,illustration3 ,,marconi ,,wireless ,,telegraph ,,station1 ,,clifden1 ,,ireland ,photographed at night while sending a message across the ,atlantic4 ,the terrific snapping of the electric discharge is heard by one standing near the station1 but no light is seen4 ,the strange light given out from the network of wires is invisible to the eye1 but is caught by the photographic plate4 ,illustration3 ,,the ,,same ,,station ,,photographed ,,by ,,daylight ,,the ,,story ,,of ,,great ,,inventions ,,by ,,elmer ,,ellsworth ,,burns ,,instructor ,,in ,,physics ,,in ,,the ,,joseph ,,medill ,,high ,,school1 ,,chicago ,,with ,,many ,,illustrations ,,harper ,,brothers ,,publishers ,,new ,,york ,,and ,,london ,,mcmx ,copyright1 #aiaj1 by ,,harper ,,brothers ,published ,november1 #aiaj4 ,printed in the ,united ,states of ,america ,,contents ,,chapter ,i ,,the ,,age ,,of ,,archimedes ,archimedes the first great inventor4--,the battle of ,syracuse4--,archimedes' principle4--,inventions of the ancient ,greeks ,,chapter ,,ii ,,the ,,age ,,of ,,galileo ,galileo and the battle for truth4--,the pendulum clock4--,galileo's experiment with falling shot4--,the telescope4--,galileo's struggle4--,torricelli and the barometer4--,otto von ,guericke and the air-pump4--,robert ,boyle and the pressure of air and steam4--,pascal and the hydraulic press4--,newton4--,gravitation4--,colors in sunlight ,,chapter ,,iii ,,the ,,eighteenth ,,century ,james ,watt and the steam-engine4--,the first steam-engine with a piston4--,newcomen's engine4--,watt's engine4--,horse-power of an engine4--,the ,leyden jar4--,conductors and insulators4--,two kinds of electric charge4--,franklin's kite experiment4--,the lightning-rod4--,galvani and the electric current4--,volta and the electric battery ,,chapter ,,iv ,,faraday ,,and ,,the ,,first ,,dynamo ,count ,rumford4--,count ,rumford's experiment with the cannon4--,davy4--,faraday's electrical discoveries4--,oersted and electromagnetism4--,ampre4--,arago4--,fa raday's first electric motor4--,an electric current produced by a magnet4--,detecting and measuring an electric current4--,an electric current produced by the magnetic field of another current4--,faraday's dynamo4--,a wonderful law of nature ,,chapter ,v ,,great ,,inventions ,,of ,,the ,,nineteenth ,,century ,electric batteries4--,the dry battery4--,the storage battery4--,the dynamo4--,siemens' dynamo4--,the drum armature4--,edison's compound-wound dynamo4--,electric power4--,the first electric railway4--,electric lighting4--,the telegraph4--,duplex telegraphy4--,the telephone4--,the phonograph4--,gas-engines4--,the steam locomotive4--,how a locomotive works4--,the turbine ,,chapter ,,vi ,,the ,,twentieth-,,century ,,outlook ,air-ships4--,the aeroplane4--,how the ,wright aeroplane is kept afloat4--,submarines4--,some spinning tops that are useful4--,the monorail-car4--,liquid air and the greatest cold4--,the electric furnace and the greatest heat4--,the wireless telegraph4--,the wireless telephone4--,wonders of the alternating current4--,x-rays and radium ,,appendix ,brief notes on important inventions ,,index ,,illustrations ,,fig4 ,,marconi ,,wireless-,,telegraph ,,station1 ,,clifden1 ,,ireland ,,the ,,same ,,station ,,photographed ,,by ,,daylight #a--,,the ,,battle ,,of ,,syracuse #b--;,,galileo',s ,,pendulum ,,clock #c--;,,an ,,air ,,thermometer #d--,,torricelli',s ,,experiment #e--;,,guericke',s ,,air-,,pump #f--;,,guericke',s ,,water ,,barometer #g--;,a ,,lift-,,pump #h--;,a ,,simple ,,hydraulic ,,press #i--;,,how ,,an ,,hydraulic ,,press ,,works #aj--;,,an ,,hydraulic ,,press ,,with ,,belt-,,driven ,,pump #aa--,,newton',s ,,experiment ,,with ,,the ,,prism #ab--,,papin',s ,,engine #ac--,,the ,,newcomen ,,engine1 ,,in ,,repairing ,,which ,,watt ,,was ,,led ,,to ,,his ,,great ,,discoveries #ad--;,,cylinder ,,of ,,watt',s ,,steam-,,engine #ae--;,a ,,fly-,,ball ,,governor #af--;,a ,,leyden ,,jar #ag--;,,franklin',s ,,kite ,,experiment #ah--,,volta ,,explaining ,,his ,,electric ,,battery ,,to ,,napoleon ,,bonaparte #ai--,,the ,,first ,,electric ,,battery #bj--;,,count ,,rumford',s ,,experiment ,,with ,,the ,,cannon1 ,,making ,,water ,,boil ,,without ,,fire #ba--,,oersted',s ,,experiment #bb--;,a ,,coil ,,with ,a ,,current ,,flowing ,,through ,,it ,,acts ,,like ,a ,,magnet #bc--;,a ,,bar ,,of ,,soft ,,iron ,,with ,a ,,current ,,flowing ,,around ,,it ,,becomes ,a ,,magnet #bd--,,two ,,coils ,,with ,,currents ,,flowing ,,in ,,the ,,same ,,direction ,,attract ,,each ,,other #be--,,two ,,coils ,,with ,,currents ,,flowing ,,in ,,opposite ,,directions ,,repel ,,each ,,other #bf--;,,arago',s ,,experiment #bg--,,one ,,pole ,,of ,a ,,magnet ,,spins ,,round ,a ,,wire ,,through ,,which ,,an ,,electric ,,current ,,flows #bh--,,when ,a ,,magnet ,,is ,,thrust ,,into ,a ,,coil ,,of ,,wire ,,it ,,causes ,a ,,current ,,to ,,flow ,,in ,,the ,,coil1 ,,but ,,the ,,current ,,flows ,,only ,,while ,,the ,,magnet ,,is ,,moving #bi--;,a ,,coil ,,of ,,wire ,,around ,a ,,compass-,,needle #cj--;,,faraday',s ,,induction-,,coil #ca--;,,historical ,,apparatus ,,of ,,faraday ,,in ,,the ,,royal ,,institution #cb--;,,faraday',s ,,first ,,dynamo #cc--;,,faraday',s ,,laboratory1 ,,where ,,the ,,first ,,dynamo ,,was ,,made #cd--,,the ,,first ,,transformer #ce--,,the ,,magnetic ,,field ,,is ,,the ,,space ,,around ,a ,,magnet ,,in ,,which ,,it ,,will ,,attract ,,iron #cf--,,magnetic ,,field ,,of ,a ,,horseshoe ,,magnet #cg--;,a ,,daniell ,,cell #ch--;,a ,,gravity ,,cell #ci--,,showing ,,what ,,is ,,in ,a ,,dry ,,battery #dj--;,a ,,storage ,,battery1 ,,showing ,,the ,,grids #da--;,a ,,storage-,,battery ,,plate ,,made ,,from ,a ,,sheet ,,of ,,lead #db--,,sturgeon',s ,,electromagnet #dc--;,,an ,,electromagnet ,,with ,,many ,,turns ,,of ,,insulated ,,wire #dd--;,,an ,,electromagnet ,,lifting ,,twelve ,,tons ,,of ,,iron #de--;,a ,,dynamo ,,with ,,siemens' ,,armature #df--,,ring ,,armature #dg--;,,first ,,dynamo ,,patented ,,in ,,the ,,united ,,states #dh--;,a ,,drum ,,armature1 ,,showing ,,how ,,an ,,armature ,,of ,,four ,,coils ,,is ,,wound #di--;,a ,,series-,,wound ,,dynamo #ej--;,a ,,shunt-,,wound ,,dynamo #ea--;,a ,,compound-,,wound ,,dynamo #eb--,,one ,,of ,,edison',s ,,first ,,dynamos #ec--;,a ,,dynamo ,,mounted ,,on ,,the ,,truck ,,of ,a ,,railway ,,car #ed--;,,first ,,electric ,,locomotive #ee--;,,first ,,edison ,,electric ,,locomotive #ef--;,,edison',s ,,first ,,passenger ,,locomotive #eg--;,,first ,,commercial ,,electric ,,railway #eh--;,,edison1 ,,america',s ,,greatest ,,inventor1 ,,at ,,work ,,in ,,his ,,laboratory #ei--;,,edison',s ,,famous ,,horseshoe ,,paper-,,filament ,,lamp ,,of #fj--;,,first ,,commercial ,,edison ,,electric-,,lighting ,,plant2 ,,installed ,,on ,,the ,,steamship ,,columbia ,,in ,,may1 #fa--;,a ,,telegraph ,,sounder #fb--,,morse',s ,,first ,,telegraph ,,instrument #fc--;,a ,,telegraphic ,,circuit ,,with ,,relay ,,and ,,sounder #fd--;,a ,,simple ,,telegraphic ,,circuit #fe--;,,first ,,telegraph ,,instrument ,,used ,,for ,,commercial ,,work #ff--;,,how ,,two ,,messages ,,are ,,sent ,,over ,,one ,,wire ,,at ,,the ,,same ,,time #fg--;,,how ,,two ,,messages ,,are ,,sent ,,over ,,one ,,wire ,,at ,,the ,,same ,,time4 ,,bridge ,,method #fh--;,,first ,,bell ,,telephone ,,receiver ,,and ,,transmitter #fi--;,a ,,telephone ,,receiver #gj--,,two ,,receivers ,,used ,,as ,a ,,complete ,,telephone #ga--;,,carbon-,,dust ,,transmitter #gb--,,the ,,phonautograph1 ,a ,,forerunner ,,of ,,the ,,phonograph #gc--;,,edison',s ,,first ,,phonograph ,,and ,a ,,modern ,,instrument #gd to--,,the ,,four-,,cycle ,,gas-,,engine #gh--,,two-,,cycle ,,gas-,,engine4 ,,crank ,,and ,,connecting-,,rod ,,are ,,enclosed ,,with ,,the ,,piston #gi--,,selden ,,explosion ,,buggy1 ,,forerunner ,,of ,,the ,,modern ,,automobile #hj--,,some ,,early ,,locomotives #ha--;,,how ,a ,,locomotive ,,works #hb--;,,hero',s ,,engine #hc--;,,an ,,undershot ,,water-,,wheel ,,with ,,curved ,,blades #hd--;,,an ,,overshot ,,water-,,wheel #he--;,,de ,,laval ,,steam-,,turbine #hf--;,a ,,modern ,,steam-,,turbine ,,with ,,top ,,casing ,,raised ,,showing ,,blades #hg--;,,diagram ,,of ,,turbine ,,shown ,,in ,,fig4 #hh--;,a ,,steam-,,turbine ,,that ,,runs ,a ,,dynamo ,,generating #ad1jjj ,,electrical ,,horse-,,power #hi--;,,british ,,army ,,air-,,ship ,,nulli ,,secundus ,,ready ,,for ,,flight #ij--;,,basket1 ,,motor1 ,,and ,,propeller ,,of ,,the ,,british ,,army ,,air-,,ship ,,nulli ,,secundus #ia--;,a ,,zeppelin ,,air-,,ship #ib--;,,count ,,zeppelin',s ,,deutschland1 ,,the ,,first ,,air-,,ship ,,in ,,regular ,,passenger ,,service #ic--,,the ,,baldwin ,,air-,,ship ,,used ,,in ,,the ,,united ,,states ,,army #id--;,,in ,,full ,,flight #ie--,,wright ,,air-,,ship ,,in ,,flight #if--;,,how ,,the ,,wright ,,air-,,ship ,,is ,,kept ,,afloat #ig--,,the ,,seat ,,and ,,motor ,,of ,,the ,,wright ,,aeroplane #ih--,,the ,,bl,,riot ,,monoplane #ii--,,the ,,plunger #ajj--,u4 ,s4 ,,submarine ,,shark ,,ready ,,for ,a ,,dive #aja--;,,first ,,submarine ,,constructed ,,in ,,the ,,united ,,states4 ,,it ,,went ,,to ,,the ,,bottom ,,with ,,seven ,,men1 ,,who ,,were ,,drowned #ajb--;,,how ,,men ,,in ,a ,,submarine ,,see ,,when ,,under ,,the ,,water #ajc--;,a ,,top ,,that ,,spins ,,on ,a ,,string #ajd--;,a ,,car ,,that ,,runs ,,on ,,one ,,rail #aje--,,manufacturing ,,diamonds--,,first ,,operation #ajf--,,manufacturing ,,diamonds--,,second ,,operation #ajg--,,manufacturing ,,diamonds--,,third ,,operation #ajh--,,marconi ,,and ,,his ,,wireless-,,telegraph ,,sending ,,and ,,receiving ,,instruments #aji--;,,diagram ,,of ,,wireless-,,telegraph ,,sending ,,apparatus #aaj--;,,diagram ,,of ,,marconi ,,wireless-,,telegraph ,,receiving ,,apparatus #aaa--,,receiver ,,of ,,bell',s ,,photophone #aab--;,a ,,gas ,,flame ,,is ,,sensitive ,,to ,,electric ,,waves #aac--;,,captain ,,ingersoll ,,on ,,board ,,the ,u4 ,s4 ,,battle-,,ship ,,connecticut ,,using ,,the ,,wireless ,,telephone #aad--;,,incandescent ,,electric ,,lamp ,,lighted ,,though ,,not ,,connected ,,to ,,any ,,battery ,,or ,,dynamo #aae--;,,an ,,electric ,,discharge ,,at ,a ,,pressure ,,of #ab1jjj1jjj ,,volts1 ,a ,,current ,,of #hjj ,,amperes ,,in ,,the ,,secondary ,,coil #aaf--;,,an ,,electric ,,discharge ,,sixty-,,five ,,feet ,,in ,,length #aag--;,a ,,physician ,,examining ,,the ,,bones ,,of ,,the ,,arm ,,by ,,means ,,of ,x-,,rays #aah--,x-,,ray ,,photograph ,,of ,,the ,,eye #aai--,,photograph ,,made ,,with ,,radium ,,introductory ,,note ,great inventions are a never-failing source of interest to all of us1 and particularly to the boy in his teens4 ,the dynamo1 the electric motor1 the telegraph1 with and without wires1 the telephone1 air-ships1 and many other inventions excite in him an interest which is deeper than mere curiosity4 ,he wants to know how these things work1 and how they were invented4 ,the man is so absorbed in the present that he cares little for the past4 ,not so with the boy4 ,he cares for the history of inventions1 and in this he is wiser than the man1 for it is only by a study of its origin and growth that we can understand the larger significance of a great invention4 ,great inventions have their origin in great discoveries4 ,the story of great inventions1 therefore1 includes the story of the discoveries out of which they have arisen4 ,the stories of the discoveries and the inventions are inseparable from the lives of the men who made them1 and so we must deal with biography1 which in itself is of interest to the boy4 ,such a story is the story of physical science in the service of humanity4 ,the interest of the youth in great inventions is unquestioned4 ,shall we stifle this interest by overemphasis of technical detail1 or shall we minister to it as a thing vital in the life of the youth of to-day8 ,a few sentences quoted from ,g4 ,stanley ,hall will indicate the author's point of view4 ,the youth is in the humanist stage4 ,nature is sentiment before it becomes idea or formula or utility4 ,the heroes and history epochs of each branch of science add another needed quality to the still so largely humanistic stage4 ,a new discovery1 besides its technical record1 involves the added duty of concise and lucid popular statement as a tribute to youth4 ,the need of a concise and lucid popular statement of the rise of the great inventions which form the material basis of our modern civilization and all of which are new to the young mind1 has no doubt been keenly felt by others as it has been by the author4 ,the story of our great inventions has been told in sundry volumes for adult readers1 but nowhere has this story1 alive with human interest1 been told in a form suited to the young4 ,it was the realization of this need growing out of years of experience in teaching these branches that led the author to attempt the task of writing the story4 ,the purpose of this book is to tell in simple language how our great inventions came into being1 to depict the life-struggles of the men who made them1 and1 in the telling of the story1 to explain the working of the inventions in a way the boy can understand4 ,the stories which are here woven together present the great epochs in the history of physics1 and are intended to give to the young reader a connected view of the way in which our great inventions have arisen out of scientific discovery on the one hand1 and conditions which we may call social and economic on the other hand4 ,if the book shall appeal to young readers1 and lead them to an appreciation of the meaning of a great invention1 the author will feel that his purpose has been achieved4 ,the author is deeply indebted to ,dr4 ,charles ,a4 ,mc,murry and ,prof4 ,newell ,d4 ,gilbert1 of the ,northern ,illinois ,state ,normal ,school2 ,profs4 ,c4 ,r4 ,mann and ,r4 ,a4 ,millikan1 of the ,university of ,chicago2 and ,prof4 ,john ,f4 ,woodhull1 of ,columbia ,university1 for reading the manuscript and offering valuable suggestions4 ,acknowledgment is further made here of valuable aid in collecting material for illustrations and letter-press4 ,such acknowledgment is due to ,prof4 ,a4 ,gray1 ,university of ,glasgow2 ,prof4 ,antonio ,favaro1 ,royal ,university of ,padua2 ,prof4 ,a4 ,zammarchi1 ,brescia1 ,italy2 ,mr4 ,nikola ,tesla2 the ,royal ,institution1 ,london2 ,mc,clure's ,magazine2 ,the ,technical ,world ,magazine2 ,the ,scientific ,american2 the ,ellsworth ,company2 ,commonwealth-,edison ,company2 ,association of ,edison ,illuminating ,companies2 ,electric ,controller and ,supply ,company2 ,kelley-,koett ,manufacturing ,company2 ,watson-,stillman ,company2 ,gould ,storage ,battery ,company2 ,thordarson ,electric ,company2 the ,westinghouse ,machine ,company2 ,marconi ,wireless ,telegraph ,company of ,america1 and the ,siemens-,schuckert ,werke1 ,berlin4 ,the drawings illustrating ,faraday's experiments are from exact reproductions of ,faraday's apparatus1 made by ,mr4 ,joseph ,g4 ,branch1 author of ,conversations on ,electricity1 and are reproduced by his kind permission4 ,e4 ,e4 ,b4 ,,chicago1 ,june1 #aiaj4 ,,the ,,story ,,of ,,great ,,inventions ,chapter ,i ,,the ,,age ,,of ,,archimedes ,archimedes1 the ,first ,great ,inventor ,archimedes1 the first great inventor1 lived in ,syracuse more than two thousand years ago4 ,syracuse was a ,greek city on the island of ,sicily4 ,the ,king of ,syracuse1 ,hiero1 took great interest in the discoveries of ,archimedes4 ,one day ,archimedes said to ,king ,hiero that with his own strength he could move any weight whatever4 ,he even said that1 if there were another earth to which he could go1 he could move this earth wherever he pleased4 ,the ,king1 full of wonder1 begged of him to prove the truth of his statement by moving some very heavy weight4 ,whereupon ,archimedes caused one of the ,king's galleys to be drawn ashore4 ,this required many hands and much labor4 ,having manned the ship and put on board her usual loading1 he placed himself at a distance and easily moved with his hand the end of a machine which consisted of a variety of ropes and pulleys1 drawing the ship over the sand in as smooth and gentle a manner as if she had been under sail4 ,the ,king1 quite astonished1 prevailed with ,archimedes to make for him all manner of machines which could be used either for attack or defence in a siege4 ,the ,battle of ,syracuse ,during the life of ,king ,hiero ,syracuse had no occasion to use the war machines of ,archimedes4 ,the grandson of ,king ,hiero1 who succeeded to the throne1 was a tyrant4 ,he attempted to throw off the sovereignty of ,rome and entered into an alliance with ,carthage4 ,his cruelty toward his own people was so great that1 after a short reign1 he was assassinated4 ,there was anarchy in ,syracuse for a time1 the ,roman and anti-,roman parties striving for supremacy4 ,the anti-,roman party gaining possession of the city1 the ,romans1 in order to bring ,syracuse again into subjection1 prepared for an attack by sea and land4 ,then it was that ,syracuse had need of the war machines made by ,archimedes 7,fig4 #a74 ,illustration3 ,,fig4 #a--,,the ,,battle ,,of ,,syracuse ,the city defended by the inventions of ,archimedes4 ,the ,romans came with a large land force and a fleet4 ,they were sure that within five days they could conquer the city4 ,but there are times when one man with brains is worth more than an army4 ,in the battle which followed1 ,archimedes with his inventions was more than a match for the ,romans4 ,the city was strong from the fact that the wall on one side lay along a chain of hills with overhanging brows2 on the other side the wall had its foundation close down by the sea4 ,a fleet of sixty ships commanded by ,marcellus bore down upon the city4 ,the ships were full of men armed with bows and slings and javelins with which to dislodge the men who fought on the battlements4 ,eight ships had been fastened together in pairs4 ,these double vessels were rowed by the outer oars of each of the pair4 ,on each pair of ships was a ladder four feet wide and of a height to reach to the top of the wall4 ,each side of the ladder was protected by a railing1 and a small roof-like covering1 called a penthouse1 was fastened to the upper end of the ladder4 ,this covering served to protect the soldiers until they could reach the top of the wall4 ,they thought to bring these double ships close to shore1 raise the ladders by ropes and pulleys until they