,,the ,,library ,,of ,,work ,,and ,,play ,,carpentry ,,and ,,woodwork ,by ,edwin ,w4 ,foster ,,electricity ,,and ,,its ,,everyday ,,uses ,by ,john ,f4 ,woodhull1 ,ph4,d4 ,,gardening ,,and ,,farming ,by ,ellen ,eddy ,shaw ,,home ,,decoration ,by ,charles ,franklin ,warner1 ,sc4,d4 ,,housekeeping ,by ,elizabeth ,hale ,gilman ,,mechanics1 ,,indoors ,,and ,,out ,by ,fred ,t4 ,hodgson ,,needlecraft ,by ,effie ,archer ,archer ,,outdoor ,,sports1 ,,and ,,games ,by ,claude ,h4 ,miller1 ,ph4,b4 ,,outdoor ,,work ,by ,mary ,rogers ,miller ,,working ,,in ,,metals ,by ,charles ,conrad ,sleffel4 ,illustration3 ,drawing by ,j4 ,hodson ,redman4 ,harold ,sending the ,c4 ,q4 ,d4 ,message 7,see page #cee74 ,the ,library of ,work and ,play ,,electricity ,,and ,,its ,,everyday ,,uses ,,by ,,john ,f4 ,,woodhull1 ,,ph4,d4 ,illustration ,mc,g,o,w,e,n-,,maier ,,co4 ,,chicago1 ,,ill4 ,,all ,,rights ,,reserved1 ,,including ,,that ,,of ,,translation ,,into ,,foreign ,,languages1 ,,including ,,the ,,scandinavian ,,copyright1 #aiaa1 ,,by ,,doubleday1 ,,page ,,company ,,preface ,why do we pursue one method when instructing an individual boy out of school1 and a very different method when teaching a class of boys in school8 ,the school method of teaching the dynamo is to begin with the bar magnet and1 through a series of thirty or forty lessons on fundamental principles1 lead up to the dynamo1 which is then presented1 with considerable attention to detail1 as a composite application of principles4 ,this might be styled the synthetic method4 ,he who teaches a boy out of school is pretty likely to reverse this order and pursue the analytic method4 ,the class in school has very little influence in determining the order of procedure4 ,the lone pupil with his questions almost wholly determines the order of procedure4 ,out of school no one has the courage to deny information to a hungry boy2 in school we profess to put a ban upon information giving1 and we do quite effectually deaden his sense of hunger4 ,the school method rarely yields fruit which lasts beyond the examination period2 on the other hand1 a considerable number of boys have become electrical experts without the aid of a school4 ,this book is the story of how my boy and ,i studied electricity together4 ,we have had no other method than to attack our problems directly1 and principles have come in only when they were needed4 ,my boy had learned to read when very young by having stories read to him while he watched the printed pages4 ,the construction of sentences out of words and words out of letters had come to him very incidentally but all in due time1 and when he first went to school rather late in life for a beginner he found himself more proficient than the other boys of his own age both in reading and in understanding the printed pages4 ,i could see no good reason why he should not pursue the same method in studying electricity4 ,we live in a modern apartment house in a great city4 ,my boy likes to visit engine rooms and talk with the engineers about their machinery4 ,his mother and ,i always encourage him to talk with us about the things in which he is most interested4 ,if the family is alone at dinner1 he is quite likely to lead the conversation into the field of electricity4 ,when particularly burdened with my work ,i have learned to find relief by giving an afternoon to ,harold1 who generally takes me to some electrical store or power station or to ride by electric train out into the country4 ,,contents ,,chapter ,,page ,i4 ,the ,dynamo and ,the ,power ,station #c ,,ii4 ,dynamo continued--,the ,magnet #aa ,,iii4 ,the ,ammeter #be ,,iv4 ,the ,wattmeter #ce ,v4 ,the ,electric ,motor #dc ,,vi4 ,applications of the ,electro-magnet #eg ,,vii4 ,electric ,heating #ig ,,viii4 ,applications of ,electric ,heating #ajg ,,ix4 ,lighting a ,summer ,camp by ,electricity #afj ,x4 ,how ,electricity ,feels #afh ,,xi4 ,the ,electric ,sparking ,equipment for a ,gasolene ,engine #agh ,,xii4 ,electricity ,from ,central ,stations #bjd ,,xiii4 ,electricity ,from an ,old ,mill #bah ,,xiv4 ,doing ,chores by ,electricity #bdj ,,xv4 ,electric currents from ,chemical ,action and ,chemical ,action from ,electric ,currents #bdh ,,xvi4 ,electrocution at ,millville #bga ,,xvii4 ,the ,telephone #bgd ,,xviii4 ,electric ,bell ,outfit for the ,cottage #bif ,,xix4 ,using ,electricity to ,aid the ,memory #cjj ,,xx4 ,the ,electric ,brick ,oven #cje ,,xxi4 ,electric ,waves #cji ,,xxii4 ,ringing ,bells and ,lighting ,lamps by ,electric ,waves #cbd ,,xxiii4 ,telegraphing by ,electric ,waves #cbi ,,xxiv4 ,halley's ,comet and ,electric ,waves #ccc ,,xxv4 ,how the ,idea of a ,universal ,ether ,developed #cci ,,xxvi4 ,electric ,currents ,cannot ,be ,confined to ,wires #cdi ,,xxvii4 ,wireless ,telegraphy ,in ,earnest #cee ,,illustrations ,harold ,sending the ,c4 ,q4 ,d4 ,message ,frontispiece ,,facing ,,page ,testing a ,generator #h ,wiring #af ,wattmeter #dj ,testing the ,telegraphy ,outfit #fb ,electric ,bell #gb ,feeling ,electricity #agd ,operating the ,switchboard #bjd ,induction ,coil of a ,wireless #ccj ,,electricity ,,and ,,its ,,everyday ,,uses ,i ,,the ,,dynamo ,,and ,,the ,,power ,,station ,one day ,harold expressed a desire to see the dynamos1 five miles away1 which furnish the electric light in our apartment4 ,so ,i told him to invite his best friend to accompany us and we would go4 ,when we were some distance from the station the boys noticed the very tall chimneys and inquired why tall chimneys were needed for dynamos4 ,i explained that the dynamos were run by steam-engines1 and steam-engines required the burning of coal4 ,oh6 said ,ernest1 ,harold's friend1 ,i read in the paper that electricity is the rival of steam and is going to drive out the steam-engine4 ,i suggested that we were about to see some steam-engines driving electricity out of that power station4 ,but more seriously1 ,i explained that steam-engines were used for many years as locomotives to draw the trains on the elevated railroads of ,new ,york ,city1 and when at last they were displaced by electric trains some people thought that it was a case of electricity driving out steam1 whereas what had really happened was that the steam power for running those trains had been concentrated at a central station1 and its power was merely transmitted to the trains by means of electricity4 ,the trains were1 therefore1 run by steam power quite as much as ever4 ,in like manner1 the surface cars of ,new ,york a few years ago were run by a cable1 which was merely a very long belt used to transmit to the cars the power of steam-engines located at a central station4 ,when they were changed to electric cars1 electricity became the successful rival of nothing else than a twisted wire cable4 ,the cars still run by steam power as before1 but that power is transmitted by electricity instead of the discarded cable4 ,steam has driven out the horse as a power for drawing street cars1 and electricity has enabled us to gather all the steam engines into central stations1 where now they are furnishing the power for moving surface1 elevated1 and subway cars for street traffic1 as also trains for suburban travel4 ,central station steam-engines are producing a vast amount of power1 distributed all over the city by means of electricity1 for doing a great variety of work and for furnishing electric light and heat1 all of which we shall presently study4 ,just before we go into this central station1 can you tell me how the elevator is run in our apartment house8 ,it is an electric elevator1 said ,harold4 ,and where does the electricity come from8 ,i inquired4 ,well1 ,i know that it comes from the street mains1 but do they come from this power station8 ,yes1 said ,i1 and we will now go in and see the steam-engines which lift you up stairs many times each day by sending electricity to run that elevator4 ,if you choose to do so1 you may claim for purposes of discussion that your elevator is run by steam4 ,as we entered the building we came first to the dynamo room and both boys noticed that the tone which met their ears was that which ,i had produced for them in the telephone the night before4 ,i shall try to show you before we get through1 ,i said1 that these dynamos are doing something which makes iron pulsate sixty times a second and that that is the cause of the pitch of this tone4 ,but let us begin with the coal which is the source of all this power4 ,this particular station at the present time is burning forty tons of coal an hour4 ,that is as much as ,mr4 ---- uses to heat his twelve-room house for a whole year4 ,one pound of coal is capable of liberating enough energy to supply #e-c_/d horse-power for an hour4 7,written for short #e-c_/d ,h4,p4,h47 ,one ton of coal is capable of furnishing 7#b1jjj #e-c_/d7 #aa1ejj ,h4,p4,h4 ,forty tons would yield #dfj1jjj ,h4,p4,h4 ,but the best furnaces1 boilers1 and steam-engines are terribly wasteful of energy4 ,about nine tenths of all this energy is wasted and only one tenth1 or about #df1jjj horse-power per hour1 is delivered by the steam-engines to the dynamos4 ,coal is already scarce in the world and the supply is rapidly being exhausted4 ,meanwhile we are growing more dependent upon coal4 ,a century ago we used scarcely any power except that of men1 horses1 and oxen1 and what little heat men then used came chiefly from wood4 ,they lived in cold houses1 attended cold churches and schools1 did not ride in steam or electric cars1 and did not have power plants4 ,our wood is nearly all gone1 our coal is going1 and we are very rapidly growing more dependent upon heat and power1 our chief source of which is coal4 ,wind power is too uncertain to depend upon1 and we turned our backs upon water-power when we began to crowd into cities4 ,what little water-power there is1 however1 is nearly all in use4 ,there is great need both that we learn how to save the major part of the energy of the coal which we now waste1 and that we find a substitute for the coal to use when that is gone4 ,a part of the heat from the forty tons of coal which is being burned in this particular power plant goes into the water in the boilers4 ,it converts this water into steam4 ,the steam1 if free to expand into the air1 would occupy about one thousand seven hundred times the volume of the water4 ,we compel it to expand through the cylinders of the steam-engine1 using its force of expansion to make wheels go around--to make the dynamo revolve4 ,these dynamos are not devices for producing power but merely for transmitting the power of these steam-engines to far away places where it may be used1 as1 for instance1 in our apartment house1 where we are unwilling to walk upstairs and want some power to carry us4 ,our own apartment is fifty feet above the street4 ,i weigh one hundred and sixty-five pounds4 ,if ,i walk up stairs from the street to our apartment in one minute1 which is the rate of a rather slow elevator1 ,i work at the rate of one quarter of a horse-power4 ,one hundred and sixty-five pounds raised two hundred feet in one minute requires one horse-power4 ,you boys each weigh about half as much as ,i do1 and if one of you walks up the same stairs in one minute you exert half the power that ,i do1 or if you run up the stairs in half a minute you exert the same power1 that is1 one quarter of a horse-power4 ,when we three walk up together in one minute we exert one half horse-power4 ,if we all three run up the stairs in half a minute we expend one horse-power4 ,now1 the speed of elevators for apartment houses is about one hundred feet a minute4 ,we are unwilling to walk up stairs1 not because we are lazy but because we have the ,new ,york haste1 and so we employ elevators which run at the rate of about one hundred feet a minute4 ,illustration3 ,photograph by ,helen ,w4 ,cooke4 ,testing a ,generator ,these dynamos enable us to employ the power of this central station to run the elevator in our apartment house4 ,here is a dynamo rolling over now in the act of sending out power1 some of which goes to that elevator2 and standing beside it is another waiting to be used when necessary4 ,examining these dynamos1 we find that they are composed of nothing else than iron and copper4 ,about all that we can say of these mysterious machines is that the moving iron generates the electricity and the copper leads it away4 ,illustration3 ,fig4 #a ,each one of these dynamos has many hundred tons of iron in it4 ,a huge wheel of iron1 thirty-two feet in diameter1 one hundred feet in circumference1 portions of which are surrounded by insulated copper conductors1 forms the centre-piece of the machine4 ,this movable part weighs four hundred tons4 ,around about this is a fixed ring of iron1 portions of which are surrounded by insulated copper conductors4 ,ordinarily the ring which is stationary is called 'the field1' and the wheel1 which rotates1 is called 'the armature1' although these terms are sometimes reversed for certain reasons4 ,the movable part in these machines rotates about once a second1 that is1 its circumference moves a little faster than a mile a minute4 ,the iron moving at this high rate of speed creates ether streams or electric currents1 which are led off by the copper conductors4 ,the generation of electricity on a large scale requires large masses of iron and high velocity4 ,i noticed that the boys stood before this machine in a state of utter bewilderment1 bewildered as a man who is told that what he had considered north is really south1 bewildered as a man who1 having wandered through a maze of city streets1 looks up at length and unexpectedly finds the building he has been seeking towering before him4 ,the questions they asked were entirely without thought4 ,what is inside of it8 ,simply more iron and copper1 such as you see on the surface1 ,i replied4 ,but what makes it go8 ,the steam engines1 of course1 four of which you see1 are coupled directly to each dynamo4 ,but where does it get its electricity8 ,don't forget that you are looking at a generator of electricity4 ,big mass of iron--rapid motion6 ,that is the whole truth4 ,but it cannot satisfy you as an answer until you have become used to it4 ,we have seen all that we ought to see here to-day4 ,let us drop the whole matter now1 but return to my laboratory to-morrow1 and ,i will give you the next step which will help you4 ,the boys did no talking upon their return journey4 ,whether one may say they were thinking or not ,i cannot tell1 but certainly their ideas were incubating4 ,,ii ,,the ,,dynamo1 ,,continued--,,the ,,magnet ,when we had gathered at my laboratory the next day ,i took down a spool of one pound ,no4 #bd cotton-covered copper wire 7,fig4 #b ,a71 which had its centre filled with wire nails4 ,the boys had seen it before and remembered it4 ,with flexible wires ,i connected the two ends of the wire on this spool to a sensitive ammeter1 ,b1 which had its zero in the middle of the scale1 and ,i laid down upon the table a bar magnet1 ,c4 ,illustration3 ,fig4 #b ,here1 ,i said1 is a dynamo complete4 ,the bar magnet furnishes the 'field' and this spool of copper wire1 ,a1 which ,i will move back and forth immediately over the magnet from end to end1 is 'the armature4' ,d and e are the line wires and the circuit is completed through the ammeter to show whether we are generating electricity4 ,and now as ,i move this armature along the field you see the needle of the ammeter move to the right from zero to ten4 ,when the armature is moved in the opposite direction along the field the needle moves in the opposite direction past zero and on to ten at the left4 ,the moving of the needle in the ammeter shows that we are generating electricity4 ,the swinging to and fro of the needle shows that we are generating an alternating current of electricity4 ,it is a mere matter of detail whether we move the armature or the field1 as ,i will show you by letting the spool ,a rest quietly upon the table and moving the magnet to and fro lengthwise across the end of the spool4 ,or ,i may accomplish the same results by moving them both in opposite directions4 ,it is simply necessary that they move with reference to each other4 ,some dynamos are made with stationary fields and rotating armatures1 some with stationary armature and rotating fields1 and some with both parts designed to rotate in opposite directions4 ,magnetism is not confined to the magnet4 ,it extends more or less widely into the region about it4 ,it is this region affected by the magnet that we designate its magnetic field4 ,by bringing this sensitive compass needle into the region of this bar magnet from all directions1 ,i show you that it has a slight power to change the direction of the needle when about a foot away4 ,this power grows rapidly greater as the distance grows less4 ,of course its field extends rather indefinitely1 but we may say that this particular magnet has an appreciable field extending about one foot in all directions from it4 ,we find upon examination that some magnets have bigger and stronger fields than others1 that all have their strongest fields when first magnetized and lose their strength gradually1 but never entirely4 ,we find that hardened iron and steel hold magnetism longer than soft iron1 but all iron is magnetized somewhat at all times4 ,iron that is feebly magnetized can be made into a strong magnet by bringing it into a strong magnetic field4 ,the earth is a feeble magnet1 and that is why it gives direction to the compass needle4 ,that is also probably the reason why every piece of iron upon the earth is a magnet1 or1 to put the cause back another step1 we may say that whatever causes the earth to be a magnet also causes every piece of iron upon the earth to be likewise a magnet4 ,but thanks to ,oersted in ,denmark in #ahai and ,faraday in ,england in #ahba and ,joseph ,henry in ,albany1 ,n4 ,y41 in #ahbg1 we have learned to make exceedingly powerful magnets by sending a current of electricity in a whirl around the iron4 ,this is the meaning of the coils of copper wire around iron cores in the dynamo1 in electric bells1 in telegraph sounders1 in motors1 etc41 etc4 ,to prevent the electric current from taking the shortest route1 through the iron core or through the successive layers of copper wire1 the iron core and the wire must be covered with something like wood or paper or cotton or silk or rubber--such things as electricity does not readily pass through--that is1 insulating material4 ,joseph ,henry1 while teaching in the ,albany ,academy1 was the first to make electro-magnets4 ,there was no such thing as wire covered with an insulating material then in the market1 and he wound all his wire with silk ribbon4 ,but in the year #ahcd he made magnets which lifted thirty-five hundred pounds1 to the astonishment of every one4 ,a pair of such electro-magnets as ,i have here 7,fig4 #c71 each consisting of one pound of ,no4 #bd cotton covered copper wire1 eight hundred feet long1 wound in one thousand turns about an iron core two inches in diameter1 will lift several hundred pounds3 much more than we three can lift1 as ,i shall now show you4 ,illustration3 ,fig4 #c ,the cores of the two magnets were bolted fast to an iron beam1 and a large bar of iron with a ring in it was laid across the other free ends of the magnet cores4 ,i made connections with the electric lighting circuit 7that in my laboratory is what is called a direct current71 and sent a current of electricity around the coils4 ,the two boys and ,i tugged at the ring in the iron bar to no avail4 ,we were unable to pull the iron bar away from the magnet4 ,but when ,i opened the switch and cut off the electric current1 one boy with one finger in the ring lifted the bar with perfect ease4 ,electro-magnets are now made with a magnetic intensity #ij1gjj times that of the earth's magnetism4 ,electro-magnets are used for hoisting iron castings weighing many tons4 ,here is a picture of an electro-magnet lifting a whole wagon load of kegs of nails from the wagon to the hold of a ship4 ,electro-magnets are our only means of utilizing electricity for power4 ,it is the pull of electro-magnets that moves the electric car4 ,electro-magnets are now used for pulling all the trains out of the ,grand ,central ,depot in ,new ,york ,city4 ,let us now compare the strength of our electro-magnet with that of the bar magnet used in our former experiment4 ,i opened and closed the switch1 which sent the electric current through my magnet coils at frequent intervals1 and the two boys1 each with a compass needle1 searched the field for magnetic effects4 ,they found that the magnetic field extended six or eight feet1 but this piece of research was broken up by a new idea which appeared to strike them both at the same instant1 for they shouted both together1 ,let's use this electro-magnet in place of the bar magnet for our dynamo experiment6 ,illustration3 ,photograph by ,helen ,w4 ,cooke4 ,wiring ,that is surely the next step in our programme1 said ,i1 but you will need a steam-engine to move an armature in this magnetic field1 will you not1 judging from the struggle we had with that iron bar a few minutes ago8 ,the boys looked quite hopeless until ,i said1 ,the best thing about the electro-magnet remains yet to be told4 ,you have perfect control of its strength by changing the amount of electricity which you send around the coil4 ,by means of an instrument which works like the motorman's controller on the electric car1 ,i may control the amount of electricity which flows1 just as well as you may control the flow of water by a faucet or stop-cock4 ,by this means ,i will control the strength of the magnet so that you may move the armature in your dynamo experiment4 ,in #ahba1 ,faraday1 at the ,royal ,institution1 ,london1 learned that he could produce magnetism by means of the electric current1 and1 in #ahca1 he learned that the reverse was also true1 namely1 that he could produce electricity from magnetism4 ,this idea coming as the result of ten years of incessant search made him shout and dance like a child4 ,you are feeling a little of the pleasure of his discovery4 ,illustration3 ,fig4 #d ,i then fastened one of the coils upon the table underneath a small bench 7,fig4 #d7 and sent an electric current around it4 ,the other coil1 ,b1 connected with the ammeter was pushed back and forth along the surface of the bench over this coil4 ,the boys found that the more electric current ,i sent around the coil ,a1 that is1 the stronger ,i made the magnetic field1 the harder it was to move the coil ,b4 ,they found that the nearer ,b was to ,a the harder it was to move it4 ,they found that the faster they moved ,b the more electricity was produced4 ,they tried laying ,b upon its side upon the bench and thus moving it4 ,they tried taking ,b off the bench and moving it on all sides of ,a4 ,they found it much harder to move in some ways than in others1 but in all cases they found that the harder they had to work the more electricity was developed1 as was shown by the ammeter4 ,the dynamo is any machine which will convert mechanical work into electricity4 ,the magneto is one form of a dynamo which you have used much at the summer cottage1 but have never seen the inside of4 ,here are several 7see ,figs4 #e1 #f1 and #h7 which ,i will let you examine inside and out1 and with these ,i must leave you to yourselves for a time4 ,when ,i returned ,i asked the boys why these dynamos were called magnetos4 ,because they have steel magnets for their fields1 they replied4 ,there are several magnets bent in the shape of a horseshoe4 ,yes1 ,i said1 in this case the field is made stronger by taking several magnets4 ,have you noticed any armature8 ,yes1 it is made of iron with insulated copper wire wound around it4 ,please recall that the amount of energy you expend in going upstairs depends on two things3 7#a7 your weight and 7#b7 the speed with which you move4 ,also recall that the amount of electricity you could generate with a dynamo depended upon the amount of energy you expended4 ,therefore1 the strength of the electric current which this machine may produce depends upon two things3 7#a7 the strength of the magnetic field against which you must pull and 7#b7 the speed of the motion of the armature4 ,evidently this field is made as strong as it is possible to make it with steel magnets4 ,now is there any device for giving high speed to the armature8 ,yes1 indeed1 said the boys1 one has a pulley so that it may be connected by a belt with a gas engine1 and the others have each a large cog-wheel working into a smaller one4 ,we found in one of them that a single revolution of the crank gave six revolutions to the armature4 ,i found that the boys had made large-sized drawings of the parts1 and were preparing to report on the magneto as a form of dynamo at the next meeting of the ,science ,club1 which we had started among the boys in school4 ,illustration3 ,fig4 #e ,i will loan you some apparatus so that you may give a very interesting demonstration on that subject1 said ,i1 only let me show you how to use it first4 ,connect the binding posts ,d and ,e of this magneto 7,fig4 #e7 with my ammeter4 ,turn the crank very slowly and notice that the needle of the ammeter swings to and fro with each revolution of the armature4 ,that shows that you have not only a dynamo1 but an alternating current dynamo4 ,illustration3 ,fig4 #f ,now connect the binding posts d and e of this magneto 7,fig4 #f7 with a short piece of copper wire4 ,turn the crank and you notice that this dynamo rings two electric bells4 ,turn slowly and you notice that the alternations of the current are numbered by the strokes on the bells4 ,the hammer swings to and fro just as the needle of the ammeter did4 ,each bell therefore receives one stroke of the hammer for each revolution of the armature4 ,now try to turn the crank steadily at the rate of one revolution per second4 ,the armature is making six revolutions1 or cycles1 per second and you now have not only an alternating current dynamo but a six-cycle alternating current dynamo4 ,the lighting circuit used in our apartment is a sixty-cycle alternating current4 ,to be sure the armature of the dynamo which generates that current revolves only once a second1 but it carries coils enough upon its rim to make that number of alternations4 ,now connect this telephone receiver with the binding posts ,d and ,e of this magneto 7,fig4 #g74 ,unscrew the cap of the receiver4 ,move to one side the iron diaphragm and turn slowly the crank of the magneto4 ,notice that the diaphragm vibrates in time with the alternations of the dynamo4 ,replace the diaphragm1 screw on the cap1 hold the receiver to your ear and turn the crank as fast as you can4 ,you will probably be able to make about sixteen cycles per second4 ,the receiver in that case is giving forth a sound of the same pitch as a sixteen-foot closed organ-pipe4 ,illustration3 ,fig4 #g ,connect the telephone receiver to the binding posts ,d and ,e of this magneto 7,fig4 #h71 and by means of a belt connect the pulley to this series of cog-wheels4 ,now you may turn the crank and readily make the armature revolve at the rate of sixty cycles per second1 and you notice that you get the same tone that we heard in the dynamo room of the power station and the same tone the telephone receiver gave when ,i connected it to a coil in our apartment4 ,the tone which is produced by sixty vibrations per second is very nearly that of the ,c two octaves below middle ,c on the piano4 ,try it along with the piano and you will find it a little flat4 ,this string on the piano is making sixty-four vibrations per second4 ,illustration3 ,fig4 #h ,illustration3 ,fig4 #i ,now connect this miniature telephone switchboard lamp with the magneto 7,fig4 #i7 and turn the crank fast4 ,the lamp lights up to full brilliancy and you notice that the light is steady1 although it is made by an alternating current passing through the filament in one direction1 stopping entirely1 and then passing in the opposite direction4 ,the filament has no time to cool off1 provided you turn fast enough1 but try turning a little slower and you will notice the flickering of the lamp4 ,,iii ,,the ,,ammeter ,illustration3 ,fig4 #aj ,at the last meeting of the ,science ,club so many questions were asked1 which the demonstrators could not answer1 that a programme committee1 to whom such questions might be referred thereafter1 was appointed4 ,it was made the duty of this committee to assign to various members the task of searching for satisfactory answers1 and when the material was ready to be reported to the club1 the programme committee determined the time and order of presentation4 ,i found that ,i had been made an honorary member of this committee and that it was expected that ,i should steer the committee4 ,i told them that ,i accepted this appointment with the understanding that the fellow who steers is always the smallest man in the crew1 and if they would do all the work ,i would enjoy the honorary title of cockswain4 ,secretly1 however1 ,i appreciated that this was in effect adding several courses to my already rather heavy programme4 ,i must1 under the rgime1 direct a large number of inexperienced students in library research1 in laboratory research1 and in the art of giving demonstrations with apparatus and experiments to audiences4 ,the most urgent questions1 as also those which were next in the natural order1 concerned the ammeter4 ,i told the committee to make that the subject of the next meeting and to send to my laboratory on a certain day the person or persons whom they might appoint to report upon it4 ,illustration3 ,fig4 #aa ,i find that the boys never come singly1 but generally in pairs4 ,when the boys came they found lying upon the table an ammeter 7,fig4 #aa74 ,i told one of them to take out the three screws in the front and remove the face of the instrument4 ,i had told the boys that the instrument cost sixty dollars and that letting them open it was like letting them open my watch4 ,as soon as the face came off one of the boys exclaimed that from my reference to the watch he had expected to see very complicated machinery with many wheels1 but from the exceeding simplicity of the mechanism he could not see why it should cost sixty dollars4 ,i told him that although it was a fine piece of workmanship it was fortunately very easy to understand1 and ,i asked them if it reminded them of anything else that they had ever seen4 ,after a few moments of reflection they agreed that it was very much like one of the magnetos4 ,well1 said ,i1 where is the field8 ,illustration3 ,fig4 #ab ,is this horseshoe arrangement a magnet8 they inquired4 ,there is a compass needle right at your hand waiting to answer that question1 ,i replied4 ,they immediately found that it was a magnet4 ,well1 ,i said1 to be really sure that it is a magnet you must find a portion of it that will repel a portion of your compass needle as well as other portions in both horseshoe and needles which attract each other4 ,whereupon1 they found that the portion marked ,n 7,fig4 #ac7 repelled the blue end of the compass needle and attracted strongly the bright end of the needle1 while the portion marked ,s did the reverse4 ,we will call ,n and ,s the poles of the magnet4 ,this is simply a steel bar magnet bent into the shape of a horseshoe4 ,illustration3 ,fig4 #ac ,you told us1 remarked one of the boys1 that steel magnets gradually lose their strength4 ,how then can this be correct as a measuring instrument8 ,it is the purpose of the iron case to enable this magnet to retain its magnetism1 and if you will examine its field1 as we did that of another magnet upon a former occasion1 you will find that although this is a strong steel magnet its field does not extend outside of the iron case4 ,it is as though we could box up magnetism and keep it from escaping4 ,now if this is like the magneto1 where is the armature8 ,the spool-like thing between the poles of the magnet looks just like the armature in one of the magnetos4 ,yes1 it has an iron core with a coil of insulated wire around it1 and you remember that when an electric current is sent around a piece of iron1 that iron is made into a magnet1 and if it is a magnet it must have poles4 ,it is very delicately poised upon a pivot and will act exactly like your compass needle1 which is also a little magnet with poles4 ,i will send an electric current through the wire which surrounds this armature1 and you notice that the needle which it carries moves to the right4 ,notice that the lower end of this armature acts like the blue end of your compass needle in that it is repelled from the pole ,n of the field and is attracted toward ,s of the field4 ,in like manner1 the upper end or pole of the armature is repelled from ,s and attracted to ,n of the field4 ,the blue end of the compass needle is called its north pole because it points north under the magnetic influence of the earth1 and so we may call the lower end of the armature its north pole4 ,the electric current which ,i am sending through the armature comes first through one ordinary #af-;candle-power electric lamp which you see lighted on this 'resistance board1' as it is called1 and you notice that the needle points to 4#e4 ,this means that half an ampere of electricity is passing through this lamp4 ,i will now send the current through a #cb-;candle-power lamp1 and you notice that the needle points to one1 indicating that one ampere is required to light that lamp4 ,but what prevents the needle from going farther1 and what brings it back to zero each time8 ,the boys discovered a very small spring1 like the hair spring of a watch1 coiled around the pivot of the armature4 ,so1 then1 one ampere of electricity gives magnetism to this armature so that it may pull against its coiled spring hard enough to carry the needle to the point one4 ,twice as much electricity will give it magnetism enough to carry it to two1 and so on across the scale4 ,the full name of this instrument is ,ampere meter1 which by usage has been shortened to ammeter4 ,it was named in honour of ,andr ,marie ,ampre1 who was born at ,lyons1 in ,france1 in #agge1 the year our ,revolutionary ,war broke out4 ,he died in #ahcf4 ,when ,oersted made his famous discovery of the action of an electric current upon a magnetic needle1 in #ahai1 ,ampre was in middle life 7forty-four71 and took up the same line of research with great vigour4 ,the next year1 #ahbj1 he discovered what you will doubtless enjoy rediscovering now4 ,you will notice that the binding posts on the bottom of this ammeter are marked1 one positive1 1 and the other1 negative -4 ,the electric current now enters the instrument by the post marked and after passing around the armature leaves by the post marked -4 ,i will reverse the connections and thus send the current around the armature in the other direction1 and you notice that its poles are now reversed4 ,the lower end which was formerly the north pole of the armature has now become the south pole1 as proven by the fact that it is repelled from the south pole of the field and attracted to its north pole4 ,this carried the needle to the left1 and inasmuch as the zero is in the middle of the scale we may with this instrument both measure the amount of current and tell its direction4 ,you will recall that when we connected the magneto with this instrument1 it indicated that the magneto sent the current first in one direction and then in the other1 which we call an 'alternating current4' ,but you notice that the current which ,i am using in this laboratory flows continuously in one direction4 ,this is called the 'direct current4' ,we shall find out how a dynamo may produce a direct current at another time4 ,let us not forget1 however1 that we have repeated ,ampre's discovery1 and found out that the direction in which we send the current around an electro-magnet determines which end shall be its north and which its south pole4 ,if you will note carefully which way the wire is wound around the armature you will see that when ,i send the current in at the positive post it is passing around the north pole of the armature opposite to the direction in which the hands of a clock move4 ,if ,i reverse the current it passes around the lower end of the armature in the same direction as the hands of a clock move and then this end becomes a south pole4 ,this is ',ampre's rule1' and it is what candidates for admission to college are very careful to learn4 ,before we replace the face of this ammeter ,i must call your attention to a wire running by a short cut from one binding post to the other1 s 7,fig4 #ad74 ,suppose a represents the wire around the armature4 ,electricity1 like water1 goes more readily through a big conductor than a small one and more readily through a short than a long conductor4 ,if s and a were water pipes1 each having a stop-cock1 we might easily adjust the cocks so that one tenth of the water would go through a and nine tenths through s4 ,or1 indeed1 without stop-cocks1 the size and length of s and a might be so apportioned that one tenth of the water would flow through a and nine tenths through s4 ,this is precisely the adjustment which has been made with reference to the flow of electricity through this instrument4 s is called a 'shunt4' ,when the shunt is out all the current goes through a and when the shunt is in only one tenth of the current goes through a4 ,i have two other shunts1 each of which may be put in the place of s4 ,with the second only one hundredth of the current goes through a and with the third only one thousandth of the current goes through a4 ,thus ,i have an instrument which will measure anything from one thousandth of an ampere up to ten amperes4 ,illustration3 ,fig4 #ad ,in this laboratory we pay about one cent for an ampere of electricity for one hour4 ,twice as much coal must be consumed to furnish two amperes as one1 and twice as much coal must be consumed to furnish an ampere for two hours as for one hour4 ,hence we need an instrument which will keep account of time as well as amount of current4 ,such an instrument we must look into next4 ,just before we pass to that1 however1 let me ask if you have ever heard of a 'shunt-wound' dynamo4 ,can you guess from the way we have just used the word 'shunt' what the expression could mean with reference to a dynamo8 ,without hesitation the boys told me that it meant that the field and armature were wound parallel to one another1 as shown by diagram in ,fig4 #ae4 ,in which case the electric current which the machine generates divides1 part of it going around the field and part around the armature4 ,another type1 called series-wound dynamos1 is indicated by diagram in ,fig4 #af1 in which case the electric current goes through field and armature in succession4 ,under either of these circumstances1 how can the armature move with reference to the field8 ,the answer will appear in the next chapter4 ,illustration3 ,fig4 #ae ,illustration3 ,fig4 #af ,,iv ,,the ,,wattmeter ,we were able to maintain connections between the binding posts of the ammeter and the movable armature of flexible wires because the armature never moves more than one third of a revolution1 but we now wish to examine an instrument in which the armature must not only make a complete revolution but must continue to revolve in the same direction indefinitely4 ,how are connections made so that an electric current may pass from the fixed binding posts to the wire of the moving coil8 ,i will lift the cover off this instrument1 which is called a wattmeter1 and let you find the answer to that question4 ,i sent through the instrument the current from a #cb-;candle-power lamp4 ,according to the ammeter1 which was also in circuit1 the amount was one ampere4 ,the armature of the wattmeter revolved slowly and it was not long before the boys reported that connections for the current were made by strips of metal sliding on metal plates4 ,the ends of the armature wire were fastened one to one plate and the other to the other plate1 and the metal strips brush along over the surfaces of the plates4 7,that is why they are called brushes1 ,i said47 ,and the brushes slide from one plate to the other each time the armature makes half a revolution4 7,that is1 the brushes change the connection and thus change the poles of the armature at the proper instant so that they are always attracted to the poles of the field toward which they are moving47 ,this is called a commutator4 ,notice that while the ammeter was like the magneto in having a steel magnet for its field1 the wattmeter is like the dynamo in having electro-magnets for both armature and field4 ,notice in the second place that this instrument is an electric motor since it is made to revolve by an electric current4 ,if it were made to revolve by some other power it would generate electricity and would then be called a dynamo4 ,indeed1 let me tell you something which must at present be nothing more than a puzzle to you4 ,every machine1 while it is being driven by an electric current as an electric motor1 is1 at the same time1 acting as a dynamo to generate a current in the opposite direction4 ,notice in the third place that this is a shunt-wound instrument4 ,the current which is sent into the instrument divides1 and part of it goes through the field1 while part goes through the armature4 ,motors1 as well as dynamos1 are either shunt-wound or series-wound4 ,but notice finally that the axle on which the armature is carried has a cyclometer arrangement which keeps account of the number of revolutions4 ,the armature is going slowly enough for us to count the revolutions4 ,with watch in hand we found that it made one hundred and twenty revolutions per minute4 ,i next brought the current to the wattmeter through a #af-;candle-power lamp and the ammeter1 connected in series1 showed that half an ampere was passing4 ,we counted the revolutions of the wattmeter and found them to be sixty per minute4 ,here1 then1 is a simple electric motor which will register the amount of electricity we use4 ,it will register the same amount whether we use one ampere for one hour or half an ampere for two hours or two amperes for half an hour4 ,in any case this product is called one ampere hour4 ,but the words printed upon the dials of this instrument are not ampere hours1 but watt hours and the name of the instrument is wattmeter4 ,this next requires explanation4 ,follow me in a little roundabout journey and the matter will be readily understood when viewed from another approach4 ,illustration3 ,fig4 #ag ,when we were estimating the energy required to climb the stairs of an apartment house1 we needed to take into account two factors1 7#a7 our weight and 7#b7 the time which we took in climbing them4 ,the amount of coal burned1 steam generated1 electricity produced1 to run our elevator depends upon two factors1 7#a7 its weight and 7#b7 its speed4 ,that idea is fundamental4 ,let us get at it in still another way4 ,suppose we have a mill pond1 7,fig4 #ag1 ,a74 ,we construct a penstock p and install a water-wheel1 ,s1 to operate a mill4 ,our business increases and we install more machinery in our mill and must have more power to run it4 ,we have two ways of getting it1 7#a7 we may lengthen our wheel and enlarge our penstock so that a greater weight of water will fall upon the wheel1 or 7#b7 we may lengthen our penstock and move the wheel farther down so that the water will fall upon the wheel with greater velocity4 ,it is just so with the electric current4 ,like water it is driven on in its course by pressure4 ,the unit for electric pressure is called a volt4 ,if we wish to drive the wattmeter or any other electric motor twice as fast as now1 we may choose whether we shall do so by doubling the volts of pressure or by doubling the amperes of quantity4 ,the electric pressure on our mains is about one-hundred and ten volts4 ,we three together weigh #ccj pounds4 ,our elevator brought us up stairs at the speed of #ajj feet per minute4 ,it requires one horse-power to raise #ccj pounds #ajj feet in a minute4 ,the ammeter in the engine room showed that #g amperes of electricity were sent through the motor of the elevator to bring us up4 ,that is1 seven amperes at #aaj-volt pressure give one horse-power4 ,in the office building across the street where they use a #bbj-volt current #c-a_/b amperes are required to take us up stairs at the same speed4 ,it is necessary that the same amount of coal be consumed to furnish the horse-power of energy whether we supply it by means of seven amperes at #aaj volts or #c-a_/b amperes at #bbj volts4 ,you notice that the product is #ggj in each case4 ,the name given to this product is watts4 ,more accurately #gdf watts of electrical power are equivalent to one horse-power4 ,the name of this unit commemorates the famous inventor of the steam engine1 ,james ,watt 7#agcf-ahai74 ,his monument now overlooks the ,clyde at his native town1 ,greenock1 ,scotland4 ,to light a certain lamp1 to heat a certain laundry iron1 to furnish a certain amount of power for an electric motor1 we must have a definite number of watts4 ,we may choose whether we will have it at high or low voltage with correspondingly low or high number of amperes4 ,illustration3 ,fig4 #ah ,we will now connect with our laboratory current a #cb-;candle-power lamp1 an ammeter1 and a wattmeter1 all in series1 ,fig4 #ah1 and in parallel with these a volt meter4 ,this last instrument indicates the electric pressure4 ,its mechanism will be examined later4 ,the volt meter indicates #aaj volts and the ammeter shows that one ampere is passing4 ,the filament in the lamp resists the passage of the current4 ,it gets quite hot and gives forth as much light as thirty-two candles4 ,its resistance is just such that #aaj volts of pressure send one ampere through it4 ,we will now take the reading of the wattmeter1 note the time and read it again later4 ,one hour later its index showed that #aaj watt hours of electrical energy had been converted into light and heat4 ,this at the usual rate1 costs #a4a cents1 one cent per hundred watt hours or ten cents per thousand watt hours1 called a kilowatt hour4 ,the more common #af-;candle-power lamp costs about half a cent an hour to operate4 ,it requires one horse-power to keep fourteen of them burning4 ,illustration3 ,photograph by ,helen ,w4 ,cooke4 ,wattmeter ,i will now take you to see the wattmeter which measures all the electric energy used in this building4 ,you note down its reading and the date and the next time you come we will read it again and thus find out how much electricity has been used for electric lights1 for electric ventilating fans1 for electric elevators1 for electric ovens1 and electric irons in the school of household arts1 for electric motors to run lathes and other machines in the school of technical arts1 for electric experiments in my laboratories and lecture room1 for electric vacuum cleaners and1 lastly1 for pumping the pipe organ in chapel4 ,i saw by the boys' faces as they departed what would be the next question that they would bring to me4 ,knowing1 however1 that the hour was up1 they were too polite to press it then4 ,v ,,the ,,electric ,,motor ,in a few days ,i received a telephone message1 asking if ,i could appoint an hour to meet the programme committee in my laboratory4 ,i must confess that my pleasure in these meetings had increased so much that ,i was quite ready to slight other duties1 if need be1 to engage in them4 ,moreover1 since my business was education it was not difficult for me to