3    #a ,the filaments in    
modern ,mazda lamps1 as made at the     
,edison ,lamp  ,works1 are strips of    
metallic tungsten4    #b ,the batteries 
we will now describe are for            
closed-circuit work  only1 and they are 
never used for open-circuit work4 ,but  

there is  a type of battery made that is
 available for either open or closed    
circuit operation4 ,this is the ,edison 
,primary ,battery1 which will be        
described later on4    #c ,practically1 
there is always one more negative plate 
than positive  plates in a regular      
storage-battery cell4 ,consequently1 a  
standard  cell always contains an odd   
number of plates4                       
,,transcriber',s ,,note    -,plain print
 and punctuation errors fixed4