rested against the wall1 then scale the wall and capture the city4 ,but ,archimedes had crossbows ready1 and1 when the ships were still at some distance1 he shot stones and darts at the enemy1 wounding and greatly annoying them4 ,when these began to carry over their heads1 he used smaller crossbows of shorter range1 so that stones and darts fell constantly in their midst4 ,by this means he checked their advance1 and finally ,marcellus1 in despair1 was obliged to bring up his ships under cover of night4 ,but when they had come close to land1 and so too near to be hit by the crossbows1 they found that ,archimedes had another contrivance ready4 ,he had pierced the wall as high as a man's head with many loopholes which on the outside were about as big as the palm of the hand4 ,inside the wall he had stationed archers and men with crossbows to shoot down the marines4 ,by these means he not only baffled the enemy1 but killed the greater number of them4 ,when they tried to use their ladders1 they discovered that he had cranes ready all along the walls1 not visible at other times but which suddenly reared themselves above the wall from the inside and stretched their beams far over the battlements1 some of them carrying stones weighing about five hundred pounds1 and others great masses of lead4 ,so1 whenever the ships came near1 these beams swung round on their pivots and by means of a rope running through a pulley dropped the stones upon the ships4 ,the result was that they not only smashed the ships to pieces1 but killed many of the soldiers on board4 ,another machine made by ,archimedes was an iron hand or grappling-hook swung on a chain and carried by a crane4 ,the hook was dropped on the prow of a ship1 and when it had taken hold the ship was lifted until it stood on its stern1 then quickly dropped1 causing it either to sink or ship a great quantity of water4 ,with such machines1 unknown before1 ,archimedes drove back the enemy4 ,on the landward side similar machines were used4 ,the ,romans were reduced to such a state of terror that if they saw but a rope or a stick put over the walls they cried out that ,archimedes was levelling some machine at them and turned their backs and fled4 ,after a long siege1 however1 hunger forced the ,syracusans to surrender4 ,marcellus so admired the genius of ,archimedes that he gave orders that he should not be injured4 ,yet1 in the sack of the city which followed1 ,archimedes was slain by a ,roman soldier4 ,the ,roman historian ,livy records that ,archimedes1 while intent on some figures which he had made in the dust1 although the confusion was as great as could possibly be1 was put to death by a soldier who did not know who he was2 that ,marcellus was greatly grieved at this1 and that pains were taken about his funeral1 while his relations also were carefully sought and received honor and protection on account of his name and memory4 ,archimedes' ,principle ,hiero1 when he became ,king of ,syracuse1 decreed that a crown of gold1 of great value1 should be placed in a certain temple as an offering to the gods1 and sent to a manufacturer the correct weight of gold4 ,in due time the crown was brought to the ,king1 and a beautiful piece of work it was4 ,the weight of the crown was the same as that of the gold1 but a report was circulated that some of the gold had been taken out and silver supplied in its place4 ,hiero was angry1 but knew no method by which the theft might be detected4 ,he therefore requested ,archimedes to give the matter his attention4 ,while trying to solve this problem ,archimedes went one day to a bath4 ,as he got into the bath-tub he saw that as his body became immersed the water ran out of the tub4 ,he quickly saw how he could solve the problem1 leaped out of the bath in joy1 and1 running home naked1 cried out with a loud voice ,eureka6 eureka6 7,i have found it6 ,i have found it67 ,using a piece of gold and a piece of silver1 each equal in weight to the crown1 and a large vase full of water1 he proved that the crown was not pure gold1 and found how much silver had been mixed with the gold4 ,the incident of the golden crown may have been the starting-point of ,archimedes' study of solid bodies when immersed in fluids4 ,every one knows that a boy can lift a heavy stone under water that he could not lift out of water4 ,the stone seems lighter when in the water4 ,a diver with his lead-soled shoes could scarcely walk on land1 but walks easily under water4 ,when the diver comes up1 the place where he was immediately becomes filled with water4 ,now1 whatever that water weighs which fills the diver's place1 just that much weight will the diver lose when he goes down4 ,what is true of the diver is true of the stone or of any object under water4 ,the stone when in the water loses just as much weight as the weight of the water that would fill its place4 ,this is the fact which was discovered by ,archimedes and which is called ,archimedes' ,principle4 ,it is said by an ancient author that ,archimedes invented more than forty machines4 ,of these the best known are the block and tackle1 the endless screw 7worm gear71 and the water snail1 or ,archimedean screw4 ,yet his delight was not in his machines1 but in his mathematics4 ,though he had invented machines to please his king1 he regarded such work as trifling1 and took little interest in the common needs of life4 ,inventions of the ,ancient ,greeks ,the common needs of life are to-day the chief concern of the greatest men1 and so we find it hard to sympathize with this view of ,archimedes4 ,his view1 however1 was that of other learned men of his time1 that the common needs of life are beneath the dignity of the scholar1 and so we can see why the ,greeks made so few great inventions4 ,hero1 who lived a century later than ,archimedes1 invented a steam-engine1 which1 however1 was only a toy4 ,a water-clock1 in which the first cog-wheels were used1 was invented by another ,greek named ,ktesibus1 who also invented the force-pump4 ,the suction-pump was known in the time of ,aristotle1 who lived about a century before the time of ,archimedes1 but the inventor is unknown4 ,concerning electricity1 the ,greeks knew very little4 ,they knew that amber when rubbed will attract light objects1 such as dust or chaff4 ,amber was called by the ,greeks electron1 because it reflected the brightness of the sunlight1 and their name for the sun was ,elector4 ,from the ,greek name for amber we get our word electricity4 ,the ,greeks possessed scarcely more knowledge of magnets than of electricity4 ,in fact1 their ideas of magnets cannot be called knowledge1 for they consisted chiefly of legends4 ,they told of the shepherd ,magnes1 who1 while watching his flock on ,mount ,ida1 suddenly found the iron ferrule of his staff and the nails of his shoes adhering to a stone2 that1 later1 this stone was called1 after him1 the ,magnes stone1 or ,magnet4 ,they told impossible stories of iron statues being suspended in the air by means of magnets1 and of ships sailing near the magnetic mountains when every nail and piece of iron in the ship would fly to the mountain1 leaving the ship a wreck upon the waves4 ,chapter ,,ii ,,the ,,age ,,of ,,galileo ,galileo and the ,battle for ,truth ,for eighteen centuries after the time of ,archimedes no inventions of importance were made4 ,men sought for truth where truth could not be found4 ,they looked within their mouldy manuscripts and asked1 ,what do the great philosophers say ought to happen8 instead of looking at nature and asking1 ,what does happen8 ,and when a man arose who dared to doubt the authority of the old masters and turn to nature to find out the truth1 all the weapons at the command of the old school were hurled against him4 ,let us1 at this distance1 blame neither the one side nor the other4 ,the conflict was inevitable4 ,it was an accident of history that the brunt of the attack fell upon a man born in ,italy in #aefd1 and that the battle was fought chiefly in the ,eternal ,city1 from which centuries before had marched the legions that conquered the world4 ,the boy1 ,galileo1 who was to become the central figure of the great conflict1 was talented in many ways4 ,in lute-playing his skill excelled that of his father1 who was one of the noted musicians of his day4 ,his skill in drawing was such that noted artists submitted their work to him for criticism4 ,he wrote essays on the works of ,dante and other classical writers4 ,he amused his boy companions by constructing toy machines which1 though ingenious1 did not always work4 ,his preference was for mechanics1 but1 as this subject offered little prospect of profitable work1 he took up the study of medicine in accordance with his father's wishes4 ,in his eighteenth year he entered the ,university of ,pisa4 ,here he found men who refused to think for themselves1 but decided every question by referring to what the ancient philosophers said4 ,galileo could not endure such slavish submission to authority4 ,so strongly did he assert himself that he was nicknamed ,the ,wrangler1 and1 by his wrangling1 he lost a scholarship in the university4 ,he neglected