regard these meetings in the light of a duty quite as important as my regular class instruction--perhaps more effective4 ,at any rate the boys and ,i managed to get together4 ,may ,god forgive the man who essays to teach boys1 but does not love to be with them4 ,of course at the last meeting of the ,science ,club every one wanted to know how we ran a pipe organ by electricity4 ,moreover the ,electrical ,show was coming on in the city1 and cows were to be milked by electricity1 dishes were to be washed by electricity1 rugs and furniture were to be cleaned by electricity1 and innumerable distracting and distressing things were to take place4 ,i told the boys that really only two kinds of things were to be done by electricity at the show1 and if they would give me two one-hour appointments ,i would furnish them with the key to the whole show4 ,we might as well begin to-day with the pipe organ question4 ,a pipe organ is operated by air4 ,it has bellows which are simply one form of an air pump4 ,a boy is often employed to turn a crank which works the bellows4 ,down in the basement underneath our pipe organ ,i will show you how a half-horse-power electric motor takes the place of a boy4 ,we found a dark and dirty corner where a boy used to stand and turn a crank every time sthetically inclined people enjoyed an organ recital in the room above4 ,science1 which has not been given credit for being humanitarian1 put an electric motor into that dark corner and sent the boy up stairs to hear the music4 ,the motor grumbled at the dirt in the corner and compelled the janitor to keep it clean4 ,the electric motor1 better than any device ,i know1 enforces justice1 but never requires mercy1 or at least rarely receives it4 ,it comes nearer than any other machine to paying back all that you put into it4 ,it is most economical when working up to its full capacity4 ,i recommend that you look it over carefully and after a few minutes tell me what you have seen in it4 ,illustration3 ,fig4 #ai ,the boys said that it looked just like a dynamo4 ,we must not forget that it is a dynamo1 but is here used as a motor by sending an electric current through it4 ,this fact1 that a dynamo might be driven by an electric current and serve as a mover of other machinery1 was first publicly exhibited in #ahgc at the ,vienna ,exhibition1 and by many believed to have been discovered by accident at that exhibit4 ,but why does it look like a dynamo8 ,it has a field whose magnetism is produced by an electric current sent through coils of wire1 and it has an armature whose magnetism is likewise produced by the electric current4 ,if it were used as a dynamo1 where would it get the electric current to magnetize its field8 ,from its own moving armature4 ,is it adapted for direct current8 ,yes4 ,it has a commutator and brushes4 ,is it shunt- or series-wound8 ,shunt-wound1 as shown by diagram in ,fig4 #bj4 ,illustration3 ,fig4 #bj ,suppose we treat the machine as a dynamo4 ,bring the ends of the line wire together1 thus1 as we say1 closing the circuit4 ,by some external force let us cause the armature to rotate and under the influence of the magnetic field it will generate an electric current1 part of which will pass through the field and part through the line circuit4 ,we may adjust the relative amount of wire in field and line so that any portion of the current we choose will pass through the field4 ,the amount of current it will generate depends1 7#a7 upon the strength of the field and 7#b7 upon the speed of the armature4 ,its field1 although never entirely without magnetism1 is very feeble at first1 and hence in the first instance a very small current will be generated in the moving armature4 ,this1 however1 will strengthen the field slightly1 and as the field is strengthened the armature will generate more current1 and thus by a mutual reaction the machine gradually builds up to full strength4 ,illustration3 ,fig4 #ba ,when now we use the machine as a motor1 an electric current must be sent along the line wires in the opposite direction 7,fig4 #ba7 from which it would come out of the machine when acting as a dynamo4 ,it will then be noticed that1 although the direction of the current through the field is the same1 whether the machine is used as a dynamo or a motor1 the direction through the armature1 when used as a motor1 is the reverse of that when used as a dynamo4 ,you may perhaps be able to notice that the amount of wire on the field is considerably more than that on the armature4 ,now if you will trace the wires carefully you will find that there is provided a way of supplementing the wire of the armature with some more wire in what is called the rheostat1 ,fig4 #bb4 ,this wire1 or portions of it1 is introduced into the armature circuit when the machine first starts4 ,when1 however1 the machine has started and the armature is moving within the influence of a magnetic field1 it plays the part of a dynamo at the same time that it is acting as a motor4 ,two conflicting and opposite electro-motive forces therefore exist in the armature at the same time4 ,in ,fig4 #bb the arrow a represents the direction of the electro-motive force which is impressed upon the armature1 and the arrow b represents the counter-electro-motive force which the moving armature develops4 ,illustration3 ,fig4 #bb ,this counter-electro-motive force1 which develops while the machine is in motion1 makes it unnecessary to hold back the current longer by the extra resistance of the rheostat and hence that is usually cut out4 ,being used only for starting purposes and looking like a box1 it is generally called the starting box4 ,if now it was intended that this motor should run at a constant speed1 as is often the case1 no other governor would be needed than this counter-electro-motive force1 for whenever the machine begins to go faster1 on account of reduced load1 its counter-electro-motive force increases as the speed and holds in check the impressed electro-motive force4 ,this acts very perfectly as a governor1 and motors operate with notoriously constant speed under variable loads4 ,but1 of course1 in this present instance the motor is required to work at a variable speed4 ,it must pump air slowly for the soft passages of music1 and it must work the pump to its utmost for the very strong passages4 ,illustration3 ,fig4 #bc ,to understand how an electric motor may pump an organ and have its speed automatically controlled1 let us examine the diagram in ,fig4 #bc4 ,the motor m causes the shaft ,s to revolve1 carrying the crank ,c around with it4 ,the rod r causes a b1 the lower side of the bellows1 to rise and fall1 this side being hinged at b4 ,the side b c1 is fixed4 ,when the side a b is pushed upward by the crank rod the valve f closes and the air in the compartment h pushes open the valve g and enters the compartment j4 ,the upper side d e1 of this compartment rises as it is filled with air4 ,weights ,k1 ,k1 ,k1 rest on the top of this and air ducts lead from this compartment to the pipes of the organ4 ,the keys of the organ operate air cocks which open and close the air ducts connected with the organ-pipes4 ,a chain connected with e passes around the axle of the wheel l and has a weight ,w upon its lower end4 ,the wheel l carries a strip of brass n1 which slides over metal points p1 p1 p1 etc4 ,the successive points are connected by coils of wire to furnish resistance4 ,this series of coils is called a rheostat4 ,the wires t and u form a loop from the armature of the motor and connect this rheostat in series with the armature4 u is connected with the brass strip n4 ,notice that when the compartment j is full of air and the side d e1 is lifted to its greatest height the strip n is moved to the lowest point p1 and the electric current must pass from u through all the resistance of the rheostat in order to get back to the armature by the wire t4 ,this makes the motor go very slowly4 ,when d e sinks down1 the strip n moves to the upper points p1 and the resistance is reduced step by step1 enabling the motor to quicken its speed and pump faster as more air is required4 ,small motors in order to be effective must travel at high speed4 ,this motor when moving at its highest speed makes #a1hjj revolutions per minute4 ,the bellows on the other hand needs to be large and move slowly in order to be efficient4 ,hence the motor is not in reality connected directly to the shaft ,s1 but causes the shaft to revolve by means of a series of pulleys and belts4 ,the pulley on the motor is three inches in diameter4 ,it is connected by a flat leather belt with a wheel thirty inches in diameter4 ,when the motor therefore1 makes #a1hjj revolutions per minute this wheel makes #ahj revolutions per minute4 ,the axle of this wheel carries a small cog-wheel three inches in diameter and it is connected by a chain belt with a cog wheel on the shaft ,s 7,fig4 #bc74 ,thus this shaft revolves thirty times per minute1 that is1 the rod r rises and falls each second4 ,a pull of one pound on the rim of the motor pulley will cause a pull of sixty pounds on the cogs of the wheel upon the shaft ,s4 ,if the second belt were leather1 a sixty-pound pull would cause it to slip on the smaller pulley4 ,hence the second belt is a steel chain and the wheels have cogs1 or sprockets1 like a bicycle4 ,illustration3 ,fig4 #bd ,the organist before beginning to play closes a double-pole1 single-throw switch 7,fig4 #bd71 which sends the electric current to the motor4 ,the motor pumps air until the bellows is full1 and if the organist delays playing1 the strip of brass n 7,fig4 #bc7 is carried below the lowest point p1 thus cutting off the current and stopping the motor4 ,as soon as he uses some of the air in the bellows1 however1 n rises and makes contact with the points p and the motor starts4 ,this suggests that a somewhat similar thing is accomplished under electric cars which have air brakes4 ,an electric motor pumps the air and compresses it in a tank4 ,when the pressure reaches a certain point1 say sixty pounds per square inch1 it automatically shuts off the electric current from the motor which works the pump4 ,but when the motorman uses some of the air to apply the brakes to the wheels1 and the pressure in the tank falls below sixty pounds1 the electric current is again automatically turned on to the motor4 ,of course if an electric motor can operate a pump to compress air it may also work a pump to exhaust air4 ,this is what is done in a vacuum cleaner4 ,the electric pump as it is called 7which means a pump worked by an electric motor71 exhausts some of the air from a compartment in the machine1 and the atmosphere pressing in through nozzle and hose carries dust from rugs and furniture with it into the compartment4 ,the best vacuum cleaners will produce a pressure of seven or eight pounds per square inch1 about half an atmosphere4 ,this will remove dust from the warp and woof of a rug better than our greatest hurricanes can when the rugs are hung upon a line4 ,there are three kinds of air pumps in use with vacuum cleaners3 7#a7 bellows1 7#b7 rotating disk or fan1 7#c7 piston4 ,to milk cows by electricity is simply to apply the vacuum-cleaner idea to the process1 and1 in general1 doing things by electricity usually means doing them by some machine that is made to go by an electric motor4 ,this then is the first key to the ,electrical ,show1 and if you will remember to look first for the motor it may remove much of the mystery from some of the exhibits4 ,in many cases it is not necessary to have a complete electric motor1 but simply an electro-magnet to do the work4 ,in booth ,no4 #ef you will find a piano played by electricity4 ,its keys are moving1 but no hands strike them4 ,there is no ghost at work here4 ,a little strip of iron has been placed upon the under side of each key and a small electro-magnet is placed under that4 ,it is only necessary that wires should run from these electro-magnets to two dry-battery cells and to push buttons1 and a person far away may play the piano4 ,in reality1 however1 it is not a person but a roll of punctured paper that opens and closes the electric circuits to these various magnets underneath the keys4 ,it often happens that you see a person playing a pipe organ with his keyboard far removed from the organ itself4 ,in this case the keys simply act as push buttons to close the electric circuit through electro-magnets placed in the organ itself4 ,these electro-magnets operate the air valves of the various pipes4 ,illustration3 ,fig4 #be ,you call at some apartment house where there is no hall boy1 but a row of push buttons labelled with the names of the tenants4 ,you push a button and the door which was locked opens apparently of its own accord4 ,to say that the door opens by electricity is only to add mystery4 ,what does happen is that an electric bell up in the apartment rings in response to your push of the button1 and in reply the tenant pushes a button and the door is unlatched by an electro-magnet concealed in the door casing 7,fig4 #be74 ,so ,i would say that the first key to the ,electric ,show or to the multitude of electrical appliances which you meet in life is the electro-magnet4 ,consider the motor as one illustration of its use4 ,if you are really to understand the ,electric ,show you should go twice4 ,i advise going with this key alone first and note down all the applications of electro-magnets which you can find there4 ,when you have done so ,i shall be glad to have your report4 ,,vi ,,applications ,,of ,,the ,,electro-,,magnet ,it became quite the rage now among the boys to find as many uses of electro-magnets as possible4 ,these were reported and explained to the club and a list kept4 ,this list included3 #a4 ,dynamo4 #b4 ,magneto4 #c4 ,ammeter4 #d4 ,wattmeter4 #e4 ,motor4 #f4 ,electric piano and organ players4 #g4 ,electric door openers4 ,already noticed in the preceding pages1 and the following3 #h4 ,the ,electric ,spinner 7,fig4 #bf74--;,a toy full of instruction4 ,the standard is a steel magnet which produces a magnetic field4 ,inside of this is an electro-magnet which serves as an armature4 ,plainly visible on its shaft is a commutator to which the electric current from a dry cell is sent4 ,this causes the armature to revolve and carry with it a series of colour disks which may be adjusted so as to show what tint or shade results from mixing colours in various proportions4 ,illustration3 ,fig4 #bf ,illustration3 ,fig4 #bg ,illustration3 ,fig4 #bh #i4 ,the ,electric ,engine 7,fig4 #bg74--,this toy1 with one dry battery cell1 develops power enough to run several other toy machines4 ,the diagram in ,fig4 #bh will make its plan of operation plain4 ,b is the battery cell1 c the electro-magnets1 a an armature of iron4 ,by a rod this armature is connected with a crank on the axle which carries the fly wheel f4 ,another crank1 d1 upon the same axle serves like a push button to close the electric circuit at the right instant4 ,the wire g from the battery cell encircles the electro-magnet c and then is connected to the iron base of the toy4 ,when the crank d touches the conductor e1 which is a spring1 the electric current passes around the magnet1 the magnet pulls the iron armature a1 and this gives an impulse to the wheel f whose momentum carries it around during that portion of the revolution when d is separated from e and a is receding from the magnet4 ,it is customary to say that the circuit is closed through the base of the machine1 but this language requires interpretation4 ,it means that a way is provided for the electric current to pass through the base4 ,a person who is expert in language but not in electricity might expect us to say the circuit is open through the base4 ,illustration3 ,fig4 #bi #aj4 ,the ,telegraph ,sounder 7,fig4 #bi74--,this was a toy half a century ago1 but since the days of ,samuel ,finley ,breese ,morse it has become of vast commercial importance4 ,the ,western ,union ,telegraph ,company in #aiji had #baa1eac miles of poles and cables1 #a1chb1ejj miles of wire1 #bd1cba offices1 sent #fh1jec1dci messages1 received #cj1eda1jgb4ee1 expended #bc1aic1ife4ff1 and had #g1cdg1ajf4hi in profits4 ,in the ,united ,states more than #ic1jjj1jjj and in the world at large more than #fjj1jjj1jjj messages are sent annually1 and there are men still living who scoffed at ,morse's ideas as impracticable4 ,it is interesting to contemplate what would happen to the ,stock ,exchange1 to the newspapers1 to the railroads1 to the congressman addressing his constituents from the floor of a legislative chamber1 to business in general1 if the world were deprived of the telegraph4 ,a few years ago a telegraph despatch was sent from ,new ,york to ,san ,francisco1 ,tokio1 ,london1 and back to ,new ,york1 #db1hgb miles1 in three minutes less than an hour4 ,electricity can travel around the world in a fraction of a second1 the time was consumed in repeating the message4 ,i once sent a message from ,new ,york to ,new ,haven to announce that ,i was coming1 and afterward took my train and reached ,new ,haven in time to receive my own message and pay the messenger boy4 ,but ,i have never lost faith in the beneficent results of ,morse's labours4 ,morse 7#agia-ahgb7 was an artist and the first ,president of the ,national ,academy of ,design4 ,he was likewise a professor in ,new ,york ,university and constructed his first experimental telegraph line upon the ,university campus in #ahce4 ,his first public line was built from ,washington to ,baltimore in #ahdd4 ,the ,western ,union ,telegraph ,company was incorporated in #ahef4 ,of course the work of ,morse rested upon that of ,oersted1 in ,copenhagen1 who1 in #ahai1 discovered electro-magnetism1 and upon that of ,joseph ,henry of ,albany1 who in #ahbg first insulated the wires4 ,illustration3 ,fig4 #cj ,the application of the electro-magnet to producing telegraphic signals will be understood by referring to ,fig4 #cj4 ,b is the generator of an electric current--sometimes a battery and sometimes a dynamo4 ,one wire from this goes to the earth1 ,e4 ,the other wire goes through a key1 which1 like a push button or a switch1 serves to open or close the circuit4 ,this is normally closed when not in use4 ,through this the current passes around the electro-magnet ,s1 which attracts the armature a1 causing it to click against a metal stop1 hence it is called the sounder4 ,from this the current passes along the line wire to a distant station and there through the sounder and closed key to the earth4 ,there is likely to be a generator at each station4 ,the current must run continually through the system4 ,if a battery is employed1 the copper sulphate1 or gravity cell1 to be described later1 is chosen1 because it will endure continued usage better than any other4 ,the operator1 in sending signals1 opens the circuit1 the magnets cease to hold down the armatures1 and they are raised by springs and strike against metallic stops above4 ,it is customary to say that the circuit is completed through the earth4 ,this statement misleads some persons into imagining an electric current capable of corroding water pipes and decomposing chemical compounds1 passing through the earth between stations4 ,illustration3 ,photograph by ,helen ,w4 ,cooke4 ,testing the ,telegraphy ,outfit ,perhaps it will help to a better understanding of the truth if we think of a city pumping water out of the ocean1 say to fight fire1 and disposing of it again into the ocean4 ,the ocean currents thus produced are not likely to be destructive4 ,indeed1 just as we measure height from the ocean level as zero1 so we measure electric pressures as from the zero level of the earth's electrical state4 ,illustration3 ,fig4 #ca ,the key used by telegraphers is represented in ,fig4 #ca4 ,it has connected with it a switch to keep the circuit closed when the key is not in operation4 ,the ,morse code of signals consists of dots and dashes1 when printed1 as follows3 a 4 - b - 4 4 4 c 4 4 4 etc4 ,operators learn to read the message by the intervals between sounds4 ,a dot consists of two taps of the sounder with a short interval between1 and a dash consists of two taps with a longer interval between4 ,one tap of the sounder is caused by its descending upon the metal stop below and another by its rising against the upper stop4 ,telegraph sounders are operated on about a quarter of an ampere of current if from a battery circuit1 or on about one tenth of an ampere from a dynamo circuit4 ,the dynamo circuit is supplied with more volts of electric pressure1 and hence its power is ample to cause the armature to strike the metal stops hard enough to be heard by the operator4 ,for example a battery circuit may supply to the sounder a current with these characteristics3 #b volts 4#be amperes 4#e watts1 while a dynamo circuit may give3 #f volts 4#a ampere 4#f watts4 ,telegraph line wires are usually bare1 the insulation being merely the glass knobs at the poles4 ,clean water is a very good insulator but dirty water is a fairly good conductor4 ,a wet telegraph pole may bring so much current to earth as to prevent all sounders on the line from operating4 ,hence the line is separated from the poles by glass4 ,the poles are about one hundred and thirty-two feet apart1 making forty to the mile4 ,the wires are usually galvanized iron one sixth of an inch in diameter4 ,copper conducts six times as well as iron1 and is now replacing iron in the lines4 ,morse laid a submarine telegraph line in ,new ,york ,harbour and suggested a cable across the ocean4 ,but that gigantic undertaking had to await the masterful intelligence of ,lord ,kelvin and the indomitable will of ,cyrus ,w4 ,field4 ,a submarine cable was laid across the ,strait of ,dover in #ahej4 ,it was cut by the anchor of a fisherman a few hours after it was laid4 ,the first attempt to lay a submarine cable across the ,atlantic ,ocean was made in #aheg4 ,two ships of war1 the ,agamemnon of ,great ,britain and the ,niagara of the ,united ,states1 engaged in this undertaking4 ,three hundred miles had been laid when the cable parted where the ocean was more than two miles deep4 ,william ,thomson was on board the ,agamemnon as electrical expert4 ,he went home to study and improve the methods4 ,the next year1 #aheh1 the ,agamemnon and the ,niagara met in midocean each with a portion of the cable on board4 ,the splice was made1 and the ,agamemnon started toward ,ireland and the ,niagara toward ,newfoundland4 ,when six miles apart the cable broke4 ,the ships met again1 made a new splice and again started in opposite directions4 ,they laid eighty miles and the cable parted a second time4 ,they met again1 spliced and laid two hundred miles when it parted for the third time4 ,they met a fourth time1 made the splice and succeeded in laying the first cable from ,ireland to ,newfoundland on ,august #e1 #aheh4 ,in a few weeks the insulation failed and no more messages could be sent4 ,seven years were spent in studying the problem1 and again in #ahfe the ,great ,eastern1 a mammoth ship1 started to lay the cable4 ,william ,thomson was again on board as the expert4 ,when twelve hundred miles had been laid the cable parted in deep water4 ,three times the cable was grappled and brought part way to the surface and lost again4 ,the ,great ,eastern returned to land4 ,the next year1 #ahff1 the ,great ,eastern1 having on board ,william ,thomson 7,lord ,kelvin71 ,mr4 ,canning1 the engineer of the expedition1 and ,captain ,anderson1 in command1 laid the cable which has worked successfully ever since4 ,thomson1 ,canning1 and ,anderson were knighted as a result of their labours4 ,sir ,william ,thomson 7#ahbd-aijg71 afterward ,lord ,kelvin1 is credited with having solved the difficult electrical problems connected with this enterprise4 ,cyrus ,w4 ,field 7#ahai-ahib71 born in ,stockbridge1 ,mass41 helped to secure the many millions of dollars necessary to carry the work to completion4 ,there are now seventy-three cables connecting ,europe and ,america1 and two across the ,pacific ,ocean4 ,cable rates are3 ,new ,york to ,england1 ,france1 ,germany1 or ,holland twenty-five cents a word1 to ,switzerland thirty cents a word1 and to ,japan one dollar and thirty-three cents a word4 ,illustration3 ,fig4 #cb ,the boys were kept very busy now looking up historical and biographical sketches1 as well as working up the many applications of the electro-magnet4 ,the next to be reported was3 #aa4 ,the ,relay 7,fig4 #cb74--,telegraphing from #c1jjj to #aj1jjj miles under the ocean is full of difficulties not now to be explained4 ,of course when we attempt to telegraph many miles upon land we find that the resistance of the wire cuts down the strength of the current so that it will not move the sounder4 ,this1 however1 is readily obviated by the relay devised by ,morse4 ,it simply serves as an automatic key to close a circuit4 ,a diagram will make this clear 7,fig4 #cc74 ,suppose the line wire to be very long and on account of its resistance the current is too feeble to operate a sounder4 ,it is likely to be about 4#jbe ampere where the local sounder may require 4#be ampere or ten times as much4 ,it is easily possible to wind a magnet 7,fig4 #cc71 ,r1 such that 4#jbe ampere will close the armature a1 so that it may complete a local circuit when it would not make noise enough for a sounder4 ,b may represent a local battery of any desired strength which may operate the sounder ,s of that station as loudly as may be desired4 ,illustration3 ,fig4 #cc ,illustration3 ,fig4 #cd #ab4 ,annunciator 7,fig4 #cd74--,we live in a fifth-floor apartment4 ,when we push the button to call the elevator a ,no4 #e appears in the annunciator in the elevator car4 ,this tells the elevator boy where the call comes from4 ,take out two or three screws and the annunciator opens1 revealing a series of electro-magnets like the one shown in ,fig4 #ce4 ,when an electric current passes around the coil it pulls back an iron catch and allows a number to drop so as to show through a small window4 ,the elevator boy1 having noted that the call is from the fifth floor1 pushes up the number and the iron catch holds it until the coil is magnetized again by an electric current4 ,illustration3 ,fig4 #ce ,illustration3 ,fig4 #cf ,illustration3 ,fig4 #cg ,the annunciator has a bell to call attention4 ,a cable of six wires enters this annunciator 7,fig4 #cf74 ,one wire goes direct to the bell and the other five reach the bell through the separate coils of the electro-magnets which control the drops4 ,but how are electrical connections made between a moving elevator car and the push buttons on various floors8 ,the diagram in ,fig4 #cg shows this in elevation4 ,b represents a battery of several dry cells located in the basement4 ,one wire from it runs direct to the push buttons #a1 #b1 #c1 #d1 #e1 located upon the five floors of the house4 ,the other wire from the battery1 together with wires from each of the five push buttons1 all run to a point1 ,a1 half-way up the elevator shaft4 ,here the six wires are gathered into a cable long enough to reach either to the top or the bottom of the elevator shaft4 ,the other end of this cable enters the elevator car and runs to the annunciator4 ,the wire from the battery goes direct to the bell4 ,the wires from the various push buttons go through correspondingly numbered electro-magnets to the bell4 ,when1 therefore1 we pushed the button on the fifth floor1 we closed the gap in the electric circuit at that point4 ,the current came up from the battery1 passed through the button1 went down the cable to the car1 went through electro-magnet ,no4 #e1 went through the bell1 and returned direct to the battery1 thus completing the circuit4 ,annunciators are used about buildings to call other attendants1 besides the elevator boy4 ,they are likewise used in burglar alarms to inform the householder which door or window is being forced4 ,they are used in the fire department to tell what part of the city the call came from4 ,illustration3 ,fig4 #ch #ac4 ,the ,electric ,bell and ,buzzer 7,fig4 #ch74--,so common a thing as an electric bell really belongs to the present generation4 ,bells were either novelties or toys when ,i was your age4 ,they cost then many times what they do now and then were poorly made4 ,nobody dared to trust them for front-door bells4 ,it was necessary to have a card permanently posted over the push button saying1 ,if the bell does not ring1 knock4 ,in those days batteries were troublesome to care for1 houses were not wired when built1 and no one had learned the art of concealing the wires neatly4 ,the buzzer is simply a bell minus gong and hammer4 ,those shown in ,fig4 #ch ring well on a single dry cell4 ,a cell costing twelve cents operated one for two years while it was used as a call bell from dining room to kitchen1 the current required being 4#ae ampere4 ,illustration3 ,fig4 #ci ,illustration3 ,electric ,bell ,the connections are shown in the diagram 7,fig4 #ci74 ,suppose the current to enter at the binding post a1 pass around the magnets b and then to the post c4 ,the armature d normally rests against the post c and the current finds its way along this to the post e and thence back to the battery4 ,but as soon as the current passes1 b becomes a magnet and pulls the armature d away from the post c1 thus breaking the circuit1 when b ceases to be a magnet and a spring pushes the armature d back against the post c to repeat the operation4 ,the armature d carries a hammer which strikes the gong f4 ,if the wire1 which is usually connected with the binding post e1 is connected with the post c1 the clatter bell is changed to a single-stroke bell1 and if the gong and hammer are removed the bell is changed to a buzzer4 ,illustration3 ,fig4 #dj ,in the case of the buzzer1 by changing the length of the armature or by weighting it1 we may change the time of its vibrations and its tone4 ,the connections between battery push button and bell form a complete circuit4 ,in ,fig4 #dj ,b represents a battery1 usually of dry cells1 ,b' represents the bell1 and ,p represents the push button4 ,the electric circuit is open1 7that is1 there is a break in the conductor7 at ,p until some one pushes the button1 that is1 simply pushes against a spring so as to cause a piece of metal to bridge the gap in the conductor4 ,then we say the circuit is closed4 ,illustration3 ,fig4 #da ,illustration3 ,fig4 #db ,push button devices and switches are innumerable4 ,in every case they are simply devices for pushing one piece of metal against another and completing the circuit for an electric current4 ,every one should unscrew and examine a few of them1 both for the pleasure of seeing how they work and to learn how to make them work when they sometimes fail4 ,not only in bells but in all other instruments where electro-magnets are used1 the magnets are placed in pairs1 fastened together upon an iron base4 ,they are wound so that the free ends are made opposite poles by the electric current4 ,like a horseshoe magnet1 they form one magnet4 ,the two poles thus placed are mutually helpful and each is stronger than it would be if separated from the other4 ,illustration3 ,fig4 #dc #ad4 ,electric ,clocks1 ,self-winding ,clocks1 ,programme ,clocks4--,a pretentious-looking thing which appeared like a dish pan with a glass bottom was opened by the boys and found to be the simplest of all clocks4 ,it had an electro-magnet like that in ,fig4 #dd4 ,a strip of iron acting as an armature across the free ends of this magnet1 pushed like a finger against the cogs of a wheel4 ,this wheel was on the axle of the minute hand and it had sixty cogs4 ,the electric circuit was closed through the magnet for an instant each minute and the armature pushed the wheel ahead one cog4 ,thus it made one complete revolution in an hour4 ,a train of four other cog-wheels caused the hour hand to trail after at one twelfth the speed of the minute hand4 ,this machinery made simply a small handful in an eighteen-inch stamped-metal dish-pan costing fifteen dollars4 ,illustration3 ,fig4 #dd ,a self-winding clock was opened and found to contain two dry battery cells1 an electro-magnet which operated very much like that of a clatter bell1 the hammer like a finger poking against the cogs of a wheel4 ,once an hour the long hand closed the circuit through the battery and the magnet and its armature swung back and forth long enough to give the cog wheel one complete revolution and wind a spring1 which it carried upon its axle4 ,this spring kept the clock running one hour1 until the next winding4 ,illustration3 ,fig4 #de ,the programme clocks which were examined were self-winding clocks1 but were connected by wires to the master clock which corrected them each hour4 ,each time the long hand of the master clock came to twelve it closed an electric circuit through all the clocks in the system4 ,in each clock the current passed around an electro-magnet and caused it to pull an armature against a metal stop and set each long hand exactly at twelve4 ,this master clock is sometimes situated many miles away and may correct the time for a whole city4 ,thus a master clock at ,washington1 ,d4 ,c41 furnishes standard time to all parts of the ,united ,states4 ,the master clock which we examined also closed the circuit at proper intervals through a series of programme bells placed in the various class rooms1 and these called and dismissed classes automatically4 #ae4 ,watchman's ,time ,detector 7,fig4 #de74--,this is a device to compel a watchman to make his appointed trips4 ,push buttons or switches are distributed about the building at various points1 and it is made his duty to close the circuits at these points at stated times4 ,when he does so1 the fact is recorded by electro-magnets puncturing1 or1 in some way1 marking a revolving time card in the clock4 ,illustration3 ,fig4 #df #af4 ,circuit ,breakers 7,fig4 #df74--;,electro-magnets are used to open switches and thus protect dynamos and other machines against a larger electric current than they are able to carry4 ,the switch is held closed by a spring which1 by an adjusting device1 may be tightened or loosened4 ,a dynamo which we examined had its circuit breaker adjusted so that it would remain closed if any current under #aejj amperes passed1 but if a greater current than that passed it would strengthen the magnet sufficiently to open the switch and thus break the circuit4 #ag4 ,separating ,iron from ,ore4--,in #ahig ,edison first proposed to use an electro-magnet to separate iron from crushed earth4 ,fig4 #dg represents the process4 ,e is an electro-magnet4 ,s is the stream of crushed ore containing iron4 ,gravity would cause all the material to fall into bin ,a1 but the electro-magnet ,e pulls that portion of the material which is magnetic to one side so that it falls into the bin ,b4 ,illustration3 ,fig4 #dg ,illustration3 ,fig4 #dh #ah4 ,lifting ,magnets4--,electro-magnets are made for use with hoisting apparatus to save the trouble of manipulating grappling hooks1 etc4 ,they may lift barrels and boxes of iron1 the wood of the barrel or box being transparent1 we say1 to the magnetic influence4 ,that is1 the magnet will attract iron through the wood just as light will shine through glass4 ,such magnets are used to pick up from the bottom of the sea cases of hardware from wrecked ships4 7,see the accompanying illustration1 ,fig4 #dh47 ,in such cases the electric conductors which lead to and encircle the magnets must be well insulated from the water of the sea1 otherwise the electric current would take the shorter path from one line wire through the sea water1 which is a fairly good conductor1 and back by the other line wire1 rather than go the path of greater resistance around the magnet4 ,electro-magnets are coming into use in foundries1 etc41 for lifting heavy iron castings4 ,illustration3 ,fig4 #di #ai4 ,electro-,magnet on ,starting ,box4--,as was explained under electric motors1 a starting box is simply a series of resistance coils r1 r1 r1 r1 r1 in ,fig4 #di4 ,when the motor is not in use the switch l rests upon the point #a and no electric current passes4 ,when the switch is moved to point #b1 the current entering at a passes to the pivot of the switch and up the metal strip l to the point #b1 then around the series of coils1 r1 r1 r1 r1 r1 to the post b and thence back to the generator4 ,as the switch is moved to the right1 the current passes through less and less of this resistance until1 when it reaches point #g1 all the coils of resistance are cut out1 that is1 they are not in the path of the current4 ,now the motor has reached its full speed and is developing enough counter-electro-motive force to protect itself against too much current4 ,through a shunt1 however1 a portion of the current passes from a to b around the electro-magnet e1 the two poles of which are presented to the metal strip l1 which must be of iron4 ,this magnet holds the switch over so long as the current is on1 but when the current is cut off1 by opening a switch in the line wire1 e ceases to be a magnet and l is carried back to point #a by a spring4 ,thus an extra resistance must always be in circuit when the motor is first started4 ,those who start motors are expected to move the lever l of the starting box slowly from point to point1 pausing a second or two on each to give the motor time to acquire proper speed for its protection4 ,how too great a current would burn out a motor will be explained later4 ,the motor man handles a lever for starting his car1 which works like that of the starting box4 ,his starting box1 however1 is called a controller4 ,although it accomplishes the same result as the starting box it has a wholly different and vastly more complex mechanism than that already described4 ,the elevator boy1 who runs our electric elevator1 handles a lever which also does the same thing through far different mechanism4 ,indeed1 in his case electro-magnets are used to prevent him from cutting out resistance too fast if he should move his lever too quickly4 #bj4 ,starting ,switches for ,electric ,elevators4--,the motor man has to be instructed particularly how he should handle the lever of his controller1 and he is trusted to follow his directions to some extent1 however lacking in intelligence and integrity he may be4 ,but the elevator boy receives scarcely any instructions about his machine1 and1 indeed1 his machine has been constructed pretty nearly foolproof4 ,it will automatically correct his errors of management4 ,if he throws the handle from one extreme to the other1 all resistance cannot be thrown out instantly1 but this is accomplished by a series of electro-magnets closing one switch after another and thus cutting out resistance gradually4 #ba4 ,arc ,lamp ,feed4--,as will be explained later1 an arc lamp must have its carbons touching one another when the current is first thrown on1 and then the carbons must be drawn apart from a quarter to half an inch4 ,the upper carbon is lifted away from the lower one by a portion of the current passing by means of a shunt around an electro-magnet4 ,illustration3 ,fig4 #ej ,illustration3 ,fig4 #ea ,illustration3 ,fig4 #eb #bb4 ,volt meter4--,the volt meter measures the pressure of an electric current4 ,the volt meter which we examined looked outside like our ammeter1 and when we removed the face it appeared inside like an ammeter4 ,there was the steel magnet of horseshoe shape to furnish a field 7,fig4 #ea71 and there was an electro-magnet poised between its poles for an armature4 ,the armature in the volt meter1 however1 had wound upon it finer wire and more of it than was the case in the ammeter4 ,there was no shunt wire in the volt meter as there was in the ammeter4 ,we connected in series a fluid cell 7to be described later71 the ammeter1 and the volt meter 7,fig4 #eb74 ,the ammeter shunt was removed so that all the current went through its armature4 ,the volt meter needle went to one which was two thirds of the scale 7,fig4 #ec71 and the ammeter needle indicated 4#jaf4 ,that is1 this particular cell can push sixteen thousandths of an ampere through the resistance of this volt meter1 and 4#jaf ampere passing through the armature of this volt meter will magnetize it sufficiently to move it against its spring1 say sixty degrees4 ,illustration3 ,fig4 #ec ,illustration3 ,fig4 #ed ,illustration3 ,fig4 #ee ,we put into the circuit a lot more fine wire for resistance1 ,r 7,fig4 #ed71 so that the volt meter needle went only half as far as before1 that is to 4#e4 ,the ammeter indicated only half as much as before1 that is 4#jjh ampere4 ,we put in resistance enough to bring the volt meter needle down to 4#be and the ammeter indicated one quarter of the original current4 ,we put in less resistance1 bringing the volt meter needle to 4#ge1 and the ammeter indicated three fourths of the original current4 ,evidently the volt meter is merely an ammeter with a different scale marked upon its card4 ,with a pen we marked upon the card of the volt meter a true ammeter scale 7,fig4 #ee74 ,illustration3 ,fig4 #ef ,in order to understand the volt meter1 let us turn our attention for a moment to ,fig4 #ef4 ,i have arranged the water tank ,t at such a height above the faucet ,f that when the faucet is opened one quart of water will flow in a minute4 ,if ,i partially close the faucet1 making the opening one half as large 7that is1 offering twice the resistance to the flow71 half a quart will flow in a minute4 ,if ,i make the resistance four times as great only one quarter of a quart will flow in a minute4 ,it is evident that ,i could arrange a scale underneath the handle of the faucet to indicate the quantity of water flowing1 just as the ammeter and volt meter indicate the quantity of electricity which flows4 ,if now that much is understood1 it will be easy to learn how the water faucet may be used to measure water pressure and the volt meter in like manner used to measure electric pressure4 ,having set the faucet so that a quart will flow per minute1 let us put on a longer tube p1 and move the tank up to another shelf so that the distance from the water level in the tank to the faucet is twice as great as before4 ,under the increased pressure water runs through the faucet twice as fast and we now get two quarts per minute4 ,i purposely placed the tank out of sight behind a partition so that you might practise judging the water pressure by the flow at the faucet4 ,we cannot very well talk about pressure in quarts4 ,we might talk about it in pounds1 but if we used this apparatus much we should probably get into the habit of talking about the pressure from one shelf1 two shelves1 three shelves1 etc4 ,in order that the pressure might remain nearly constant during the experiment we would probably introduce resistance 7that is1 partially close the faucet7 so that the water level should not fall much4 ,we might1 for example1 set the faucet so that half a pint would flow in a minute when the tank was on the first shelf4 ,then a pint per minute would flow when the tank was on the second shelf and one and a half pints per minute when the tank was on the third shelf1 etc4 ,thus we should infer the pressure by measuring the quantity4 ,one more illustration and the case will be clear4 ,to save the trouble of measuring the quantity of water which flows through the faucet1 suppose ,i introduce the device represented in ,fig4 #eg4 ,w is a small water wheel comparable to the armature of the volt meter4 ,it carries a pointer which moves over a scale just as in the case of the volt meter4 ,illustration3 ,fig4 #eg ,it has a spring coiled around its axle which tends to keep the pointer at #j1 as in the case of the volt meter4 ,the tank is placed upon the first shelf1 the faucet is fixed so that a small amount of water flows and the needle moves to a certain figure upon the scale4 ,we will mark this point one and call it first-shelf pressure4 ,the tank is lifted to the second shelf and the index moves to another point1 which we will mark two and call it second-shelf pressure4 ,the tank is lifted to the third shelf and the index moves to a third point1 which we will mark three and call it third-shelf pressure1 etc4 ,ordinarily we measure water pressure with an instrument which allows no water to run to waste1 but in measuring electric pressure by the volt meter some current must pass through the instrument1 just as in the case of our water-wheel illustration in ,fig4 #eg4 ,we put in large resistance so as to make this current as small as possible1 while we let enough pass to move the armature4 ,illustration3 ,fig4 #eh ,now let us return to the volt meter itself4 ,by referring to ,fig4 #ee1 we see that it requires 4#jbd ampere to move the needle of the volt meter clear across the scale1 and we have found that one fluid cell was able to send enough current through the resistance of the armature to move the needle two thirds of the way across the scale4 ,at this point we find ,fig4 #a1 which might be read one-cell pressure4 ,we prefer to commemorate the name of one of the workers in the field of electricity and call this pressure a volt after ,alessandro ,volta 7#agde-ahbg71 born at ,como1 ,italy4 ,it is the electric pressure which is produced by one fluid cell of a certain kind4 ,we say1 then1 that one volt pushes through the resistance of this armature 4#jaf ampere4 ,half a volt would push through the resistance of the armature half as much current or 4#jjh ampere4 ,at this point we put 4#e4 ,thus each of the figures in the lower row 7,fig4 #ee7 shows what part of a volt is required to send enough current through this particular armature to move the needle to that point4 ,illustration3 ,fig4 #ei ,we found out how much wire was wound upon the armature and put exactly the same amount in the outside resistance1 ,r 7,fig4 #ei74 ,the needle now showed that one volt is able to push through twice the resistance of the armature only half as much current1 and the needle stopped at 4#jjh ampere4 ,if this were to be the resistance in the volt meter circuit one volt should stand under 4#jjh ampere and two under 4#jaf and three under 4#jbd4 ,it is evident then1 that1 if we know the internal resistance of a volt meter1 we may make it capable of measuring greater electrical pressures by adding the proper amount of resistance4 ,by putting at ,r1 7,fig4 #ei7 nine times the internal resistance of the instrument1 thus multiplying the total resistance tenfold1 the figures upon the scale of volts may be read as whole numbers from one to fifteen4 ,in this case it will require fifteen cells to push the needle clear across the scale and ten cells to push it two thirds of the way across4 ,if now we add enough external resistance to multiply the resistance of the armature a hundred fold it will require #aej volts to push 4#jbd of an ampere through the armature and pull its needle clear across the scale4 ,in this case the figures upon the scale of volts are multiplied by one hundred and read from ten to one hundred and fifty4 ,such a scale would adapt this volt meter for use with our #aaj-volt lighting circuit4 ,volt meters are made with a series of such external resistances1 called multipliers1 attached so that they may be easily thrown into the circuit4 ,it is evident that we need some term so that we may speak of quantities of resistance4 ,this need has given rise to a unit of resistance called an ohm1 after ,george ,simon ,ohm 7#aghi-ahed7 born at ,erlanger in ,bavaria4 ,two inches of ,no4 #cf ,german silver wire1 such as is wound upon the armature of this volt meter1 gives one ohm of resistance4 ,there are #abe inches of this wire upon the armature4 ,its resistance is1 therefore1 #fb4e ohms1 and we may1 therefore1 say that one volt of electric pressure can push through #fb4e ohms of resistance 4#jaf of an ampere of current4 ,ohm discovered this relationship in #ahbg1 and formulated it as follows3 volts_/ohms amperes 7not1 however1 using these words74 7#a volt7_/7#fb4e ohms7 4#jaf ampere4 #fb4e7 #a4jjjj 74#jaf #fbe ---- #cgej #cgej ---- ,this is called ,ohm's law1 as every candidate for college admission will hear and hear again4 ,illustration3 ,fig4 #fj ,volt meters and armatures for the alternating current have electro-magnets for their fields as well as for their armatures4 ,such instruments are equally well adapted for either direct or alternating currents4 ,for when the current reverses its direction it reverses in field and armature alike1 and thus a repulsion between like poles is maintained4 ,such an instrument1 however1 cannot respond to as slight a current as those previously described1 since they must consume some energy in both field and armature4 #bc4 ,telephone ,receiver 7,fig4 #fa74--;,it requires a stretch neither of the imagination nor of the truth to call a telephone receiver an electro-magnet1 although perhaps it has never been called that before4 ,we took it apart and found that it consisted of a steel-bar magnet m 7,fig4 #fb71 with a small spool of wire w around one end of it4 ,the ends of the wire on the spool run along inside the hard rubber shell to the two binding posts a and b at the other end4 ,a disk of sheet iron ,s is held in the large end of the case very near to1 but not quite touching1 the end of the magnet4 ,when an alternating current is sent through the wire upon the spool it causes rapid changes in the strength of the magnetic field1 if not reversals of the poles of the field1 and the iron disk is made to vibrate1 keeping time with the alternations of the current4 ,illustration3 ,fig4 #fa ,illustration3 ,fig4 #fb ,in this laboratory we have seen that our current has sixty alternations per second4 ,when it is connected with the receiver the disk1 therefore1 makes sixty vibrations per second1 and produces a tone which has very nearly the pitch of ,c two octaves below the middle ,c upon the piano4 #bd4 ,spark ,coil 7,fig4 #fc74--,the automobile spark coil which we have already used is an electro-magnet4 ,the battery sends a current through wire coiled around an iron core4 ,at one end of this iron core is an iron armature which is made to vibrate in precisely the same manner as the armature of an electric bell4 ,this makes and breaks the current and causes rapid changes in the strength of the field4 ,a rapidly changing magnetic field may be used to develop electricity in a conductor1 as we have already seen in the case of the dynamo4 ,illustration3 ,fig4 #fc ,how it is used in the automobile spark coil will be shown later4 ,it is sufficient now to mention it as a case of a magnetic field produced by an electric current passing through a wire coiled around an iron core1 or1 in short1 an electro-magnet4 ,induction coils1 ,ruhmkorff coils1 and transformers1 to be described later1 are closely related to this4 ,they all create magnetic fields in the same way and are all electro-magnets4 ,illustration3 ,fig4 #fd4 ,transformers ,,vii ,,electric ,,heating ,it was ,washington's birthday4 ,the schools were to have a holiday and the ,science ,club was to hold a special1 open meeting at which ,i had been asked to present the subject of electricity in the household4 ,i replied to the programme committee that that was too large a subject1 but that ,i would talk upon electric heating4 ,i warned them1 however1 that it would be a dry study1 and not an entertainment4 ,they replied that the father of his country had been born at a time of the year when the weather was unfavourable to outdoor sports1 and that ,february usually found them acclimated to vigorous study4 ,neither they nor their friends objected to study if it seemed to have a motive4 ,i found an audience composed of old and young1 men and women1 girls and boys4 ,most of them had left school--many of them because their teachers thought they were incompetent to continue4 ,illustration3 ,fig4 #fe ,not far from here is a wheel in the middle of a wheel 444 as for their rings they are so high that they are dreadful 444 and the spirit of the living creature is in the wheels4 ,those wheels are now sending the electric current to this room for our experiments4 ,i propose to show that we convert electricity into heat by offering resistance to its flow4 ,experience teaches us that resistance to motion always produces heat4 ,at ,niagara ,falls thousands of tons of water descend at the rate of one hundred and sixty feet in three seconds4 ,when the water reaches the bottom of the falls1 it is moving a little faster than a mile a minute4 ,the resistance which this mass meets after its fall retards its motion and generates heat4 ,hundreds of meteors fall into our atmosphere daily1 travelling a thousand times as fast as the waters of ,niagara ,falls4 ,the resistance to their motion1 which our atmosphere offers1 heats them white hot1 melts them1 vaporizes them1 burns them up1 so that very few of them reach the solid earth in a solid condition4 ,an iron spile driver1 measuring two cubic feet1 weighs about half a ton4 ,when it falls sixteen feet upon the end of a spile it is moving at the rate of twenty miles an hour4 ,the energy of this moving mass depends upon both its weight and its velocity1 and when its motion is arrested by the spile that energy of motion is largely converted into heat energy1 from which both the spile and the spile driver get hot4 ,a piece of iron may be made red hot by pounding it with a trip hammer4 ,count ,rumford found1 in #agih1 while boring cannon in the arsenal at ,munich1 that the resistance which the iron offered to the motion of the boring tool furnished heat enough to boil water4 ,seven hundred and seventy-eight foot pounds of mechanical energy when converted into heat would raise one pound of water 7one pint7 one degree4 ,this is called the ,british thermal unit4 ,the spile driver1 weighing #ajjj pounds1 falling #af feet upon a spile1 produces heat enough to raise #a pint of water #bj degrees4 ,illustration3 ,fig4 #ff ,here are two binding posts1 a and b1 #h feet apart 7,fig4 #ff71 connected by copper wires with the dynamo circuit4 ,the volt meter indicates #aab volts of pressure4 ,i will close the circuit by stretching between a and b #h feet of ,no4 #bd iron wire4 7,this wire is about the thickness of a common pin47 ,the iron wire offers resistance to the flow of the electric current1 thereby producing heat--heat enough as you see to make the wire white hot1 indeed heat enough to raise it to something over two thousand degrees ,fahr41 for now you see it has melted4 ,we will put in a fresh piece of wire and connect also the ammeter in the circuit 7,fig4 #fg74 ,as ,i close the circuit the needle of the ammeter at first indicates #bj or #cj amperes1 but in a second drops to #h amperes1 and remains there a second until the wire melts and falls apart4 ,one hundred and twelve volts of electric pressure are able to push #h amperes of electricity through this wire when hot4 ,illustration3 ,fig4 #fg 7#aab volts7_/7#ad ohms7 #h amperes #aab volts #h amperes #hif watts #gdf watts one horse-power ,hence it required about one and one fifth horse-power to melt the wire in a second1 and the heat produced was a little less than one ,british thermal unit1 a unit much used by engineers4 #a pound raised #a foot #a foot pound #eej foot pounds per second #a horse-power #ggh foot pounds 7#a4d ,h4-,p47 #a ,b4 ,t4 ,u4 7,british thermal unit7 heat required to raise #a pound of water #a ,fahrenheit #a volt #a ampere #a watt #gdf watts #a horse-power ,in order to hold back #aab volts of electric pressure so that not more than eight amperes of electricity should pass1 the iron wire must have offered about #ad ohms of resistance4 ,the behaviour of the ammeter needle showed that the wire offered very much less resistance when cold than when hot4 ,indeed eight feet of ,no4 #bd iron wire offers about one and one third ohms resistance when cold1 hence heat had increased its resistance to the passage of the electric current tenfold4 ,this piece of iron wire offered resistance to the flow of the electric current4 ,it offered resistance to the motion of the dynamo4 ,this offered resistance to the steam-engine which drives the dynamo4 ,this caused the governor of the engine to open and pass more steam from the boiler4 ,this reduced the pressure at the steam gauge4 ,this caused the fireman to shovel more coal into the furnace4 ,the heat of the burning coal melts the wire1 but it does it only after several changes4 ,first1 it is converted into mechanical energy in the steam-engine with great loss--about nine tenths being lost4 ,second1 it is converted into electrical energy by the dynamo1 with some loss1 and1 third1 it is conducted to the iron wire and converted back to heat with still further loss4 ,it is evident that the most economical way to heat the wire would be to take it to the furnace4 ,yet all electric cooking is done by sending electric current through wires embedded in the walls of the cooking utensils1 and it is the most wasteful method of using the energy stored in coal that has yet been devised4 ,illustration3 ,fig4 #fh ,that merely connecting the binding posts a and b 7,fig4 #fg7 by a small piece of wire should throw a load upon the dynamo miles away2 should offer resistance to its motion1 and make it require #a4ah horse-power more of energy to keep up its speed of revolution1 is1 indeed1 uncanny4 ,i will attempt to make it seem more real4 ,at one end of the lecture table ,i have a rotary pump ,p 7,fig4 #fh74 ,the end of the rubber tube a1 which leads to the pump is lying upon the table outside of the tank of water1 ,t4 ,while things are in this condition ,i move the crank which operates the pump with perfect ease4 ,now while still turning the crank ,i pick up the tube a and drop its free end into the water tank4 ,i cannot now conceal the fact1 even if ,i were disposed to do so1 that ,i must work hard to keep the pump going4 ,the pump itself tells you by its laboured sound that it is working hard1 and the stream of water which issues from the pipe b tells how much work ,i am performing4 ,the pump is discharging five and a half pints of water per second1 that is #e4e pounds1 and it raises this water #aj feet4 ,hence ,i am doing #ee foot pounds of work per second1 which requires one tenth of a horse-power4 ,here is a lad who consents to try the experiment for us4 ,he turns the crank easily while ,i am holding the tube a out of the water1 but when ,i lower it into the water he finds the resistance so great that1 tug however much he may1 he is unable to keep the pump going4 ,at the other end of the table ,i have a small hand dynamo1 ,d 7,fig4 #fh71 ,m is an ammeter1 ,v is a volt meter1 ,s is a switch4 ,all the wires are good-sized copper1 and offer little resistance1 except that stretched between the binding posts a and b4 ,this is a piece of fine ,german silver wire4 ,while the switch is open ,i turn the crank of the dynamo with perfect ease4 ,a small amount of current is going through the volt meter1 but this is too slight to offer any perceptible resistance to the motion of the machine4 ,notice that the volt meter needle moves according to the speed of revolution4 ,if ,i turn the crank once a second the needle stands at #be volts4 ,the electric pressure increases or decreases according to whether ,i rotate the armature faster or slower4 ,now ,i will attempt to keep the machine revolving at a constant rate while ,i close the switch ,s1 and surely you must see that ,i have hard work to do so4 ,the wire a b has now become red hot4 ,the volt meter shows #be volts of pressure1 and the ammeter shows #c amperes of current4 ,twenty-five volts #c amperes #ge watts1 which require one tenth of a horse-power 7#gdf watts #a horse-power74 ,the lad now takes my place at turning the machine and finds it easy when the switch is open1 but ,i actually overload him by merely closing the switch4 ,heating the wire red hot requires more energy than he is able to put forth4 ,i proposed to the president that my lecture close at this point1 and that each one in the room have a chance to feel the load which was thrown upon the dynamo each time it was required to heat the wire4 ,i suggested that each person should get a realizing sense of this fact1 first by doing the work himself1 and second by going home and reflecting upon this hint4 ,when the switch is closed three amperes of electricity pass around the circuit4 ,this increases the magnetism in both the field and the armature of the dynamo1 and it requires one tenth of a horse-power more to keep the armature moving within the field against this magnetic pull4 ,i further desired to announce that during this hour ,i had delivered to them the second key to the ,electrical ,show which ,i had promised a few days ago4 ,the second key is3 ,heat 7and light7 is produced by offering resistance to the flow of the electric current4 ,the first key is the electro-magnet4 ,these two unlock all the mysteries of the show4 ,the president closed the formal exercises with the facetious remark that ,i had warned them before the lecture that they must work1 so now each would be expected to take a turn at the cranks of the pump and dynamo4 ,,viii ,,applications ,,of ,,electric ,,heating ,the programme committee decided that each member of the ,science ,club should busy himself looking for applications of electric heating and should consult me freely about the matter4 ,my telephone was kept busy1 my laboratory was in great demand1 and we were all getting a good deal more education than the school was giving us credit for4 ,the boys generally came to me in pairs1 and each pair having worked up some illustration of heat produced by electricity reported it to the club4 ,these were spread by the secretary in due form upon the minutes of the club and constituted ,the ,proceedings of the ,science ,club4 ,illustration3 ,fig4 #fi #a4 ,the ,electric ,sad ,iron 7,fig4 #fi74--,removing three screws the iron comes apart1 revealing a lot of ,no4 #bd ,german silver wire wound upon a sheet of mica4 ,this is put between other sheets of mica 7,fig4 #gj7 and tucked away within the body of the iron4 ,german silver offers about twice the resistance of iron when it is cold1 but1 at the temperature of the sad iron when in use1 there is not much difference between the resistance of the two metals4 ,german silver wire1 however1 does not rust as iron wire would1 and hence it is chosen4 ,german silver is an alloy of copper1 zinc1 and nickel4 ,illustration3 ,fig4 #gj ,we put the #aab-volt current upon this wire of the iron1 and according to the ammeter it passed #d amperes4 ,its resistance must therefore have been #bh ohms4 7#aab volts7_/7#bh ohms7 #d amperes ,electricity costs us about #aj cents per kilowatt hour4 ,that is #aj cents for #ajjj watts for an hour1 or #a cent for a hundred watts for an hour1 or1 on a #ajj-volt current1 #a cent for an ampere for an hour4 ,it1 therefore1 costs about #d cents or1 more accurately1 #d-a_/b cents an hour to heat this iron4 ,persons sometimes carry electric irons with them1 when they travel1 to iron pocket handkerchiefs and other small articles while stopping at a hotel4 ,before connecting an iron in a chandelier one must know the voltage used in the building4 ,if the voltage in use in the building is not the same as that stamped upon the iron1 it is not safe to connect it4 ,not knowing this1 many persons have had the embarrassment of blowing a fuse and extinguishing their own lights1 and perhaps those of others in the same building1 and very likely also ruining the iron4 ,suppose we take for example this iron stamped #aaj ,v2 #djj ,watts4 7,a slight variation of #e or #aj volts will not injure an iron47 ,the wire in this iron we found to offer about #bh ohms resistance when hot1 and it lets pass #d amperes4 ,this is about all the current which it is able to carry without melting4 ,now suppose a #bbj-volt current is used in the building where it is proposed to connect the iron4 ,this would force through the wire enough current to melt it4 ,the wire was seen to be at a very dull-red heat when examined in a dark room4 ,its temperature was about nine hundred degrees4 ,at this temperature its resistance is about three times what it is when cold4 ,we estimated by measurements that the iron contained about twenty-five feet of the wire4 ,the boys then took twenty-five feet of ,no4 #bd ,german silver wire and stretched it between two nails driven up in the laboratory 7,fig4 #ga1 a b74 ,the dynamo current was then sent through this4 ,the end1 c1 of the wire from the dynamo was provided with a metal clip which could be slid along on the ,german silver wire4 ,sliding this to the left1 and thus shortening the distance on the ,german silver wire through which the current must pass1 increased the amount of current and heated the wire hotter4 ,the resistance decreases as the wire is shortened4 ,illustration3 ,fig4 #ga ,the boys wound this wire upon a piece of asbestos board 7,fig4 #gb71 about nine inches square and one eighth of an inch thick1 taking care to keep the successive turns half an inch apart4 ,asbestos paper was wrapped around this4 ,the two ends of the wire were left free for connections4 ,this they called a hot plate4 ,illustration3 ,fig4 #gb #b4 ,electric ,hot ,plate 7,fig4 #gc74--,this when opened was found to have wire coiled up inside in the same manner as the sad iron4 ,indeed the sad iron supported bottom side up makes a perfectly good hot plate4 ,the particular hot plate which we examined had a three-point switch which gave three different heats for the plate4 7,see ,fig4 #gd47 ,when the switch ,s is upon the first point the current goes through #aab ohms of resistance and #a ampere passes3 7#aab volts7_/7#aab ohms7 #a ampere ,illustration3 ,fig4 #gc ,illustration3 ,fig4 #gd ,this warms the plate slightly--enough to keep food warm which has been already cooked4 ,this costs about one cent an hour4 ,when the switch is placed upon the second point the current goes through #ef ohms of resistance and #b amperes pass4 7#aab volts7_/7#ef ohms7 #b amperes4 ,this makes the plate warmer and is adapted to certain cooking processes4 ,it costs about two cents an hour4 ,when the switch is placed upon the third point the current goes through #bh ohms of resistance and #d amperes pass4 7#aab volts7_/7#bh ohms7 #d amperes4 ,illustration3 ,fig4 #ge ,we placed upon this hot plate a basin containing #a pint of water 7equals #a pound7 and heated it from the temperature of the room 7#fh degrees7 to boiling 7#bab degrees7 in #g minutes and then put an egg in and boiled it #c minutes4 ,using #d amperes for #aj minutes cost two thirds of a cent4 ,if it takes #g minutes to boil a pint of water it would require #a hour to boil a gallon upon this hot plate using #d amperes1 or #ddh watts4 ,that is1 it costs us about #d4e cents a gallon to boil water by electricity4 ,the cost is usually put at three and a half cents per gallon1 but much depends upon conditions4 #c4 ,traveller's ,cooker 7,fig4 #ge74--,this consists of a hot plate with a covered basin permanently attached to it4 #d4 ,electric ,coffee ,percolator 7,fig4 #gf7 consists of a hot plate with a coffee percolator to sit upon it4 ,the coffee percolator might sit upon any other hot plate or this hot plate might serve any other purpose1 but people do not seem to think of that4 ,illustration3 ,fig4 #gf #e4 ,electric ,chafing-,dish 7,fig4 #gg7 consists merely of an electric hot plate with a chafing-dish attached4 ,the electric coffee percolators and chafing dishes require from #cjj to #fjj watts according to size4 ,if used on the #aaj-volt current they take about #c to #f amperes1 and if adapted to the #bbj-volt current they take from #a-a_/b to #c amperes1 but cost the same to operate in either case4 ,they have connected with them flexible cords and plugs to screw into the lamp sockets4 ,illustration3 ,fig4 #gg #f4 ,electric ,broilers are merely hot plates1 generally corrugated to conduct off the melted fat4 ,one that we examined had a switch for three heats3 low1 requiring #cfj watts--costs #c4f cents per hour2 medium1 requiring #fjj watts--cost #f cents per hour2 high1 requiring #abhj watts--cost #ab4h cents per hour4 #g4 ,electric ,oven4--,this one has double walls to retain the heat and has two large hot plates1 one on the bottom and one on the top4 ,it is large enough to hold four loaves of bread4 ,it required #aebj watts for #dj minutes to heat it to the baking temperature and one hour to bake the bread4 ,hence the cost of the electricity is about #be cents1 about what the bread would cost in the market4 #h4 ,electric ,incubator4--,this is simply a well-ventilated oven warmed by an electric hot plate and automatically controlled so that it keeps a constant temperature of #ajc degrees4 ,under these conditions chickens hatch from hens' eggs in three weeks4 ,an incubator for #e dozen eggs was found to take #be cents' worth of electricity for the whole process of incubation4 #i4 ,electric ,toaster4--,the wire coiled up in sad irons and hot plates becomes hot enough to scorch cloth and paper1 and even set fire to them if they come in direct contact4 ,we proved this by opening the iron and touching paper to the wire while it was carrying the current4 ,we also lighted a cigar by touching it to the wire4 ,electric toasters have the hot ,german silver wire simply covered by a screen4 #aj4 ,electric ,cigar ,lighters 7,fig4 #gh74--,the one we examined hung by a flexible cord from the chandelier4 ,it had a small disk on the side which contained a lot of fine wire covered by perforated mica4 ,the wire became red hot when the push button in the handle was pressed4 ,it took half an ampere of #aaj-volt current1 and operated only while the button was pushed4 ,as near as we could calculate it cost 4#jjjc of a cent to light a cigar4 ,illustration3 ,fig4 #gh ,illustration3 ,fig4 #gi #aa4 ,electric ,curling ,iron 7,fig4 #gi74--,one who has flat hair needs no curling iron1 but those who have round hair may curl it temporarily1 if they will unscrew an electric light bulb and screw into its socket the plug of an electric curling iron4 ,the flexible cord contains two wires insulated from each other4 ,one of these wires is attached to the outer shell of the plug1 the other wire is attached to the central button of the plug4 ,these make connections with the two separate dynamo wires in the socket4 ,the current comes down one of the wires in the flexible cord1 passes through a coil of fine ,german silver wire inside of the curling iron1 and returns by the other wire in the flexible cord4 ,the small wire in the curling iron offers #bbj ohms of resistance when hot and passes half an ampere of the #aaj-volt current4 7#aaj volts7_/7#bbj ohms7 4#e ampere4 #ab4 ,electric ,soldering ,irons 7,fig4 #hj74--,or coppers1 as they should be called1 are ideal implements for soldering4 ,they remain continually at the proper temperature and are free from corrosion4 ,they require from #ee to #bbj watts4 ,on the #aaj-volt current they take from one half to two amperes4 ,illustration3 ,fig4 #hj #ac4 ,electric ,heating ,pad 7,fig4 #ha74--,this consists of resistance wire inside of a pad of soft material4 ,it maintains a temperature of #ahj degrees1 and is an excellent substitute for a hot water bag4 ,it contains about two hundred and twenty ohms of resistance and requires the same current as a #af-;candle-power lamp4 ,illustration3 ,fig4 #ha #ad4 ,electric ,fuses 7,fig4 #hb74--;,fuses are made of short pieces of wire or thin sheet metal4 ,the metal is an alloy of lead and tin which melts at a low temperature4 ,they derive their name from the fact that they readily fuse or melt4 ,a building is wired in various separate circuits4 ,the size of the copper wires used in each circuit is determined by the amount of current which the circuit is expected to carry4 ,each circuit is protected by one or more fuses4 ,these melt and cut off the current whenever too much passes for the copper conductor to carry without getting hot4 ,the fuse wire melts at about six hundred degrees1 while the copper will not melt until it reaches nearly two thousand degrees4 ,this temperature is sufficient to set fire to wood1 paper1 and cloth4 ,when any fuse melts1 the current is cut off from all chandeliers1 etc41 in the particular circuit controlled by the fuse4 ,this produces consternation among people who do not understand the function of a fuse4 ,they become panic-stricken and begin to trample their neighbours to death in the theatre or on the electric train when they hear that a fuse is blown 7which is the electrician's way of saying that it has melted74 ,everyone should know that a fuse is a safety device4 ,it is always enclosed in a box lined with sheet iron or asbestos1 so that it is impossible for the flash1 which occurs when the circuit is broken1 to set fire to anything4 ,illustration3 ,fig4 #hb ,illustration3 ,fig4 #hc #ae4 ,electric ,gas ,lighter 7,fig4 #hc74--,these usually have two or three small1 dry battery cells in the handle4 ,by pushing a button in the handle connection is made between this battery and a short piece of resistance wire in the tip4 ,this wire gets red hot and lights the gas4 ,it is a surprise to many that we can light illuminating gas without bringing a flame to it1 and it is equally surprising that some flames1 or at least sparks1 may not be able to light the gas4 ,the fact is that it is wholly a matter of temperature and kind of gas4 ,iron heated to dull red will not light the illuminating gas now being furnished in ,new ,york ,city1 while iron at a bright red heat will do so4 ,iron may be hot enough to light illuminating gas but too cool to light gasolene vapour1 which requires a dazzling white heat4 ,iron which is just under the temperature at which it gives any light may set fire to wood and paper4 ,after it has cooled a good deal below that1 it will set fire to sulphur1 and when it has cooled so that one may hold it in the hand1 it is still hot enough to set fire to phosphorus4 ,the glowing end of a lighted cigar1 the spark made by striking flint1 or the spark from a spark coil with a feeble battery1 all fail to set fire to gasolene vapour1 simply because they are not hot enough4 ,fresh battery cells must occasionally be put in the handle of the electric gas lighter4 ,four facts regarding the resistance of wires it is well to remember3 #a4 ,the longer the wire the more resistance it offers to the electric current4 #b4 ,the smaller the diameter of the wire the more resistance it offers4 #c4 ,some materials offer more resistance than others1 for example1 iron about six times as much as copper and ,german silver about twelve times as much as copper4 #d4 ,the common metals offer more resistance when hot than when cold1 about double the resistance when heated to five hundred degrees4 ,it is the reverse with carbon1 which offers more resistance when cold than when hot4 ,the carbon filament lamp offers about double the resistance when cold as when lighted to full brilliancy4 #af4 ,electric ,flasher 7,fig4 #hd74--;,for automatically flashing electric lights4 ,the one which we examined was constructed according to the plan shown in ,fig4 #he4 ,the lighting circuit is brought to the binding posts b and c4 ,a small insulated wire of high resistance connects b and c1 being wound around the metal bar a b4 ,the resistance of this wire1 when added to that of lamps1 permits not more than one fifth of an ampere to pass1 and this warms the wire slightly4 ,the bar a b is composed of two strips of metal1 brass above and iron below4 ,heat expands brass more than iron4 ,the result is that when the current is turned on1 the bar begins to curve downward until presently it touches the metal base of c4 ,then the full current required to light the lamps which are in circuit passes4 ,while the circuit is closed through the large metal strips not enough passes through the fine wire to warm it4 ,on cooling1 a b curves upward and breaks the connection with c1 and now the current begins again to warm up the small wire4 ,illustration3 ,fig4 #hd ,illustration3 ,fig4 #he ,the flasher that we examined was adapted to operate3 one #cb-;candle-power lamp2 or two #af-;candle-power lamps2 or four #h-;candle-power lamps1 on a one ampere circuit of #aaj-volt pressure4 ,let us see what would happen if it were connected either with a current of higher voltage or a circuit of more lamps4 ,suppose we have a #cb-;candle-power carbon filament lamp in circuit4 ,this requires one ampere to light it4 ,its resistance when hot is #aaj ohms4 7#aaj volts7_/7#aaj ohms7 #a ampere4 ,when cold its resistance is about double or #bbj ohms4 ,the ,german silver wire of the electric flasher offers #ccj ohms of resistance1 and together they make #eej ohms4 ,thus the current is cut down to 4#b ampere4 7#aaj volts7_/7#ccj #bbj ohms7 4#b ampere ,suppose now we should undertake to use the same flasher and the same lamp on a #bbj-volt current4 ,this might push more current through than the small wire could carry4 ,it might melt1 or its insulation might burn off before a made contact with b2 if not the lamp would certainly burn out after the contact4 ,if we undertook to operate with this flasher several #cb-;candle-power lamps instead of one upon the #aaj-volt circuit1 the result would be the same1 for in that case the resistance would be reduced and1 therefore1 a greater current would pass than the wire could carry without undue heating4 ,illustration3 ,fig4 #hf ,the boys were at first troubled to see how increasing the number of lamps in a circuit would decrease the resistance in that circuit4 ,fig4 #hf was drawn to explain the matter4 ,the lamps l1 l1 l1 etc41 are connected in parallel4 ,each lamp makes an independent connection from one feed wire to the other4 ,the flasher a acts as a switch to close the circuit for the whole4 ,now if we think of these wires as pipes to conduct water we would say that water flows from ,d to ,e through ten pipes more readily than through one4 ,it would meet with only one tenth as much resistance4 ,the result would be the same1 if we should substitute for the ten pipes one pipe ten times as large in cross section4 ,so it is with wires which are conducting electricity4 ,introduce two in parallel1 and you allow twice as much current to pass by reducing the resistance to one half4 ,ten parallel conductors reduce the resistance to one tenth and allow ten times as much current to pass4 ,illustration3 ,fig4 #hg ,it is to be noticed that this flasher is an automatic switch which is opened or closed according to temperature4 ,remove the fine wire from a and we have precisely the device which regulated the temperature in our electric incubator4 ,suppose the thermostat 7as it is called in that case7 is placed within the egg chamber which is to be kept at #ajc degrees4 ,a screw in the metal strip c underneath the end of a may be set so that it will normally touch a4 ,suppose now the brass strip is underneath the strip of iron in a4 ,as the hot plate warms up the egg chamber1 the brass will expand more than the iron1 and the bar will curve upward and break the connection with c4 ,as soon as the current stops the temperature of the chamber begins to fall1 and the bar curves downward again until connection is made4 ,this device is capable of adjustment so as to keep the temperature constantly at #ajc degrees or any other desired degree4 ,the device is in use for scores of different purposes1 including the regulation of temperature in school rooms4 #ag4 ,electric ,car ,heaters4--,ten or fifteen years ago there were no heated street cars in ,new ,york ,city4 ,now they are all heated by electricity and their maximum and minimum temperatures are regulated by law4 ,the resistance wire may be seen in coils underneath the car seats4 ,electric street cars usually operate on a #ejj or #fjj-volt current4 ,the amount of current used for heating varies from #b to #ab amperes4 ,perhaps #c amperes may be taken as an average4 #ejj ,v #c a #aejj w #a-a_/b kilowatts4 ,it costs the large electric railway companies about #a4e cents per kilowatt hour to generate their supply of current4 ,eighteen hours is considered a car day4 #a-a_/b kilowatts #ah hours #bg kilowatt hours4 #bg kilowatt hours at #a4e cents #dj cents per car day4 #ah4 ,heating ,apartments by ,electricity4--,for heating apartments by electricity the same sort of apparatus is used as that already described for heating cars4 ,a family of four adults1 living in an eight-room apartment with at least #abj cubic feet of fresh air admitted per minute1 will use on an average ten amperes of the #aaj-volt current4 ,the cost will be about two dollars and fifty cents per day or seventy-five dollars per month4 ,although this is as much as the entire rental of a perfectly comfortable apartment1 the novelty and the convenience attract tenants and the extra cost of rent does not deter them4 ,illustration3 ,fig4 #hh #ai4 ,electric ,bedroom ,heater4--,one of the boys constructed a heater for his own room as follows3 ,he procured a box eight inches deep by eighteen inches square on the bottom4 ,this he lined with asbestos paper4 ,he then stood it upon its side and arranged four incandescent light sockets as shown in ,fig4 #hh4 ,these were connected by a flexible cord to a plug which he could insert in place of a lamp in the chandelier4 ,he placed this heater on the floor underneath the window and usually had #af-;candle-power lamps in the sockets4 ,he claimed that it was a jolly foot warmer and kept the room comfortable without other heat4 ,he turned on from one to four lamps according to his need and replaced the #af-;candle-power lamps by #cb-;candle-power lamps when the weather was extremely cold4 ,i remarked that he must have light along with heat by this arrangement1 and ,i should think that might be objectionable when he desired to sleep at night4 ,he said that he always turned it off1 and opened the window at night1 always preferring a cold room to sleep in4 ,illustration3 ,fig4 #hi #bj4 ,cooking with ,incandescent ,lamps4--,this piece of apparatus was devised by the boys and used in my laboratory4 ,a sheet iron basin a1 was inverted over four #af-;candle-power incandescent lamps1 shown in elevation by ,fig4 #hi1 and shown in plan by ,fig4 #ij4 ,the sides of the basin were cut so as to admit the glass globes of the lamps1 but the sockets and keys were outside1 so that it was convenient to turn on and off the lamps separately1 thus using one half to two amperes of current1 as desired4 ,this rested upon another basin1 b4 ,basin b was covered with asbestos for the lamps to lie on and the whole was attached to a board base1 c4 ,a flexible cord and plug allowed us to attach this to the chandelier4 ,a pint of water was boiled upon this stove in fifteen minutes1 and refreshments have been served hot from it repeatedly4 ,illustration3 ,fig4 #ij #ba4 ,electric ,fireless ,cooker4--,there are five indictments against ordinary cooking processes4 #a4 ,they heat the house in summer4 #b4 ,they convert what would be pleasant flavours in the food into noxious odours about the house4 #c4 ,they cannot be controlled with regard to time and temperature as scientific experiments should be4 #d4 ,they confine the cook too closely and are not sufficiently automatic4 #e4 ,they are wasteful of fuel4 ,it would seem that electricity might enable us to cure most of these evils4 ,to be sure the production of heat by electricity is wasteful of fuel1 and it seems doubtful how the account will balance regarding the fifth item4 ,but the remaining four items furnish a very hopeful field for research4 ,i use the last word advisedly1 and think it is just as applicable to high school boys as to university students4 ,after experimenting awhile the boys and ,i concluded to give a dinner party in the laboratory and invite a few friends to test the results of our cooking4 ,we procured a cylinder of magnesia such as is used for covering large steam-pipes4 ,this was inverted over our electric stove which was illustrated in ,fig4 #hi4 ,the magnesia was cut at the bottom1 so as to give access to the key sockets of the lamps1 7,fig4 #ia74 ,first upon the electric stove was placed a covered dish containing a roast of lamb4 ,above this was another dish containing a vegetable1 and upon the top of that was a pudding4 ,a flat piece of magnesia was used as a cover to the whole4 ,through a hole in this was suspended a thermometer4 ,illustration3 ,fig4 #ia ,this fireless cooker was sitting in the centre of the dinner table when the guests gathered around it4 ,we had these problems for investigation3 #a4 ,will this cooker heat the house in summer8 ,all testified that they did not know that there was any heat about it until they laid their hands upon it1 and then they found it only very slightly warm4 #b4 ,is there any smell of cooking here8 ,the process has been carried on from start to finish right on this table4 ,all agreed that no smell could be detected4 ,i then turned off the electric current which had been running until now and served the meat and vegetable1 leaving the pudding inside to be kept warm by the hot walls of the cooker4 #c4 ,regarding the control of the process3 we were using #cb-;candle-power lamps1 which gave us a variable current1 from #j to #d amperes1 and a watch and a thermometer4 ,we had control1 but as yet lacked knowledge of how it should be used4 ,in the present case we had arbitrarily decided to begin with temperature of #djj degrees1 continue it for #bj minutes1 then turn off all the electric current1 and let the temperature fall gradually4 ,this had been done at our convenience in the morning before school4 ,at a quarter before twelve we had found the temperature at #bjj degrees1 and turned on all the current1 and now1 at five minutes past twelve o'clock1 all testified that the lamb was particularly good--neither too well done nor undercooked1 and that its flavour was better than usual4 ,as for economy of fuel1 we find at least that we get better results from incandescent lamps than from hot plates used in the same apparatus1 and the electric equipment enables us to put the heat exactly where it is needed and nowhere else4 #bb4 ,incandescent ,lamp4--,we feel quite justified in putting the incandescent lamp under the heading1 ,applications of ,electric ,heating1 since the electric lamps in general use convert #if per cent4 of the electric energy into heat and only #d per cent4 into light4 ,they were originally made by introducing a short piece of fine wire into the circuit1 choosing the kind of wire1 its diameter1 and its length so as to make the proper relation between resistance and voltage1 in order that enough current might pass to make it white hot1 but not quite melt it4 ,platinum wire was first chosen because it would stand the highest heat without melting and without rusting4 ,we will pass our #aab-volt current through #i feet of the ,no4 #bd iron wire4 ,the wire is heated to bright red1 but does not melt as it did when we used #h feet in a former experiment4 ,the increased length has added resistance1 and1 as you see by the ammeter1 cut the current down from #h to #g4e amperes4 ,i will now darken the room and you find that it is giving light enough to read by4 ,but you notice that the light is growing dimmer1 its colour is growing redder1 and the ammeter indicates that less current is passing4 ,i will cut off the current and let you examine the wire and you notice that a crust has formed upon it4 ,this is due to the oxygen of the air which unites with the iron1 forming iron rust4 ,iron rust does not conduct electricity4 ,we have converted ,no4 #bd iron wire into a wire of smaller diameter with a sheath of iron rust around it4 ,we might prevent the rusting by putting the wire in a glass globe and exhausting the air from it4 ,i have here a piece of ,no4 #bd platinum wire which has about the same resistance as iron wire when cold1 but you notice that ,i may use a very much shorter length than ,i did of the iron wire because it will endure a very much higher heat without melting4 ,reducing the length would reduce the resistance1 but reducing the resistance would allow more current to pass4 ,if more current should pass it would make the wire hotter1 and raising the temperature would increase the resistance1 which would cut down the current1 etc4 ,by sliding the clip c 7,fig4 #ib71 along1 ,i finally reach a point where conditions balance so that ,i get a very brilliant light1 dangerously near the fusing point of the platinum which is three thousand degrees above the boiling point of water4 ,in #ahgi ,mr4 ,thomas ,a4 ,edison literally searched the whole world for something better than platinum for the filament of an incandescent lamp4 ,he finally decided upon charred threads of a bamboo which he found in ,japan4 ,no research was ever more timely than this4 ,whereas there was practically no electric lighting before #ahhj1 soon after that there began a phenomenal demand for carbon filament lamps4 ,in #ahij1 #hjj1jjj of these lamps were manufactured in the ,united ,states4 ,in #aijj the number had risen to #be1jjj1jjj4 ,in #aiji central stations were supplying electric current to #da1hjg1idd incandescent electric lights4 ,by far the greatest number are still made with carbon filaments4 ,illustration3 ,fig4 #ib ,illustration3 ,fig4 #ic ,we examined an ordinary #aaj-volt #af-;candle-power carbon filament lamp1 7,fig4 #ic74 ,as near as we could estimate1 its filament measured about eight inches in length4 ,we broke open the bulb of this lamp by laying it upon the table and tapping it with a board4 ,the bulb broke with rather a loud noise and the brittle carbon filament broke into many pieces4 ,we found one of these pieces and measured its diameter with a wire gauge1 7,fig4 #id74 ,it was the same size as ,no4 #cc wire1 which we also found by the wire gauge was the size of ,no4 #ij sewing cotton4 ,the diameter of ,no4 #cc wire was given upon the wire gauge as 4#jjg inch4 ,when lighted1 the filament of this lamp had looked to be about the size of ,no4 #ah wire1 which has a diameter of 4#jd4 ,that is1 the filament when lighted looked six times as thick as it really was4 ,those who use sewing cotton learn quickly to know the size of the thread by its number4 ,so those who have much to do with wire easily learn the system of designating sizes by numbers4 ,here are some selected figures easy to remember4 ,a trolley wire is about one third of an inch in diameter4 ,it is designated as ,no4 #j4 ,notice in the following table that as the numbers rise by six the diameters are divided by two4 ,notice also that as the diameters diminish by two the resistance increases by four4 ,illustration3 ,fig4 #id ,,table ,,of ,,resistance ,,of ,,copper ,,wires ,nos4 ,diameter ,resistance #j 4#cb inch #ajefj feet to the ohm #f 4#af #bfdj #ab 4#jh #ffj #ah 4#jd #afe #bd 4#jb #dj #cj 4#ja #aj #cf 4#jje #b4e #db 4#jjc #a #aj1efj feet equal two miles4 ,number #cf is the wire used upon the spools of telegraph receivers4 ,they offer #ge ohms of resistance and therefore contain #cj feet of wire 7#cj #b4e #ge74 ,these resistances are for ordinary school room temperatures4 ,since iron has six times1 and ,german silver twelve times the resistance of copper1 divide the figures of the third column by six1 and the table will answer for iron wire1 or divide those figures by twelve and the table may be used for ,german silver wire1 thus3 ,number ,feet to the ,ohm ,nos4 ,diameter ,copper ,iron ,german ,silver #j 4#cb inch #ajefj #agfj #hhj #f 4#af #bfdj #ddj #bbj #ab 4#jh #ffj #aaj #ee #ah 4#jd #afe #bg #ad #bd 4#jb #dj #f #cb inch #cj 4#ja #aj #a4e #h #cf 4#jje #b4e 4#de #b #db 4#jjc #a #b inch #a ,these figures are not exact1 but useful4 ,we procured a string of eight small lamps 7,fig4 #ie71 such as are used in lighting ,christmas trees4 ,each was marked #ad volt1 #b-;candle-power4 ,the carbon filament of each was about one inch long and apparently the same diameter as that of the #af-;candle-power lamp4 ,when the #aaj-volt current was sent through the group of eight connected in series they seemed to give about the same light as the single #af-;candle-power lamp4 ,it is as though the filament of the #af-;candle-power lamp had been cut into eight pieces1 and distributed through eight small lamps4 ,we introduced an ammeter into the circuit and found that half an ampere of electricity passed through the single #af-;candle-power lamp--and half an ampere likewise passed through the group of eight #b-;candle-power lamps4 ,illustration3 ,fig4 #ie ,the #aaj-volt current can push an ampere of electricity through eight inches of carbon thread seven thousandths of an inch in diameter1 and when this happens the filament gets hot enough to give out as much light as sixteen standard candles4 ,in the place of the #af-;candle-power lamp1 we put a #cb-;candle-power #aaj-volt lamp4 ,the ammeter indicated one ampere4 ,the carbon filament was larger 7,no4 #cj1 diameter 4#ja inch71 so as to allow more current to pass4 ,an #h-;candle-power #aaj-volt lamp was substituted2 one quarter of an ampere passed4 ,a #d-;candle-power #aaj-volt lamp was used2 one eighth of an ampere passed4 ,a #ajj-;candle-power #aaj-volt lamp was substituted2 three amperes of current passed through it4 ,in all these cases the lamps which passed the larger current had the larger filaments4 ,a little practice would enable one to distinguish between these lamps without labels by examining their filaments4 ,among these #aaj-volt lamps1 it is to be noted that the amount of light which they give is proportional to the amount of current which they pass4 ,and it is convenient to remember that one ampere of electricity for one hour costs about one cent4 ,we introduced into the socket a ,hylo lamp 7,fig4 #if74 ,the filament1 ,a1 took half an ampere of electricity1 gave #af-;candle-power of light1 and cost half a cent an hour4 ,when the lamp was turned in its socket the current was switched off of the filament ,a1 and on to the filament a4 ,this took 4#jc of an ampere1 gave one candle-power of light1 and cost 4#jc of a cent an hour1 or at the rate of about #c4jj a year1 burning continuously day and night4 ,illustration3 ,fig4 #if ,the uses of such a lamp are apparent in rooms which have no daylight4 ,however1 a wall switch at the entrance of such a room1 making it easy to throw on and off the light entirely1 seems to be a more satisfactory arrangement4 ,one of the boys connected a wattmeter in the circuit with a hylo lamp and found that the small filament did not pass current enough to move the armature of the wattmeter4 ,hence that may be burned alone without affecting the consumer's bills4 ,we took a #af-;candle-power #bbj-volt lamp1 and lighted it by a #bbj-volt current4 ,the meter showed that it allowed only one quarter of an ampere to pass4 ,the filament was very much smaller than that in the #aaj-volt1 #af-;candle-power lamp4 ,the pressure was twice as great as before1 but the resistance was four times as great1 and hence only half as much current passed4 ,we find that it costs just as much to generate one quarter of an ampere at #bbj-volt pressure as it does to generate half an ampere