his medical studies and secretly studied mathematics4 ,his father1 learning of this1 consented to his becoming a mathematician4 ,thus he followed his bent1 though it seemed to lead directly to poverty4 ,the ,pendulum ,clock ,it was while a student at the ,university of ,pisa that he discovered a law of pendulums which makes possible our pendulum clocks4 ,while at his devotions in the cathedral1 he observed the swinging of the bronze lamp which had been drawn back for lighting4 ,timing its swinging by means of his pulse1 the only timepiece in his possession1 he found that the time of one swing remained the same1 though the length of the swing grew smaller and smaller4 ,this discovery led to his invention of an instrument for physicians' use in timing the pulse4 ,about fifty years later he invented the pendulum clock 7,fig4 #b74 ,illustration3 ,,fig4 #b--;,,galileo',s ,,pendulum ,,clock ,it had only one hand1 which is not shown in the picture4 ,lack of funds compelled him to leave the university without completing his course4 ,he returned to the parental roof and continued his scientific studies4 ,the writings of ,archimedes were his favorite study4 ,with ,archimedes' famous experiment on ,king ,hiero's crown as a starting-point1 he discovered the laws of floating bodies1 which explain why a ship or other object floats on water1 and invented a balance for weighing objects in water4 ,but such employment won nothing more substantial than honor and fame4 ,food and clothing were needed4 ,for two years he strove without success to secure employment4 ,at the end of that time he was appointed professor of mathematics in the ,university of ,pisa at the magnificent salary of sixty scudi 7about sixty-three dollars7 per year4 ,but any port in a storm2 and in ,galileo's needy circumstances even this wretched salary was not to be rejected4 ,moreover1 he could add somewhat to his income by private tutoring4 ,galileo's ,experiment with ,falling ,shot ,while teaching at the ,university of ,pisa1 he performed his famous experiment of dropping from the top of the leaning tower two shot1 one weighing ten pounds1 the other one pound4 ,now1 according to ,aristotle1 the ten-pound shot should fall in one-tenth the time required by the one-pound shot4 ,but the assembled company of professors and students saw the two shot start together1 fall together1 and strike the ground at the same instant1 and still refused to believe their own eyes4 ,they continued to affirm that a weight of ten pounds would reach the ground in a tenth of the time taken by a one-pound weight1 because they were able to quote chapter and verse in which ,aristotle assured them that such is the fact4 ,thus ,galileo made enemies of the other professors1 but for a time they could do nothing more than annoy him4 ,about this time ,galileo incurred the wrath of the ,grand ,duke of ,tuscany1 from whom he had received his appointment4 ,he was commissioned to examine a machine invented by a nephew of the ,grand ,duke for the purpose of cleaning harbors4 ,galileo plainly said that the machine was worthless4 ,it was tried1 and his opinion proved true4 ,but like the kings of olden time who killed the bearer of evil tidings even though the tidings were true1 his enemies made his position so unpleasant that he resigned4 ,he had neither employment nor money4 ,his father's death occurring about this time1 threw upon him the care of a mother1 a worthless brother1 and two sisters4 ,in his distress he sought help from a friend1 and secured an appointment as professor of mathematics in the ,university of ,padua4 ,his salary was one hundred and eighty florins 7about ninety-five dollars71 while other professors received more than ten times as much4 ,while at ,padua1 ,galileo was busy inventing4 ,he invented the sector1 which is to be found in most cases of mathematical instruments and is used in certain kinds of drawing4 ,he also invented an air thermometer 7,fig4 #c71 the first instrument for measuring temperature4 ,illustration3 ,,fig4 #c--;,,an ,,air ,,thermometer ,when the air in the bulb grows cooler it contracts1 and the air outside forces the ,water up the tube4 ,when the air in the bulb grows warmer it expands and forces the water down in the tube4 ,in #afjd there appeared a new star of great brilliancy4 ,it continued to shine with varying brightness for eighteen months1 and then vanished4 ,this was a strange event1 and ,galileo made use of it4 ,he proved that the new star must lie among the most distant of the heavenly bodies1 and this fact did not agree with ,aristotle's view that the heavens are perfect1 and therefore never change4 ,a heated controversy followed1 and ,galileo came out boldly in favor of the theory that the earth revolves about the sun1 the prevailing notion then being that the earth does not move1 but that the sun and other heavenly bodies revolve around it4 ,the ,telescope ,in #afji ,galileo learned of a discovery that was to be of great value to the world1 but a source of untold trouble to himself4 ,an apprentice of a ,dutch optician1 while playing with spectacle lenses1 chanced to observe that if two of the lenses were placed in a certain position objects seen through them appeared much nearer4 ,galileo1 learning of this1 set to work to construct a spy-glass1 applying his knowledge of light4 ,in one day he had constructed such an instrument1 in which he used two lenses like the lenses of the modern opera-glass4 ,thus1 while the ,dutchman's discovery was by accident1 ,galileo's was by reasoning1 and was the more fruitful1 as we shall see4 ,galileo continued improving his telescope until he had made one which would magnify thirty times4 ,he was the first to apply the telescope to the study of the heavenly bodies4 ,the most startling of his discoveries was that of the moons of the planet ,jupiter1 which he called new planets4 ,this aroused the fury of his enemies1 who ridiculed the idea of there being new planets2 for1 they said1 to see these planets they must first be put inside the telescope4 ,the excitement was intense4 ,poets chanted the praise of ,galileo4 ,a public fte was held in his honor4 ,one of his pupils was imprisoned in the tower of ,san ,marco1 where he had gone to make observations with his telescope1 and could not escape until the crowd had satisfied their curiosity4 ,some of the philosophers refused to look lest they should see and be convinced4 ,galileo's ,struggle ,his enemies sought to steal from him the honor of his discoveries4 ,some claimed to have made the discoveries before ,galileo did4 ,others claimed that his discoveries were false1 that their only use was to gratify ,galileo's vanity and thirst for gold4 ,in these trying times the friendship of the great astronomer ,kepler warded off some of the most exasperating attacks4 ,galileo's fame spread throughout ,europe4 ,students came in great numbers1 so that he had little leisure left for his own studies4 ,he therefore decided to leave ,padua1 and secured an appointment as mathematician and philosopher to the ,grand ,duke of ,tuscany4 ,this appointment took him to ,florence4 ,it was here that an incident occurred that marked the beginning of a persecution which continued to the end of his life4 ,as we read the story of this conflict let us remember that it was not primarily a conflict between the ,roman ,catholic ,church and ,galileo4 ,it was a conflict of principles4 ,on the one side were arrayed those who said that men should always believe as the ancient writers did2 on the other1 those who said men should think for themselves4 ,in the first party were most of the university professors and others who dreaded the introduction of new beliefs1 whether in religion or science4 ,in the second party were ,galileo and a small band of devoted followers4 ,at a dinner at the table of the ,grand ,duke in ,pisa the conversation turned on the moons of ,jupiter4 ,some praised ,galileo4 ,others condemned him1 saying that the ,holy ,scriptures were opposed to his theory of the motion of the earth4 ,a friend reported the incident to ,galileo1 and he replied to the arguments of his opponents in a letter which was made public4 ,no doubt the sting of his sarcasm made his enemies more bitter4 ,he admitted that the ,scriptures cannot lie or err1 but this1 he said1 does not hold good of those who attempt to explain the ,scriptures4 ,in another letter1 he quoted with approval a saying of ,cardinal ,baronius1 ,the ,holy ,spirit intended to teach us in the ,bible how to go to ,heaven1 not how the heavens go4 ,the first shot had been fired4 ,the battle was on1 and the ,church1 because it possessed the most powerful weapons of attack1 was used by the combined forces to break the power of ,galileo's reasoning4 ,he went to ,rome to make his defence1 but was commanded by the ,holy ,office not to hold or teach that the sun is immovable1 and that the earth moves about the sun4 ,during another visit to ,rome there was shown to ,galileo an instrument which1 it was said1 would show a flea as large as a cricket4 ,galileo recalled that some years before he had so arranged a telescope that he had seen flies