at #aaj-volt pressure4 ,we must1 of course1 pay for electricity according to the cost of producing it4 ,to produce 4#e ampere at #aaj-volt pressure costs the same as one ampere at #ee-volt pressure1 or 4#be amperes at #bbj volts4 ,it will be noticed that the products of the two factors in each case are the same4 ,the product of an ampere multiplied by a volt is a watt4 ,in each of the above three cases the amount of electrical energy is #ee watts4 ,this will produce a definite quantity of light--about #af candle-power when the carbon filament is used1 and this quantity does not vary as either volts or amperes1 but as the product of these1 namely1 watts4 ,each of these lamps is called a #ee-watt lamp1 and1 since they each give #af candle-power of light1 a carbon filament lamp gives one candle-power of light for three and a half watts of electricity4 ,electricity for lighting purposes usually costs #aj cents per kilowatt hour1 that is1 #aj cents for #ajjj watts for one hour1 or one cent for #ajj watts for one hour4 ,hence a #ee-watt lamp costs a trifle more than half a cent for one hour1 or exactly 4#ee cents1 and a #cb-;candle-power lamp costs #a4a cents per hour4 ,we introduced into the socket a #dh-;candle-power #aaj-volt tungsten lamp 7,fig4 #ig71 and turned on the #aaj-volt current4 ,the ammeter showed #ee ampere4 ,hence the lamp is a #fj-watt lamp1 and requires one and a quarter watts per candle-power4 ,that is1 the metal tungsten is nearly three times as efficient as carbon for producing light from electricity4 ,illustration3 ,fig4 #ig ,with pincers we broke off the tip of a #cb-;candle-power carbon filament lamp1 making a small hole in the large end of the bulb4 ,the air rushed in4 ,we then put the lamp in the socket and turned on the current4 ,the carbon filament glowed as usual1 and slowly burned up1 growing smaller as it did so4 ,the ammeter which was in circuit showed that the current1 which was one ampere at the beginning1 grew steadily less as the filament grew smaller1 until finally when it was about one quarter of an ampere1 the circuit was broken by the filament burning in two4 ,we removed the lamp from the socket and with a dropper tube introduced a little lime water1 and shook it to absorb any gas which might have been formed in there4 ,it became milky white1 as it always does when introduced where carbon has been burned4 ,this would be a sufficient proof that the filament was made of carbon1 if we did not already know it4 ,the air is exhausted from these bulbs to prevent the carbon filament from burning up4 ,illustration3 ,fig4 #ih ,the carbon filament lamps were1 as has been said1 the invention of ,mr4 ,thomas ,a4 ,edison in #ahgi4 ,such a statement must1 however1 be qualified by the assertion that this1 like nearly all invention1 was but the consummation of a long line of researches made by many men for many years4 ,the early filaments were made of bamboo thread1 charred1 but now they are drawn like spider's web out of a sticky liquid and carbonized at a high temperature4 ,they are attached in the lamp to short pieces of platinum wire which are sealed through the glass walls of the bulb4 ,one wire connects with the brass collar of the bulb1 and the other with the central piece of brass at the base of the bulb4 ,we dissected a socket and found that when the lamp is placed in the socket1 the collar of the lamp is screwed into the collar of the socket1 and the base of the lamp comes in contact with a brass spring in the bottom of the socket 7,fig4 #ih74 ,the spring is connected with one copper wire bringing electricity from the dynamo4 ,the collar is connected with the other wire from the dynamo4 ,this connection is made and broken by turning the key of the socket4 ,the wires are made of copper since copper is a particularly good conductor of electricity4 ,no electricity can flow unless this circuit is complete4 ,socket keys and wall switches make or close gaps in this circuit4 ,no copper wires for carrying electric-lighting current are smaller than ,no4 #ab1 which has a diameter of 4#jh or about one twelfth of an inch4 ,the intention is to have as little resistance to the current as possible1 except in the filament of the lamp itself4 ,there resistance is purposely introduced in order to convert electricity into light1 light without heat if that were possible1 but since that has not yet been found possible1 heat for the sake of the accompanying light4 ,unhappily only #d per cent4 of the electrical energy goes into light and #if per cent4 goes into useless1 or even harmful1 heat4 ,the tungsten lamps1 which are now coming into use1 are nearly three times as efficient in the production of light as are the carbon filament lamps4 ,the dynamo exerts its entire pressure upon the lamp and furnishes current as follows3 ,a dynamo of #aaj-volt pressure gives3 #a ampere #aaj watts1 through a #cb-;candle-power lamp1 cost one cent an hour1 or 4#e ampere #ee watts1 through a #af-;candle-power lamp1 cost half a cent an hour1 or 4#be ampere #bg-a_/b watts1 through an #h-;candle-power lamp1 cost a quarter of a cent an hour4 ,a dynamo of #bbj-volt pressure gives3 4#e ampere #aaj watts1 through a #cb-;candle-power lamp1 cost one cent an hour1 or 4#be ampere #ee watts1 through a #af-;candle-power lamp1 cost half a cent an hour1 or 4#abe ampere #bg-a_/b watts1 through an #h-;candle-power lamp1 cost a quarter of a cent an hour4 ,the carbon filament lamps1 barring accidents1 have a natural life varying from #fjj to #ajjj hours of actual incandescence4 ,at the end of that period the filament has become so thin that it will fall apart by ordinary usage4 ,it is never profitable1 however1 to use them for their whole lifetime4 ,the lamp gradually volatilizes carbon and deposits it upon the inner walls of the bulb1 producing a smoky appearance and shutting off light4 ,as the filament grows thinner by this process1 it offers greater resistance to the current1 and as the amount of current grows less the proportion of light to current grows rapidly less1 so that at last instead of paying for #c4e watts of electricity per candle-power of light one must pay for perhaps seven or eight watts per candle-power4 ,we pay fifteen cents apiece for #af-;candle-power lamps1 and it is economy to renew them about twice a year1 if they are burned1 say three hours a day1 or a little over five hundred hours4 ,it is interesting to note that when a direct current is used the evaporation from the carbon filament always takes place at the negative end alone1 that is1 the end from which the current is leaving the lamp4 ,if an alternating current is used the evaporation goes on from all parts of the filament alike4 ,this is a case of evaporation from the solid state4 ,carbon does not boil below #f1jjj degrees1 and the filament reaches about #b1dej degrees4 ,tantalum1 tungsten1 and osmium lamps have metal filaments4 ,these metals are better conductors than carbon but unlike carbon their resistance increases as their temperature rises1 and their special virtue is that they are capable of enduring an extremely high temperature without melting4 ,the wire used in some of these filaments is as small as 4#jjb of an inch1 or ,no4 #dd4 ,in order to furnish sufficient resistance to prevent the #aaj-volt current from melting1 they often have a length exceeding two feet4 ,this is laced back and forth within the small bulb4 ,at the temperature of bright incandescence their resistance may be increased as much as fivefold and sometimes becomes about ten ohms to the inch4 ,like all metals they are more brittle when cold than hot4 ,hence when cleaning such lamps it is advisable to turn on the current to avoid breaking the filament by jarring4 ,filaments which are too fragile to endure the jar of ordinary railway travel1 when cold1 have gone through railway wrecks safely when lighted4 ,it is a general rule that good conductors of electricity grow more resistant as the temperature rises while non-conductors resist less as the temperature rises4 ,hence the insulating material which is used to cover copper wires fails to protect if highly heated4 ,if a #aaj-volt lamp is put into a #bbj-volt circuit1 one might expect that the lamp would burn out without doing further damage to the circuit1 but this is not the case4 ,as the filament approaches its melting point1 #fjjj degrees1 it becomes so good a conductor that it carries current enough to melt a fifteen ampere fuse4 ,it is1 therefore1 the fuse that protects the circuit and not the burning out of the lamp4 ,the bulb containing the highly heated carbon vapour would conduct the current as an arc lamp does4 ,illustration3 ,fig4 #ii #bc4 ,arc ,lamp4--,we fastened two electric light carbons to the ends of copper wires connected for the #aaj-volt current4 ,a rheostat1 ,r 7,fig4 #ii71 in circuit1 was set at #f4e ohms4 ,one lower carbon was fastened into a clamp1 and the other was touched to it1 and then drawn away about three-eighths of an inch4 ,a very brilliant light was produced4 ,probably about #ahjj candle-power4 ,the ammeter ,a showed #aj amperes1 and the volt meter ,v showed #de volts4 #de volts #aj amperes #dej watts1 #ahjj candle-power1 #be watts per candle-power4 ,the arc light is the cheapest of all lights but is too dazzlingly bright for household purposes4 ,it is used for outdoor lighting chiefly1 and particularly for large search-lights4 ,the temperature is over #fjjj degrees1 which boils the carbon and fills the gap between the two pencils with a stream of carbon vapour4 ,this conducts the current like the filament in an incandescent lamp4 ,the air gap between the carbon pencils would have a resistance of many thousand ohms if it were not for the presence of the carbon vapour4 ,the hot carbon vapour reduces the resistance of this space to #d4e ohms4 7#de volts7_/7#d4e ohms7 #aj amperes4 or 7#aaj volts7_/7#f4e #d4e ohms7 #aj amperes4 ,the carbon pencils account for part of this resistance--not more than a third of an ohm however4 ,it is evident that arc lamps in use must have an automatic mechanism which shall permit the carbons to touch whenever the current is not passing1 but which shall draw them apart to the proper distance after the carbon vapour has been formed1 or1 as we say1 after the arc has been established4 ,this mechanism is nothing else than electro-magnets which are operated by the lighting circuit itself4 ,it may require thoughtful examination to recognize these as electro-magnets1 in every case1 but that is what they are4 ,sometimes they are coils of wire1 which do not have iron cores and armatures separate to be sure--but nevertheless they have both of these united in one movable rod1 and they produce magnetic fields4 ,suppose ,i pass an electric current around this coil ,a 7,fig4 #ajj74 ,the region about the coil becomes a magnetic field with its north pole situated at a point in space1 say ,n4 ,the influence of this field causes the iron rod to become a magnet with its south pole uppermost1 and if the current is strong enough1 and the field which it produces is strong enough1 it will lift the iron rod up into the coil4 ,by varying the strength of the current you see ,i may make this rod dance up and down in space touching nothing--a veritable ghost dance4 ,illustration3 ,fig4 #ajj ,it may be pettifogging to say that the upper portion of this iron rod is the core of the magnetic field1 and its lower portion is the armature4 ,yet this is right1 and pettifogging may be right when it is the only way to bring out the fact4 ,our great study now is to produce light without heat1 or at least to come as near to it as the firefly does4 ,the firefly gives #ih per cent4 light and two per cent4 heat4 ,the arc lamp gives #ab per cent4 light and #hh per cent4 heat4 ,the carbon filament gives #d per cent4 light and #if per cent4 heat4 ,when we have made considerable progress in that direction we shall take electric lamps out of the chapter on electric heating and form a new chapter on electric lighting4 ,one might expect that a rod made of carbon would quickly burn up1 particularly when raised to the exceeding high temperature of the electric arc4 ,while it is true that carbon in the form of charcoal burns so readily that it is used instead of kindlings for lighting a fire1 carbon in the form of graphite in our so-called lead pencils and carbon as it is prepared for electric light pencils burns only very slowly even at exceedingly high temperatures4 ,the carbon rods used in arc lamps endure a temperature of over #fjjj degrees1 without losing more than one inch an hour1 and half of that is simply volatilized--not burned4 ,one of the most interesting improvements ever made in the arc light is that of enclosing the arc in an inner glass globe4 ,this globe is closed airtight below with a small opening above4 ,when the arc is formed the oxygen of the air in the inner globe is soon consumed and then combustion is no longer possible4 ,we illustrated this by an experiment4 ,an ordinary cork was chosen to fit the large end of an argand lamp chimney and through a hole in this was passed one of the carbon rods 7,fig4 #aja74 ,a metal clamp made connections between this carbon and the negative wire from the dynamo4 ,the other carbon1 attached by a clamp to the positive wire1 was thrust down into the upper end of the chimney until it touched the negative carbon1 and then drawn upward a short distance1 drawing an arc1 as we say4 ,this soon makes an atmosphere within the chimney where combustion cannot go on for want of oxygen4 ,the arc1 however1 continues to glow as in the open air1 and the carbons may be drawn further apart than in the open air without breaking the arc1 hence more of the external resistance may be cut out and a higher voltage put upon the lamp4 ,illustration3 ,fig4 #aja ,carbons which burn out in a single night if used in open arc lamps last two weeks in enclosed arc lamps4 ,the lower carbon1 when removed from the lamp chimney of the last experiment1 served as a lead pencil to write on paper4 ,the positive carbon would not make a mark on paper4 ,in all arc lamps carbon is distilled from the positive pencil1 condensing upon the negative pencil as graphite1 which is the material used in making lead pencils4 ,they are called lead pencils because they were originally made of lead1 but now they are made of graphite which is mined from the earth4 ,as soon as the arc is broken it becomes evident that the positive carbon has been heated much the hotter of the two1 a fact that could not be detected while it was lighted because of the dazzling brightness of the arc4 ,the negative carbon turns black almost immediately1 while the positive carbon remains at a bright red heat for some time4 ,this fact needs to be borne in mind when adjusting arc light carbons in search-lights1 stereopticons1 and all like apparatus in which the light must be placed at the focus of a lens4 ,that is1 it is necessary to know from what point the light really comes and it is necessary to have some adjusting device to keep this point continually at the focus of the lens4 #bd4 ,search-,light4--7,fig4 #ajb74 ,this is simply an arc lamp with reflectors behind it and lenses in front of it4 ,the whole apparatus is pivoted so as to be easily made to shine in any direction4 ,the function of the lenses and the reflectors is to collect stray rays of light and send them all out in the same direction4 ,this is shown in ,fig4 #ajc where for simplicity the lens is represented as a single piece4 ,l represents a point of light which will naturally send its rays out in all directions as the radii of a sphere2 m1 m1 m represents a bright reflecting surface which is given that peculiar curve called a parabola4 ,it has the unique faculty of reflecting in a parallel direction all the rays which may fall upon it from ,l1 so long as ,l is kept at that particular point called the focus1 a b is a lens of glass which has that peculiar curve that enables it to bend all rays which fall upon it from ,l1 so that they may pass out parallel4 ,illustration3 ,fig4 #ajb #be4 ,stereopticon4--,this also has the necessary devices to gather the rays of the arc lamp and send them forth parallel1 and in addition it has a series of lenses which produce upon a distant screen an enlarged picture of any transparent object held in these parallel rays4 ,illustration3 ,fig4 #ajc ,illustration3 ,fig4 #ajd #bf4 ,burglar's ,flash-,light4--,there are many forms of this4 ,the one we examined is represented in ,fig4 #ajd4 ,we unscrewed a metal ring at the left-hand end and found1 first a glass lens and behind that a miniature electric light1 requiring three volts and half an ampere4 ,we knew1 therefore1 that it must be supplied with two cells1 since one cell may give not more than #a4e volts4 ,we also knew that it would only be used to flash a light1 since if dry cells are required to furnish half an ampere continuously they soon run down4 ,behind the lamp there was a bright metal reflector--the lens and reflector are fairly well represented in ,fig4 #ajc4 ,the filament of the lamp is connected with two small battery cells in the handle4 ,these may be removed and replaced by new ones by unscrewing a cap at the right-hand end4 ,the circuit is closed by a metal spring on the side of the tube1 which acts as a push button4 ,it is situated where it may be conveniently pressed by the thumb4 ,the small batteries necessarily have a short life and must be replaced quite frequently4 ,being a special thing they cost nearly twice what the regular dry cell does4 ,illustration3 ,fig4 #aje #bg4 ,mercury ,vapour ,lamp4--,this is an interesting variety of arc light in which the vapour of mercury takes the place of the vapour of carbon4 ,g1 in ,fig4 #aje1 represents a glass tube from which the air has been exhausted4 ,the wires of the lighting circuit are fused into the ends of the tube4 ,at one end1 and in contact with one of these wires1 is a small pool of mercury4 ,by pulling the cord c the tube is tilted on the pivot p1 so that a stream of mercury flows along the whole length of the tube and closes the electric circuit4 ,when the tube falls back into its normal position1 as represented in the figure1 the electric arc persists upon the mercury vapour4 ,incandescent mercury vapour gives light strong in green1 blue1 and violet1 but deficient in red and yellow4 ,it1 therefore1 gives nothing its natural appearance but casts a ghastly hue over everything4 ,this lamp was invented in #aijb1 by ,peter ,cooper-,hewitt1 grandson of the founder of ,cooper ,union in ,new ,york ,city4 ,it gives a very suitable light for making photographic prints1 and is much used for that4 ,this lamp operates upon the #aaj-volt circuit4 ,it is the longest step yet taken toward getting light without heat1 but perhaps shows what we must expect when we reach that goal1 namely1 unsatisfactory colour values in the light4 ,probably such is the case with the firefly4 #bh4 ,the ,moore ,light4--,in #ahif ,prof4 ,d4 ,mc,farland ,moore brought out his vacuum tube light 7,fig4 #ajf74 ,we visited an ordinary dry goods store which had been equipped with this4 ,glass tubing is put together very much as one would put up a stove pipe or a job of plumbing4 ,the joints are fused and made air-tight by playing a flame upon them after the pipe is up in place4 ,this pipe is led around into all nooks and corners where there would be dark places4 ,the air is pumped out of this tube and a trifling amount of some vapour is introduced1 the kind varying according to the tint of colour which is desired4 ,illustration3 ,fig4 #ajf ,metal terminals are fused into the ends of this tube4 ,the tube we saw was seventy-five feet long4 ,a #ajjj-volt alternating current is applied to the terminals and the vapour becomes incandescent1 filling the whole tube full of light4 ,the first thing that the boys remarked was that although the room was brilliantly lighted no object cast a shadow4 ,it seemed as though light was everywhere and there was no chance to screen it off4 #bi4 ,the ,nernst ,lamp4--,in #ahig the ,nernst lamp appeared in ,germany4 ,it is a good illustration of an insulating substance becoming a conductor when heated to a high temperature4 ,the glower1 as it is called1 is composed of one or several short rods of clay-like material4 ,this is first heated by sending the electric current through resistance wire placed directly underneath it and connected in shunt with it4 ,when it gets hot1 current begins to pass through it1 and is automatically cut off from the resistance coil4 ,the glower produces an intensely bright and white light although it does not itself exceed the temperature of #agdb degrees4 ,electric installations are now so carefully constructed that fires from poor insulation are very rare4 ,less than one fire in three hundred appears to be traceable to that cause4 #cj4 ,electric ,welding4--,nothing is more common in electrical matters than heat produced by poor contacts4 ,in this laboratory are two chandeliers1 each controlled by a wall switch4 ,after the current has been on the chandeliers for half an hour you will always find one of those wall switches warm1 while the other is not perceptibly warmer than other objects in the room4 ,the explanation is that there is poor contact in one of them4 ,when two metal conductors touch one another at a mere point the electric current1 in passing from one of these conductors to the other across such a narrow bridge1 meets resistance and develops heat--sometimes heat enough to fuse the point1 and either break the contact1 or1 what is more likely1 start a minute arc at that point4 ,in some cases this makes the apparatus dangerously hot1 and in other cases it bridges the gap with a broader and better contact--a true electric weld4 ,electric welding is applied to everything1 from chicken fence to railway rails4 ,enormously large currents are used for the purpose1 in some cases as high as #ej1jjj amperes being employed4 ,the rails of railroads are welded end to end by a current of several thousand amperes sent through the joint by perhaps two or three volts4 ,the joint heats and fuses together merely because the poor contact offers resistance to this enormous current4 ,,ix ,,lighting ,a ,,summer ,,camp ,,by ,,electricity ,summer had arrived4 ,the ,science ,club had held its last meeting for the season4 ,harold had engaged three other boys to spend the summer at the farm4 ,i had the roof of an old mill reshingled and gave it to them for a camp4 ,they were to make it over inside4 ,i sent the boys to the country as early as it was possible for them to get away4 ,it would be six weeks later before ,i could follow them4 ,illustration3 ,fig4 #ajg ,when ,i did arrive ,i found they had elaborate schemes indeed4 ,the first floor of the mill had been partitioned off into rooms1 as shown in diagram 7,fig4 #ajg71 a1 b1 c and d being bedrooms2 e was a wash room1 the like of which has never been seen before4 ,it had not occurred to me that the mill pond m1 which came to the very corner of the building1 would furnish the boys a complete system of city water-works4 ,at g1 in the corner of this room1 they had cut a hole in the floor and nailed slats across upon the under side of the timbers1 making a depressed floor for a shower bath4 ,this was directly over a stream of water which issued from the mill pond4 ,hanging from the ceiling over this spot was the nozzle of a garden hose4 ,the other end of this hose ran into the mill pond4 ,the nozzle was capable of delivering either a stream or a shower1 according to which way it was twisted in its socket4 ,it was also capable of shutting off entirely the flow of water4 ,the boys asked me to hold my hand in the shower1 and to my astonishment it was warm4 ,what1 pray1 is your heating system8 ,i inquired4 ,they invited me to go and see4 ,moored outside in the mill pond at the corner of the building was our motor boat1 which the boys were allowed to use freely and which they understood as well as any one4 ,illustration3 ,fig4 #ajh ,they said that ordinarily they used for the shower the cool water of the lake1 which they much preferred1 and which ran of its own accord1 the lake being a trifle higher than the nozzle of the shower1 but knowing my antipathy for the cold bath they had slipped the end of the rubber hose over the outlet pipe of the pump which served to cool the gasolene engine in the boat4 ,the engine uncoupled from the propeller was heating and pumping water for my shower bath1 and ,i immediately accepted the invitation to enjoy it4 ,certainly no bath was ever more delightful than that one1 coming1 as it did1 at the close of a hot1 dirty ride from the city4 ,i had hastened the bath1 because it was already dusk and ,i had no candle at the mill1 but suddenly the room lighted up as if by magic4 ,i saw then what had before escaped my notice1 a miniature electric lamp1 six-volt1 two-candle-power1 tungsten1 such as are used for tail lights on automobiles4 ,since tungsten requires about #a4be watts per candle-power it was a #b4e-watts lamp1 and since it was adapted to six volts it would take about four tenths of an ampere4 #f volts 4#d ampere #b4d watts4 ,the little wire filament looked to be about #a4e inches long4 ,its resistance must have been #ae ohms4 #f volts_/#ae ohms 4#d ampere4 ,a battery of five cells was used to furnish electric current for the lamp4 ,lamps were installed in the bedrooms also and were not intended to be used more than half an hour at a time4 ,dry battery cells are excellent for this purpose1 and for so small a current the cheapest dry cells are as good as the more expensive ones4 ,these cost fifteen cents a cell4 ,they were connected by short pieces of bare copper wire2 ,no4 #ah in series1 as shown in ,fig4 #aji4 ,a wire ran from the central 7carbon7 binding post of one cell to the marginal 7zinc7 binding post of the next cell4 ,this battery was placed on a shelf in a convenient place4 ,a bare copper wire1 ,no4 #ah1 was attached to the carbon post at one end of the battery and another to the zinc post at the other end of the battery1 and these two wires ran to all the rooms where lamps were placed4 ,the wires were fastened up on the walls by staples1 taking care that they should nowhere come in contact with each other and short circuit the battery4 ,whenever it was necessary for one wire to cross another1 small pieces of pasteboard were tacked up to prevent their touching each other4 ,the lamps ,l 7,fig4 #aji7 were connected to these wires in parallel4 ,they cost forty cents apiece1 and the miniature sockets1 into which they were screwed1 cost five cents each4 ,one of these sockets was screwed to the side of the door casing in each bedroom4 ,wires were attached to the line wires1 simply by twisting them together4 ,one of these came down to one side of the socket and the other came to the other side of the socket through a switch1 s1 made of a strip of sheet zinc4 ,the cost of the entire installation was as follows3 #e dry cells at #ae;c 4#ge #e4b cp41 #f-volt tungsten lamps at #dj;c #b4jj #e miniature wall sockets at #e;c 4#be ,wire1 etc4 4#bj ---- #c4bj ,illustration3 ,fig4 #aji ,suppose each lamp is used thirty minutes a day for #ajj days1 making a total of fifty hours4 ,there are five lamps1 making a total of #bej lamp hours4 ,each lamp takes 4#d of an ampere1 making a total of #ajj ampere hours4 ,the lamps are operated at six volts1 making a total of #fjj watt hours4 #ajj days 4#e an hour each day --- #ej hours #e lamps --- #bej lamp hours 4#d ampere for each lamp --- #ajj ampere hours #f volts --- #fjj watt hours ,this amount of electrical energy would cost six cents if generated by a dynamo4 ,it is generally stated that electricity costs fifty times as much if generated by battery as by dynamo4 ,in this case the battery actually did serve for the whole season of #ajj days and was not exhausted at the end of the season4 ,indeed1 since that season1 the boys have found that battery cells which had been too much exhausted for use on the engine served very well on the lamps4 ,by use the cells lose1 not much in voltage1 but in the ability to furnish sufficient quantity in amperes to make the hot spark required for igniting the mixture of gasolene and air in an engine cylinder4 ,when they have been discarded for use with the engine they may still furnish the small amount of current required for the lamps--provided not too many lamps are used at one time4 ,the dynamo current is always surprisingly cheap when compared with that produced by a battery1 but1 on the other hand1 we are never as economical in the use of the dynamo current as we are with that of the battery4 ,if all five of the lamps in the above equipment were lighted at the same time and kept burning for half an hour1 the battery would run down rather badly and would not fully recover4 ,but if one only is used at a time and for not more than thirty minutes1 or if more than one is used at a time and for a proportionately shorter period1 the battery will receive no damage4 ,dry battery cells may be purchased for either twenty-five cents or fifteen cents each4 ,the chief difference is that the former are capable of giving larger current than the latter1 when working against very small resistance4 ,for example1 the former may give twenty to twenty-five amperes on a short circuit1 that is1 connected directly with the ammeter without other resistance1 while the latter may give not more than six to ten amperes under similar conditions4 ,for most purposes1 other than igniting gasolene engines1 in which dry cells are used1 an exceedingly small current is required4 ,the electric bell1 for example1 may not require more than 4#b of an ampere and that intermittently4 ,now it is found by experience that the dry cells which are only capable of furnishing on short circuit six to ten amperes will last quite as long in bell work as one which may give on short circuit twenty to twenty-five amperes4 ,hence it is good economy to buy them4 ,what a fine sitting room you have here6 7,fig4 #ajg1 f47 ,when do you expect to fit it up8 said ,i4 ,instantly reminding myself1 however1 that boys do not want a sitting room1 ,i inquired what they intended to use this fine1 large room for4 ,they told me that they had plans for making a machine shop out of that4 ,the idea had been suggested by a counter shaft which still hung from the ceiling1 and they had discovered that the old mill wheel would still roll over if the penstock were repaired4 ,i replied that ,i would see what could be done about that sometime4 ,on the next day matters concerning the motor boat engaged our attention4 ,x ,,how ,,electricity ,,feels ,what is more fickle and yet more fascinating than a motor boat8 ,on the morning after my arrival at ,millville the boys wanted me to go out with them in the motor boat on the mill pond1 as our beautiful little lake is called4 ,each one took a hand at trying to start the boat1 but although she had acted perfectly well the day before1 on this morning no one could get a single explosion4 ,the switch was closed4 ,the gasolene was turned on4 ,the carburetor valves were set at the mark4 ,the spark coils responded with their familiar buzz4 ,she had been primed and1 when she had refused to respond to this treatment1 the pet valves were opened and the wheel rolled over several times to sweep out the cylinders4 ,but absolutely nothing moved her--neither coaxing nor gibes4 ,suddenly some one rolled the wheel over for the five-hundredth time and she started and behaved well all day4 ,all this would not have given us the slightest aggravation if we could only have found out what was the matter and what it was we finally did to correct it4 ,but this we shall probably never know1 and hence we are worshippers of the motor boat while we continue to distrust it and complain of it4 ,while the boat was running one of the boys noticed that a binding post at the end of one of the spark plugs seemed to be loose4 ,he inadvertently put out his hand to tighten it and received a terrific shock4 ,this raised the question among the boys1 why one gets a shock from some of the binding posts in the electrical equipment but not from others4 ,i suggested that we run in and call at the house to get my portable measuring instrument 7,fig4 #aaj7 and a little lunch1 and then go up to the upper end of the lake and take our time in examining the electrical equipment of the boat4 ,illustration3 ,fig4 #aaj ,the engine had two cylinders4 ,there were two batteries--one for each cylinder4 ,each battery consisted of five dry cells like the one represented in ,fig4 #aaa4 ,now1 why don't ,i feel the electricity when ,i touch the binding posts of this dry cell8 inquired one of the boys as he handled one of the cells which we had taken out4 ,well1 ,i'll give you two reasons why do you not feel it1 said ,i4 ,first1 because you were touching only one binding post at a time4 ,you must touch both of the binding posts of the battery cell at the same time1 so that the electric current may pass from one post to the other through your body4 ,second1 even when you do touch both binding posts at the same time you feel no current1 simply because you offered probably about #ajj1jjj ohms of resistance to the passage of the current and inasmuch as the one cell exerts only #a4e volts of pressure1 it could send only about 4#jjjjjae of an ampere through you4 ,this you cannot feel4 ,illustration3 ,fig4 #aaa 7#a4e volts7_/7#ajj1jjj ohms7 4#jjjjjae amperes4 ,i now connect my instrument as a volt meter between the binding posts of the cell and you see it indicates #a4e volts1 and when ,i connect it for an instant as an ammeter you see it indicates twenty amperes4 ,that is twice as much as they use for executing criminals by electricity4 ,so you see if you could reduce your resistance sufficiently this one battery cell might kill you4 ,some people have less resistance than others4 ,the resistance of the body is chiefly in the outer skin4 ,if one's hands are dry and his skin has been made tough and horny by hard work1 he has many times the resistance of one whose hands are moist and whose skin is thin and tender4 ,suppose we select the tip of the tongue as the portion of the body which will offer the least resistance and will be most sensitive to slight electric currents4 ,let us then connect one dry cell with the ammeter and place the tip of the tongue between the bare ends of the wire at ,t 7,fig4 #aab74 ,illustration3 ,fig4 #aab ,i have connected the ammeter so that it will indicate thousandths of an ampere1 and you see that the needle moves only slightly4 ,we cannot call it more than 4#jja ampere4 ,each boy in turn tried sending the current through his tongue and each tried to tell how it felt4 ,one said it tingled1 another said it felt warm1 another said it tasted sour and the other said he did not feel or taste anything4 ,well1 ,i said1 whether you feel anything or not one-thousandth of an ampere is passing through your tongue and you are offering fifteen hundred ohms of resistance4 7#a4e volts7_/7#aejj ohms7 4#jja ampere ,your hand offers nearly seventy times as much resistance as your tongue4 ,suppose we try increasing the voltage1 or pressure1 of our electric current4 ,we will connect in series the ten cells1 making a battery which you see by the volt meter gives fifteen volts of pressure4 ,we now find that having ten times the pressure it sends ten times as much current as formerly through the tongue4 7#ae volts7_/7#aejj ohms7 4#ja ampere ,each one now testified that the battery sent all the current he cared to take through his tongue4 ,if they send one thousand times as much as that through a criminal no wonder it kills him4 ,it produces a twitch when the contact is first made1 afterward a decided sensation of warmth and acid taste4 ,if we should increase the voltage tenfold more1 say the #aaj-volt dynamo current 7direct current71 and touch the bare conductors with our hands1 the ammeter would indicate about 4#jja ampere4 ,that is1 although this current has about seventy times as much push1 or voltage1 as a dry cell1 no more electricity passes through the fingers than did through the tongue in the preceding experiment with one cell4 ,the fingers offer so much greater resistance4 ,by wetting the fingers and pressing them firmly upon the bare wires1 we may make the ammeter read 4#ja1 that is1 we may increase the current tenfold by reducing the resistance to one tenth4 ,but there is nothing disagreeable about the feeling4 ,if the same experiment is tried with the #aaj-volt alternating current1 although the quantity of current which passes through the fingers is the same as before1 the tingling is more perceptible than in the case of the direct current4 ,if we join together seventy-five dry cells1 giving a voltage of #aab1 and press the bare wires with our wet fingers1 the ammeter will indicate 4#ja1 but there is no tingling sensation1 merely a slight warmth4 ,the battery current1 being continuous1 causes no twitching of the muscles while the contact is closed4 ,the direct current dynamo furnishes a slightly pulsating current4 ,hence1 one may tell by the feeling whether an electric current comes from a battery or a direct current dynamo4 ,the alternating-current dynamo gives a surging of electricity back and forth in the wires1 and this may be distinguished from the direct current by its feeling2 when1 however1 the number of alternations per second is increased very greatly1 one may receive through the body considerable quantities of electricity without feeling it4 ,with a very high frequency current one may put himself in circuit and light a #af-;candle-power lamp without any disagreeable sensation4 ,the outer skin is our chief insulation4 ,if it is dry and well toughened by work it offers a resistance of over #ajj1jjj ohms upon gentle contact4 ,a wounded spot1 or places like the tongue with moist1 thin skin1 may offer a resistance as low as #ejj ohms4 ,if one has a pin prick or a splinter in his hand which he cannot locate1 he may hold one bare wire of a #aaj-volt alternating circuit in one hand and move the other bare wire about on the suspected region1 and know when it reaches the spot by a tingling sensation4 ,illustration3 ,photograph by ,helen ,w4 ,cooke4 ,feeling ,electricity ,one may touch lightly the #bbj-volt direct current and scarcely note any difference between this and the #aaj-volt direct current1 because one is not very sensitive to the difference between 4#jja ampere and 4#jjb ampere passing through his body4 7#ajj volts7_/7#ajj1jjj ohms7 4#jja ampere1 and 7#bjj volts7_/7#ajj1jjj ohms7 4#jjb amperes ,physicians treat certain ailments by the use of the electric current4 ,for this purpose they invariably use a pulsating or alternating current and reduce the resistance by using metal handles and wet sponges for contact with the skin1 but even so a very small amount of current passes4 ,the moderate twitching of the muscles seems to be the end sought4 ,men who are supposed to be killed by electric shocks often die from other causes4 ,a man perching upon an electric light pole1 repairing wires1 may come in contact with a wire charged1 say1 to #bjjj volts4 ,he may receive a shock which throws him in an unconscious condition across another live wire which burns its way into his flesh1 or he may fall to the ground and be killed by the fall4 ,a workman may hold a tool so as to short circuit a current through it1 making it red hot in his hands4 ,so many men who have been shocked into unconsciousness by high voltage currents have recovered consciousness later that we cannot say how much current is required to kill a man4 ,for the execution of criminals #ahjj to #bjjj volts are used1 and by special metal contacts ten to fourteen amperes are forced through the body4 ,the first execution of a criminal by electricity was performed in ,sing ,sing ,prison1 ,new ,york ,state1 in #ahij4 ,there was at that time a hot controversy among experts over the question whether death1 or merely unconsciousness1 could be produced by electricity4 ,to be on the safe side the legislature passed a law requiring that the electrocution of a criminal should be followed immediately by the dissection of his body4 ,only six states out of forty-nine have thus far adopted that method of capital punishment1 five have abolished capital punishment1 and thirty-eight still prefer hanging to electrocution4 ,but it should be remembered that it is amperes1 not volts1 that kill4 ,one often hears the meaningless expression1 he received #bjjj volts into his body4 ,the volts indicate the pressure1 analogous to pounds per square inch of water pressure4 ,amperes of electricity are analogous to gallons of water4 ,it is possible to have exceedingly high voltage of electricity without amperes enough to do damage4 ,when one holds his finger near to a rapidly moving leather belt and a stream of sparks passes between the finger and the belt1 the voltage may be #ej1jjj or even #ajj1jjj1 but the quantity in amperes is too small to do any damage or even produce much sensation4 ,a similar thing is true when one produces sparks by rubbing a cat's back1 or lights the gas by a spark produced by rubbing the feet upon a carpet4 ,such sparks are miniature lightning discharges4 ,the real lightning does damage because it furnishes quantity1 measurable in amperes1 as well as extremely high volts of pressure4 ,at this point ,i was reminded by the boy who had received a shock from the engine that morning that he had touched only one binding post4 ,how then had he closed a circuit through his body1 and how could he receive such a terrible shock when there were only a few battery cells to produce the electric current4 ,i replied that he had the distinction of having encountered about a #ejjj-volt current4 ,in the language of the newspapers he might say1 ,took #ejjj volts and still live4 ,we must next proceed to show how he really did close the circuit and how the spark coil enables a battery of a few dry cells to produce exceedingly high voltages4 ,,xi ,,the ,,electrical ,,sparking ,,equipment ,,for ,a ,,gasolene ,,engine ,under the shade of a great sugar maple1 with ,millville ,lake spread before us1 we took apart and examined the entire equipment for producing the electric sparks to explode the mixture of gasolene and air in the cylinders of our motor boat4 ,the engine has two cylinders4 ,for each cylinder there is a separate battery and spark coil4 ,inasmuch as the electrical outfit is duplicated for each cylinder it will be necessary for us to consider the case of one cylinder only4 ,when this engine is running1 #gjj explosions per minute are produced in each cylinder4 ,in one-twelfth of a second the following four events take place3 #a4 ,the cylinder is swept clear of the products of combustion formed by the last explosion4 #b4 ,four drops of gasolene are vaporized and mixed with one quart of air and pushed into the cylinder by the pressure of the atmosphere4 #c4 ,this mixture is compressed by the piston in the cylinder to about one-fifth its original volume4 #d4 ,the mixture is heated to its kindling temperature1 which is above #bjjj degrees4 ,it then burns with a sudden expansion1 which drives the piston before it and pushes the crank which is concealed in the lower end of the cylinder half-way around4 ,the crank is attached to the shaft1 which carries the fly-wheel upon one end and the propeller wheel upon the other end4 ,the momentum of the moving parts--chiefly that of the fly-wheel--suffices to accomplish the remaining half of the revolution4 ,that any machine could be devised which could repeat these four events #gjj times a minute was unthinkable a few years ago4 ,the first men who thought that a gasolene engine could be a practical thing were considered visionaries1 but now they are found to be more practicable than steam engines4 ,they are so efficient that they compete with the steam engine upon its own ground1 and1 in addition1 they have opened up regions of usefulness which the steam engine can never exploit4 ,so far as we can see1 they have a permanent monopoly of the navigation of the air4 ,it is with the fourth event mentioned above1 viz41 kindling the explosive mixture1 that we are now concerned4 ,the high temperature required for this is obtained by forcing an electrical current against resistance4 ,five dry battery cells would very readily heat a short piece of fine wire to a sufficiently high temperature to explode the mixture1 but it is impossible to alternately heat and cool a wire twelve times a second4 ,it is too slow an operation4 ,the only other method known at present is to imitate the lightning and force an electric current against the resistance of the air with sufficient power to produce the required heat4 ,this1 however1 requires an extremely high voltage--at least #ejjj volts1 and our battery of five cells has not more than seven and a half volts of pressure4 ,the interesting question then is1 how does the spark coil enable us to raise the voltage from #g to #ejjj4 ,to help toward an understanding of the matter ,i took seven small wire nails which ,i found in the boat--they were sixpenny finishing nails4 ,i then took two or three yards of ,no4 #bd insulated magnet wire1 such as is used upon electric bells1 etc4 ,i use it more often than any other wire1 and always have some about the boat4 ,i fastened one end of this wire to one of the binding posts of a dry cell 7,fig4 #aac71 a1 and attached branches c and d to it4 ,the other end1 b1 was left free to act as a switch for closing the circuit by touching it to the remaining binding post4 ,illustration3 ,fig4 #aac ,illustration3 ,fig4 #aad ,illustration3 ,fig4 #aae ,one boy then touched the bare ends c and d to the tip of his tongue1 while ,i touched repeatedly the binding post with b4 ,there was1 of course1 no sensation4 ,we now wound a portion of the wire upon the bundle of nails1 laying on about fifty turns4 7,see ,fig4 #aad47 ,the tongue was now placed at ,t and b was touched a few times to the free binding post4 ,a very decided shock was felt1 not while the end of the wire was resting upon b1 but at the instant of touching and again at breaking the connection4 ,the shock was noticeably stronger at the instant of breaking than of making the connection4 ,there was also a spark formed when the connection was broken1 which did not appear before the coil was made4 ,we next wound on more of the wire--about fifty more turns 7,fig4 #aae74 ,when now connections were made and broken at b the tongue at ,t felt a much more decided shock1 and a larger spark occurred at b when the circuit was broken4 ,both the tongue and the spark indicate that the voltage is creeping up very rapidly in this series of experiments4 ,we next connected two cells in series1 then three1 four1 and finally five cells in place of the one4 ,the spark grew larger and fatter1 as the boatmen say1 with each addition of a cell4 ,it was not pleasant to use the tongue in the experiment after the number of cells exceeded two4 ,i removed the branch d from the wire b and connected it to the binding post1 as shown in ,fig4 #aaf4 ,i then removed the crystal from my watch and poured into it a little gasolene4 ,i rubbed the ends of b and d together over this1 and when they separated the spark which was produced would not light the gasolene4 ,we had made a coil which produced a spark that looked like a miniature flame1 but still was not hot enough to set fire to gasolene vapour4 ,it simply needs more iron in the core and more turns of wire about it4 ,bringing the ends of the wires together and