which he said looked as big as a lamb1 and were covered all over with hair4 ,this was the first microscope4 ,galileo quickly improved the instrument1 and soon his microscopes were in great demand4 ,in violation of the decree of the ,church1 to which he had submitted1 he published his most famous work in which he defended the theory that the earth moves about the sun4 ,the book was the outcome of his life-work1 but the ,church believed it dangerous4 ,he was summoned to ,rome4 ,confined to a sick-bed1 he pleaded for delay1 which was granted4 ,before he recovered1 however1 the summons was made imperative4 ,he must go to ,rome1 or be carried in irons4 ,he went in a litter1 carried by servants of the ,grand ,duke4 ,in ,rome he was to appear before the ,inquisition4 ,there he was treated with a consideration never before accorded to a prisoner of the ,inquisition4 ,nor was he subjected to torture1 as has been stated by some4 ,he was found guilty of teaching the doctrine that the sun does not move1 and that the earth moves about the sun4 ,he was compelled to recant1 and sentenced to the prison of the ,holy ,office and1 by way of penance1 to repeat once a week for three years the seven penitential ,psalms4 ,he yielded without reserve to the decree of the ,inquisition1 renounced his errors and heresies1 and1 with his hand on the ,bible1 took oath never again to teach the forbidden doctrine4 ,and now1 though a shattered old man of seventy-four1 enjoined to silence on the chief results of his life-work1 nothing could quench his devotion to science4 ,in these last years1 he published a new book which1 with his earlier work1 entitles him to be regarded as the founder of the science of mechanics4 ,in his study of machines ,galileo found that no machine will do work of itself4 ,whenever a machine is at work1 a man or a horse1 or some other power1 is at work upon the machine4 ,in no case will a machine do work without receiving an equal amount of work4 ,torricelli and the ,barometer ,galileo had a pump which he found would not work when the water was thirty-five feet below the valve4 ,he thought the pump was injured1 and sent for the maker4 ,the maker assured him that no pump would do better4 ,this led ,torricelli1 one of ,galileo's pupils1 to the discovery of the barometer4 ,men had said that water rises in a pump because nature abhors a vacuum4 ,torricelli believed that air-pressure and not nature's horror of a vacuum is the cause of water rising in a pump4 ,he invented the barometer to measure air-pressure4 ,the first barometer was a glass tube filled with quick-silver or mercury 7,fig4 #d74 ,the tube was closed at the upper end1 and the lower end1 which was open1 dipped in a dish of mercury4 ,he allowed the tube to stand1 and saw that the height of the mercury changed4 ,this he believed was because the air-pressure changed4 ,wind1 ,torricelli said1 is caused by a difference of air-pressure1 which is due to unequal heating of the air4 ,for this reason a cool breeze blows from the mountain top to the heated valley1 or from sea to land on a summer day4 ,illustration3 ,,fig4 #d--,,torricelli',s ,,experiment ,otto ,von ,guericke and the ,air-,pump ,about this time a ,german burgomaster1 ,otto von ,guericke1 of ,magdeburg1 was performing experiments on air-pressure4 ,the ,thirty ,years' ,war had been raging for thirteen years4 ,the ,swedish ,king1 ,gustavus ,adolphus1 had landed in ,germany1 and was winning victory after victory over the imperial troops4 ,magdeburg had entered into an alliance with the ,swedish ,king1 by which he was granted free passage through the city1 while1 on the other hand1 he promised protection to the city4 ,the imperial army under ,tilly and ,pappenheim laid siege to the city4 ,on the one side there was hope that ,gustavus would arrive in time to effect a rescue2 on the other1 a determination to conquer before such aid could arrive4 ,while ,gustavus was on his way to the rescue1 ,magdeburg was taken by storm1 and the most horrible scene of the ,thirty ,years' ,war was enacted4 ,tilly gave up the city to plunder1 and his soldiers without mercy killed men1 women1 and children4 ,in the midst of the scene of carnage the city was set on fire1 and soon the horrors of fire were added to the horrors of the sword4 ,in less than twelve hours twenty thousand people perished4 ,guericke's house and family were saved1 but the sufferings of the city were not yet ended4 ,in five years the enemy was again before the walls1 and ,magdeburg1 then in the possession of the ,swedes1 was compelled to yield to the combined ,saxon and imperial troops4 ,guericke entered the service of ,saxony1 and was again made mayor of the city4 ,in the midst of these scenes of war1 he found time to continue his studies4 ,he made the first air-pump1 and with it performed experiments which led to some very important results4 ,the experiments which ,guericke made with his air-pump aroused the attention of the princes1 and especially ,emperor ,ferdinand4 ,guericke was called to perform his experiments before the ,emperor4 ,the most striking of these experiments he performed with two hollow copper hemispheres about a foot in diameter1 fitted closely together4 ,when the air was pumped out1 sixteen horses were barely able to pull the hemispheres apart1 though1 when air was admitted1 they fell apart of their own weight4 ,another experiment which astonished his audience was performed with the cylinder of a large pump 7,fig4 #e74 ,a rope was tied to the piston4 ,this rope was passed over a pulley1 and a large number of men applied their strength to the rope to hold the piston in place4 ,when the air was taken out of the cylinder1 the piston was forced down by air-pressure1 and the men were lifted violently from the ground4 ,this experiment1 as we shall see1 was of great importance in the invention of the steam-engine4 ,illustration3 ,,fig4 #e--;,,guericke',s ,,air-,,pump ,men lifted from the ground by air-pressure4 ,guericke's study of air-pressure led him to make a water barometer 7,fig4 #f74 ,this consisted of a glass tube about thirty feet long dipping into a dish of water4 ,the tube was filled with water1 and the top projected above the roof of the house4 ,on the water in the tube he placed a wooden image of a man4 ,in fair weather the image would be seen above the housetop4 ,on the approach of a storm the image would drop out of sight4 ,this led his superstitious neighbors to accuse him of being in league with ,satan4 ,illustration3 ,,fig4 #f--;,,guericke',s ,,water ,,barometer ,in fair weather the image appeared above the housetop4 ,when a storm was approaching the image dropped below the roof into the house4 ,the first electrical machine was made by ,guericke4 ,this was simply a globe of sulphur turning on a wooden axle4 ,he observed that when the dry hand was held against the revolving globe1 the globe would attract bits of paper and other light objects4 ,robert ,boyle and the ,pressure of ,air and ,steam ,robert ,boyle1 in ,england1 improved the air-pump and performed many new and interesting experiments with it4 ,one of his experiments was to make water boil by means of an air-pump without applying heat4 ,it is now well known that water when boiling on a high mountain is not so hot as when boiling down in the valley4 ,this is because the air-pressure is less on the mountain top than in the valley4 ,by using an air-pump to remove the air-pressure1 water may be made to boil when it is still quite cold to the hand4 ,boyle compared the action of air under pressure to a steel spring4 ,the spring of the air is evident to us in the pneumatic tire of the bicycle or automobile4 ,boyle found that the more air is compressed the greater is its pressure or spring1 and that steam as it expands exerts less and less pressure4 ,this is important in the steam-engine4 ,pascal and the ,hydraulic ,press ,it was ,blaise ,pascal1 a ,frenchman1 who proved beyond the possibility of a doubt that air-pressure supports the mercury in a barometer1 and lifts the water in a pump 7,fig4 #g74 ,he had two mercury barometers exactly alike set up at the foot of a mountain4 ,the mercury stood at the same height in each4 ,then one barometer was left at the foot of the mountain1 and the other was carried to the summit1 about three thousand feet high4 ,the mercury in the second barometer then stood more than three inches lower than at first4 ,as the barometer was carried down the mountain the mercury slowly rose until1 at the foot1 it stood at the same height as at first4 ,the party stopped about half-way down the mountain1 allowing the barometer to rest there for some time1 and observing it carefully4 ,they found that the mercury stood about an inch and a half higher than at the foot of the mountain4 ,during all this time the height of the mercury in the barometer which had been left at the foot of the mountain did not change4 ,illustration3 ,,fig4 #g--;,a ,,lift-,,pump ,air pressing down on the water in the well causes the water to rise in the pump4 ,the air can do this only when the plunger is at work removing air or water and reducing the pressure inside the pump4 ,it is now known that when a barometer is carried up to a height of nine hundred feet1 the mercury stands an inch lower than at the earth's surface4 ,for every nine hundred feet of elevation the mercury is lowered about one inch4 ,in this way the height of a mountain can be measured1 and a man in a balloon or an air-ship can tell at what height he is sailing4 ,for this purpose1 however1 a barometer is used that is more easily carried than a mercury barometer4 ,pascal invented the hydraulic press1 a machine with which he said he could multiply pressure to any extent1 which reminds us of ,archimedes' saying that1 with his own hand1 he could move the earth if only he had a place to stand4 ,pascal could so arrange his machine that a man pressing with a force of a hundred pounds on the handle could produce a pressure of many tons4 ,in fact1 a man can so arrange this machine that he can lift any weight whatever 7,fig4 #h74 ,illustration3 ,,fig4 #h--;,a ,,simple ,,hydraulic ,,press ,a one-pound weight holds up a hundred pounds4 ,the hydraulic press has two cylinders4 ,one cylinder must be larger than the other4 ,the two cylinders are filled with a liquid1 as water or oil1 and are connected by a tube so that the liquid can flow from one cylinder into the other4 ,there is a tightly fitting piston in each cylinder4 ,if one piston has an area of one square inch1 and the other has an area of one hundred square inches1 then every pound of pressure on the small piston causes a hundred pounds of pressure on the large piston4 ,a hundred pounds on the small piston would lift a weight of ten thousand pounds on the large piston4 ,but we can see that the large piston cannot move as fast as the small one does4 ,though we can lift a very heavy weight with this machine1 we must expect this heavy weight to move slowly4 ,there must be a loss in speed to make up for the gain in the weight lifted 7,fig4 #i74 ,an hydraulic press with belt-driven pump is illustrated in ,fig4 #aj4 ,illustration3 ,,fig4 #i--;,,how ,,an ,,hydraulic ,,press ,,works ,one man with the machine can exert as much pressure as a hundred men could without the machine4 ,the arrows show the direction in which the liquid is forced by the action of the plunger p4 ,the large piston ,p is forced up1 thus compressing the paper4 ,illustration3 ,,fig4 #aj--;,,an ,,hydraulic ,,press ,,with ,,belt-,,driven ,,pump ,newton ,sir ,isaac ,newton as a boy did not show any unusual talent4 ,in school he was backward and inattentive for a number of years1 until one day the boy above him in class gave him a kick in the stomach4 ,this roused him and1 to avenge the insult1 he applied himself to study and quickly passed above his offending classmate4 ,his strong spirit was aroused1 and he soon took up his position at the head of his class4 ,it was his delight to invent amusements for his classmates4 ,he made paper kites1 and carefully thought out the best shape for a kite and the number of points to which to attach the string4 ,he would attach paper lanterns to these kites and fly them on dark nights1 to the delight of his companions and the dismay of the superstitious country people1 who mistook them for comets portending some great calamity4 ,he made a toy mill to be run by a mouse1 which he called the miller2 a mechanical carriage1 run by a handle worked by the person inside1 a water-clock1 the hand of which was turned by a piece of wood which fell or rose by the action of dropping water4 ,at the age of fifteen1 his mother1 then a widow1 removed him from school to take charge of the family estate4 ,but the farm was not to his liking4 ,the sheep went astray1 and the cattle trod down the corn while he was perusing a book or working with some machine of his own construction4 ,his mother wisely permitted him to return to school4 ,after completing the course in the village school he entered ,trinity ,college1 ,cambridge4 ,gravitation ,it was in the year following his graduation from ,cambridge that he made his greatest discovery--that of the law of gravitation4 ,a plague had broken out in ,cambridge1 to escape which ,newton had retired to his estate at ,woolsthorpe4 ,here he was sitting one day alone in the garden thinking of the wonderful power which causes all bodies to fall toward the earth4 ,the same power1 he thought1 which causes an apple to fall to the ground causes bodies to fall on the tops of the highest mountains and in the deepest mines4 ,may it not extend farther than the tops of the mountains8 ,may it not extend even as far as the moon8 ,and1 if it does1 is not this power alone able to hold the moon in its orbit1 as it bends into a curve a stone thrown from the hand8 ,there followed a long calculation requiring years to complete4 ,seeing that the results were likely to prove his theory of gravitation1 he was so overcome that he could not finish the work4 ,when this was done by one of his friends1 it was found that ,newton's thought was correct--that the force of gravitation which causes bodies to fall at the earth's surface is the same as the force which holds the moon in its orbit4 ,as the earth and moon attract each other1 so every star and planet attracts every other star and planet1 and this attraction is gravitation4 ,colors in ,sunlight ,about the same time that he made his first discoveries regarding gravitation1 he took up the study of light with a view to improving the construction of telescopes4 ,his first experiment was to admit sunlight into a darkened room through a circular hole in the shutter1 and allow this beam of light to pass through a glass prism to a white screen beyond4 ,he expected to see a round spot of light1 but to his surprise the light was drawn out into a band of brilliant colors4 ,he found that the light which comes from the sun is not a simple thing1 but is composed of colors1 and these colors were separated by the glass prism4 ,in the same way the colors of sunlight are separated by raindrops to form a rainbow4 ,the colors may be again mingled together by passing them through a second prism4 ,they will then form a white light4 ,suppose that the light of the sun were not composed of different colors1 that all parts of white light were alike1 then there would be no colors in nature4 ,all the trees and flowers would have a dull1 leaden hue1 and the human countenance would have the appearance of a pencil-sketch or a photographic picture4 ,the rainbow itself would dwindle into a narrow arch of white light2 the sun would shine through a gray sky1 and the beauty of the setting sun would be replaced by the gray of twilight 7,fig4 #aa74 ,illustration3 ,,fig4 #aa--,,newton',s ,,experiment ,,with ,,the ,,prism ,sunlight separated into the colors of the rainbow4 ,the seven colors are3 violet1 indigo1 blue1 green1 yellow1 orange1 red4 ,one of ,newton's inventions was a reflecting telescope--that is1 a telescope in which a curved mirror was used in place of a lens4 ,he made such a telescope only six inches long1 which would magnify forty times4 ,newton was a member of the ,convention ,parliament1 which declared ,james ,,ii4 to be no longer ,king of ,england and tendered the crown to ,william and ,mary4 ,he was made a knight by ,queen ,anne in #agje4 ,his knowledge of chemistry was used in the service of his country when he was ,master of the ,mint4 ,it was his duty to superintend the recoining of the money of ,england1 which had been debased by dishonest officials at the mint4 ,he did his work without fear or favor4 ,once a bribe of #fjjj 7#cj1jjj7 was offered him4 ,he refused it1 whereupon the agent who made the offer said to him that it came from a great duchess4 ,newton replied3 ,tell the lady that if she were here herself1 and had made me this offer1 ,i would have desired her to go out of my house2 and so ,i desire you1 or you shall be turned out4 ,although ,newton's discoveries in the world of thought were among the greatest ever made by man1 he regarded them as insignificant compared with the truth yet undiscovered4 ,he said of himself3 ,i do not know what ,i may appear to the world1 but to myself ,i seem to have been only like a boy playing on the sea-shore and diverting myself in now and then finding a smoother pebble or a prettier shell than the ordinary1 whilst the great ocean of truth lay all undiscovered before me4 ,chapter ,,iii ,,the ,,eighteenth ,,century ,james ,watt and the ,steam-,engine ,if you had visited the coal-mines of ,england and ,scotland three hundred years ago1 you might have seen women bending under baskets of coal toiling up spiral stairways leading from the depths of the mines4 ,at some of the mines horses were used4 ,a combination of windlass and pulleys made it possible for a horse to lift a heavy bucket of coal4 ,there came a time1 however1 when slow and crude methods such as these could not supply the coal as fast as it was needed4 ,the shallower mines were being exhausted4 ,the mines must be dug deeper4 ,the demand for coal was increasing4 ,the supply of coal1 it was thought1 would not last until the end of the century4 ,the wood supply was already exhausted4 ,it seemed that ,england was facing a fuel famine4 ,there