separating them is somewhat like drawing an arc with the arc light carbons4 ,it requires a vastly higher voltage to make a spark jump across an air gap than it does to lead it across thus4 ,illustration3 ,fig4 #aaf ,the kind of coil we have made 7only larger7 is very much used in houses as a gas-lighting coil 7to be described later74 ,it is very much used also for exploding gasolene engines4 ,it generally passes under the name of the make and break coil4 ,the revolving shaft of the engine is made to push together the ends of the wire and separate them at the right instant to make the spark for explosion4 ,of course this is done inside of the engine cylinder4 ,that type of coil does not offer resistance enough to protect the battery1 and dry cells soon run down if used with it4 ,the coils that we have in this boat are somewhat different from that1 the details of which we cannot now entirely explain4 ,they offer enough resistance to cut the current required of the battery down to one third what the make and break coil would take and at the same time they raise the voltage so much higher that the spark will jump across an air gap without being led across as an arc4 ,hence they are called jump spark coils4 ,illustration3 ,fig4 #aag ,it will be remembered that when we were studying the dynamo we produced an electric current by moving a magnet4 ,we may now add that an electric current may be produced by simply changing the strength of a magnetic field4 ,the coil that we have just made creates a magnetic field in the region about itself whenever a current is passing through it4 ,the tongue at ,t 7,fig4 #aag7 detects an extra current while the magnetic field is being produced1 or while it is dying away1 or it will detect any slight variations in the strength of the current which produces the magnetic field4 ,it is customary to distinguish between these two currents4 ,the battery current which produced the magnetic field is called the primary current and the current which is detected by the tongue is called the secondary current4 ,the primary current in our experiments had only a few volts of pressure1 from one to seven4 ,the secondary current had many volts1 as indicated by the spark4 ,if we rub the end of the wire c across the binding post under b 7,fig4 #aag7 no spark occurs4 ,the current does not in this case go through the coil1 and no secondary current is produced4 ,whenever we touch the wire b to that post we have1 in addition to the primary current which has not voltage enough to produce a spark1 a secondary current flowing in the same wire at the same time and having voltage enough to produce a spark4 ,the primary current is continuous while the contact is closed2 the secondary current is momentary1 as the tongue detects1 and is produced only while changes are being made in the strength of the magnetic field4 ,we will now take another piece of wire and wind upon the coil about two hundred more turns1 leaving this outer coil wholly disconnected from the inner one1 7,fig4 #aah74 ,i connect c and d1 the terminals of what we may call the secondary coil1 with my measuring instrument and ,i connect a1 one of the terminals of the primary coil1 with the battery4 ,i then rub b1 the other primary terminal across the free binding post of the battery4 ,at the instant of closing the primary circuit--that is1 of building up the magnetic field--a secondary current is induced in the secondary coil1 which lasts for only an instant1 too brief a time for the needle to measure it1 although its motion indicates both the presence and the direction of the induced current4 ,while the primary circuit remains closed--that is1 while no change is occurring in the strength of the magnetic field--the needle returns to zero1 indicating no secondary current4 ,but when now the primary circuit is broken and the magnetic field loses its strength1 the needle indicates a momentary current in the secondary coil and in the opposite direction from what it had been at first4 ,illustration3 ,fig4 #aah ,if1 therefore1 ,i rapidly make and break the current at b ,i produce an alternating current in the secondary coil4 ,i will connect c and d with a miniature lamp and1 resting a coarse file upon the free binding post1 ,i will rake the end of the wire b up and down upon this file so that1 as it dances along upon the file1 it will rapidly make and break the primary circuit1 and therefore rapidly change the strength of the magnetic field4 ,you notice that the lamp lights up moderately well4 ,it is being lighted by an alternating current4 ,i move the wire a little more slowly and you see the flicker of the alternations4 ,according to the label upon the lamp it requires ten volts1 and our battery could not give that4 ,we have therefore stepped up the voltage as we say and we have a veritable step-up transformer4 ,in this case the primary and secondary circuits are entirely separate4 ,it is a familiar fact that different electric currents may pass through the same wire at the same time without apparent conflict4 ,we send numerous telegraph despatches through the same wire at the same time4 ,it is quite as easy for several pairs of persons to telephone over the same wire at the same time as it is for those same several pairs to carry on separate conversations in the same room at the same time1 at1 say1 an afternoon tea4 ,we may use the same wire at the same time to carry direct and alternating currents4 ,this fact was first discovered in #aijb by ,bedell of ,cornell ,university4 ,primary and secondary currents do not require separate primary and secondary coils to convey them4 ,they may or may not be connected into one continuous coil4 ,it is quite immaterial whether they are connected or not so long as they are in the same magnetic field4 ,indeed1 it seems that the field outside of the wire may be quite as important as the wire itself4 ,illustration3 ,fig4 #aai ,we have now #ajj turns in the primary and #bjj turns in the secondary coils4 ,let us connect b with c so as to make one continuous circuit of #cjj turns4 ,let us then put a branch upon b to connect with the battery1 thus having #ajj turns for the primary circuit1 and put a branch upon a to connect with the lamp1 thus having #cjj turns upon the lamp1 7,fig4 #aai74 ,when now we rub b upon the file1 as before1 the lamp lights up more brightly than before1 indicating that we have stepped up the voltage still higher4 ,varying the strength of the magnetic field induces a secondary current and the voltage of the induced current is determined1 in part1 by the number of turns in the secondary circuit4 ,if what we have been saying is true we ought to be able to get these same results from an electric bell4 ,to test this we connected wires with a and c1 7,fig4 #abj71 and since ,i knew that the secondary current at ,s would be too severe for the tongue we decided to feel it with the hands4 ,for this purpose we want a larger surface than the wires themselves offer for contact with the hands1 and so ,i twisted the bare end of each wire around an iron spike4 ,the four boys then arranged themselves in line1 joining hands1 and the boy at each end of the line held a spike in his free hand4 ,thus we had put the enormous resistance of four human bodies joined in series in the secondary circuit4 ,when now ,i connected two dry cells with a and b 7,p1 ,fig4 #abj7 the hammer of the bell acted1 like the file in the former case1 as interrupter of the primary circuit4 ,as it rapidly made and broke the primary circuit1 it produced rapid changes in the strength of the magnetic field and thus induced a secondary current which the boys all felt4 ,the fact that it forced its way through four bodies shows that its voltage was high4 ,the high voltage was also indicated by the spark which always occurred in the bell4 ,the primary circuit in this case has not more than three volts while the secondary has more than a hundred4 ,we have it in our power to give the secondary current almost any voltage we choose1 with this limitation each increase in voltage necessitates a proportional sacrifice of quantity4 ,the watt power induced in the secondary circuit cannot exceed that contributed to the primary circuit--indeed cannot quite equal it since there is some loss in heat4 ,illustration3 ,fig4 #abj ,suppose we operate a bell on a primary current having three volts and 4#be ampere1 that is1 4#ge watt4 ,suppose then the voltage of the secondary current is stepped up to fifty times three1 or #aej volts4 ,the quantity of secondary current will be found to be somewhat less than one fiftieth of 4#be or 4#jje ampere4 ,the #aej-volt alternating current from the bell is more tolerable than that from a #aej-volt dynamo1 because the quantity is limited in the former case4 ,our spark coil has a vibrator which acts precisely like the hammer of the bell to make and break the primary circuit and thus make rapid changes in the magnetic field produced by the primary coil4 ,the primary coil of the spark coil is many times larger than the coil of the bell1 that is1 it contains many more turns of wire4 ,it has much more iron in the core4 ,we use upon it five cells instead of the two cells upon the bell4 ,the result of all this is that we have a much more powerful magnetic field than that in the bell and many more watts of energy from which to induce a secondary current4 ,now the number of turns employed in the secondary circuit of our spark coil is very great1 stepping its voltage up to thousands where the bell induced hundreds4 ,illustration3 ,fig4 #aba ,suppose we now repeat our experiment in which we tried to light the gasolene in the watch crystal1 using now the spark coil of the boat instead of our small home-made coil4 ,in ,fig4 #aba1 ,b is the battery of five dry cells4 ,s is a switch4 ,v is the vibrator1 which1 like the hammer of an electric bell1 makes and breaks the primary circuit4 ,of course the coil has a core of iron1 although that is not here represented1 and1 of course1 the coil has many hundred turns instead of the few here represented1 and of course also it is built up of many layers instead of one as here represented4 ,the secondary has very many more turns than the primary1 but those in which the primary current passes are common to both circuits4 ,there is also a condenser--not here represented1 and not to be described in this book4 ,the result of all this is that the secondary circuit has a voltage of between #ejjj and #aj1jjj1 and a spark jumps across the gap at c between one sixteenth and one eighth of an inch long4 ,this spark is hot enough to light the gasolene which ,i have put in the watch crystal at c4 ,illustration3 ,fig4 #abb ,let us return to the bell for a few minutes4 ,i have here a miniature lamp which requires #aj volts and 4#a ampere1 that is1 #a watt1 which ,i will connect at ,s 7,fig4 #abb74 ,when now ,i close the primary circuit with two cells at ,p you notice that the lamp lights up1 but faintly4 ,it is not receiving 4#a ampere4 ,remember we have only 4#ge watt at our disposal and this lamp requires #a watt4 ,hence it is getting only three quarters enough energy4 ,we connect in a third cell and now it lights up to full brilliancy4 ,the resistance of this lamp must be about #ajj ohms4 7#aj volts7_/7#ajj ohms7 4#a ampere ,the resistance of the four boys might have been #fj1jjj ohms1 and the voltage of the secondary circuit might in that case have been1 say1 #aej4 7#aej volts7_/7#fj1jjj ohms7 4#jjeb ampere ,how does it happen that the secondary current had a pressure of #aej volts on the boys but cannot supply even the #aj volts required by the lamp8 ,perhaps we can be brought to appreciate the answer to that question best by asking ourselves some others quite like it4 ,why did not the man who built our mill two generations ago locate it upon the small stream that flowed near his house8 ,the small stream was more conveniently located for him and it has quite as much fall as he got at the foot of this lake4 ,we sometimes express the fact by saying that the head of water or the water pressure was quite as much in one of these cases as the other4 ,one boy said that the stream sometimes gives out4 ,another one said that it never did have water enough to run that wheel4 ,undoubtedly the trouble is with the quantity1 said ,i1 but ,i want to show you that we cannot maintain the pressure unless there is sufficient quantity back of it4 ,illustration3 ,fig4 #abc ,in ,fig4 #abc1 suppose ,a represents a small1 slim tank of water three feet high4 ,the water-wheel ,w1 requires one gallon of water a minute pushed along by a three-foot head of water pressure to run it4 ,the supply pipe ,s is bringing into the tank not more than one quart of water per minute4 ,a gate at ,r enables us to regulate the flow of water1 as we regulate the flow of electricity1 by using more or less resistance4 ,now it is evident that if we close the gate1 or partially close it1 and allow the tank to fill with water1 we may then open the gate and run the wheel for a short time1 but the level of the water in the tank soon begins to fall and the pressure grows less and the wheel stops moving4 ,it is just so with all generators of electric current4 ,if we take from them more than they can supply continuously the voltage falls4 ,this is notoriously true of dry cells4 ,like the water tank represented in ,fig4 #abc1 they run down if used continuously to furnish1 say1 one ampere of current1 but they may furnish it for a short time1 the voltage rapidly falling meanwhile4 ,then if given a short rest they pick up and will again furnish full pressure4 ,the voltage of a dry cell falls somewhat when it is required to give the very small amount of current required to actuate a volt meter1 say 4#jae ampere4 ,hence1 our volt meter will not quite correctly show what the voltage of a single cell would be on open circuit4 ,notice that1 when ,i put one cell upon this volt meter the needle shows #a4db volts2 but when ,i put four cells in series upon it the needle indicates six volts1 as nearly as we can read it4 ,that is1 the voltage of each cell in this case appears to be #a4e4 ,what has increased the voltage of a cell from #a4db to #a4ej8 ,simply this3 when 4#jae ampere1 the amount required by the volt meter1 was taken from one cell it reduced its pressure1 but when a multiplier with ten times the resistance was added we secured our reading by using only 4#jjf ampere of current1 and this did not appreciably reduce the true pressure of the cells4 ,the induced current from our bell when held back by #fj1jjj ohms of resistance in the four boys was able to push with #aej volts of pressure1 and 4#jjbe ampere passed without noticeably reducing this pressure1 but when the same current was held back by only #ajj ohms in the filament of the lamp nearly forty times as much current passed1 and the pressure dropped to something less than ten volts4 ,we will try an experiment to show how the voltage will suddenly fall when we reduce the resistance of your four bodies4 ,illustration3 ,fig4 #abd ,fill these two empty tin pails in which our lunch was brought with water from the lake and sprinkle in the salt left over from the lunch4 ,now twist a bare copper wire around the bail of each pail and connect these with the bell so as to get the induced current from its magnet4 7,see ,fig4 #abd47 ,let the two pails of water be the terminals of the two wires at ,s4 ,now you four boys wet your hands in the water and then join hands1 and those at the two ends of the line put your free hands upon the outside of the pails of water while ,i close the primary circuit4 ,you of course feel the current just as you did when you held the spikes in your hands in a former experiment4 ,but now you two end boys put your free hands into the salt water1 and you instantly get a very smart shock4 ,the resistance is no longer #fj1jjj4 ,it has dropped way down to #bjjj1 and if the voltage had remained at #aej you would have received a terrible shock1 but the voltage has dropped down to five4 ,it is as though you had been pushing very hard against a post and it suddenly gave way4 ,you cannot push against a thing which offers no resistance4 ,so the voltage falls when resistance is reduced1 and particularly if the source of supply has very little capacity4 ,here is another experiment you must try when you go back to the city4 ,at a certain water faucet in my laboratory the pressure is disagreeably high4 ,the water flows with great force and spatters badly4 ,we can easily reduce the pressure so that the water will flow in a limpid stream4 ,fig4 #abe shows the situation2 f is the faucet1 and in the pipe underneath the sink there is a stop-cock c4 ,this may be adjusted permanently so that the faucet f will act pleasantly4 ,the same thing is represented again at the gas stove4 ,let f in the ,fig4 #abe represent a gas cock at the stove4 ,suppose the pressure is so high that the gas flames pass more gas than is readily consumed4 ,it is possible to adjust a stop-cock like c further back in the pipe so as to produce hotter flames1 get rid of the poisonous fumes of half burned gas1 and cut down the monthly gas bills one half4 ,illustration3 ,fig4 #abe ,my garden hose will usually throw a stream across the street1 which is very desirable when one wishes to sprinkle the street1 but this pressure is disastrous when ,i wish to sprinkle the flowers4 ,turning down the stop-cock at the nozzle makes it shoot a smaller stream but more spiteful in pressure1 knocking the flowers to pieces and washing the soil away from their roots4 ,but if ,i partially close the stop-cock at the side of the house where the hose is attached ,i may have the stream of water flow as gently as ,i choose4 ,i should meet precisely the same situation if ,i tried to ring an ordinary electric bell by a #aaj-volt current1 and ,i should use the same method of overcoming the difficulty4 ,the great virtue of the dynamo is that it can furnish a large supply so that the voltage is kept constant on a great flow of current4 ,illustration3 ,fig4 #abf ,i have not forgotten the question1 but have tried to work toward its answer all this time4 ,the question is1 why did ,ernest get a shock this morning when he touched only one binding post1 and when the battery of five cells is not capable of giving shocks to any one who touches its binding posts directly8 ,we need one more diagram to give the final answer4 ,in ,fig4 #abf e represents the binding post from which the shock was received4 ,b is the battery of five cells1 ,c is the spark coil1 ,g is the engine cylinder1 f is the spark plug4 ,when one wishes to start the engine he closes the switch ,s4 ,this makes a continuous conductor from the battery to the metal cylinder itself4 ,as the engine rolls over it closes the gap in the conductor at d for an instant4 ,the primary circuit is then completed and the current passes from ,b to the cylinder1 through the metal of the cylinder to d1 then to the coil ,c1 where it passes through a portion of the coil and then back to the battery4 ,the vibrator on the coil causes the magnetic field to rapidly vary in strength4 ,this induces a secondary current in the whole coil which1 because it passes through a very great number of turns1 has a high voltage4 ,this passes from ,c through ,b to the base of the engine1 then up the walls of the cylinder to the plug f1 then jumps across the gap at a1 causing the spark which explodes the mixture of gasolene and air in the cylinder4 ,the spark plug f is porcelain--an exceedingly good insulator4 ,through the centre of this passes a wire from a to e4 ,the current passes up this and back to ,c4 ,now the engine rests upon the floor of the boat1 and ,ernest stood upon the same floor4 ,the wood of this floor when dry and clean is a very good insulator1 but when wet1 and particularly when wet with water that has ever so slight an amount of any salt in solution1 it becomes a conductor for such high tension currents4 ,when therefore ,ernest1 standing upon the floor of the boat1 touched the binding post1 e1 this induced current of high voltage found it about as easy to pass from the metal of the engine cylinder through the wood to his body and through his body to e as to jump across the short air gap at a4 ,there are two things upon which he may congratulate himself4 #a4 ,while the coil stepped up the voltage so high it reduced the available quantity of the current1 so that the shock was a safe one4 #b4 ,he received only a portion of the current which passed4 ,the major part of it passed across the gap at a1 otherwise we should have noticed that the engine missed an explosion when he touched the binding post4 ,the only part of this electrical outfit from which one may receive a shock is that line from e to ,c4 ,the greatest difference in electric pressure is always to be found between the two extremities of the electric generator2 as1 for example1 between the carbon end and the zinc end of the battery1 the positive and negative poles of the dynamos2 the right-hand and left-hand end of this coil4 ,since the right-hand end is connected by good conductors with the metal of the engine and with the floor of the boat and through it with our bodies1 we are in the same electrical condition as the right end of the coil2 but the left-hand end and the wire connecting it with e are forced by the varying magnetic field into a very different state of electric tension1 and it is insulated from the engine and from us by the porcelain spark plug4 ,we say that the difference in potential between the two sides of this system is #ejjj to #aj1jjj volts4 ,the water in this lake flows through the stream at the other end of the lake to the ocean4 ,the water of the ocean evaporates to form clouds4 ,clouds drift over the land and drop their rain to replenish the lake4 ,the difference in water level between this lake and the ocean is twenty feet4 ,a difference in water level is what makes it a water power and it is what occasioned the building of our mill4 ,this difference of water level corresponds in our electric generators to the difference in potential4 ,the difference in potential maintained by our battery of five cells when not producing current is #g4e volts4 ,the difference in potential between the two ends of our coil1 when the battery is agitating its magnetic field1 is perhaps a thousand times as much1 or #gejj volts4 ,the boys took their swim in the lake and afterward1 while we were all on shore lying on the grass1 they brought up again the question of the machine-shop4 ,they were anxious to know if ,i had any plans in regard to it4 ,i said ,i had been thinking about it a good deal over night but had been waiting to hear their plans4 ,well1 they thought it would be good to have a turning lathe1 but could not think of anything else unless it might be a grindstone run by power4 ,i said ,i had thought of a ,central ,station ,electric ,plant4 ,at this they all sat up4 ,hydro-electric stations are the proper thing now1 ,i remarked4 ,on the ,rio ,grande ,river in ,colorado they are constructing several plants where water power will be utilized to generate electricity for use more than one hundred and fifty miles away4 ,for transmitting electricity to such a distance they step up the voltage1 or electro-motive force as it is called1 to #ajj1jjj volts4 ,they are harnessing the ,au ,sable ,river in ,michigan to generate electricity and transmit it at #ace1jjj volts e4 m4 f4 to towns nearly two hundred miles away4 ,electricians use e4 m4 f4 for electro-motive force1 just as you boys use exams4 as slang for the motive force in school4 ,of course we are aware that since #ahif some of the water power of ,niagara had been converted into electric power to run street cars and factories and furnish electric light and electric heat as far away as ,buffalo1 twenty-six miles distant4 ,about #ah1jjj1jjj are now being invested in hydro-electric enterprises even in ,mexico4 ,by this time the boys were all standing up and staring at me1 while ,harold inquired if ,i were talking in my sleep4 ,i have at any rate succeeded in waking you all up1 said ,i1 and what ,i have said is not altogether a joke4 ,let me explain somewhat at length4 ,,xii ,,electricity ,,from ,,central ,,stations ,large dynamos generate electricity very much more cheaply than small machines can1 and machines which have a full load continually produce the current very much more cheaply than those which run upon very light load part of the time4 ,the largest central stations with load evenly distributed for the whole day could furnish electricity profitably at four cents per kilowatt hour4 ,there are many small electric lighting plants which furnish current from sundown to midnight only at fifteen cents per kilowatt hour1 with little profit4 ,the transformer 7,fig4 #abg7 makes it possible to gather all this generation of electricity for sparsely settled districts into large central stations1 located sometimes far away from the consumer perhaps1 where there is abundant power in some water-fall1 thus saving the expense of coal for running the dynamos4 ,illustration3 ,photograph by ,helen ,w4 ,cooke4 ,operating the ,switchboard ,a few years ago there were no central stations for this purpose4 ,now according to the latest census reports there are in the ,united ,states about #cj1jjj plants1 including those which belong to certain cities1 that generate electricity for sale1 and there are twice as many more isolated plants to furnish light and power in factories1 hotels1 etc4 ,illustration3 ,fig4 #abg ,the money invested in central station business now exceeds six billion dollars1 and the annual output of electric current is sufficient to keep eight billion #af-;candle-power carbon filament electric lights burning continuously night and day4 ,all this has more than doubled in the last five years4 ,central stations are now furnishing about five times as much current for heating1 cooking1 and charging automobiles as they did five years ago4 ,about one third of all the central stations depend on water power4 ,illustration3 ,fig4 #abh ,illustration3 ,fig4 #abi ,we might take as the type of hydro-electric central station1 that is1 one which generates electricity by water-power1 the ,glenwood ,station of the ,central ,colorado ,power ,company4 ,this station has two #ijjj horse-power water turbines4 ,each water-wheel drives an alternating-current generator which develops #djjj volts of e4 m4 f4 ,these water wheels and generators are shown in ,fig4 #abi4 ,the penstocks are to be seen coming through the back wall of the building4 ,they bring water at #agj foot head1 or about seventy-five pounds per square inch static 7standing7 pressure4 ,three huge transformers1 each weighing twenty-six tons1 step up the e4 m4 f4 from #djjj to #ajj1jjj volts4 ,these are the cylinders shown in ,fig4 #acj4 ,they simply contain a great many coils of copper wire with a vast amount of iron at the centre4 ,they accomplish in a large way what our spark coil does in a lesser degree4 ,but why go to all this expense to produce such a dangerous and troublesome voltage8 ,the answer briefly is1 that while it is dangerous and troublesome the expense is not so great as it would be to supply by any other method the electric current required4 ,denver and numerous other places1 large and small1 require electric current4 ,from one to two hundred miles away on the ,grande ,river1 there is vast power running to waste4 ,we have to choose on the one hand between buying power in the shape of coal and distributing power plants to those various localities where electricity is needed1 and on the other using this water-power1 which is now running to waste1 to generate electricity which we may transmit and distribute throughout the one hundred and eighty-five miles to ,denver1 ,leadville1 ,boulder1 ,dillon1 ,idaho ,springs1 etc4 ,but electric energy transmitted a long distance suffers great loss4 ,illustration3 ,fig4 #acj ,suppose1 for instance1 ,i needed to supply fifty amperes at one hundred-volt pressure ten miles distant from the generator1 and had a conductor the size of a trolley wire to bring the current4 ,the resistance of the trolley wire is one ohm for every two miles1 or five ohms4 ,the drop in voltage is found by multiplying the amperes of current by the ohms of resistance4 ,ten miles from the central station1 therefore1 the drop on fifty amperes would be #ej #e #bej volts4 ,it would1 therefore1 be necessary to maintain a pressure of #cej volts at the generator to deliver the fifty amperes at #ajj volts4 ,the energy supplied by the generator is #cej volts #ej amperes #ag1ejj watts #ag4e ,k4 ,w4 ,the energy delivered to the consumer is #ajj volts #ej amperes #ejjj watts #e ,k4 ,w4 ,in order to deliver fifty cents' worth of electricity per hour to the consumer it would1 in this case1 be necessary to generate #a4ge worth of electricity at the central station4 ,that is1 about seventy per cent4 of the energy generated would be wasted in transmission4 ,if now we decide to generate this electrical energy at ten times as high voltage it will be necessary to transmit only one tenth as many amperes1 or five4 ,in this case the drop in voltage would be #e amperes #e ohms #be volts4 ,it would be necessary to maintain #ajbe volts of pressure at the generator to deliver to the consumer the five amperes at #ajjj volts #ejjj watts4 ,that is1 to deliver #ejjj watts in this case we must generate #ajbe volts #e amperes #eabe watts1 and less than #b-a_/b per cent4 of the energy generated would be lost in transmission4 ,if now the consumer must have his energy delivered at #ajj volts1 we must introduce a step-down transformer at his end of the line which may give him #ej amperes at #ajj volts #ejjj watts4 ,this transformer1 being small1 will cause a loss of #ae or #bj per cent41 but if there were a very large amount to transform it might be done with a loss of only #d per cent4 ,illustration3 ,fig4 #aca ,illustration3 ,fig4 #acb ,it is not thought to be advisable to raise the voltage at the generator higher than #djjj4 ,this will not suffice to supply large working currents to a greater distance than about six or eight miles4 ,for a distance of #aj miles #fjjj volts are desirable2 for #ej miles #cj1jjj volts2 for #ajj miles #fj1jjj volts2 for #afe miles #ajj1jjj volts2 and for #bjj miles #abj1jjj volts4 ,notice that in this table the voltage rises at the rate of #fjj per mile4 ,since it is not desirable for the generator itself to produce a higher voltage than #djjj1 we must depend upon transformers to produce these high voltages4 ,let us then consider1 a little more in detail1 the construction of a transformer4 ,i have here some drawings of one which ,i propose that we make in the machine shop1 and use in our central station equipment in the future4 ,we will procure the thinnest and softest sheet iron possible and cut out of it a lot of pieces shaped like the letter ,h with the dimensions shown in ,fig4 #aca4 ,these are to be piled one upon another1 with strips of paper between1 until the pile is #a-a_/b inches thick4 ,then four pieces of board are to be bolted to the sides of these 7,fig4 #acb74 ,the dimensions of each of the four blocks1 is to be #g-a_/b inches long by #c inches wide by #a-a_/b inches thick4 ,upon the cross bar of the ,h we will wind #djj turns of ,no4 #ab double cotton-covered copper wire1 bringing out the ends for future attachments1 and then wind on #abjj turns of ,no4 #aj double cotton-covered copper wire4 ,the wire will fill the space between the blocks as indicated by the diagram in ,fig4 #acc4 ,we will then cut strips of the sheet iron #f inches long by #a-a_/d inches wide1 and bridge across the ends of the ,h1 prying open the leaves of sheet iron and tucking them in between as shown in ,fig4 #acd4 ,we shall then drill a hole at each corner and bolt them in place4 ,binding posts will be placed at a1 b1 c1 and d 7,fig4 #acd71 and the two ends of the ,no4 #ab wire will be brought to a and b and those of the ,no4 #ah wire will be brought to c and d4 ,going through all this detail of construction has probably made you lose sight of the essential features of this transformer4 ,let us for a moment turn back and see what they are4 ,we have a large coil of wire #c inches long and #g-a_/b inches in diameter4 ,it is composed of a coarse winding and a fine winding1 which we may designate as the primary and secondary coils1 if we choose4 ,of course the only reason for having different sizes of wire is so that we may send larger currents through one than the other4 ,the coil has a laminated iron core1 that is1 it is composed of layers of sheet iron4 ,these layers are insulated from one another4 ,this is essential1 although we cannot explain why now4 ,but perhaps the most essential feature of the transformer is that iron extends clear around from one pole of this electro-magnet to the other4 ,fig4 #ace represents a section through the coil made in the plane of e f g 7,fig4 #acd74 ,the core of the magnet is represented as heavily shaded4 ,the magnetic circuit is said to be closed from one pole of this magnet to the other through the strips of iron which pass across the ends and down the sides of the coil4 ,the arrows show the path of the magnetic circuit4 ,the dotted portion shows where the copper wire may be supposed to have been cut across4 ,inasmuch as the electric current is induced in the secondary circuit by continually varying the strength of the magnetic field as much as possible1 the alternating current is the most desirable to use in the primary4 ,if the direct current were used an interrupter would be necessary1 which would of course produce too much sparking when any but low tension currents are used in the primary circuit4 ,the most interesting and curious fact about the transformer is that the voltages of the primary and secondary currents are in exact proportion to the number of turns in the wire of the two circuits4 ,illustration3 ,fig4 #acc ,illustration3 ,fig4 #acd ,illustration3 ,fig4 #ace ,in our transformer the number of turns in the coil between the binding posts a and b is #djj and the number of turns between c and d is #abjj4 ,if now we connect a #aab-volt alternating current with the binding posts a and b1 a volt meter connected across between c and d will show #ccf volts1 and if b and c be connected by a short wire1 bringing in #afjj turns into the secondary circuit1 a volt meter connected across between a and d will show a voltage of #ddh4 ,or if1 leaving b and c still connected by a short wire1 we connect the #aab-volt alternating current to a and d a volt meter connected across between a and b will show #bh volts1 or if connected between c and d it will show #hd volts1 and if finally the #aab-volt current is connected to c and d the pressure between a and b will be #cg-a_/c4 ,illustration3 ,fig4 #acf ,the story1 then1 of the central station which we have chosen as a type is briefly this3 ,falling water makes dynamos revolve1 generating a #djjj-volt alternating current4 ,this current is sent through the primary windings of transformers4 ,the secondary windings of these transformers have twenty-five times as many turns as the primary coils4 ,this steps up the voltage from #djjj to #ajj1jjj1 making it necessary to send only one twenty-fifth as many amperes over the lines as would be required at #djjj volts1 and reduces the loss in transmission to nearly one twenty-fifth4 ,at the other end of the line the current traverses the secondary windings of transformers1 and the consumer receives his current from primary coils which may step the e4 m4 f4 down to any required volts of pressure1 generally #aaj4 ,now ,i shall be glad to have you consider whether this suggests any practicable problems for us here in ,millville4 ,the sun is nearly setting and ,i suppose the family is expecting me home4 ,illustration3 ,fig4 #acg ,,xiii ,,electricity ,,from ,,an ,,old ,,mill ,millville is only a name or rather a reminiscence4 ,there was once a village here1 but now its population has all gone with the tide down the river1 even its ghost appears to have departed4 ,the ruins have all fallen1 except the mill1 which we propose to revivify4 ,i had built a summer cottage on the shore of the lake1 about one mile from the mill4 ,the absolute stillness of the place charmed me when worn out by the noise and heat and dirt and smell of the city4 ,here even the owl twittered softly as if afraid to disturb the silence4 ,the silence which was such a boon to me seemed to be oppressive to the younger members of the family4 ,to prevent therefore their becoming dissatisfied with the place and wishing to go to other resorts1 ,i planned to have some of their best friends spend much of the summer with us1 and ,i encouraged their plans for making use of the mill4 ,i will not offer this as an excuse for introducing electricity into a sleeping valley4 ,indeed1 electricity has always disported itself there in the lightning1 jumping from cloud to mountain peak as ,i have seen it nowhere else on earth4 ,the next time ,i saw the boys they had ambitious plans indeed4 ,the penstock at the mill was to be repaired4 ,the water-wheel was to drive an alternating current dynamo4 ,the voltage of this current was to be stepped up by a transformer4 ,it was to be transmitted to the cottage and there the e4 m4 f4 was to be stepped down again by another transformer4 ,my wife suggested that if it interfered with the simple life it would have to step down and out4 ,harold1 however1 assured his mother that they were going to simplify everything--even the subject of electricity4 ,their plans were3 ,to light the cottage by electricity2 introduce a number of electric back logs1 with coloured glass bottles2 heat the fireless cooker by electricity2 pump the water for the house by electricity2 run mother's sewing machine by electricity2 run the washing machine and wringer by electricity2 heat sad irons by electricity2 percolate coffee1 wash dishes and run the vacuum cleaner by electricity2 operate the door bell and the telephone and wind the clock by electricity4 ,i was sure that if they carried out these plans they would stay in ,millville at least that summer1 so ,i said go ahead4 ,we fixed the penstock4 ,the boys estimated that #aj cubic feet of water per second would pass through it4 ,they said that a cubic foot of water weighed #fb4e pounds and #aj cubic feet weighed #fbe pounds4 ,they said it fell at the rate of #g vertical feet a second1 making #dcge foot-pounds per second4 ,but #eej foot-pounds per second is one horse-power1 hence this is about #h horse-power4 ,since one horse-power is equivalent to #gdf watts of electricity1 we have1 if we could generate it without loss1 said the boys1 nearly the equivalent of #f kilowatts of electricity1 or about #ed amperes at #aaj volts4 ,there were several things they wanted to know before they could go further with their plans4 #a4 ,how many of these electrical appliances we would be likely to use at one time4 #b4 ,how much current each device would require4 #c4 ,how much they must allow for losses in generating the current1 in transmitting it1 and in transforming it4 ,we assured them that we would never use more than twenty amperes1 say1 two thousand watts at one time4 ,they might install a fuse1 or circuit breaker in our line to protect their plant against a greater load from us4 ,i told them that they might allow #bj per cent4 loss of energy at the dynamo in converting water-power into electric-power4 ,i would suggest generating their current at #aae e4 m4 f4 and stepping it up to #dfj for transmission to us1 and then stepping it down to about one hundred and ten volts for our use4 ,they might count on about one-third loss on our supply1 that is1 they would need to generate about three thousand watts in order to deliver us #bjjj watts4 ,i suggested making our line of ,no4 #f copper wire1 which has a resistance of two ohms to the mile4 ,the distance from the mill to the cottage is one mile1 and the complete circuit therefore would require two miles of wire1 or four ohms of resistance4 ,if we start with #cjjj watts and lose #ad per cent4 in transforming we shall have #behj watts to transmit4 ,if the voltage has been stepped up fourfold there will be about #e4f amperes to transmit which will suffer a loss of #bb4d volts in passing through four ohms of resistance on the line4 ,the loss in transmission will be about #e per cent41 and we shall have on arrival at the cottage about two thousand four hundred and fifty watts with a voltage of #dcg4f4 ,if now in stepping this down to one fourth the voltage1 viz41 #aji4d1 we lose #ad per cent41 we shall have left something over two thousand one hundred watts1 or nearly twenty amperes4 ,assuming that you are able to generate #dhjj watts of electricity and that #cjjj watts must be furnished for transmission to the cottage1 you have left #ahjj watts1 which will give you something over fifteen amperes at #aae volts for use in your machine shop4 ,i suggest that we get a dynamo which will generate both alternating and direct current--the alternating current you will send to the cottage1 and the direct current you will have for use at the machine shop4 ,but how is it possible for a dynamo to generate both alternating and direct current at the same time8 ,illustration3 ,fig4 #ach ,illustration3 ,fig4 #aci ,recall that all dynamos are generators of alternating current4 ,if the brushes rest upon rings upon the axle they send forth alternating current--but if the brushes rest upon commutator bars they send forth direct current4 ,now we will have two sets of brushes1 one pair of which shall rest upon the rings on the axle1 and they will collect alternating current for the cottage1 while the other pair will slide over the commutator bars and collect direct current for the machine shop4 ,i have constructed a model which will make it plain4 ,here is a piece of a broom handle 7,fig4 #ach71 one foot long1 which shall represent the axle of an armature4 a b c d is a stout wire which represents the coil of the armature4 ,in this case it has no iron at its centre4 ,nevertheless it will serve as an armature having one loop of its coil left4 e and f are rings1 sawed from a piece of brass pipe1 which fit snugly upon the axle4 ,another ring of the brass pipe was sawed lengthwise1 as shown in ,fig4 #aci4 ,these two halves are also fastened upon the axle and one end of the wire loop1 c1 is fastened to one of these1 and the other end of the loop1 b1 is fastened to the other half of the ring4 ,these two halves of the piece of brass pipe are placed so that their edges are near to each other but do not touch on either side of the axle4 ,the two ends of this wire loop are also connected with the rings e and f4 ,a short wire connects b and e and another connects c and f passing through the wood of the axle1 as shown by the dotted line4 ,we will now revolve this loop slowly about its axle in a strong magnetic field4 ,to produce this field ,i will send two amperes of electricity through the coils of wire 7,fig4 #adj71 which surround two iron pole pieces that are screwed into an iron base4 ,between the poles ,n and ,s of this electro-magnet we will thrust this wire loop and revolve it as an armature very slowly4 ,meanwhile ,i connect two wires to my sensitive ammeter and let their free ends brush along on the rings e and f4 ,the needle of the ammeter swings to and fro for each half revolution of the armature1 showing an alternating current of 4#ja amperes4 ,if this armature had many turns of wire instead of this one loop1 if it had an iron core1 and if it should revolve at high speed1 the results would differ in degree but not in kind4 ,illustration3 ,fig4 #adj ,we will now move the wires which are acting as brushes over to the metal pieces b and c4 ,when now we revolve the armature the needle swings to the right1 and just as the needle is about to swing back each brush slides from the plate on which it is rubbing to the opposite one and the needle gets another impulse forward4 ,if the armature is turned rapidly the pulses disappear and the needle stands constantly at about 4#jae amperes4 ,this then is both an alternating and a direct current dynamo4 ,it simply needs more iron1 more copper wire1 and more rapid motion1 to give us the #dhjj watts of electrical energy we are seeking4 ,but how shall we produce the current which we wish to send around the spools of the field8 inquired the boys4 ,connect the field with the brushes which rub upon the commutator1 ,i replied4 ,it will magnetize its own field4 99 99 99 99 99 ,as good luck would have it1 we found that the ledge of rock which furnished the basis for the mill dam was immediately underneath the floor at the north end of the machine shop4 ,upon this we built up a solid foundation for the dynamo4 ,our water-wheel gave a speed of #bdj revolutions per minute to the counter shaft4 ,a pulley of two feet in diameter upon this counter shaft was belted to the pulley of one foot in diameter upon the dynamo--thus giving its armature a speed of #dhj revolutions per minute4 ,we had to fix a governor upon the water-wheel to keep this speed constant at varying loads4 ,the voltage is very sensitive to slight changes in the speed of the generator4 ,we had next to plan what equipment we should need for the machine shop and to decide where to locate each machine4 ,the first machine we installed was a lathe adapted for use both with metals and wood4 ,among the adjuncts of this were all sorts of drills1 chisels1 circular saws1 grinding and burnishing tools1 etc4 ,the second machine located was a small forge with an electric fan to furnish the blast4 ,these were followed by a small band saw and a small planer4 ,the fifth machine was a big grindstone and the sixth was an emery wheel4 ,the boys had a long discussion1 running through several days1 on the question whether these machines should be belted to the counter shaft1 and thus get power directly from the water-wheel1 or whether each machine should be operated by an electric motor attached to it4 ,harold said3 ,suppose ,i want to saw a piece of wood requiring a horse-power1 ,i must start an eight horse-power water-wheel which will run a six-horse-power dynamo which will operate a two-horse-power motor that will revolve the saw4 ,there is a loss in each machine1 and the lighter the load the greater the loss4 ,in order that the motor may deliver one horse-power to the saw1 it must receive from the dynamo1 say1 one and one-half horse-power1 and in order that the dynamo may deliver to the motor one and one-half horse-power1 it must receive from the water-wheel1 say1 two horse-power4 ,what is the matter with my saving time and energy by sawing off the block with my own right arm8 ,but1 said ,ernest1 you forget that this water-wheel and the dynamo must run all the time by the terms of our agreement with the cottage1 and they will run fairly well loaded1 so that the starting of the saw will not entail any such losses as you reckon4 ,furthermore the water-power is running to waste1 anyway4 ,you simply divert its channel when you start all this machinery4 ,that's all4 ,and lastly1 if the saw requires a horse-power1 as you say1 your right arm could not furnish it4 ,oh1 interposed ,dyne1 it would take a horse-power to do it as quickly as the machine does1 but ,harold simply proposes to take more time in sawing the block and less in running the machinery4 ,an infant can do the work of a horse if you give him proportionally more time4 ,i don't like the idea1 drawled ,erg1 that this machinery has got to be kept running all the time4 ,when will a fellow get a chance to sleep or go a-fishing or have any vacation1 with this central-station machine shop on his hands all the time8 ,i had inquired how the last two boys won their nicknames of ,dyne and ,erg and had been informed that one was very keen about dining and the other had a great aversion for work4 ,they had doubtless seen these terms somewhere in their reading of physics1 but they appeared to have forgotten their significance by a too familiar use of them4 ,i told them that these were sacred terms1 the first being a name for the unit of force1 while the second designated the unit of work4 ,both boys said that under those circumstances they would like to shed the names4 ,the names1 however1 stuck and the boys themselves might1 ,i think1 be said to exercise a maximum of power with the least waste of energy4 ,this idea of running the plant continuously had evidently received no attention hitherto and it bid fair to quench all the enthusiasm until ,i came to the rescue by proposing a storage battery4 ,if we can procure a battery in which we may store energy1 which shall always be on draught by merely pushing a button1 one which is not injured by overcharging nor too rapid discharging1 nor even by complete discharge2 one which is not injured by standing idle for any length of time1 either charged or discharged2 and finally one which is practically foolproof--we want to try it4 ,i propose that you appoint a committee to look into it4 ,but at any rate this enterprise must go on even if ,i have to hire a man to live in the loft of the mill and keep the machinery going4 ,illustration3 ,fig4 #ada ,no man in the loft1 said ,dyne1 while ,i have my rations4 ,there will be no need for him so long as ,i can store energy here1 said ,erg1 so let the job of equipping the establishment go on in the regular fashion4 ,after a long confab one evening at the mill we settled upon the arrangement shown in ,fig4 #ada4 ,d represents the location of the doors and ,w that of the windows4 ,the equipment is designated as follows3 ,a1 saw2 ,b1 planer2 ,c1 lathe2 ,e1 emery wheel2 ,f1 grindstone2 ,g1 dynamo2 ,h1 forge2 ,i1 storage battery2 ,j1 switchboard2 ,k and ,l1 counter shafts suspended from the ceiling4 ,the water-wheel is belted directly to the counter shaft ,l4 ,this revolves at the rate of #bdj r4 p4 m4 ,a two-foot pulley on this shaft is belted to a one-foot pulley on the dynamo ,g1 giving the dynamo a speed of #dhj4 ,a #d-;inch pulley on this counter shaft is belted to a #af-;inch pulley on the grindstone ,f1 giving the stone a speed of #fj r4 p4 m41 or one revolution per second4 ,a #cb-;inch pulley on shaft ,l is belted to an #h-;inch pulley on the counter shaft ,k1 giving a speed of #d times #bdj1 or #ifj r4 p4 m4 #ab-;inch pulleys on this shaft are belted to #f-;inch pulleys on each of the machines ,a1 ,b1 and ,c1 giving them a speed of #aibj r4 p4 m41 and a #af-;inch pulley on this shaft is belted to a #d-;inch pulley on the emery wheel1 giving it a speed of #chdj r4 p4 m4 ,as soon as everything was in running order1 ,harold took his mother down to the machine shop and started all the machinery going at once1 and while they stood in the middle of the room ,i heard him explaining to her how she might find out the speed of each machine4 ,he said that she must start with the grindstone1 because that goes slowly enough to count4 ,she held her watch in hand and counted the number of revolutions in a minute1 as he directed1 and found them to be sixty4 ,then he asked her to judge how much larger the pulley on the grindstone was than the corresponding one on the counter shaft4 ,she said that she thought it looked four times as large4 ,he told her that she had it just right1 and explained that the shaft must move four times as fast as the stone1 or #bdj4 ,now how fast do you think the emery wheel is going8 ,she acknowledged that she had no idea4 ,well1 said he1 when you get real used to it you can tell by the tone a wheel makes just about how fast it is going4 ,then he explained how she might calculate its speed by looking at the pulleys1 and she found that the counter shaft was going four times as fast as the shaft ,l and that the emery wheel was going four times as fast as ,k4 ,hence it was going sixteen times as fast as ,l1 or #chdj r4 p4 m4 ,his mother said she thought that it was fascinating to stand in the middle of the room with the slowly moving grindstone on one hand and emery wheel moving sixty-four times as fast on the other hand and think that they were propelled by the same water-wheel4 ,i handed ,harold a speed indicator which ,i had just received1 7,fig4 #adb71 the mechanism of which was all visible4 ,harold looked at it for a minute and found stated upon it that the wheel ,b had #ajj cogs1 and he very quickly inferred that the axle ,a1 whose screw threads fitted into these cogs1 must revolve one hundred times each time the wheel ,b revolves once4 ,the tip end of this axle had a soft rubber cap ,c4 ,without suggestion from me he soon held this rubber shoe against the end of the axle of the emery wheel and counted1 not thirty-eight1 but thirty-six revolutions of the wheel of the speed indicator in one minute4 ,this puzzled him and he inquired how it happened that the emery wheel made only #cfjj rather than #chdj revolutions per minute4 ,illustration3 ,fig4 #adb ,well1 said ,i1 we always have to count on belts slipping some1 particularly upon very fast moving pulleys and upon very small pulleys4 ,here are two belts to slip1 and still you are losing only the effect of one revolution of the counter shaft ,l in a minute4 ,grind something on the emery wheel and you will find that the belts will slip more4 ,in fact1 grinding upon the emery wheel will compel the water-wheel to go more slowly until its governor opens and gives it more water4 ,the water-wheel makes fifteen revolutions per minute and the emery wheel goes #bef times as fast as that4 ,one pound of resistance at the emery wheel is like #bef pounds of resistance at the water-wheel4 ,you notice the same thing when you use the saw or planer1 or even present a chisel to a piece of soft wood in the turning lathe4 ,the only machine here that it is important to keep running at constant speed is the dynamo4 ,we shall probably notice the dimming of our lights at the cottage every time you saw a block or grind with the emery wheel or even polish with the felt buffer1 because the speed of the dynamo will slacken for a moment and the voltage will drop a little4 ,in addition to sending electric current to the cottage the dynamo was to keep the battery stored all the time4 ,each machine had an appropriate motor attached to it which could run it by drawing current directly from the battery when the water-wheel was not running4 ,thus if one wanted to sharpen his pocket knife he merely closed a switch at the lathe and used the small stone1 or if he wished to sharpen his lead pencil he put it in the lathe and applied a chisel to it4 ,these motors were all adapted to the #aaj-volt direct current and the battery contained fifty-seven cells1 each cell being rated a little under two volts4 ,the boys frequently discussed possible combinations in this system4 ,i spent a great deal of time loafing around among them in a comatose condition1 and they talked quite as freely when ,i was around as when they were alone among themselves4 ,one day ,i heard ,dyne say1 ,suppose we should store in a reservoir the water which comes down the penstock during a day and store all the electricity it will generate in a day in a storage battery1 then at night let the battery run the dynamo backward as a motor1 and that turn the water-wheel backward as a rotary pump1 we should have the water in the upper reservoir to begin work with the next morning and the problem of perpetual motion would be solved4 ,aw1 why do you want to do all that1 said ,erg1 when nature is doing it for us8 ,ernest said he had a better scheme than that4 ,he would turn the battery current on to all the motors in the room and they would run the counter shafts forward and the counter shafts would run the dynamo forward and the dynamo would charge the battery1 and so you could keep up the motion perpetually if you wanted to4 ,get out your pencils1 said ,harold1 as he took down a copy of ,houston and ,kennelly4 ,let us see how we would come out if we tried ,dyne's proposition for1 say1 twenty hours1 storing the energy from the falling water for ten hours in the battery and then using this energy during the next ten hours for re-storing the water in the upper pond4 ,we will say that the water-wheel furnishes eight horse-power for ten hours--eighty horse-power hours4 ,i notice it is stated in this book that small dynamos are usually unable to deliver more than #ge per cent4 of the energy impressed upon them1 and storage batteries and motors deliver about #hj per cent4 of the energy impressed upon them4 ,the accounts would1 therefore1 stand as follows3 ,dynamo ,horse-power ,hours ,dr4 ,cr4 ,to energy impressed by water-wheel #hj ,by energy delivered to storage battery #fj ,by loss in heat #bj --------- #hj #hj 7,assuming that the battery was able to receive all the dynamo could give47 ,,storage ,,battery ,,account ,to energy impressed by dynamo #fj ,by energy delivered back to dynamo running as motor #dh ,by loss in heat #ab --------- #fj #fj ,dynamo ,running as ,motor ,horse-power ,hours ,dr4 ,cr4 ,to energy impressed by battery #dh ,by energy delivered back to water-wheel #cf ,by loss in heat #ab --------- #dh #dh 7,this dynamo being a particularly inefficient motor47 ,we cannot give the account of a water-wheel acting as a pump1 because such a machine has not yet been perfected4 ,it is evident however that if a water-wheel could be devised that should be a perfect pump1 the losses in this chain of machinery are more than half2 indeed1 the accounts show them to be #fj per cent4 ,we should1 therefore1 be able to return less than half the water drawn from the lake each day1 and we should rapidly move toward bankruptcy4 ,well1 said ,ernest1 my proposition is more successful than that1 because it sets out to be a fool proposition4 ,it was first suggested by the snake who undertook to swallow himself4 ,suppose the account does taper down from eighty to one1 so does the snake1 but he still remains wise as a serpent4 ,our account would stand as follows3 ,dynamo ,battery ,motors #cf #bg #bg #bj #bj #ae #ae #ab #ab #i #i #g #g #e #e #d #d #c #c #b #b #a #a 4#h 4#h 4#f 4#f 4#dh 4#dh 4#cf 4#cf 4#bg 4#bg 4#bj 4#bj 4#ae 4#ae 4#ab 4#ab 4#ji 4#ji 4#jg 4#jg 4#je 4#je 4#jd 4#jd 4#jc 4#jc 4#jb 4#jb 4#ja 4#ja 4#jjc ,it is evident that while our energy would dwindle continually we should never quite come out of the little end of the horn1 since any number may diminish by #bj per cent4 of itself indefinitely4 ,let us get at something practical1 said ,erg4 ,how are we going to furnish electricity to the cottage when the dynamo is not running8 ,if we put a storage battery at the cottage1 how are we going to store it having nothing but alternating current up there2 and if we attempt to transmit current from our central station battery1 how are we going to get along with the drop in the voltage8 ,i'll tell you how to do that1 said ,dyne4 ,they want #bj amperes and the line offers #d ohms of resistance4 ,that means a drop of #hj volts4 ,we have simply to provide a subsidiary battery of #dh cells1 which we may throw in series with our #eg cells when we supply electricity to the cottage1 and then they will have the right voltage for use out there4 ,yes1 said ,erg1 as he rolled over1 they will have the right voltage when they use #bj amperes1 but what will happen if they simply turn on one lamp4 ,the drop in voltage then will be 74#e amperes #d ohms 7 #b volts2 #aje cells at #a4h volts a cell will send out there #ahi volts minus the drop of #b volts1 leaving #ahg volts upon a lamp adapted to #aaj volts1 and it will immediately burn out4 ,the same thing would happen to any single piece of apparatus if the current was turned upon it alone4 ,the only thing they could do if they wanted to light a lamp1 say in the middle of the night to take a dose of medicine1 would be to start up all together1 all their lamps1 sewing machine1 wringer1 dishwasher1 fireless cooker1 vacuum cleaner1 etc41 etc41 to keep down the voltage so that one lamp would not burn out4 ,i have read1 said ,ernest1 that they use rectifiers1 which convert the alternating into direct current1 for storing batteries4 ,these are much used over the country4 ,electric automobiles run by storage batteries1 and in the great majority of communities there is no other electric current than the alternating4 ,so they would be helpless without the rectifier4 ,we should then get another battery of fifty-five cells for the cottage and keep it stored by using a rectifier with our alternating current4 ,but all their equipment up there1 said ,ernest1 is adapted to the alternating current4 ,of what use would a direct current be to them8 ,well1 said ,harold1 it is all the same whether you have alternating or direct current on lamps1 cooking apparatus1 etc41 and ,i have understood that they have motors which run on both alternating and direct currents4 ,if so1 that would fix them up all right4 ,the boys now turned to me for the first time to inquire whether motors could be obtained which would run on both alternating and direct current1 and ,i replied that small motors for running sewing machines1 vacuum cleaners1 etc41 were made which would serve us1 perhaps not economically1 but as they were the only solution to our problem we could get along with them4 ,why don't they have alternating current batteries8 inquired ,erg4 ,well1 it is time that we learned about the nature of batteries1 said ,i1 if you boys are going to have two storage batteries to care for4 ,,xiv ,,doing ,,chores ,,by ,,electricity ,chores were my salvation in youth1 and those chores were not trifles4 ,i was made to feel that the whole family depended on my milking the cows1 bringing in the eggs1 keeping the wood box full of wood1 the water pail full of water brought from the old well1 churning the butter1 feeding and watering the animals1 and performing a multitude of regular daily and weekly tasks4 ,as ,i grew older my responsibilities were allowed to increase proportionally so that ,i might feel some measure of the dignity of being a mainstay and a support of the family4 ,long before ,i reached manhood occasional opportunities were presented for me to play the full part of a man4 ,these sometimes came during a temporary absence or sickness of my father1 but more often1 as ,i learned afterward1 by his skilfully eliminating himself from the situation so that ,i might try my powers4 ,we attempt in the present generation to furnish a substitute for the old time chores by our daily programme in school or in summer camp1 but ,i often wonder whether this round of trifles can make men4 ,can one grow great without having a chance to feel occasionally that the world depends upon what he does8 ,illustration3 ,fig4 #adc ,the great advantage of ,millville to us all lies in the fact that my wife is a good organizer4 ,she immediately saw that the introduction of electricity into the cottage enabled her to assign chores to us all4 ,these chores were assigned so that the establishment ran like clock-work4 ,on ,monday morning in a large room1 called the wash room1 she arranged the soiled clothes in five piles4 ,pile ,no4 #a contained sheets and pillow cases2 ,no4 #b1 white shirts1 shirtwaists1 and other starched clothes2 ,no4 #c1 underclothes2 ,no4 #d1 towels1 etc41 and ,no4 #e1 coloured clothes4 ,here stood a washing machine run by electric motor and a wringer run by the same motor 7,fig4 #adc74 ,by the side of it sat a tub for rinsing water and next to that a tub for bluing water4 ,two boys placed a wash boiler over a two-burner oil stove1 put five pails of water into it1 and cut up one cake of laundry soap which they also put in4 ,when this was boiling hot1 about half of it was poured into the washing machine4 ,the other half was to take its place later in the washing machine4 ,the first pile of clothes was put in and the motor run for five minutes4 ,this batch was then run through the wringer into the rinsing water1 and then again through the wringer into the bluing water1 and then through the wringer a third time into the clothes basket1 and hung upon the line out doors in the clear sunshine1 which did more than all else to make them sweet and clean4 ,a basket of such clothes from the line makes you want to plunge your face right into it and take a good whiff4 ,there is nothing like it except a mow full of new hay4 ,the piles of soiled clothes follow one another through this series of tubs on about a fifteen to twenty minutes headway1 so that the whole family washing is done wholly by two boys inside of two hours4 ,each pile after the first is given ten minutes in the washing machine4 ,on ,tuesday the ironing is done with electric irons 7,fig4 #add74 ,on ,friday the house is cleaned by the vacuum cleaner1 run by electricity 7,fig4 #ade74 ,illustration3 ,fig4 #add ,illustration3 ,fig4 #ade ,on ,saturday a lot of baking is done in a series of fireless cookers 7,fig4 #adf74 ,the sewing machine runs more than ever before4 ,i hear ,it is such fun to sew with an electric motor4 ,and the electric fan which ,harold installed for his mother over the sewing machine makes that the coolest spot in the house4 ,illustration3 ,fig4 #adf ,illustration3 ,fig4 #adg ,chores do not take all of the time1 nor most of the time4 ,they are simply the important things which must be done right on time4 ,meanwhile there is plenty of time for other things and a vast lot of experimenting goes on down at the mill4 ,it is my chief entertainment to stroll down there every day and look on4 ,one day ,i found this project on trial3 ,on the floor 7,fig4 #adh1 f7 of the room over the wash room at the mill a large dripping pan ,a1 was set on blocks of wood so that one corner was lower than the rest4 ,a rubber pipe1 ,b1 brought water to this pan from the mill pond1 an inverted faucet1 c1 regulating the flow4 ,the overflow from the pan fell into a funnel1 d1 the stem of which went through a hole in the floor4 ,a short piece of rubber pipe connected this with the nozzle1 e1 of a gardener's sprinkling can1 which hung from the ceiling in the compartment for the shower bath4 ,electric lamps attached to a board1 g1 were inverted over the pan of water1 so that the bulbs of the lamps were immersed in the water4 ,the electric current for these lamps was controlled by a switch1 h1 placed by the side of the water faucet4 ,when one wanted a shower he could have it as cold or as hot as he chose by adjusting properly the switch and the faucet4 ,moreover1 it was not necessary for him to wait1 for warm water flowed immediately4 ,illustration3 ,fig4 #adh ,in discussing this the boys said that a #cb-;candle-power lamp used #aaj watts1 and that since #if per cent4 of the energy supplied to the lamps went into heat each lamp transformed #aje watts of electrical energy into heat4 ,but #ajj watts sufficed to raise one pint 7one pound7 of water five degrees in one minute4 ,they used seven lamps or about one horse-power1 and adjusted the flow so that the shower delivered one quart of lake water per minute warmed for a tepid bath4 ,illustration3 ,fig4 #adi ,the next time ,i sauntered down to the mill the boys were working on what they called an electric shower bath4 ,they had fastened upon the wall of the bath room an electric bell 7,fig4 #adi71 and placed on a shelf near by a battery of two dry cells1 ,p4 ,the switch which closed this primary circuit was on the wall by the side of the faucet and electric heating switch 7,fig4 #adh74 ,one of the wires1 ,s1 for the secondary circuit was carried up and connected to the pan ,a 7,fig4 #adh74 ,the other wire was fastened to a sheet of zinc about a foot square1 which lay upon the floor of the shower bath4 ,the idea was that when one was taking a shower bath1 if he chose to vary his sensations he might step upon the sheet of zinc1 close the switch in the primary circuit and let the secondary current pass through his body by way of the shower4 ,they said that it was particularly prescribed for slow people4 ,speaking of chores1 of course the most insistent chore was to keep the storage batteries stored4 ,this process gave rise to many questions1 through which the information contained in the next chapter was brought out4 ,,xv ,,electric ,,currents ,,from ,,chemical ,,action ,,and ,,chemical ,,action ,,from ,,electric ,,currents ,luigi ,galvani 7#agcg-agih7 of ,bologna1 ,italy1 in #aghf unwittingly produced an electric current from chemical action4 ,because he was eagerly seeking other results he misinterpreted this4 ,several words in the dictionary are becoming either obsolete or misnomers4 ,for example1 galvanism is an old-fashioned word for an electric current4 ,the expression galvanic electricity is a relic of the abandoned idea that there are several kinds of electricity1 of which ,galvani discovered one4 ,galvanized iron is wholly a misnomer4 ,it is a name used for iron which has been coated with zinc1 and it suggests the idea that somehow the zinc is coated upon the iron by means of an electric current1 whereas in fact it is done by dipping the iron into melted zinc4 ,alessandro ,volta 7#agde-ahbg7 of ,como1 ,italy1 took up the discovery of ,galvani1 interpreted it correctly1 and perfected the method of producing electricity by chemical action4 ,what these two men really discovered was that it is possible to produce continuous currents of electricity4 ,before that electricity was known only by the instantaneous discharge or spark4 ,from the name of ,volta is derived the word volt1 which designates the unit of electro-motive force4 ,the adjective voltaic is synonymous with galvanic1 as voltaic or galvanic cell1 voltaic or galvanic current4 ,for a long time it was thought that such an adjective was needed to designate electric currents generated by chemical action as a peculiar kind of electricity4 ,we no longer think of electricity which is generated by chemical action as different from that generated by a dynamo or from any other source4 ,for about seventy-five years after the discovery of ,galvani chemical action was our only method of generating currents of electricity1 and it is largely owing to the inadequacy of this method of production that so few uses for electricity were discovered previous to the perfection of the dynamo about a third of a century ago4 ,two things have conspired to bring about this age of electricity4 7#a7 ,the dynamo reduced the cost of production from five dollars to ten cents per kilowatt hour4 7#b7 ,mankind grew extravagant1 greatly increased the number of things which it considered necessary1 and at length became both able and willing to spend more for the things which it demanded4 ,the so-called voltaic cell is of scarcely more than academic interest now4 ,the school which1 as a rule1 follows half a century behind practical life1 has taught and still teaches the philosophy of the galvanic cell with great particularity4 ,it is now being urged to undertake the teaching of the dynamo4 ,meanwhile the dynamo has almost driven out of existence all electric battery cells except the storage cell and the so-called dry cell1 and each year the dynamo is encroaching more and more upon the territory of the dry cell4 ,in the present day1 when a passenger upon a street car pushes a button to stop the car1 he uses1 not a voltaic cell1 but a #ejj-volt dynamo current to ring a small buzzer1 and it costs the company not one-hundredth part as much as it would to furnish him a battery equipment to do the same thing4 ,small dynamos and magnetos are displacing dry battery cells in the sparking equipment of motor boats and automobiles4 ,we lifted a dry battery cell out of its pasteboard case and found that it was contained in a metal cup of sheet zinc4 ,the top of this was sealed over airtight with pitch1 the purpose of which is to prevent this dry cell from drying up4 ,we dug away the hardened pitch and found a black powder which was distinctly moist4 ,in case the pitch becomes cracked or a hole appears in the zinc cup1 the moisture passes out and the cell ceases to act as a generator of electric current4 ,the zinc cup had a lining of pasteboard on the sides and the bottom1 similar to the pasteboard which enveloped the outside1 only the lining was quite moist4 ,a corrugated rod of carbon about an inch in diameter occupied the middle of the cup1 and the space around it was packed full of a mixture of ammonium chloride1 manganese dioxide1 and other substances like plaster1 etc41 which differ with different cells4 ,a dry cell which has been long in use is quite apt to show stains upon its pasteboard case4 ,these are caused by holes which appear in the zinc4 ,the production of electric current by the cell is dependent wholly upon a chemical action between the zinc and the ammonium chloride which results in the destruction of both4 ,this chemical action cannot go on without moisture4 ,the zinc cup of the particular cell which we were examining appeared to be intact1 and we proceeded to dig out the black powder4 ,its black colour is due to the manganese dioxide4 ,ammonium chloride is white4 ,we lifted out the carbon rod and scraped the zinc cup clean4 ,the binding posts attached to both the zinc cup and the carbon rod were left intact4 ,into the zinc cup we now poured a tumblerful of water and added about a quarter of its volume of hydrochloric acid1 setting the whole into a large bowl to guard against disaster4 ,bubbles of gas were formed rapidly1 causing the liquid to effervesce as a tumbler of soda water would do4 ,we inverted an empty tumbler over the cup so as to collect this gas4 ,in about two minutes we lifted the tumbler1 still holding its mouth downward1 and brought a lighted match to it4 ,there was a flash and the contents burned with a pale-blue flame4 ,some of the zinc had united with some of the hydrochloric acid and set free hydrogen gas1 which is one of the constituents of the acid4 ,this is typical of chemical actions4 ,something similar takes place between the ammonium chloride and the zinc4 ,three interesting things occur in this experiment3 #a4 ,chemical action1 just described1 is produced4 #b4 ,heat is produced4 ,this was very evident when we took the zinc cup up in our hands4 ,it was as hot as though boiling water had been put into it4 #c4 ,an electro-motive force is produced4 ,this we showed by connecting one end of a piece of copper wire to the binding post of the zinc cup and the other end of the wire to an electric bell4 ,another wire ran from the bell to the carbon rod4 ,when the carbon rod was lowered into the acid the bell rang4 ,within ten minutes holes began to appear in the side of the zinc cup4 ,the acid contents began to flow out into the bowl1 and not long after the zinc fell to pieces4 ,after fifteen or twenty minutes the action began to grow less4 ,the acid was being used up as well as the zinc4 ,if enough acid is added the zinc will wholly disappear4 ,we have chosen substances which would produce striking results in this experiment1 but the same sort of thing is going on about us continually4 ,one summer by the seashore ,i fastened a brass plate upon my boat with two screws--one of brass and one of galvanized iron4 ,the plate was attached below the water line so that it might be acted upon by the salt water4 ,within three weeks the head of the galvanized iron screw had entirely dissolved1 while the brass screw was as good as ever4 ,a galvanized iron screw near by but not in contact with the brass was still in as good order as ever4 ,i had simply made an electric battery cell out of the ocean by dipping into it zinc and brass in contact4 ,a most interesting relationship exists between the three kinds of activity in the cell1 which have been mentioned1 viz43 7#a7 chemical action2 7#b7 production of heat2 7#c7 production of electric current4 ,as has been already noted1 chemical action produces heat4 ,conversely1 if we apply heat to the cell we greatly increase its chemical action4 ,we have also noted that chemical action produces an electric current1 but unless the current is allowed to flow through some external channel like a closed circuit of wire the chemical action is greatly restrained or entirely checked4 ,illustration3 ,fig4 #aej ,in a glass tumbler ,i put a rod of pure zinc 7,fig4 #aej1 ,zn71 and an electric light carbon1 ,c4 ,a short wire1 a1 was arranged for connecting the two externally4 ,in the tumbler was put some water with about one tenth its volume of sulphuric acid4 ,no chemical action was evident until the wire was touched to the zinc1 closing the circuit4 ,then bubbles of hydrogen gas gathered upon the surface of the carbon rod1 and clung to it very tenaciously4 ,we lifted out the carbon rod and rinsed off the bubbles in another tumbler of water1 and then returned the carbon to its place in the cell4 ,the experiment was repeated many times1 and each time no bubbles of hydrogen1 which is in this case the sign of the chemical action1 appeared until the circuit was closed for the flow of the electric current4 ,incidentally it should be said that the amount of hydrogen produced by the chemical action is a measure of the amount of electric current produced4 ,incidentally also it should be said that the bubbles of hydrogen clinging to the carbon rod check and almost stop both the chemical action and the production of electric current when the circuit is closed4 ,if now we put in sodium bichromate to use up the hydrogen as fast as it is produced we may have a continuous current whenever the circuit is closed4 ,chemical action does not entirely cease in this cell when the circuit is opened4 ,but if two cells are prepared1 and one is left with its circuit closed while the other remains with its circuit open1 it will be found that the zinc disappears and the acid is used up in the closed cell in a short time1 while these remain not greatly changed for a long time in the cell on which the circuit is open4 ,no cell will remain forever without chemical action1 yet a dry cell which might use up its zinc and ammonium chloride in a few hours if the circuit is closed may be kept idle three or four years1 and still be able to furnish electricity enough to ring a bell4 ,some persons feel defrauded if the author of a book fails to give them all the new words and conventional terms which belong to any subject4 ,for such here is a page or so4 ,it is conventional to speak of the electric current as flowing from the carbon through the wire to the zinc1 although every one has suspicions that it may flow in the other direction or even that it may not flow at all4 ,it is conventional to designate any part of the circuit from which the current comes as positive 77 to any other part toward which it flows1 this latter being considered negative to the former and designated 7-74 ,the current is conceived of as making a complete circuit1 from carbon to zinc through the wire and from zinc to carbon through the liquid4 ,hence1 the binding post of the carbon rod is called the pole and that of the zinc is called the-pole1 while the zinc rod or plate beneath the surface of the fluid is called the plate and the carbon is called the-plate4 ,the liquid is termed the electrolyte4 ,the sodium bichromate1 introduced to cause the hydrogen to unite with oxygen1 is called an oxidizing agent or even a depolarizing agent1 and hydrogen collecting upon the negative plate is said to polarize the cell4 ,hydrogen may be made to collect upon the carbon or negative plate until the electric current reverses its direction4 ,the hydrogen is said to be more - than the zinc4 ,if we connect the zinc and carbon rods with the wires bringing an electric current from the dynamo we may make either one positive as we choose1 according to which is connected with the positive wire4 ,hydrogen bubbles will collect upon whichever plate we make the negative one4 ,when we send an electric current from the dynamo into this cell it is called an electrolytic cell1 and when it is used to generate an electric current it is called a battery cell4 ,in either case the electrolyte is decomposed and put through a chemical change1 though the chemical action in one case is the reverse of that in the other1 and the direction of the electric current in one case is the reverse of that in the other4 ,for example let us consider the case of a zinc rod and a carbon rod immersed in sulphuric acid and the external circuit closed4 ,the current passes as indicated by the arrows in ,fig4 #aea1 and the chemical actions result in hydrogen leaving the sulphuric acid and zinc taking its place1 forming zinc sulphate4 ,this is a white salt and for purposes of this experiment must remain dissolved in water4 ,so far we have been considering a generator of electricity--a battery cell4 ,we may introduce something at m1 say a motor1 which will indicate that an electric current is flowing4 ,at length the cell ceases to generate current and is1 as we say1 run down4 ,suppose now we substitute a dynamo in place of the motor in this circuit1 connecting it so that the carbon rod shall be its positive pole and the zinc its negative pole4 ,we now call this an electrolytic cell1 7,fig4 #aeb74 ,the current will decompose the zinc sulphate4 ,the zinc will be coated upon the zinc rod and hydrogen will be procured from the water present1 of which it is a constituent1 to form again sulphuric acid as originally4 ,illustration3 ,fig4 #aea ,illustration3 ,fig4 #aeb ,we shall thus restore the conditions which prevailed in the first case as represented in ,fig4 #aea4 ,h#b,,so#d is the chemist's designation of sulphuric acid and ,zn,s,o#d is his expression for zinc sulphate4 ,the experiment illustrates a storage battery so called4 ,it might better be called a chemical transformer4 ,it is wholly unnecessary that one rod be composed of zinc4 ,if we begin with both rods of carbon immersed in a solution of ,zn,s,o#d1 and send into this cell the dynamo current1 the carbon which acts as the negative pole will be coated with zinc in a short time1 and we shall have in effect a rod of zinc and one of carbon as before4 ,after a minute or two we may disconnect the generator and substitute in its place a bell as indicator1 and it will ring1 showing that we have transformed electrical energy into chemical energy which is now being retransformed into electrical energy4 ,we say that we store electricity by this means1 which is1 however1 no more true than that a farmer stores his farm in the bank when he sells it and deposits the money until he shall need it to buy another farm4 ,here is a very beautiful blue salt4 ,i will drop a few crystals of it into a tumbler of water and dip in two carbon pencils connected to the dynamo current1 using between fifty and sixty ohms of resistance in the circuit so as to have two amperes flowing4 ,after a minute or two ,i lift out the negative carbon and you see that it is well plated with copper4 ,the blue salt is copper sulphate4 ,if we weigh the negative carbon1 both before and after the experiment1 we shall find that copper has been depositing at the rate of one ounce in twelve hours4 ,if we reduce the current one half1 making it one ampere1 it will deposit copper at the rate of one ounce in twenty-four hours4 ,one ampere will separate three ounces of lead in a day from a solution of any lead salt2 it will separate 4#i ounce of iron in a day from a solution of any iron salt1 and it will liberate from water1 which is a compound of hydrogen1 one gallon of the gas in ten hours4 ,the amount of chemical action is a measure of the amount of electrical energy expended4 ,before the present form of commercial wattmeter was devised electrolytic cells were used to determine what the consumer's bill for electricity should be each month4 ,these chemical meters contained a solution of zinc sulphate for the electrolyte and both the positive and the negative plates were of zinc4 ,while the current is passing1 zinc from the solution is coated upon the negative plate and zinc from the positive plate takes its place in the solution1 thus maintaining a constant strength of solution4 ,here are three iron nails4 ,i propose that you plate one with zinc and another with copper and then expose all three to the weather and see which will rust4 ,i propose that you replate all the spoons at the cottage and the metal tops of the salt cellars with silver4 ,electro-plating results better if done slowly4 ,ten volts and 4#a ampere will be sufficient current4 ,in the storage battery we generally use lead for both positive and negative plates and dilute sulphuric acid for the electrolyte4 ,hydrogen is liberated at the positive plate and oxygen unites with the negative plate4 ,when the charging current is cut off the chemical action reverses1 and an electric current is produced by the cell4 ,in all other batteries there is a destruction of one plate and of the electrolyte1 which cannot be fully restored by a charging current1 although in the case of the lead and sulphuric acid combination the charging and discharging of the cell may go on alternately for a very long period without permanent change or loss of any substance except water4 ,there is1 however1 plenty of loss of energy in this as in other transformers4 ,one hundred ampere hours of current expended to charge a storage battery will yield from seventy-five to eighty-five ampere hours while the battery is discharging4 ,the lead storage battery is1 however1 full of disappointments for those who do not properly care for it4 ,it is irretrievably ruined if neglected and allowed to charge too far1 or discharge too far1 or evaporate too much water1 etc4 ,the voltage of a lead cell must not rise above #b4b nor fall below #a4h4 ,it must not be allowed to furnish at any one time a greater number of amperes than it is rated for4 ,it must not stand idle too much4 ,it must not be cleaned up and put away for a period4 ,in fact1 the lead-sulphuric acid battery is so poorly adapted to our need that ,i feel disposed to try ,mr4 ,edison's new storage battery4 ,this has nickel hydrate packed in tubes of metallic nickel for the positive plates and iron oxide pressed into pockets in a sheet of metallic iron for the negative plate4 ,a solution of potassium hydrate in water is used for the electrolyte4 ,this is said to be uninjured by being emptied out and left idle1 as our batteries must be for a large part of the year4 ,the e4 m4 f4 of this battery is less than that of the lead battery1 being only #a4b volts4 ,we shall therefore need ninety-six cells 7type ,b-#d7 for the machine shop and ninety-one cells of the same kind for the cottage4 ,our dynamo will be unable to charge at one time more than sixty of these cells connected in series4 ,the particular chore which you boys must perform is to see that the voltage of these batteries is maintained at about #a4b4 ,it should be charged up to #a4h volt at least once a week and never allowed to discharge to a lower pressure than one volt4 ,the level of the electrolyte must be maintained one half inch above the plate by adding distilled water occasionally4 ,a few years ago every student of chemistry was more or less agitated by the thought that more than half of every clay bank was composed of metal nearly as valuable1 or at least as costly1 as gold4 ,this is aluminum4 ,by all the methods then known it was a very difficult and expensive process to extract the metal from the clay4 ,at length1 by the perfecting of the dynamo1 the chemist had under his control great and powerful electric currents which enabled him to unlock any chemical compound however refractory and isolate its elements4 ,as a result aluminum became common enough and cheap enough for even kitchen utensils4 ,the metal calcium which a short time ago was an exceedingly rare substance worth #dj an ounce is now fairly abundant and cheap for chemical experiments1 although it has no qualities which will give it an extended use4 ,powerful electric currents1 such as are obtained at ,niagara1 enable us to combine elements into hitherto unknown chemical compounds4 ,carbon and silicon are made to unite to form carborundum1 which vies with the diamond for hardness4 ,carbon and calcium unite to form calcium carbide1 used with water to form acetylene gas4 ,in such processes the intense heat of the electric arc--perhaps #fjjj degrees--is employed1 together with the electrolytic action of the current1 to separate and combine substances4 ,enormous currents are used in the electric furnaces for producing chemical reactions--from #ajjj to #cj1jjj amperes at a time4 ,electric currents passing through the human body expend their energy partly in heat and partly in electrolysis4 ,so simple and harmless a thing as common salt would become a virulent poison if it could be electrolized in the body into its elements sodium and chlorine4 ,let us make use of an electric current to decompose water into its elements1 hydrogen and oxygen4 ,i have a three-ounce wide-mouthed bottle 7,fig4 #aec7 and through its cork ,i pass two short pieces of ,no4 #bd platinum wire by pushing a stout needle through first4 ,i fill this bottle with pure water and cut a slight furrow in the side of the cork1 where water may drip out when the gas is produced in the bottle4 ,we crowd the cork firmly into the mouth of the bottle and invert it4 ,no water drops out4 ,we bend the ends of the platinum wires into hooks and hang upon them the wires bringing the dynamo direct current4 ,there is no evidence of chemical action4 ,pure water is an exceedingly poor conductor of electricity4 ,let us now put about fifty-five ohms of resistance into the dynamo circuit1 so that it will pass about two amperes1 and put a very small pinch of salt into the water1 which makes it so good a conductor that its resistance may be ignored4 ,when now we close the circuit1 as before1 a brisk effervescence takes place4 ,bubbles of gas rapidly form on the platinum wires and break away1 rising through the liquid4 ,twice as many form on the negative wire as on the positive one4 ,as these gases rise to the top of the bottle an equal volume of the water drips out through the small hole in the cork4 ,illustration3 ,fig4 #aec ,two amperes of electricity will liberate two fluid ounces of hydrogen at the negative pole and one fluid ounce of oxygen at the positive pole1 in five minutes4 ,hence in five minutes the bottle should be full of a mixture of two gases1 two thirds of which1 by volume1 is hydrogen and one third oxygen4 ,we will catch the water which drips out so that we may measure it4 ,the bottle being now full of gas ,i shut off the current1 and removing the cork ,i bring a flame to its mouth4 ,a very loud and startling explosion takes place4 ,we pour the water back into the bottle1 and it seems to fill it as well as before4 ,we have decomposed a few drops of water--not enough to measure--into two gases1 one of which1 the hydrogen1 occupied two thirds of the bottle1 and the other1 oxygen1 occupied the remaining third4 ,at ordinary temperatures they would not reunite1 but when raised to their kindling temperature they united1 producing light1 heat1 a loud noise1 and the few drops of water which had been originally decomposed by the current4 ,this is the electrolysis of water4 ,i wonder if any such chemical action took place in ,ernest's body when he received that severe shock on the motor boat the other day4 ,it is significant that the dry battery cell must be moist in order that chemical action may go on in it4 ,compare with that fact several others that we may learn from observation1 for example3 ,baking powders must be kept dry to retain their strength4 ,that is1 if they get moist chemical action will begin in them1 and the gas which is one of the products of this chemical action will pass off4 ,now it is the sole function of baking powders to produce gas within the dough1 and if the gas has wholly or partially escaped they will fail to make the bread stuff light4 ,the same reasons obtain for keeping seidlitz powders and other effervescing salts1 such as vichy and kissingen1 dry4 ,it is to prevent the chemical action which is provoked by the presence of water4 ,the same thing is true of the rusting of iron1 and the various kinds of corrosion of metals4 ,we may prevent such action indefinitely by keeping them dry4 ,berries1 fruits1 meats1 milk1 eggs1 grain--all kinds of foods--are preserved from spoiling--from chemical changes--by drying them and keeping them dry4 ,the same thing is true of wood1 paper1 cloth1 etc4 ,a wooden fence post may last from five to ten years4 ,a fence rail1 being less exposed to moisture1 may last two or three times as long4 ,the interior wood of a house may last a century or two1 while the exterior wood1 being exposed to the weather1 may require repairs very frequently4 ,shingles on the roof do not last as long as shingles on the side of the house4 ,those on a steep roof last longer than those on a flatter one4 ,a pitch of at least forty-five degrees in a roof is desirable to keep it dry4 ,the north and west sides of a house being least exposed to storm in this climate last the longer4 ,precious books1 records1 deeds1 wills1 etc41 on paper must be preserved in dry air4 ,a sail will keep strong and white if kept dry4 ,but it is impressed upon us by our experiences that sunlight is even more potent than moisture to produce chemical change4 ,photographic processes are dependent upon the power of light to produce chemical changes4 ,the fading of our tapestries and our garments1 the tanning of our skins1 the development of green material in the leaves of plants1 all are evidently the direct result of sunlight4 ,a picture hung on the wall prevents the wall paper behind it from being faded by the light1 or it prevents the wood behind it from being turned yellow by the light4 ,folds in our garments prevent them from being faded all alike4 ,very many substances to be found in a chemical laboratory1 in a drug store1 or in a kitchen must be kept in the dark if they are to be guarded against chemical change4 ,no experienced housewife would let a barrel of flour or potatoes sit in the sun1 and every housewife knows that the sun is the best agent for bringing about those chemical changes which she desires4 ,hence she puts her bedding1 her milk pans1 her bread box1 her butter jar1 etc41 out to sun4 ,she has open plumbing1 that the sun may enter those dark and dirty corners4 ,if you would guard a substance against chemical change1 keep it in a dry1 dark place4 ,we have come to associate the sun and the weather as disintegrating forces4 ,hence the south and east sides of the building need most frequent repairs4 ,every one who has made time exposures in photography knows that the sunlight from the east is1 as a rule1 two or three times as powerful as that from the west4 ,there is less moisture and dust in the air to screen us from the early morning sun than from the late afternoon sun4 ,when there is enough moisture in the air to make the sun look red1 those rays from it which would produce chemical action1 called actinic rays1 are cut off4 ,photographic processes are then exceedingly slow4 ,it is like exposing a plate in a dark room behind the ruby glass4 ,but our daily experiences teach us that not only moisture and light but also heat stimulates chemical action4 ,we restrain chemical action by cold when we put things in the ice box4 ,we hasten chemical action by heat when we put things on the stove4 ,winter restrains all the chemical activities of nature1 and summer quickens all the vegetable and mineral kingdoms into chemical activity4 ,if we would preserve a substance from chemical change we must keep it in a cool1 dark1 dry place4 ,now those conditions which will favour the chemical activity of a battery cell will enable it to produce electricity1 and those conditions which will restrain chemical action will enable us to preserve the cell from running down4 ,but we have lately learned that other forms of radiation besides light and heat exist and aid in chemical action4 ,we may produce radiographs--pictures on photographic plates--without light but with invisible rays1 which are akin to light and to electricity4 ,,xvi ,,electrocution ,,at ,,millville ,the old mill was infested with rats4 ,my wife laid down to the boys the principle that good housekeepers were never troubled with vermin of any kind4 ,the rats' sole occupation is to search for food4 ,if you don't feed them they will not stay with you4 ,but the boys said that they were glad of a chance to try an experiment on the rats4 ,so one day when ,i went down to the mill ,i found them discussing the possibility of killing the rats by electricity4 ,harold said that he had read that it took much less electricity to kill any animal than to kill a man1 and he would like to try1 for instance1 whether the shock which they had received from a bell would kill a rat4 ,well1 who's going to sit by1 said ,erg1 to close the primary circuit when the rat happens to get himself into the secondary circuit8 ,make him close it himself by some device1 said ,ernest4 ,they have a regular thoroughfare1 a beaten highway1 along by the wall1 under the mill and up through a hole in the floor of my bedroom1 said ,dyne4 ,illustration3 ,fig4 #aed ,illustration3 ,fig4 #aee ,well1 said ,harold1 ,i propose an electric trap which shall have two compartments4 ,we will keep cheese in the inner compartment1 the walls of which shall be of wires so that the rats may see the cheese4 ,the floor of the outer apartment shall be covered with wire1 as shown in ,fig4 #aed4 ,the wires of the secondary circuit from the bell 7,fig4 #aef7 shall be fastened to the binding posts b and c 7,fig4 #aed74 ,the partition d shall be a swing door into the apartment ,a where the cheese is4 ,this is shown in profile in ,fig4 #aee4 d must act as a switch to close the primary circuit through the bell ,p 7,fig4 #aef74 ,we will have three dry cells in the primary circuit4 ,now this is the way it will work3 ,a rat comes up from under the mill with wet and slimy feet--just suited for making contact for the electric current to enter his body4 ,the smell of the cheese attracts him4 ,he circles around the trap several times1 watching the cheese in apartment ,a through the wire screen4 ,he sees a narrow opening into this apartment under the door d4 ,he puts himself in position upon the floor of the outer apartment ,b1 his feet bridging the gaps between the two systems of wires belonging to the secondary circuit4 ,when he thrusts his head under the door and pushes it1 it swings in a little1 bringing one metal strip against another1 which belongs to the primary circuit4 ,this closes that circuit4 ,he will never hear the bell ring1 for the electric current which will shock him to death travels #ahf1jjj miles per second1 while his sensations travel only sixty miles an hour4 ,if the involuntary recoil of his muscles does not make him jump back1 so that the door will shut and stop the bell from ringing1 ,dyne will be awakened and he will close the door1 since we will put the trap at that hole where the rats enter his bedroom4 ,illustration3 ,fig4 #aef ,the next night three rats were electrocuted by this device4 ,i told the boys they had so many interesting things going on at the mill that we should have to have a telephone between it and the cottage so that we could talk them over4 ,,xvii ,,the ,,telephone ,the telephone was the great invention of our centennial year1 #ahgf4 ,elisha ,gray and ,alexander ,graham ,bell each claimed to have been the inventor4 ,it is quite probable that each did discover it independently1 but the result of the long patent suit was that the court awarded the claim to ,bell4 ,it is1 therefore1 known as the ,bell telephone4 ,many who installed telephones during the first few years of their existence had them taken out again as nuisances4 ,they are far greater nuisances now than at that time1 but the necessity of them has come upon us and entirely enslaved us4 ,there were more than eleven billion messages sent by telephone in the ,united ,states in #aijg4 ,the capital invested in telephone business was #had1faf1jjd4 ,the income for that year was #ahd1dfa1gdg4 ,all of these items had more than doubled during the previous five years4 ,in #ahhj there were about eight times as many miles of telegraph wires as of telephone wires4 ,in #aijg1 there were about eight times as many miles of telephone wires as of telegraph wires4 ,the ,bell system had #c1acb1jfc stations1 and independent companies had #b1ihf1eae stations in #aijg4 ,the first telephone line ran from ,salem to ,boston1 ,mass4 ,this was in #ahgg4 ,the next year the first telephone exchange was established4 ,it was eight years before a telephone line was extended from ,boston to ,new ,york4 ,on ,october #ah1 #ahib1 the first telephone message was sent from ,new ,york to ,chicago4 ,previous to #ahie telephoning1 like telegraphing1 was done by one wire1 using the earth1 as we say1 to complete the circuit4 ,but at about that time electric car and electric lighting lines became so common that they interfered with telephoning4 ,these currents running in lines parallel to the telephone wires induced currents in them1 and when a person put a receiver to his ear for conversation he heard the hum of electric light dynamos and the buzz of electric cars so loud that conversation was quite impossible4 ,the next step was to introduce a return wire--the double metallic circuit as we call it4 ,thus outside currents induce equal and opposite currents in the two wires of the circuit1 which neutralize each other4 ,it was this same year1 #ahie1 that the central battery system was introduced into telephone equipment4 ,this is not usually a battery at all1 but a dynamo4 ,the price of all electrical supplies in #ahie was about one tenth what it had been in #ahhe1 and at the same time the goods were of far better quality4 ,important telephone patents expired in this year1 and immediately private and independent lines began to be established4 ,it was also in #ahie that the telephone company began to use an automatic registering device which enabled it to charge telephone rates according to the number of calls4 ,the boys unscrewed the end of a telephone receiver 7,fig4 #aeg7 and found inside a permanent magnet made of several steel bars bolted together 7,fig4 #aeh74 ,this was shown to be a magnet by presenting a small pocket compass to either end4 ,the left-hand end of this magnet proved to be its north pole by repelling the blue end of the compass needle4 ,illustration3 ,fig4 #aeg ,illustration3 ,fig4 #aeh ,illustration3 ,fig4 #aei ,on the left-hand end of the magnet was a small spool of ,no4 #cf copper wire1 silk covered4 ,it offered #ge ohms of resistance1 and since it takes #b-a_/b feet of this wire to furnish #a ohm of resistance the spool contains #ahg-a_/b feet4 ,a thin disc of soft iron 4#ja inch in thickness is held by the hard rubber case very near to but not quite touching this end of the magnet4 ,we drew this disc to one side1 as shown in ,fig4 #aei1 and connected the receiver by wires to a magneto4 ,we turned the crank of the magneto slowly and the iron disk danced up and down1 keeping time with the revolutions of the armature4 ,the magneto furnished an alternating current1 which1 when it flowed around the coil in one direction1 strengthened the pole of the magnet1 and in the reverse direction weakened the pole4 ,when the crank was turned so as to produce twenty to thirty revolutions of the armature per second the dancing of the disc sounded like the low hum produced by the wing of a humming bird4 ,when a large1 wide-mouthed bottle was brought near to this the sound was greatly reinforced1 as the sound of a bee becomes louder when he appears at your open window4 ,we next replaced the iron disc and put on the cap again4 ,we then connected the receiver at ,s 7,fig4 #afj7 and connected two dry cells at p4 ,when the primary circuit was closed the disc vibrated in time with the hammer of the bell making the same tone4 ,we substituted for the bell a series of buzzers4 ,the smallest had an armature about one inch long1 while that of the largest was about two inches long4 ,the shorter the armature the faster it vibrated1 and the higher was the pitch of its tone4 ,we arranged these as shown in ,fig4 #afa4 ,a1 ,c1 ,d1 ,e and ,f are the buzzers4 ,b is a battery of two cells and ,g1 ,h1 ,i1 ,j and ,k are springs of sheet brass which act as push buttons4 ,by operating upon these springs with one's fingers1 as upon the keys of an organ1 it was possible to represent the tones of a reed organ after a fashion4 ,the armatures are reeds and they are made to vibrate by electro-magnets4 ,we called it an electric organ4 ,the telephone receiver was connected at ,t1 and the wires which led to it were lengthened so that the receiver might be a long distance away4 ,the disc in the receiver kept time with the armature of each buzzer when it sounded and faithfully reproduced its sound4 ,but the strangest thing was that when any two buzzers sounded together1 or1 indeed1 if all five buzzers sounded together1 the receiver responded to them all at the same time1 so that a person in another room or in another house1 with the receiver at his ear1 might hear exactly what those did who were in the same room with the buzzers4 ,the wires from the receiver were connected with the coil in each buzzer so as to get the induced current1 as shown in detail in ,fig4 #afj4 ,illustration3 ,fig4 #afj ,illustration3 ,fig4 #afa ,illustration3 ,fig4 #afb ,we took a telephone induction coil 7,fig4 #afb7 and fastened it to a board as represented in ,fig4 #afc1 ,i4 ,one wire of the primary circuit was fastened to the binding post a4 ,the other wire from the primary coil passed to the switch ,s and then to the battery4 ,from the battery the wire ran to the binding post b4 ,c is a steel tuning fork4 ,the secondary circuit is closed through a telephone receiver4 ,these wires are extended so that the receiver is too far distant for the tuning fork to be heard through the air4 ,when the switch ,s is closed the tuning fork acts as the interrupter for the primary circuit1 and it interrupts according to its time of vibration4 ,if1 for instance1 the fork gives the tone of middle ,c on the piano it vibrates #bef times a second4 ,it interrupts the primary circuit #bef times a second4 ,it induces an alternating current of the same frequency in the secondary circuit4 ,the diaphragm of the telephone receiver vibrates in perfect time with the tuning fork and produces the same tone as the tuning fork4 ,we had a series of tuning forks giving a variety of tones1 which we could substitute one after another in place of this one4 ,the receiver reproduced accurately the tone of each one of them4 ,illustration3 ,fig4 #afc ,illustration3 ,fig4 #afd ,we took a small induction coil 7,fig4 #afd7 c and fastened one end of the primary circuit to a battery1 ,b4 ,the wire at the other end of the primary circuit was bent into a hook h4 ,this hook was adjusted about a quarter of an inch from the end of the iron core of the coil4 ,the other wire from the battery was attached to the steel strings of a piano1 ,p4 ,when the coil c was brought over a string and the hook h was allowed to pass beneath the string and touch it very gently1 the primary circuit was closed through the string1 which served as an interrupter of the current and vibrated according to its tone4 ,the secondary coil1 not represented in the figure1 was connected to a distant telephone receiver1 which reproduced the tones of the piano strings4 ,producing a tone is merely a matter of making something vibrate with the required frequency4 ,it may be a piano string1 or a tuning fork1 or a reed of an electric buzzer1 or the diaphragm of a telephone receiver4 ,if it vibrates #bef times a second1 it will produce the same tone as middle ,c on a piano2 if it vibrates #eab times a second it will produce the ,c which is an octave above1 and if #abh times a second an octave below middle ,c4 ,the human voice is produced by vocal cords in the throat1 which vibrate with the proper frequency to give any required tone4 ,but how can we make the human voice act as an interrupter of the primary circuit8 ,an examination of the telephone transmitter will supply the answer to this question4 ,illustration3 ,fig4 #afe ,illustration3 ,fig4 #aff ,the boys after taking the transmitter 7,fig4 #afe7 apart proceeded to make one which should answer the purpose as follows3 ,a block of wood about one inch thick and three inches square 7,fig4 #aff71 ,a1 was hollowed out1 making a cone-shaped cavity about one half inch deep and one inch broad4 ,this cavity was filled with small pieces of graphite1 ,g1 made by cutting up a lead pencil4 ,an old tin-type1 ,d1 was laid over this as a diaphragm and tacked around the edges4 ,a binding post1 ,e1 passed through the block1 its head being buried in the graphite at the bottom of the cavity4 ,the binding post ,f furnished contact with the tin-type4 ,one dry cell was placed at ,b and the sensitive ammeter was connected at ,c4 ,the needle showed that although a small current was passing it was constantly varying in strength4 ,tapping upon the table1 walking across the floor of the room1 shouting1 and particularly whistling1 caused variations in the conducting power of the graphite and consequently variations in the current strength4 ,this is precisely the condition we wished to produce in the primary circuit4 ,illustration3 ,fig4 #afg ,we next substitute for the ammeter at ,c the primary and secondary coil of the telephone4 ,in ,fig4 #afg ,t is the transmitter1 ,b is a battery of two dry cells1 ,p is the primary winding of the coils1 and ,s is the secondary winding4 ,to this a telephone receiver1 ,r is connected by wires long enough to reach into another room4 ,a person holding the receiver at his ear could hear everything said or done in the room where the transmitter was almost as plainly as though he were present in the room4 ,illustration3 ,fig4 #afh ,two such transmitters were made and the second one was placed in the room where the receiver had been1 while a second receiver was installed near the first transmitter4 ,the arrangement is shown in ,fig4 #afh4 ,t is the transmitter at one end of the line and ,t' the transmitter at the other end4 ,b and ,b' are the batteries at each end1 ,p and ,p' the primary coils1 ,s and ,s' the secondary coils and ,r and ,r' the receivers4 ,with this arrangement two persons carried on a conversation with perfect ease1 holding the receivers to their ears1 presenting their mouths to the transmitters and speaking in moderate tones4 ,h and ,h' are hooks upon which the receivers are to be hung when not in use4 ,these hooks act as switches to open and close the primary circuit4 ,a spring normally pushes the hook upward and closes the circuit1 but while the receiver is hanging upon it the circuit is open at this point4 ,thus the battery is saved from running down when the telephone is not in use4 ,the wires were finally extended from the mill to the cottage and this equipment was installed at each end4 ,it will be noticed that the secondary circuit includes two receivers and two secondary coils besides the wire of the lines to offer resistance4 ,the receivers offer #ge ohms of resistance each4 ,the secondary coils offer #bej ohms each and the line wires between the mill and the cottage offer #ajj ohms4 ,this makes a total of #gej ohms for the secondary circuit4 ,but the rapid alternations which are induced in the secondary circuit impede the electric current ten times as much as the resistance already mentioned4 ,when considering alternating currents passing through coils of wire we are obliged to take into account two kinds of resistance3 #a4 ,ohmic resistance4 #b4 ,impedance4 ,you boys understand the resistance to the flow of the electric current1 which we have so often measured in ohms4 ,but ,i want to show you that there is another kind of resistance which alternating current meets4 ,here is a coil containing #ajjj feet of ,no4 #bj copper wire4 ,i throw on to it1 for only an instant1 the #aaj-volt direct current1 and the ammeter reads #aa amperes1 showing that it offers a resistance of #aj ohms to the direct current4 ,i now throw on the alternating current1 and the ammeter shows only a small fraction of an ampere4 ,the surging of the current back and forth induces a counter electro-motive force1 in the successive layers of the coil1 which we call impedance4 ,in the experiment which we have just performed impedance is fifty times as important a factor as ohmic resistance4 ,impedance depends chiefly upon the frequency of alternation4 ,the impedance in telephone circuits is particularly large because of the extremely high frequency of the alternations produced by the tones of the human voice1 these being usually not far from ten times as rapid as those of alternating currents in common use4 ,we may estimate the total resistance of our telephone circuit as equivalent to #gejj ohms4 ,our secondary coils have forty times as many turns as the primary coils1 and by means of them the voltage is stepped up to somewhere near one hundred on open circuit4 ,when closed through the line1 however1 the voltage drops down to about ten4 ,the result is that the actual current which passes between the cottage and the mill when we telephone is not far from 4#jja ampere4 ,we may1 however1 hear a whisper transmitted by 4#jjjjja ampere or less4 ,the tone ,e which is produced by the tenth key above middle ,c on the piano1 is the one most readily heard over the telephone4 ,it is produced by anything which vibrates #fdj times per second4 ,illustration3 ,fig4 #afi ,we used ,no4 #ab galvanized iron wire for our telephone lines4 ,two miles of ,no4 #ab copper wire would offer #af ohms of resistance4 ,the iron wire offers about #ajj ohms4 ,but this is a trifle when compared with the total resistance4 ,we used a double metallic circuit so as to avoid the effects of inductance from our electric lighting circuit4 ,illustration3 ,fig4 #agj ,the next thing that we were obliged to consider was some arrangement for calling persons to the telephone for conversation4 ,we decided to use magnetos and alternating current bells4 ,fig4 #afi shows the essential mechanism of the bells4 ,the bell at each end of the line consists of two gongs a1 b and a b1 with a hammer c1 c between them4 ,this hammer is attached to an iron armature h1 h1 pivoted over the electro-magnets1 m1 m1 in such a way that it rocks back and forth when an alternating current passes through the lines d e1 f g4 ,the bells at both ends of the line always ring together1 since they are connected in series4 ,a magneto 7,fig4 #agj7 is situated at each end of the line4 ,this1 as has been previously explained1 is a generator of electricity1 in which the field is furnished by steel magnet1 ,m4 ,the armature ,a is a coil of wire whose ends are in contact with the leading out wires d and c by means of brushes which slide upon rings4 ,the armature is revolved by hand4 ,the crank and cog wheels employed to produce high speed are not shown in the figure4 ,by turning the armature rapidly this magneto will develop #fj volts e4 m4 f4 on open circuit4 ,the magnets of the bells are wound with a very large number of turns of very fine wire1 so that 4#jbe ampere is sufficient to ring them4 ,illustration3 ,fig4 #aga ,figure #aga shows how the magneto at either end of the line is introduced into the circuit for the purpose of ringing the bells4 ,b and ,b' represent the bells1 m and m' the magnetos1 and ,p and ,p' represent switches4 ,springs push them upward so that they normally close the circuit through the bells4 ,when a person at ,p wishes to call another at ,p' he pushes the switch ,p down so as to bring his magneto m into series with the bells4 ,when now he turns the crank and generates the electric current1 both bells ring4 ,his own bell serves the purpose of telling him that the line is operating all right4 ,the other bell calls the party desired for conversation4 ,as soon as the operator removes his finger from the switch ,p the spring throws it upward again1 leaving his bell in circuit1 so that he may be called at any time1 but cutting out of the circuit his magneto1 which would introduce unnecessary resistance4 ,the same wires which carried the current for ringing the telephone bells carried also the current for operating the telephone receiver4 ,when the receiver is removed from the hook it releases a twofold switch4 ,this serves the double purpose of closing the primary circuit through the local battery and substituting the telephone receiver circuit for the bell-ringing circuit upon the line4 ,we used fifty chestnut poles to carry our line between the mill and the cottage4 ,each pole had a cross bar1 on one end of which the electric light and power wires were carried and on the other end the telephone wires4 ,glass insulators prevented the wires from coming in contact with the wood of the cross bars4 ,the necessity for this was impressed upon the boys by something which happened while they were stringing the wires4 ,the telephone apparatus at the mill had been installed and the two leading out wires had been connected to it4 ,one of these was coiled up on the floor1 while the other had been strung along upon the poles for half a mile1 but had not yet been attached to the insulators on the poles4 ,while the boys were lunching at the mill1 one of them gave the crank of the magneto a turn1 when1 to the astonishment of all1 the bell rang4 ,the circuit had been completed through the damp wood of the mill1 through the damp wood of some of the poles1 and through the earth4 ,after lunch the wire1 so far as it had been strung1 was fastened to the insulators upon the poles4 ,but when some one turned the crank of the magneto the bell still rang4 ,we walked along the line to see where the difficulty was4 ,we found the end of the line about half a mile from the mill dangling free from the ground1 but touching a tall spear of grass4 ,when this was moved away from the spear of grass the magneto could no longer ring the bell4 ,the slight current required to ring this bell--4#jbe ampere--had found its way through the spear of grass1 through the woodwork of the mill and through the earth4 ,we had no sooner got the two telephone wires properly strung and attached to the hundred glass insulators when a thunder storm came up1 and drove us back to the mill for shelter4 ,pretty soon the bell rang and we1 supposing that some one at the cottage was trying to call1 went to the instrument1 but could get no response1 nor could we make the bell ring4 ,lightning had sent an alternating current over the line which rang the bell1 but the strength of the current was too great for our coils of fine wire and one of them was burned out1 as we say4 ,in other words1 the wire had melted at the point where it offered the greatest resistance4 ,the burned-out coil was replaced1 and then we installed lightning arresters which were of two kinds4 ,the first were simply fuses which were introduced into the line to protect it against any current too large for the apparatus to carry1 and the second was a plate1 c 7,fig4 #agb74 ,these are to be found upon the top of the magneto cases4 ,a wire is connected with c1 and its other end is grounded by being connected with a piece of iron pipe which is driven deep into moist earth4 ,illustration3 ,fig4 #agb ,the plate a b is inserted in the line1 and the gap between this and the plate c offers sufficient resistance so that the telephone circuit suffers no leakage at this point1 but lightning has such extremely high tension that it readily passes across this gap and finds its way to the earth without damaging the instruments4 ,we have already noticed that our alternating current dynamo1 which produces #fj vibrations per second in the telephone receiver1 causes it to give a tone very nearly like the ,c1 which is two octaves below middle ,c upon the piano4 ,c requires #fd vibrations per second4 ,we may speed up our dynamo so as to make it yield a tone exactly like ,c or even above it4 ,dr4 ,cahill of ,holyoke1 ,mass41 has devised an organ in which alternating current dynamos produce the necessary number of vibrations for each tone4 ,the name telharmonium has been proposed for this organ4 ,it has a separate dynamo for each tone1 each dynamo having a frequency corresponding to the tone required of it4 ,the dynamo1 for instance1 which produces middle ,c makes the electric currents surge back and forth #bef times a second1 and this causes the diaphragm of a telephone receiver to vibrate #bef times a second1 and this sends forth #bef air waves per second1 and when these reach our ears we recognize the tone we call middle ,c4 ,the frequency of alternation in a dynamo may be increased by either increasing its speed of revolution or by increasing the number of coils upon its armature4 ,mr4 ,cahill's great organ looks like a large machine shop with many counter shafts geared so as to run at different speeds4 ,on each shaft are a large number of little dynamos whose armatures have various numbers of coils4 ,the organist1 who may be far removed from this machine shop1 fingers an ordinary keyboard4 ,each key opens and closes a switch1 thus bringing into action its own dynamo4 ,if the key which is known as ,c1 one octave below middle ,c1 is pressed down1 a switch closes the circuit between the telephone and a dynamo which gives #abh double alternations of current4 ,the tone which is produced by #abh vibrations per second is the one most often heard from a man's voice in ordinary conversation4 ,another key brings into action upon the same telephone receiver--and at the same time if desired--a dynamo which gives twice as many alternations per second and produces the tone most often heard in female conversation4 ,it is middle ,c4 ,another key might bring into action a dynamo which gives #fd vibrations per second to the diaphragm of the telephone receiver4 ,this would send forth a tone very nearly like the base note of our #fj-;cycle alternating current dynamo4 ,the following table shows a series of ten tones which might be produced by the same little piece of sheet iron in a telephone receiver played upon by ten dynamos at the same time4 ,the whole list of ten tones would sound well when produced simultaneously4 ,the great mystery is that the iron disc can vibrate in such a complex manner4 ,it is important to note1 however1 that the number of vibrations in each of the upper tones is a multiple of that of the lowest tone3 #bnd octave above ,c--#ajbd 7 #af #fd7 ,middle ,c ,g -- #gfh 7 #ab #fd7 ,e -- #fdj 7 #aj #fd7;,a #ast octave above ,c -- #eab 7 #h #fd7 ,middle ,c ,g -- #chd 7 #f #fd7 ,e -- #cbj 7 #e #fd7 ,middle ,c ,c -- #bef 7 #d #fd7;,b #ast octave below ,g -- #aif 7 #c #fd7 ,middle ,c ,c1 -- #abh 7 #b #fd7;,c #bnd octave below ,c11-- #fd 7 #a #fd7 ,middle ,c ,c ,the tone most easily reproduced by the vocal cords of a man4 ,b ,the tone most easily reproduced by the vocal cords of a woman4 ,a ,the tone which the telephone receiver responds to most readily4 ,the table covers the range of the human voice1 male and female4 ,all the intermediate tones1 with their sharps and their flats1 are produced each by its own separate dynamo4 ,the insignificant amount of current required to operate a telephone receiver makes it possible to furnish the music of these dynamos to many and far distant telephones4 ,this naturally suggests the idea of having a great musician perform upon the keyboard and have many auditors scattered about the city in their private homes or even in many public halls1 for the telephone receiver can readily be made audible to a good-sized audience4 ,,xviii ,,electric ,,bell ,,outfit ,,for ,,the ,,cottage ,the boys asked me what arrangement of electric bells we needed at the cottage and so ,i gave them this problem to work out by themselves3 #a4 ,we want a bell in the kitchen to be rung by a push button at the front door4 ,but there are times when no one is in the kitchen and hence1 #b4 ,we want a bell upstairs to make a single stroke whenever the kitchen bell is rung from the front door4 #c4 ,we want a floor push under the dining-room table which will cause the kitchen bell to ring a single stroke4 #d4 ,we want a push button in the dining-room which will cause both bells to clatter and call people from their beds1 from the piazza1 the lawn1 etc41 to their meals4 ,this equipment needs only one battery of two dry cells1 two bells1 three push buttons and about two hundred feet of wire4 ,it should cost less than five dollars4 ,the boys drew many plans and tried many schemes and at last determined upon the plan shown in ,fig4 #agc4 ,p is the floor push under the dining-room table4 ,when the circuit is closed at this point the current leaves the battery from the carbon pole c1 passes up and around the magnets of the kitchen bell and back to the zinc pole of the battery z by way of the push button ,p4 ,all other circuits are open4 ,illustration3 ,fig4 #agc ,p is the push button at the front door4 ,when the circuit is closed at this point the current leaves the battery at c1 passes up to the right-hand binding post of the kitchen bell and divides1 part going through each bell4 ,the portion of the current which goes through the kitchen bell passes around the magnets and through the armature to the left-hand binding post before it can find a path back to the battery4 ,hence1 the kitchen bell clatters4 ,the portion of the current which passes to the upper bell goes around its magnets and finds a path back from the middle binding post to the battery by way of ,p4 ,hence the bell upstairs rings with a single stroke4 ,p is a push button situated upon the wall by the side of the door which leads from the dining-room to the kitchen4 ,when the circuit is closed at this point1 the current leaves the battery at c1 passes up to the right-hand binding post of the kitchen bell and divides1 part of it going through each bell4 ,the portion which goes through the kitchen bell passes around its magnets and through its armature to the left-hand binding post1 then up to the middle binding post of the upper bell1 through its armature to its left-hand binding post and back to the battery by way of the push button ,p4 ,the other portion of the current passes directly up to the right-hand binding post of the upper bell1 around its magnets1 and through its armature to its left-hand binding post1 thence back to the battery by way of the push button ,p4 ,hence1 both bells clatter and keep time with each other4 ,the upper bell will ring independently of the lower bell1 but the lower bell is dependent upon the upper one to open and close its circuit1 somewhat as a relay4 ,soon after the cottage had been equipped with electric bells ,i went to the mill one day and found a push button at the door4 ,upon going in ,i was curious to examine the electric bell outfit of that place and found what is illustrated in ,fig4 #agd4 ,illustration3 ,fig4 #agd ,a switch1 ,s1 had been attached to the bell4 ,the boys said that when they felt well they kept the switch upon the left-hand point and the bell rang as a clatter bell4 ,when they felt a little sick they put the switch upon the middle point and the bell rang with a single stroke1 but when they felt very sick they put the switch upon the dead point and the bell did not ring at all4 ,,xix ,,using ,,electricity ,,to ,,aid ,,the ,,memory ,for the sparking equipment of the motor boat we use dry cells which have an internal resistance of not more than 4#jf ohm4 ,they will1 when short circuited through the ammeter for only an instant1 give #be amperes4 7#a4e volt7_/74#jf ohm7 #be amperes ,when we allow for a slight resistance in the ammeter itself1 and for the drop in voltage1 we see that the internal resistance of a cell must be even less than 4#jf ohm4 ,after being used about two months upon the motor boat these cells develop more internal resistance1 and they will then show not more than six to ten amperes when short circuited through an ammeter4 ,they are then not reliable for ignition of the engine1 but are quite as good as ever for bell-ringing1 and often continue so for more than a year4 ,the result is that we always have more partly run-down dry cells than we can use4 ,seeing them about has stimulated the boys to devise ways for using them4 ,the housekeeper is distracted by carrying on so many cooking processes at one time4 ,she forgets the eggs1 and lets them boil five minutes instead of three because the coffee must percolate twelve minutes1 and she lets the coffee percolate twenty instead of twelve minutes because the biscuit must bake twenty minutes1 and the biscuit are forgotten because the pies must come out in thirty minutes1 and the cake in forty minutes4 ,all this worries the cook4 ,harold is a sympathetic boy and enters into the troubles of others4 ,i had at one time shown him how to bore a hole in a glass plate in five or ten minutes by using a round file wet with water4 ,one day he presented the kitchen with a clock1 intended to relieve the burdened memory of the cook4 ,this is represented in ,fig4 #age4 ,illustration3 ,fig4 #age ,an ordinary kitchen clock had a hole bored through the glass which covers its face4 ,this glass is easily moved around in its metal rim1 bringing the hole over any desired minute upon the face4 ,one wire of the battery is attached to a leg of the clock1 the other goes to a bell1 and then the wire from the bell is poked through this hole4 ,when the minute hand reaches that point the electric current is closed through the metal of the clock1 and the bell rings warning that the eggs1 coffee or what not are done4 ,we each urged that our memories should share in the vacation1 and applied for one of these outfits4 ,i took one of the clocks and cut back the minute hand so as to make it shorter than the hour hand1 and then had the hole in the glass made so that the hour hand should close the electric circuit4 ,this was kept at my study table and reminded me of my appointments4 ,some used these clocks to alarm themselves in the morning when they slept overtime4 ,another reminder is shown in ,fig4 #agf4 ,c is a float which rises and falls with the water in our house tank4 ,a cord running over two pulleys connects this with a weight1 d1 hanging in front of a scale upon the wall of the kitchen4 ,this indicates how much water there is at any time in the tank1 which is situated in the garret4 ,the boys arranged a bell and battery so that when the tank is nearly empty the weight d will pull upward a spring1 a1 and make it close the circuit through the bell to warn that water must be pumped4 ,when the tank is nearly full the weight d pushes down the spring b and rings the bell again4 ,illustration3 ,fig4 #agf ,harold said that yeast cakes were the heaviest tax upon our memories4 ,if some one started for the village store1 before he got out of hearing1 a call would come after him1 ,i forgot the yeast cake4 ,please put that on the list4 ,when one returned from the village store with numerous packages1 he would generally hear1 ,my yeast cake was forgotten4 ,we tried all sorts of schemes to get rid of this yeast-cake nuisance1 and finally adopted ,harold's curled bread project4 ,we had built a brick oven out back of the house for experimental purposes4 ,harold proposed that the boys bake a month's supply of bread at a time1 and1 when it was a day or two old1 cut it all into thin slices and let it dry4 ,these slices curled up as they dried and were known as curled bread4 ,a flour barrel was filled with it each month4 ,it kept perfectly any length of time4 ,the family voted it to be better than crackers and better than fresh breadstuff of any kind4 ,harold's suggestion regarding yeast cakes worked so well and was such a relief to our memories that ,i proposed he next attack the problem of the often forgotten salt in cooking4 ,,xx ,,the ,,electric ,,brick ,,oven ,we had no end of experiments with brick ovens4 ,one of the most interesting was that wherein we used the brick fireplace as an oven and did the family baking in it4 ,on a cold morning we would build up a smart wood fire in the fireplace and enjoy it during breakfast time4 ,then we shovelled out the coals and the ashes1 and shut it up tight with a sheet iron arrangement and utilized the heat stored in the bricks for doing all sorts of cooking4 ,our outdoor brick oven and our monthly baking day were such a success that they led to the construction of another oven of smaller dimensions for the kitchen4 ,this one was heated by electric lamps--one in each of the eight corners4 ,it had double glass doors in front so that the cooking process might be watched4 ,the glass of the inner door would be clouded with moisture for a while1 when the cooking first began1 but this would soon clear up1 and then the lamps enabled us to watch the colour changes in baking1 etc4 ,the lamps in the upper part of the oven were connected with a different switch from those in the lower part of the oven1 so that we were able to control the browning on top or bottom at pleasure4 ,harold introduced a device for automatically controlling the temperature of this oven4 ,illustration3 ,fig4 #agg ,strips of brass and iron1 ,b and ,i 7,fig4 #agg71 were riveted together4 ,these were fastened in the socket ,a4 ,they are shown edgewise in the diagram4 ,the upper end of this compound strip is free to bend back and forth in the plane of the paper1 as here represented4 ,they normally touch the screw ,c4 ,one of the electric light wires runs from the lamps in the oven to this screw ,c4 ,one wire of the dynamo circuit ,g goes to the lamps1 and the other connects with ,a4 ,thus the compound strip acts as a switch to open and close the circuit upon the lamps4 ,this thermostat1 as it is called1 was placed inside of the oven4 ,heat causes brass to expand more than iron and therefore when the temperature reaches a certain height the thermostat curves1 so as to break the contact with ,c1 and the lamps go out4 ,when the temperature falls a little the thermostat straightens until contact is again made with ,c4 ,c is a screw and can be made to advance or recede in its socket ,e1 so that the temperature of the oven may be maintained at any point desired4 ,the wire of the screw ,c extends to the outside of the oven1 where it carries an index1 ,d1 over the face of a dial1 as shown in ,fig4 #agh4 ,illustration3 ,fig4 #agh ,the cook may set this index at any desired degree1 and the lamps will indicate when that degree has been reached4 ,the thing to be baked is then put inside and the clock1 illustrated in ,fig4 #age1 is set so as to warn when the time is up4 ,the electric spark which occurs when the thermostat breaks contact with ,c causes the metals to corrode at that point1 and corroded metals are poor conductors4 ,this corrosion is due to the oxygen of the air4 ,there is one metal--the expensive platinum--which is not corroded by the electric spark4 ,we drilled small holes in the end of the screw ,c and in the brass strip and pounded into these holes little pieces of platinum wire4 ,harold said he felt like a dentist filling a tooth4 ,this furnished good1 clean contact at all times4 ,it takes a long time to heat up the brick oven1 but it holds its heat a long time and makes an excellent fireless cooker after the lamps are turned out4 ,it does not allow heat to escape into the kitchen1 which makes it a comfort in our summer cottage4 ,we are all becoming daft on slowly cooked food--a sort of ripening process which gives time for the chemical changes to take place and develops the finest flavours of the food4 ,,xxi ,,electric ,,waves ,much has been said about bringing young people up to do what they don't like to do so as to make them strong and virtuous4 ,my own life has always been guided by a different principle4 ,it is3 ,find something worth while which you will enjoy doing1 and do it with your might4 ,i am bringing up my boy on the same principle4 ,in ,september we have a real desire to get back to our work in the city1 and in ,june we have an eager longing for the occupations of ,millville4 ,i am not aware that there is any part of my work which ,i would like to be relieved from1 and ,harold and his mother said that they were now ready to return to the city apartment with real pleasure for a winter4 ,one evening we were seated about the dinner table when ,harold asked me how electricity could travel without wires4 ,i replied1 ,it travels as light does4 ,but ,i am very much puzzled to know why it ever follows a wire when light does not4 ,this did not settle the question and left us both unsatisfied1 so ,i told him to invite two or three of his best friends in to-morrow evening1 and ,i would perform some experiments for them that would at least help them to think further upon this subject4 ,when the evening came ,i showed the boys an automobile spark coil to which ,i had attached two knobs1 a and b 7,fig4 #agi71 and with which ,i had connected two dry battery cells4 ,when ,i touch the wire c to the binding post d a spark passes between the knobs a and b4 ,when this spark occurs at least four kinds of waves pass out in all directions from the spark gap between the knobs4 ,illustration3 ,fig4 #agi ,first1 sound waves go through the air4 ,our ears detect these4 ,if the air is removed from around the apparatus no sound wave can go forth4 ,a careful examination of the internal ear shows us that it is constructed so as to respond to such air waves4 ,second1 light waves go forth4 ,these affect our eyes4 ,we are blind to the first kind of waves and deaf to the second4 ,the light waves travel without air--somewhat better without air than with air4 ,a microscopic examination of the eye indicates that it is constructed so as to respond to waves4 ,we believe there are waves in the ether which fills all space4 ,sound waves travel in air at the rate of one mile in five seconds4 ,we had this nicely illustrated at the sea shore one summer4 ,the steamer touched each morning at a wharf which we could plainly see two miles distant4 ,we could see the steam arise when she blew the warning whistle1 and with our watches we found that it always required ten seconds for the sound to reach us after we saw the steam of the whistle4 ,this at least showed us that it takes five seconds longer for sound waves to travel a mile than it does for light waves to travel the same distance4 ,for light had to travel the same distance before we could see the steam arise from the whistle4 ,although the time it takes for light to travel a mile is inconceivably small1 we have a simple method of finding out that it requires eight minutes for light waves to come to us from the sun4 ,the satellites of the planet ,jupiter1 in revolving about that body1 disappear and reappear at regular intervals1 acting as flash lights to mark time4 ,illustration3 ,fig4 #ahj ,the earth1 being #ib1jjj1jjj miles distant from the sun1 is #ahd1jjj1jjj miles farther from ,jupiter when at ,b than it is when at ,a4 7,see ,fig4 #ahj47 ,it is found by observation that sixteen minutes more are required for the light waves from a reappearing satellite to reach us at ,b than when we are at ,a4 ,hence eight minutes would be required for light waves to travel the distance from the sun to the earth4 ,although light travels at the inconceivable velocity of #ahf1jjj miles per second1 the nearest star is so far distant that it takes light three and a half years to come from it to us4 ,the ,north star requires forty-two years to send its light to us1 and ,arcturus is so far away that waves of light sent out from it one hundred and sixty years ago are only just reaching us now1 and if it should cease to send forth light now men would continue to see it for five generations yet to come4 ,a third kind of wave which goes forth in the ether from the spark gap of our coil is a heat wave4 ,this affects neither our eyes nor our ears1 but ,i will undertake to make you conscious of it by another method4 ,illustration3 ,fig4 #aha ,before a mixture of gasolene vapour and air can be ignited its temperature must be raised to about #bjjj degrees ,fahrenheit4 ,i will show that heat waves pass out from this spark gap by placing my watch crystal filled with gasolene underneath the knobs of the spark coil1 7,fig4 #aha74 ,when now ,i close the electric circuit at the battery the mixture of gasolene vapour and air just above the watch crystal is ignited4 ,if ,i increase the distance between the knobs you still hear the crackle of the sound waves and see the light waves1 but the mixture of gasolene vapour and air does not ignite1 because there are not heat waves enough4 ,the automobilist expresses this fact by saying a fat spark or a warm spark is needed4 ,a battery which has ceased to give a sufficiently hot spark to explode the mixture of gasolene and air in the cylinder of a gasolene engine may serve all other purposes quite as well as ever4 ,it may ring bells almost as long as it ever would4 ,i proved that the temperature for igniting a mixture of gasolene vapour and air was nearly as high as melting iron1 by heating an iron rod to a dull red heat and bringing it to the watch crystal containing gasolene4 ,it did not take fire4 ,i showed that it could not be ignited by a lighted cigar1 nor even by a glowing coal taken from the fire4 ,it was necessary to heat the iron rod to a very bright red heat--nearly white heat1 or nearly to its melting point1 before it would ignite the mixture4 ,these heat waves are ether waves1 differing from light only in having greater wave length4 ,they travel at the speed of light1 they travel better without air than with air4 ,they come from the sun and all other light-giving bodies4 ,indeed1 an ordinary incandescent electric lamp gives out about twenty-four times as much energy in heat as in light4 ,heat waves are being thrown off from all bodies which are around us4 ,the steam radiators are placed in this room for the express purpose of sending out heat waves through the ether in this room4 ,this is the chief method of distributing heat1 and it is hindered rather than helped by the presence of the air4 ,the walls1 ceiling1 floor1 furniture1 people--everything here is sending out heat waves4 ,the fourth kinds of waves1 which go out from the spark gap of our coil1 are also waves in the ether4 ,they are still longer than heat or light4 ,we have ears for sound1 eyes for light1 and temperature sensation for heat1 but as yet we have not evolved a delicate sense organ for detecting electric waves4 ,at least few of us claim to have such a sense4 ,i will1 however1 undertake to make you feel electricity4 ,i then adjusted the coil so that each boy might take a mild electric shock from it by touching the two knobs4 ,that is by placing himself in the spark gap4 ,they agreed that although they could not hear1 see1 taste1 or smell electricity they were a little more familiar with it now1 having felt it4 ,sound waves in air1 as given out by the piano1 vary in length from1 say1 four inches to forty feet1 those having the shorter wave length being the higher pitched tones4 ,light waves in the ether1 as given out by the sun1 vary in length from1 say1 #a_/fjjjj to #a_/hjjjj of an inch1 those having the shorter wave length being the violet-coloured light1 which may be seen in the rainbow1 and those having the longer wave length being the red-coloured light of the rainbow or the sunset4 ,heat waves1 which are also waves in the ether1 vary in length from above #a_/hjjjj to1 say1 #a_/ejjj of an inch4 ,roentgen or ,x waves are ether waves1 shorter than light2 while ,hertzian1 or wireless telegraph waves are very long ether waves1 varying from a few feet to many rods in length4 ,those used by ,marconi in sending despatches across the ,atlantic ,ocean are as long as #ajjj feet1 four or five of them cover a mile1 and #ab1jjj of them cover the whole distance from ,cape ,cod to ,poldhu4 ,electric waves are easily broken up into the shorter heat waves1 or the still shorter light waves4 ,on the other hand ,roentgen waves are readily transformed into the longer light waves1 and are thus brought within our powers of vision4 ,sound waves of various lengths 7of high and low pitch7 all travel at the same speed 7one mile in five seconds71 else how would the piccolo and the bass horn of the distant band sound together4 ,so ether waves of various lengths 7light1 heat1 electricity1 etc47 all travel at the same speed1 i4 e41 #ahf1jjj miles per second4 ,for detecting the electric waves which may be sent out from the spark gap of our automobile spark coil ,i shall ask you to help me prepare a special piece of apparatus4 ,one boy may file this silver ten-cent piece and another may file this nickel five-cent piece1 each gathering the filings upon a piece of paper4 ,a third boy may select a piece of glass tubing about one eighth of an inch in the inside diameter1 and with a three-cornered file cut off a short piece1 about one and a half inches long1 and smooth the ends with a wet file4 ,a fourth boy may select a piece of stout copper wire nearly as large as the bore of the glass tubing1 and cut from it two pieces1 each about two inches long4 ,wind one end of each of these with thread to make them fit snugly in the glass tubing4 ,illustration3 ,fig4 #ahb ,coherer ,we thrust one of the wires into the tube1 then mixed equal parts of the silver and nickel filings and put as much of the mixture into the tube as we could hold upon the tip of a penknife blade1 and then thrust in the other copper wire4 7,see ,fig4 #ahb47 ,the ends of the wire were about one eighth of an inch apart and the gap was loosely filled with the metal filings4 ,this was connected by short pieces of copper wire1 as shown in ,fig4 #ahc1 to a dry battery cell1 ,b1 and a sensitive ammeter4 ,when all connections were made the needle of the ammeter remained at zero1 showing that no electric current was passing1 that is1 the battery cell was unable to send any electricity through the metal filings4 ,this is the apparatus which is to help us detect electric waves when they pass about us4 ,electricity has been called invisible light1 that is1 invisible to our eyes1 and this apparatus has been called an electric eye because it will detect electric waves in the ether1 just as our eyes may detect light waves passing through the ether4 ,illustration3 ,fig4 #ahc ,we placed the automobile spark coil upon the table near to the tube containing the filings of silver and nickel1 and as soon as we made a spark pass between the knobs the ammeter needle moved half way across the scale1 indicating that the spark had somehow influenced the metal filings in the tube so that now they permitted the battery cell to send some electric current through them and through the ammeter4 ,i asked one of the boys to tap the tube slightly with a lead pencil so as to jar the metal filings1 and as soon as he did so the needle of the ammeter went back to zero4 ,illustration3 ,fig4 #ahd ,the spark coil sent electric waves out in every direction1 and those which hit the metal filings made them cohere together4 ,in that condition they allowed the dry cell to send through them enough current to move the needle of the ammeter4 ,tapping the tube made the metal filings break apart again1 in which condition they do not allow the current of the cell to pass in sufficient quantity to move the needle4 ,this tube is called a coherer1 because the filings in it cohere together4 ,the apparatus then serves to indicate when electric waves are passing4 ,as yet1 however1 it would not respond when the spark coil was more than one foot away4 ,our next step was to attach extra pieces of wire1 each ten or twelve feet long1 at either end of the coherer1 as indicated in ,fig4 #ahd4 ,one of these wires was stretched out upon the floor while the other one was connected with the wire of a picture hanging upon the wall4 ,we now found that the coherer would respond when the spark coil was operated several feet away4 ,the extra wires which we had attached to the coherer are called antenn1 because they suggest the long feelers or antenn of some insects4 ,illustration3 ,fig4 #ahe ,our next step was to put antenn upon the spark coil also1 as shown in ,fig4 #ahe4 ,one of these wires was stretched out upon the floor1 while the other one was connected with the wire of a picture hanging upon the wall on the opposite side of the room from where the coherer was4 ,we now found that the coherer would respond when the spark coil was operated in the farthest part of the room4 ,with the wires which were lying upon the floor extending toward each other1 but lacking several feet of touching1 the coherer responded when the spark coil was operated in various other rooms of the house1 although the doors between were shut4 ,when the floor wires were connected to the water pipes the coherer would respond when the spark coil was operated in a neighbouring house4 ,we tried a similar experiment1 substituting an ordinary electric bell for the spark coil4 ,the coherer or electric eye detected that ether waves were sent forth from an electric bell every time a spark was produced in the bell4 ,for this purpose connections were made1 as shown in ,fig4 #ahf4 ,one dry battery cell was used to ring the bell4 ,the floor wire a1 or1 as it is usually called1 the ground wire1 was connected to the binding post #a1 and the other antenna was connected to the screw #c1 and then supported aloft on a picture hung upon the wall4 ,with this transmitter we sent waves across the room which were detected by the coherer4 ,illustration3 ,fig4 #ahf ,we constructed a simple spark coil as follows3 ,we bought a pound of ,no4 #bd single cotton covered copper wire1 such as is used in the electro-magnets of bells4 ,it was1 when we bought it1 wound upon a wooden spool4 ,we filled the hole in the centre of this spool with wire nails4 ,one dry cell was connected with this 7,fig4 #ahg74 ,when the wires at d were touched together1 and then separated1 a spark was produced at that point4 ,a ground wire was connected at b1 and an antenna at c1 as before4 ,using this apparatus now as a transmitter of ether waves1 we found that the coherer detected them4 ,illustration3 ,fig4 #ahg ,we next gave our attention to making changes in the receiving apparatus1 not to change the coherer1 but to provide substitutes for the ammeter4 ,a sensitive relay was procured1 which is essentially like a bell or buzzer except that it does not clatter4 ,it will be readily understood1 by referring to the accompanying ,fig4 #ahh1 that ,r is a coil of insulated wire around an iron core exactly like what we see in the electric bell4 7,in practice there will be a pair instead of one of them47 ,such coils are called electro-magnets1 because when electricity flows in the wires they become magnets1 and will attract iron4 ,a is an iron spring1 ,b is a dry battery cell and ,c is the coherer4 ,whenever an ether wave passes the coherer permits the battery cell to send a current around the magnet of the relay1 and it attracts the iron spring a1 so that it hits against the metal post d with a click4 ,whenever we used this to respond to ether waves the click of the relay suggested the telegraph sounder4 ,how it served in wireless telegraphy will appear in the following pages4 ,illustration3 ,fig4 #ahh ,,xxii ,,ringing ,,bells ,,and ,,lighting ,,lamps ,,by ,,electric ,,waves ,illustration3 ,fig4 #ahi ,harold was to have a birthday party1 to which many of his school friends were invited4 ,for this occasion he prepared1 with my help1 to perform for the girls and boys some electrical experiments1 and particularly to give all who chose to try it an electric shock4 ,for this purpose he had them all join hands1 and the electric charge was sent through the whole line at once4 ,one thing he did shocked his mother more than anything else4 ,he instituted a mock court1 at which one of the boys was tried1 convicted and condemned to be executed by electricity4 ,the whole affair was enacted with no great solemnity1 but the electrical experiment was voted a great success by the executed criminal4 ,the following group of experiments1 however1 seemed to give the most satisfaction3 ,on a table was placed the coherer connected to the relay1 and in another room was placed the spark coil for sending ether waves4 ,he had this operated by a confederate whom he chose for the purpose4 ,he then connected two wires to the relay1 one at d and the other at e 7,fig4 #ahi74 ,these ran to a battery cell and a bell in a far corner of the room4 ,at a given signal 7a cough7 the confederate made a spark at the spark coil in the other room2 this sent ether waves through the partition between the rooms2 the ether waves caused the coherer to pass electricity from the dry cell ,no4 #a1 to close the relay spring ,r4 ,this acted like a switch to close the second circuit through the dry cell ,no4 #b and the bell1 which rang out to the surprise of all4 ,it continued to ring until he tapped the coherer tube and broke apart the filings4 ,when this had been tried to the satisfaction of all1 the company was invited to another room4 ,here they found an electric train with tracks1 train sheds1 stations1 tunnels1 bridges1 switches1 signals1 etc41 arranged upon a centre table4 ,the electric train was to be started by ether waves4 ,a wire from the railroad track was connected with e of the relay 7,see ,fig4 #aij74 ,a wire from d of the relay was connected to the third rail through a battery of sufficient strength 7,battery #b74 ,the electric train completed the circuit by connecting the tracks with the third rail4 ,all heard the crack of the spark coil in the adjoining room1 and saw the train start immediately4 ,ether waves had caused battery #a to close the relay ,r4 ,this had closed the circuit so that battery #b might run the train1 of course by means of a motor in the train4 ,he tapped the coherer4 ,the relay spring ,r flew open and the train stopped4 ,presently another crack from the adjoining room1 and the train instantly started again4 ,when all the details of the electric train had been examined the company was invited to go to the dining room1 which was dimly lighted by candles4 ,all were seated and busily conversing when the crackling noise of the spark coil was again heard1 and a group of little electric lights flashed forth upon a birthday cake4 ,the wires from the lamps and a battery to run them had been connected with the binding posts d and e of the relay4 ,illustration3 ,fig4 #aij ,the chandelier over the dining-room table had a pendant push button ,a 7,fig4 #aia71 with which the regular electric lights could be turned on and off4 ,this ,i had removed and extended the wires down upon the table4 ,it was only necessary to connect these to the binding posts d and e of the relay1 and the next wave from the spark coil lighted the chandelier4 ,illustration3 ,fig4 #aia ,the flexible wires underneath the dining-room table with which the maid is usually summoned from the kitchen were next extended up and connected with d and e of the relay1 and the maid was called in by an ether wave4 ,she brought with her a tray in the centre of which stood an earthenware cup1 such as is used for baking custard4 ,this had been filled with a mixture of granulated sugar and powdered potassium chlorate4 ,four dry battery cells stood around this upon the tray connected in series 7,fig4 #aib74 ,a very small iron wire connecting two of these cells dipped into the sugar mixture4 ,two wires from the battery were connected to d and e of the relay4 ,at the proper signal an ether wave was sent out by the spark coil4 ,the coherer closed the relay and the relay acted as a push button to close the circuit of the four cells upon the tray4 ,the fine wire dipping into the sugar and potassium chlorate got red hot4 ,this caused the mixture to flash up and burn in most beautiful coloured flames4 7,fig4 #aic74 ,illustration3 ,fig4 #aib ,illustration3 ,fig4 #aic ,on this occasion ,harold's friends gave him1 with due formalities1 the degree of ,e4 ,e41 which they said meant electrical expert1 and ever since that night he has been called the expert4 ,i inquired of the young folks1 as their party was breaking up1 if they understood ,harold's explanations of all these things1 and he replied that he at any rate understood them better having attempted to explain them4 ,,xxiii ,,telegraphing ,,by ,,electric ,,waves ,the next time ,harold and ,i experimented we arranged something to save us the trouble of tapping the coherer each time we used it4 ,we employed simply an electric bell1 ,b 7,fig4 #aid71 from which we removed the gong4 ,by reference to the figure the arrangement will be understood4 ,each time ether waves cause the metal filings to cohere and the battery ,b#a closes the relay ,r1 battery ,b#b causes the hammer of ,b#c to tap against the coherer4 ,this causes the current to cease to flow from ,b#a and the relay opens again by its own spring4 ,illustration3 ,fig4 #aid ,illustration3 ,fig4 #aie ,our next addition was a telegraph sounder as shown in ,fig4 #aie4 ,b#a is a single dry cell1 ,c is the coherer1 ,r is the relay1 ,b#b is now a battery of three cells4 ,part of its current goes to ,b#c1 the tapper for the coherer1 and part of its current goes to the electro-magnet of the telegraph sounder ,s4 ,ordinarily a spring holds the iron strip d up against the metal stop a1 but when the current passes through the electro-magnet it pulls down this iron strip with a click against the metal stop e4 ,but while this is happening ,c is being tapped by ,b1 and is ready to respond to each wave4 ,it was only necessary now to have some code of signals in order to communicate by telegrams4 ,we learned the system of dots and dashes1 or short and long periods marked off by the sounder1 which all telegraphers use and which is known as the ,morse alphabet1 and very soon ,harold and ,i were telegraphing from one room to another messages of several sentences at a time1 the ,morse alphabet being told off on the spark coil and being received through the coherer and telegraph sounder4 ,it was not long before ,harold and one of the neighbours' boys were exchanging messages between their homes1 each having a spark coil and the necessary receiving apparatus1 and having extended their antenn to the top of the buildings into what are called in the wireless language aerials4 ,illustration3 ,photograph by ,helen ,w4 ,cooke4 ,induction ,coil of a ,wireless ,the fever for wireless telegraphy spread like wild-fire among the boys4 ,in a few months they had formed a wireless club4 ,they had each read anywhere from ten to thirty books and articles upon the subject1 and had secured the latest improved apparatus4 ,they made it a practice to spend hours daily at their instruments picking up and keeping on file messages which were sent to and from steamers leaving the harbour for ,european ports4 ,on one occasion they showed me from these files scores of messages--fond1 personal1 and supposedly private farewells to friends and communications between business partners which they would never have made on land without first closing the office door4 ,the boys had acquired a mass of technical knowledge upon the subject which far exceeded my comprehension4 ,but their teachers in school complained that they would learn nothing else1 and some of the boys had already received warning that they might fail of promotion4 ,how to have compelling interests without riding hobbies is the great problem for both boys and men4 ,i have known many boys who could1 or at least would1 do nothing well in school or out1 except some specialty like manual training or science4 ,in later years they were so deficient in education that they could hold no worthy position in anything4 ,my anxiety was to save my boy from such a fate4 ,i was determined that he should have a fair share of all kinds of culture4 ,to this end we read together much of biography1 history and classical literature1 ancient and modern1 through the medium of the ,english language4 ,as both prevention and cure of the wireless telegraph mania ,i deemed it not necessary to suppress enthusiasm1 nor to introduce obviously useless tasks for the sake of the training which might be in them4 ,my method was1 on the contrary1 to encourage my boy to have several hobbies which he might ride with enthusiasm1 but to make it a rigorous rule to exchange his mount occasionally4 ,,xxiv ,,halley',s ,,comet ,,and ,,electrical ,,waves ,illustration3 ,fig4 #aif ,it was the year #aiaj and ,halley's comet was approaching the sun4 ,on ,may #ah its tail might be expected to reach the earth4 ,astronomers had requested all who might be possessed of wireless telegraph apparatus to watch on that day for any peculiar behaviour of their apparatus so that evidence might be obtained whether or not the comet sends forth such ether waves as we call electricity4 ,harold desired me to explain the whole matter to his group of friends1 which ,i did on a subsequent evening1 as follows3 ,although ,halley's comet has come within the earth's orbit about three thousand times since its first recorded appearance1 ,i know of no man living who can give a satisfactory account of having seen it4 ,any one who has seen it before must be at least seventy-five years old1 for it requires seventy-five years to make one complete circuit of its own orbit4 ,but no one who is now seventy-five could have observed it intelligently1 and even one who is now eighty-five years old would have to tell what he saw when he was ten years old and has remembered for seventy-five years4 ,furthermore1 any account of how it looked on a former return is no guide to how it may appear on this trip4 ,you may properly think of the comet as a group of solid pieces no bigger than the stones you may throw1 scattered1 two or three to the mile1 through a space #ab1ejj miles broad4 ,this extremely thin cloud of particles does not reflect enough sunlight to be visible1 even in a telescope1 in any part of its journey1 and hence we should be wholly unaware of its existence if it did not sometimes have the strange faculty of giving out light of its own while in that part of its own orbit nearest to the sun4 ,at such a time there is a hazy light enveloping the mass of small bodies1 and streaming away sometimes many million miles from them4 ,the mass of small bodies is generally referred to as the nucleus1 and the stream of luminous gas which the nucleus gives forth is called the tail1 though it reminds me more of a search-light4 ,it does not trail along behind the comet but always points away from the sun 7,fig4 #aig74 ,the normal thing for a comet to do is to begin to develop a faint light and a short streamer as it gets near to the sun1 to have its light grow brighter and its streamer to grow longer until it reaches the point nearest the sun1 and then to have its light grow dimmer and the streamer grow shorter as it recedes from the sun4 ,illustration3 ,fig4 #aig ,it has many times been suggested that this strange search-light appearance may be an electrical phenomenon1 some form of ether waves which the comet sends forth when under the immediate influence of the sun4 ,but not all comets are alike in this matter1 nor does the same comet always act alike on succeeding trips1 so that we may not predict what ,halley's comet will do on this visit4 ,it would be natural to suppose that ,halley's comet1 like radium1 might in time lose the power to radiate off material1 in which case it might at length become wholly invisible to us1 even though it continued to travel in its wonted path4 ,our only way of knowing of its existence then would be that on its returns some of its small pieces might be attracted to the earth and enter our atmosphere as meteors4 ,this sort of thing is continually happening1 and may be the last reminders of once brilliant comets4 ,for almost a century it has been the common belief that light is merely a wave motion in the ether4 ,our eyes respond to ether waves of certain length only4 ,waves a little longer than those which affect our eyes are felt by us as heat waves4 ,waves still longer than those of heat are the so-called electric waves4 ,these we use in wireless telegraphy4 ,there are still shorter waves than those of light4 ,these affect the sensitive plate in photography4 ,they help to form the green material in the leaves of plants and the brilliant colours in flowers4 ,they assist in the fading of our clothes and the tanning of our skin4 ,these are called chemical waves4 ,still shorter waves in the ether than those of which we have just spoken are the ,x rays1 and all the strange things which they may do have not yet been determined4 ,certain it is that they can make dreadful sores in our flesh4 ,they can penetrate through wood and paper1 but not metals4 ,they pass readily through flesh1 but not bones4 ,all such ether waves are treated in a book by ,sylvanus ,p4 ,thompson1 entitled ',light ,visible and ,invisible1' in which he points out that electricity1 heat1 light1 chemical rays1 etc41 are all alike in being ether waves1 and this was suspected by ,james ,clerk ,maxwell and others half a century ago1 and has come now to be quite generally believed4 ,halley's comet1 already having been seen upon this return1 must be sending out those ether waves which we call light2 whether it is also sending forth some of the other kinds of ether waves may yet be determined4 ,my audience being chiefly composed of those persons who were present at ,harold's birthday party1 they pressed me to tell them more about wireless telegraphy and similar matters1 and so ,i agreed to give them at some future date some account of the history of these ideas4 ,but my present purpose was to start an interest in astronomy as an antidote for the wireless epidemic1 and so ,i invited all who desired to do so to come again one week from that evening1 bringing with them such opera and field glasses as they might be able to secure4 ,i promised to show them how to make a telescope such as ,galileo had more than three hundred years ago4 ,i agreed to go out with them several evenings and scan the sky with our telescopes1 and to tell them of some readable books and articles upon astronomical matters4 ,,xxv ,,how ,,the ,,idea ,,of ,a ,,universal ,,ether ,,developed ,the evening for the meeting of the ,science ,club had arrived4 ,its membership had increased tenfold within a year4 ,at its monthly meetings1 which were open to the public1 an audience of two hundred1 old and young1 was usually present--a number about three times that of the regular membership4 ,general science was now the study of this club4 ,at its weekly meetings1 which only members attended1 the studies of specific topics by individuals1 oftentimes illustrated by experiments1 were reported4 ,these meetings were held in one of my laboratories1 while the open monthly meeting was always held in my lecture room1 with some rather famous speakers to instruct the audience4 ,an enthusiastic friend of science had given a fund with the stipulation that we should engage the services of those who both knew their subjects and had acquired the art of presentation4 ,the fund was #aj1jjj and it yielded #ejj a year4 ,i think beyond question it was doing more for science than any other fund of ten times that amount which can be mentioned4 ,on the particular evening of which ,i am about to speak1 the lecturer told the members of the ,science ,club frankly how1 beginning at the age of thirteen1 he had spent forty years of enjoyment in study1 that he had always found great satisfaction in the study of ancient civilizations and literatures4 ,he had been fortunate1 he said1 in having teachers early in life who could make these subjects full of meaning to him4 ,his greatest satisfaction1 however1 during the last twenty-five years had been found in tracing the development of modern science1 both in the evolution of its theories and in its applications to modern industries4 ,he said he was sure that young people of high-school age would find it profitable to learn1 for instance1 how the modern theory of combustion had developed slowly through the centuries1 even if to do so they must curtail somewhat their study of how ,greece and ,rome developed and declined4 ,he said that science furnished a tremendously rich field of study for young people1 which as yet had been untouched by our schools1 first1 because educational conservatism had made it impossible to determine the relative importance of subjects of study1 and1 second1 because education in science had1 for a brief period1 found its worst enemies within its own camp4 ,he would like especially to commend on this evening some historical studies in science1 and had chosen for his subject1 ,how the ,idea of a ,universal ,ether ,developed4 ,men seem to talk freely now about the transmission of light1 heat1 and electricity by means of the ether4 ,how did this idea arise8 ,is it a product of wild imagination8 or did the idea develop out of experiences which1 if given to any person of fair intelligence1 would yield the same result8 ,a little over thirty years ago1 at the ,royal ,institution of ,great ,britain1 ,james ,clerk ,maxwell 7#ahca-ahgi7 delivered a lecture on ,action at a ,distance4 ,it was no new subject1 but rather one of the oldest and most often discussed subjects from the days of the ancient ,greeks down to the present4 ,we talk of gravitation as an attraction or pull between the various bodies of the universe1 but how can they pull one another without some material bond between8 ,this was ,sir ,isaac ,newton's great puzzle which he never solved1 though he expended upon it the greatest efforts of his great intellect4 ,the sun appears to repel the tail of the comet1 yet how can there be a push without intervening material with which to push8 ,when we speak of light pouring or streaming in1 do we think of it as a substance8 ,when we speak of warm bodies losing heat1 or when we cover them to keep the heat in1 are we thinking of heat as a substance8 ,what are heat1 light1 electricity1 magnetism1 and gravitation8 ,these are no new questions4 ,they are certainly older than history4 ,various ideas have prevailed at different times4 ,it is much easier to change our ideas than to change our language4 ,you occasionally see and hear the words calorie and caloric used in connection with heat4 ,they stand for an idea1 abandoned for three generations1 that heat is a substance called caloric1 which saturates warm bodies and drains out of them when they cool off4 ,i hardly think these ideas either arise or fall without good and sufficient reason4 ,each theory has been the natural conclusion from our observations of nature as far as we have gone with them4 ,to be sure1 it is difficult for us to see how men acquired1 from any observations of nature1 the idea of light which seems to have prevailed previous to the time of ,aristotle1 three and a half centuries ,b4,c4 ,this idea was that objects were made visible by something projected from the eye itself4 ,still1 the questions which ,i have indicated regarding heat1 light1 and electricity have impelled men for many centuries to observe nature for hints as to the answers4 ,the doctrine of the universal ether as a medium for transmitting wave motions1 and of light1 heat1 and electricity as being motions of different wave length1 is the natural conclusion of the present time4 ,it may give place to another theory when we have further facts to reason upon4 ,imagine your never having seen a harp or other musical instrument4 ,would it require a long time1 do you think1 for you to find out its use1 at least to this extent1 that it will produce tones whenever the strings are made to vibrate8 ,that the short strings vibrate more rapidly than the long ones1 and at the same time produce tones of a higher pitch8 ,imagine that having become familiar with the harp you should successively come upon scores of other musical instruments of very differing types4 ,you would soon become adept at divining their uses4 ,now1 a study of the microscopic structure of the eye1 for one thing1 would suggest that light may be in the nature of a vibration4 ,scores of other lines of study in a similar manner have at length brought all who pursue them to the conclusion that light is a form of vibration4 ,robert ,hooke in ,england 7#afca-agjc7 and ,christian ,huygens in ,holland 7#afbi-afie71 back in the seventeenth century seem to have been the first to give expression to this idea1 which was nothing more than an inkling in ,hooke's mind1 but which was the necessary result of observations on the part of ,huygens4 ,for nearly a century the idea lay dormant1 largely because ,sir ,isaac ,newton 7#afdb-agbg71 the cleverest thinker of his time1 opposed it4 ,it was perhaps unfortunate for the success of the theory that ,huygens1 its founder1 adopted the word ether1 for that was an old term1 and had been very badly overworked4 ,the word ether1 or ther as it was often written1 had been invented in the days of ignorance1 for such foolish reasons as3 7a7 because nature abhors a vacuum1 or 7b7 for planets to swim in1 or 7c7 to constitute electric atmospheres and magnetic effluvia1 or 7d7 to convey sensations from one part of our bodies to another4 ,when we remember1 says ,maxwell1 the mischievous influence on science which hypotheses about thers used formerly to exercise1 we can appreciate the horror of thers which sober-minded men had during the eighteenth century4 ,newton in ,england 7#afdb-agbg7 and ,laplace in ,france 7#agdi-ahbg7 stoutly opposed the undulatory theory of ,huygens and championed a corpuscular or emission theory1 that light-giving and heat-giving bodies emit a subtile fluid4 ,there is no other instance in the whole history of modern physics in which truth was so long kept down by authority4 ,fresnel 7#aghh-ahbg7 and ,arago 7#aghf-ahec7 in ,france appear to be the only persons during the eighteenth century who caught a clear vision of the truth of the undulatory theory4 ,but it remained for ,mr4 ,thomas ,young 7#aggc-ahbi71 a colleague of ,sir ,humphrey ,davy at the ,royal ,institution1 in his ,bakerian lecture 7#ahja7 on ,theory of ,light and ,colour to bring together such good evidence for the ether wave theory that it has hardly been questioned since4 ,young1 like ,davy1 was a most remarkable man in literature and in science4 ,it was he who first deciphered the ,rosetta ,stone1 now in the ,british ,museum1 and gave us a key to the ,egyptian hieroglyphics4 ,probably he was the only man who was able to overthrow the influence of ,newton's authority even a century after ,newton did his work4 ,faraday's 7#agia-ahfg7 chief work as director of the laboratory of the ,royal ,institution1 ,london1 was a study of ether phenomena1 particularly electric and magnetic4 ,about seventy-five years ago he became impressed with the fact that although wires may give direction to an electric current the electric influence is not confined to the wires1 but may permeate more or less widely the region about them4 ,nearly fifty years ago ,maxwell 7#ahca-ahgh7 professor of physics at ,cambridge ,university1 ,england1 conceived the idea that light is electricity of a very short wave length4 ,nearly twenty-five years ago ,heinrich ,hertz 7#aheg-ahid71 in ,germany1 proved by experiments the existence of electric waves1 and measured their length and velocity1 determining their various characteristics as compared with light4 ,about fifteen years ago ,marconi developed a wireless telegraph apparatus1 which made it possible to use electric waves for purposes of communication4 ,thirteen years ago 7#ahig7 the first wireless telegraph company was formed4 ,eleven years ago 7#ahii7 the international yacht races in ,new ,york ,harbour were reported by wireless telegraph1 and bulletin boards in ,new ,york ,city announced to waiting crowds the details of the race while it was in progress4 ,nearly ten years ago 7#aija7 wireless despatches were first sent across the ,atlantic ,ocean4 ,wireless telegraphy was opened for public use in #aije1 and very soon the company began to coperate with the regular telegraph companies4 ,nearly all coastwise and trans-,atlantic steamers are now equipped with wireless telegraph outfits1 and a law has passed both houses of ,congress making it obligatory on the part of steamers which carry fifty or more passengers to have such equipment4 ,on several disabled steamers1 notably the ,republic1 loss of life has been averted by the wireless emergency call for help1 to which the captains of all steamers feel obliged to respond4 ,if you desire to communicate with a friend who left for ,europe several days ago1 you simply write him a telegram1 addressing it to his ship1 and deliver it at your nearest telegraph office4 ,each telegraph office has a record of the location of every ship having a wireless telegraph outfit4 ,it despatches your message to the wireless station along the coast which is nearest to your friend's steamer1 and from this station it is sent on the ether to the ship4 ,or in some cases it may be repeated from one ship to another along the ,atlantic highway until it reaches the desired one4 ,thus also news of important events on either continent is distributed daily on board ships which are crossing the ocean4 ,there are said to be more than #ej1jjj amateur wireless stations in the ,united ,states1 and already ,congress is taking steps to regulate the use of the wireless telegraph in order to prevent interference with ,government and other important messages4 ,more than three dozen books and countless magazine articles have already been written upon wireless or ether wave telegraphy4 ,hundreds have and thousands are contributing to our knowledge of ether wave phenomena4 ,if the names of all who have said or done something to render stable the foundations of this idea of a universal ether1 whose undulations account for the phenomena of heat1 light1 and electricity1 were to be mentioned1 the list would contain nearly all the important workers in the field of physics for the last century4 ,,xxvi ,,electric ,,currents ,,cannot ,,be ,,confined ,,to ,,wires ,harold said that if electricity was so much like light that it could go without wires he thought light ought to be enough like electricity to be conducted by wires on occasions4 ,i told him that ,i had no hope of being able to confine light to a wire2 indeed1 if the ,science ,club would give me an opportunity ,i would show them that even when electricity follows the general direction of a wire its influence is not confined to the wire4 ,as a result of this bid ,i received an invitation to address an open meeting of the ,science ,club4 ,illustration3 ,fig4 #aih ,in my first experiment on that occasion ,i took a one-pound spool of ,no4 #bd cotton-covered copper wire and crowded the hole in the spool full of wire nails ,a 7,fig4 #aih74 ,i disconnected the wires from an electric drop lamp and connected them to b and c1 the ends of the wire from the spool4 ,our electric lighting circuit was what is called the alternating current4 ,i also had a second spool1 ,b1 precisely like the first4 ,the wires from this were connected to a miniature lamp1 ,l1 such as is used at the switchboard of a telephone exchange4 ,we then screwed the drop-light plug into the chandelier and turned on the electric current4 ,i brought spool ,b with the miniature lamp near to spool ,a1 as shown in ,fig4 #aii1 and when it was within a distance of about two inches the little lamp lighted up to full brilliancy1 thus showing that while the electric current is passing in the wire of spool ,a its influence is not confined to the wire1 but exhibits itself in the region outside of the wire4 ,to illustrate still further this fact we substituted an electric bell in the place of the lamp ,l1 and when the spool ,b was brought near to ,a the bell rang4 ,but the most striking illustration was obtained when a telephone receiver was put in the place of ,l4 ,with this held to the ear while the spool ,b was brought toward ,a a humming sound could be heard when ,b was about a foot distant from ,a4 ,this sound grew rapidly louder as ,b approached ,a1 until1 when the spool ,b rested upon the spool ,a1 a sound like the peal of a pipe organ was heard all over the apartment4 ,the tone was very nearly that of the key on the piano which is two octaves below middle ,c4 ,i unscrewed the cap on the large end of the telephone receiver1 took it off1 and moved the thin iron diaphragm to one side1 when it began to dance about at great speed4 ,it was keeping time with the dynamo1 five miles away1 which generated the electric current4 ,the dynamo changed the direction of the electric current sixty times per second1 and this made sixty vibrations per second4 ,the dynamo sent out ether waves which affected the telephone receiver1 although the receiver was not connected to the dynamo by wires4 ,to emphasize the fact that the dynamo had lighted the lamp1 rung the bell and made the telephone receiver hum without being connected with them1 ,i repeated all these experiments in a different way4 ,spool ,a1 connected as before with the electric lighting circuit1 was concealed beneath the table4 ,for spool ,b ,i substituted spool ,c 7,fig4 #aii71 on which the wire was wound so as to appear like a candlestick4 ,on the top of this was placed the miniature electric lamp screwed into a miniature socket and connected to the wires of the spool4 ,this ,witches' ,candle1 as we called it1 was sitting unlighted upon the table when ,i called attention to the fact that if ,i moved it to a certain spot upon the table it flashed into full light4 7,of course this spot was directly over spool ,a47 ,i moved it slowly away from that spot and its light slowly grew dim and disappeared4 ,illustration3 ,fig4 #aii ,on the table was also sitting a cream pitcher in which ,i had placed spool ,b with a buzzer attached to it4 ,remarking that this pitcher groaned for more cream whenever it was empty1 and thus of its own accord called the waiter1 ,i moved it to the spot on the table directly over spool ,a1 when the buzzer gave forth a sound like a husky bumble-bee shut up in a resounding bottle4 ,at this signal my assistant came in and took up the pitcher and placed my silk hat upon the table1 when it instantly boomed forth a base note two octaves below middle ,c of the piano4 ,out of the hat ,i took a coil and the telephone receiver and the mystery was solved4 ,illustration3 ,fig4 #bjj ,in #ahai ,hans ,christian ,oersted in ,denmark 7#aggg-ahea7 first noted that the region about a wire carrying an electric current has an influence upon a magnet4 ,i will show this fact by a simple experiment4 ,i magnetize a stout sewing needle by drawing it from end to end across the pole of a steel magnet1 and by means of a triangular piece of paper and a fine thread ,i suspend it a few inches above the table 7,fig4 #bjj74 ,i then lay upon the table a piece of wire parallel with the needle and fasten one end of it to one binding post of a dry cell4 ,whenever ,i touch the other end of the wire to the other binding post of the cell1 thus sending an electric current through the wire1 the magnetized needle is deflected at right angles4 ,this experiment1 performed by ,oersted1 seems to have started ,faraday upon that wonderful series of researches which has resulted in giving us the dynamo4 ,,xxvii ,,wireless ,,telegraphy ,,in ,,earnest ,we had decided to let ,harold make a trip to ,europe alone4 ,the first message from him after his departure was a brief note to his mother saying that they had had a turbulent voyage1 but all had landed safely upon the other side1 none the worse for their experiences4 ,the next day a number of letters came to me from total strangers4 ,one of these ran as follows3 ,my ,dear ,sir3 ,prompted by my own impulses1 and urged to do so by the passengers under my charge1 ,i improve this first opportunity to express to you our high appreciation for your noble but very modest son1 to whom more than to any one else we owe the lives of all on board our fated ship4 ,i am sending this direct to you both1 because ,i understand a father's heart and because the young man escaped as soon as we came to land1 without any of us learning his address4 ,i beg you will communicate to him the desire of the president of our company to meet him and personally to thank him for his gallant conduct4 ,i am also instructed to say that whenever ,harold desires to cross the ocean the best which any ship ,i may command can afford will be his without charge4 ,very respectfully yours1 -------- ,captain4 ,s4 ,s4 ,another letter was the following3 ,my ,dear ,sir3 ,permit me to congratulate you on having such a heroic and self-possessed son4 ,we1 his fellow passengers1 are1 if possible1 as proud of him as you must be4 ,i fear that his account of the affair will not do himself full justice1 and so1 with your permission1 ,i will give you the full details as ,i have gathered them from the passengers1 from the crew1 and from my own observation4 ,during the last night of our voyage a thick fog closed about us4 ,the constant blowing of the fog whistle made the night dismal4 ,few persons slept at all4 ,about two o'clock in the morning the ship struck a reef1 and instantly it seemed as though every person on that ship reached the decks at the same time4 ,the water poured in and put out the fires4 ,the ship heeled badly1 and it seemed that any minute she might slip off the reef on which she was resting into deep water and go down4 ,to add to our horror fire broke out4 ,it seems to have started in the wireless operator's room4 ,very much damage was done to the wireless outfit itself1 and the operator was badly burned1 so much so that he was taken to the ship's hospital suffering with many painful and dangerous wounds4 ,meanwhile the flames spread rapidly and we were unable to summon help4 ,the crew and many of the passengers fought the flames1 but with little success4 ,in the midst of our despair word passed around the ship that an unknown boy from among the passengers was sending the ,c4 ,q4 ,d4 message to all the world by wireless4 ,it was afterward learned that your ,harold was the youth4 ,he had repaired the damaged apparatus sufficiently to establish connection with a storage battery which he found1 and1 under the captain's direction1 was sending forth that hurry call for help known to all the wireless fraternity and heeded by all sea-faring men4 ,i learned that your boy was not a regular operator1 but that somehow he had learned to send this message and also to send out the captain's calculations of our position at sea4 ,he was also able to detect that his call had been heard and that help was coming1 although he could not understand much that came to his instrument in reply to his calls4 ,i learned1 also1 that he was one of the first to reach the operator's room and to give assistance4 ,he was himself badly burned1 so much so that one hand was being dressed by a nurse while he was continually using the other to operate his instrument4 ,i can testify1 my dear sir1 that he appeared to be the calmest and most self-possessed person on board that ship1 as ,i saw him in the glare of the dreadful flames which lit up the blackest night4 ,i am an artist and would like to attempt to paint that scene1 which has left its lasting impression upon my soul4 ,i beg that you will allow me to exhibit it for a time in several of our galleries and finally present it to your family4 ,help came none too soon4 ,we were all transferred to other boats1 but the sea was rising1 and scarcely had we reached a safe distance when the burning ship slipped into the sea and disappeared4 ,i do not know by which boat your son reached the land4 ,in the great confusion ,i lost sight of him at last4 ,he has doubtless communicated with you by this time1 and ,i shall esteem it a great favour if you will put me in communication with him again4 ,in order that ,i may do justice to him in the painting ,i would like to arrange with him a few sittings while he is in ,europe4 ,could you kindly send me a photograph of him which will assist me somewhat8 ,most sincerely and gratefully yours1 --------4 ,the letter contained several references to mutual acquaintances4 99 99 99 99 99 ,harold's letters have been frequent and full of the pleasure he is having in ,european travel1 but the only thing he has said about the voyage is that it was not worth so much fuss4 ,illustration ,,the ,,country ,,life ,,press ,,garden ,,city1 ,n4 ,y4 99 99 99 99 99 ,transcriber's ,notes3 ,obvious typos and inconsistencies in spelling have been corrected3 p#ca4 intrument - instrument p#ce4 mantain - maintain p#dh4 represents the the counter-electro-motive force p#fd4 #b volts 4#a ampere 4#f watts4 - #f volts 4#a ampere 4#f watts4 ,the correct voltage is deduced from the preceding paragraph4 p#ada4 #ee ampere - 4#ee ampere p#afh4 familar - familiar p#agc4 preceptible - perceptible p#bbi4 - p#bcj4 countershaft - counter shaft p#bei4 ,h#b,,so#d - ,h#b,,so#d p#bie4 ,note ,c refers to ,c not ,c and these should be labelled ,c1 and ,c11 to denote octaves below middle ,c4 p#caf4 electri-tricity - electricity p#cef4 oufit - outfit ,throughout the text3 ,the few cases of volt-meter have been changed to volt meter which has been used for the majority of the text4 ,the single instances of watt meter and watt-meter have been changed to wattmeter which has been used for the majority of the text4 ,the few cases of electro magnet have been changed to electro-magnet which has been used for the majority of the text4 ,in the ,table of ,contents3 ,chapter ,,xii page number changed from #aah to #bah ,chapter ,,xv name changed from ,electricity from ,chemical ,action and ,chemical ,action from ,electricity to match text which reads ,,electric ,,currents ,,from ,,chemical ,,action ,,and ,,chemical ,,action ,,from ,,electric ,,currents ,in the ,table of ,illustrations3 ,operating a ,switchboard changed to match caption which reads ,operating the ,switchboard p#fc4 ,the example of ,morse code given is correct for ,original or ,american ,morse4 ,it has some differences from ,continental or ,international ,code which is the current standard4 ,the spacing of the dots is significant4