was only one way out of the difficulty4 ,a machine must be invented that would do the work of the women and horses1 a machine strong enough to raise coal with speed from the deepest mines4 ,then it happened that two great inventors1 ,newcomen and ,watt1 arose to produce the machine that was needed4 ,when the world needs an invention it seldom fails to appear4 ,it is true of the world1 as of an individual1 that ,necessity is the mother of invention4 ,in the mean time ,torricelli had performed his famous barometer experiment1 and ,otto von ,guericke had astonished princes with proofs of the pressure of the air4 ,there was no apparent connection between these experiments and the art of coal-mining1 yet these discoveries made possible the steam-engine which was to revolutionize first the coal-mining industry and1 later1 the entire industrial world4 ,the ,first ,steam-,engine with a ,piston ,the first steam-engine with a piston was made by ,denys ,papin1 a ,frenchman4 ,papin had observed that1 in ,guericke's experiment1 air-pressure lifted several men off their feet4 ,so he thought the air could be made to lift heavy weights and do useful work4 ,but how should he produce the vacuum8 ,his first thought was to explode gunpowder beneath the piston4 ,the gunpowder engine had been tried by others and found wanting4 ,he next turned his attention to steam1 and discovered that if the piston were forced up by steam and then the steam condensed1 a vacuum was formed beneath the piston1 and air-pressure forced the piston to descend4 ,if the piston were attached to a weight by a rope passing over a pulley1 then1 as the piston descended1 it would lift the weight4 ,papin's engine consisted simply of a cylinder and piston 7,fig4 #ab74 ,there was no boiler1 but the water was placed in the cylinder beneath the piston4 ,a fire was placed under the cylinder and1 as the water boiled1 the steam raised the piston4 ,then the fire was removed and1 as the cylinder cooled1 the steam condensed1 and the piston was forced down by air-pressure4 ,this was a slow and awkward method4 ,the engine required several minutes to make one stroke4 ,illustration3 ,,fig4 #ab--,,papin',s ,,engine ,the first steam-engine with a piston4 ,when the piston ,b was forced down by air-pressure1 a weight was lifted by means of a rope ,,tt passing over pulleys4 ,the principle of ,papin's engine was first successfully applied by ,thomas ,newcomen4 ,newcomen was a blacksmith by trade1 and his great successor1 ,watt1 was a mechanic4 ,thus we see that great discoveries soon become common property4 ,the blacksmith and the mechanic soon learn to use the discoveries of the scientist4 ,newcomen's ,engine ,in the ,newcomen engine the piston moved a walking-beam to which was attached a pump-rod4 ,steam was used merely to balance the air-pressure on the piston and allow the pump-rod to descend by its own weight4 ,the steam was condensed in the cylinder1 and the pressure of the air forced the piston down4 ,thus the work of raising water in the pump was done by the air4 ,newcomen's first engine made twelve strokes a minute1 and at each stroke lifted fifty gallons of water fifty yards4 ,he used this engine in pumping water from the mines1 and also made engines for lifting coal4 ,at first the steam was condensed by throwing cold water on the outside of the cylinder4 ,but one day the engine suddenly increased its speed and continued to work with unusual rapidity4 ,the upper side of the piston was covered with water to make the piston air-tight1 and it was found that this water was entering the cylinder through a hole that had worn in the piston1 and this jet of cold water was rapidly condensing the steam4 ,this was the origin of jet condensation4 ,after this steam and water were alternately admitted to the cylinder through cocks turned by hand4 ,a boy1 ,humphrey ,potter1 to whom this work was intrusted1 won fame by tying strings to the cocks in such a way that the engine would turn the cocks itself and the boy1 ,humphrey1 was free to play4 ,this device was the origin of valve-gear4#a #a ,any device by which a steam-engine operates the valves which admit steam to the cylinder is called valve-gear4 ,one form of valve-gear is the link motion invented by ,stephenson4 ,this form will be described in connection with the locomotive4 ,a simple valve-rod1 worked by an eccentric such as is used on most stationary engines1 is also a form of valve-gear4 ,newcomen's engine was extensively used4 ,the tin and copper mines of ,cornwall were deepened4 ,coal-mines were sunk to twice the depth that had been possible4 ,but as the mines were deepened the cost of running the engines increased4 ,the largest engines consumed about #ae1jjj worth of coal per year4 ,the ,newcomen engine required about twenty-eight pounds of coal per hour per horse-power1 while a modern engine consumes less than two pounds4 ,again1 because of increased cost1 mines were being abandoned4 ,such was the situation when ,james ,watt came into the field of action4 ,watt had learned the mechanic's trade in one year in a ,london shop1 and1 because he had not passed through an apprenticeship of seven years1 the ,guild of ,hammermen1 a labor-union of his time1 refused him admission1 and this refusal meant no employment4 ,he found shelter1 however1 in the ,university of ,glasgow1 and was there provided with a small workshop where he could make instruments for sale4 ,watt's ,engine ,a small ,newcomen engine belonging to the ,university of ,glasgow was out of repair4 ,london mechanics had failed to make it work4 ,the job was given to ,watt4 ,that he might do a perfect piece of work on this engine1 he made a study of all that was then known relating to steam 7,fig4 #ac74 ,illustration3 ,,fig4 #ac--,,the ,,newcomen ,,engine1 ,,in ,,repairing ,,which ,,watt ,,was ,,led ,,to ,,his ,,great ,,discoveries ,preserved in the ,university of ,glasgow4 ,he saw that there was a great loss of heat in admitting cold water into the cylinder to condense the steam1 and that1 to prevent this loss1 the cylinder must be kept always as hot as the steam that enters it4 ,while thinking upon this problem the idea came to him that1 if connection were made between the cylinder and a tank from which the air had been pumped out1 the steam would rush into the tank1 and might there be condensed without cooling the cylinder4 ,this was the origin of the condenser4 ,we have seen that1 in the ,newcomen engine1 the steam acted only on the under side of the piston1 air acting on the upper side4 ,it occurred to ,watt that the steam should act on both sides of the piston4 ,so he proposed to put an air-tight cover on the cylinder with a hole and stuffing-box for the piston to slide through and to admit steam to act upon it instead of air4 ,thus he was led to invent the double-acting engine4 ,the action in the cylinder of ,watt's engine was the same as that of the modern engine4 ,to save the power of steam1 ,watt arranged the valve in his engine in such a way that the steam was cut off from the cylinder when the piston had made about one-fourth of a stroke4 ,the steam in the cylinder continues to expand and drive the piston4 ,this device more than doubles the amount of work that the steam will do 7,fig4 #ad74 ,illustration3 ,,fig4 #ad--;,,cylinder ,,of ,,watt',s ,,steam-,,engine ,arrows show the course of the steam4 ,horse-,power of an ,engine ,when horses were about to be replaced by the steam-engine at the mines1 the question was asked3 ,how many horses will the engine replace8 ,tests were made by ,watt and others before him of the rate at which a horse could work in pumping water or in lifting a weight by means of a pulley4 ,watt's experiments showed that a good ,london horse could go on lifting #aej pounds over a pulley at the rate of #b-a_/b miles an hour or #bbj feet per minute1 and continue the work eight hours a day4 ,this would be equal to lifting #cc1jjj pounds one foot high every minute4 ,this rate of doing work he called a horse-power4 ,it is more than the average horse can do1 but this number was used by ,watt that he might give good measure in his engines4 ,the horse-power of an engine at that time meant the rate of work in lifting water or coal4 ,now it means the rate of work done by the steam upon the piston1 so that to find the useful horse-power of an engine we must deduct the work wasted in friction4 ,the indicator for measuring the pressure of steam in the cylinder and the fly-ball governor are also inventions made by ,watt 7,fig4 #ae74 ,the fly-ball governor replaced the throttle-valve which was at first used by ,watt to regulate the speed of his engines4 ,the throttle-valve is still used on locomotives4 ,illustration3 ,,fig4 #ae--;,a ,,fly-,,ball ,,governor ,the balls as they rotate regulate the admission of steam to the cylinder by means of the lever ,l and the rod ,r4 ,at the end of the eighteenth century the steam-engine was full grown4 ,it remained for the nineteenth century to apply the engine to locomotion on sea and land1 to develop the steam-turbine1 and so to increase the power of the steam-engine that1 early in the twentieth century1 a #fh1jjj-;horse-power engine should speed an ocean liner across the ,atlantic in five days4 ,the ,leyden ,jar ,the first electrical invention of practical use was made by ,benjamin ,franklin4 ,in ,franklin's time great interest in electricity had been aroused by the strange discovery of a ,german professor1 ,pieter van ,musschenbroek1 of the ,university of ,leyden4 ,this professor had tried what he called a new but terrible experiment4 ,he had suspended by two silk threads a gun-barrel which received electricity from an electrical machine4 ,from one end of the gun-barrel hung a brass wire4 ,the lower end of this wire dipped in a jar of water4 ,he held the jar in one hand1 while with the other he tried to draw sparks from the gun-barrel4 ,suddenly he received a shock which seemed to him like a lightning stroke4 ,so violent was the shock that he thought for a moment it would end his life4 ,out of this experiment came the ,leyden jar1 which for a century and a half was of no practical use1 but which now forms an important part of every wireless telegraph equipment4 ,the ,leyden jar is simply a glass bottle or jar coated with tin-foil both inside and outside 7,fig4 #af74 ,when charged with electricity the jar will hold its charge until the two coatings are connected by a metal wire or other good conductor of electricity4 ,a person may receive a strong shock by holding the jar in one hand and touching a knob connected to the inner coating with the other hand4 ,illustration3 ,,fig4 #af--;,a ,,leyden ,,jar ,popular interest in electricity was aroused by this discovery4 ,the friction electrical machine and the ,leyden jar were simple and easy to make4 ,people of fashion found them interesting and amusing1 the more so because of the shock felt on taking through the body the discharge from the wonderful bottle1 and the fact that several persons could receive the shock at the same instant4 ,on one occasion the ,abb ,nollet discharged a ,leyden jar through a line composed of all the monks of the ,carthusian ,monastery in ,paris4 ,as the line of serious-faced monks a mile in length jumped into the air1 the effect was ridiculous in the extreme4 ,conductors and ,insulators ,about this time other great electrical discoveries were made4 ,early in the century1 ,stephen ,gray discovered that some objects conduct electricity and others do not4 ,he discovered that1 when a glass tube is electrified by rubbing1 it will attract and repel light objects4 ,in the same way a comb or penholder of rubber may be electrified by rubbing it on the sleeve4 ,a bit of paper which touches the comb becomes electrified4 ,electricity can be transferred from one object to another4 ,gray discovered further that contact is not necessary1 that a hempen thread or a wire will carry an electric charge from one object to another4 ,a silk thread will not carry the electric charge4 ,some things convey electricity1 he said1 and some do not1 and those which do not can be used to prevent the electricity escaping from those which do4 ,could this obscure inventor have seen a modern telegraph line with the glass insulators on the poles1 which prevent the electric current escaping from the telegraph wire1 he might have realized the importance of his discovery4 ,he set up a line of hempen thread six hundred and fifty feet long1 and with an electrical machine at one end of the line electrified a boy suspended from the other end4 ,two ,kinds of ,electric ,charge ,a ,frenchman1 ,du,fay1 while carrying further the experiments of ,gray1 was watching a bit of gold-leaf floating in the air4 ,the gold-leaf had been repelled after contact with his electrified glass tube4 ,thinking to try the action of two electrified objects on the gold leaf1 he rubbed a piece of gum-copal and brought it near the leaf4 ,to his astonishment the leaf1 which was repelled by the glass tube1 was attracted by the gum-copal4 ,he repeated the experiment again and again1 and each time the leaf was repelled by the glass and attracted by the gum4 ,he concluded from this that there are two kinds of electricity1 which he named vitreous and resinous4 ,the two kinds of electric charge were called by ,franklin positive and negative4 ,franklin made a battery of ,leyden jars1 connecting the inner coating of one to the outer coating of the next throughout the series4 ,in this way he could get a much stronger spark than with a single jar4 ,on one occasion he nearly lost his life by taking a shock from his battery of ,leyden jars4 ,he magnetized and demagnetized steel needles by passing the discharge from his ,leyden jars through the needles4 ,franklin's ,kite ,experiment ,the conjecture that lightning is of the same nature as the spark from the ,leyden jar or the electrical machine had gained a hold on the minds of others before ,franklin4 ,in ,france sparks had been drawn from a rod ninety-nine feet high1 but this did not reach into the clouds4 ,franklin determined to send a kite into a thunder-cloud1 thinking electricity from the cloud would follow the string of the kite and could be stored in a ,leyden jar1 and used like the charge from an electrical machine4 ,he had felt the power of a ,leyden-jar discharge1 and through it had nearly lost his life4 ,he knew that lightning is far more powerful than any battery of ,leyden jars1 and yet to test the truth of his theory1 that lightning is an electrical discharge1 he was about to draw the lightning to his hand4 ,he knew little of conductors of electricity4 ,whether the cord would draw little or much of the electric fire he knew not4 ,so far as he knew he was toying with death4 ,the kite was made of two light strips of cedar placed crosswise1 and a large silk handkerchief fastened to the strips4 ,a sharp wire about a foot long was fastened to one of the strips4 ,to the lower end of the cord he attached a key and a silk ribbon4 ,by means of the ribbon he held the cord to insulate it from his hand4 ,the kite soared into the clouds1 and ,franklin and his son stood under a shed awaiting the coming of the electric fire 7,fig4 #ag74 ,soon the fibres of the cord began to bristle up4 ,he approached his knuckles to the key4 ,a spark passed4 ,he brought up a ,leyden jar and charged it with electricity from the cloud1 and found that with this charge he could do everything that could be done with electricity from his machine4 ,he had proved the identity of lightning and electricity4 ,illustration3 ,,fig4 #ag--;,,franklin',s ,,kite ,,experiment ,taking electricity from the clouds4 ,the ,lightning-,rod ,some time before1 he had discovered the action of a point in discharging electricity4 ,he said3 ,if you fix a needle to the end of a gun-barrel like a little bayonet1 while it remains there the gun-barrel cannot be electrified so as to give a spark1 for the electric fire continually runs out silently at the point4 ,in the dark you may see a light gather upon the point like that of a firefly or glow-worm4 ,if the needle is held in the hand and brought near to an object charged with electricity1 the object is quietly discharged1 and a light may be seen at the point of the needle4 ,this action of points explains the light sometimes seen on the tops of ships' masts1 called by sailors ,saint ,elmo's fire1 and perhaps1 also1 the observation of ,csar that1 in a certain ,african ,war1 the spears of the ,fifth ,roman ,legion appeared tipped with fire4 ,the lightning-rod was the outcome of ,franklin's observations1 and this was the first practical invention relating to electricity4 ,a building may be electrified by an electrified cloud passing over it4 ,if the building is protected by pointed rods1 the electric charge will quietly escape from the points4 ,the lower ends of the rods must be in the moist earth below the surface4 ,the lightning-rod has not proved so great a protection as ,franklin supposed it would4 ,he supposed that a lightning-stroke is a discharge in one direction only2 but we now know that it is a rapid surging back and forth1 and this fact accounts for the failure of the lightning-rods to furnish perfect protection4 ,in surging back and forth1 the lightning may skip from the lightning-rod to some metal object within the building1 as a stove or radiator4 ,the lightning-rod robbed the thunder-storm of its terrors to the timid1 and in time dispelled the superstition of people who believed that thunder and lightning are evidence of the wrath of the ,deity4 ,franklin was the first to propose an answer to the question3 ,what is electricity8 ,he believed electricity to be a subtle fluid existing in all objects4 ,if an object has more than a certain amount of this fluid1 it is positively electrified2 if less than this amount1 it is negatively electrified4 ,the one-fluid theory of ,franklin was soon met by the two-fluid theory proposed by ,robert ,symmer1 for ,franklin's theory had failed to explain why two bodies negatively electrified should repel each other4 ,according to ,symmer1 an uncharged body contains an equal quantity of two different electrical fluids4 ,an excess of one of these produces a positive charge1 an excess of the other a negative charge4 ,symmer's experiments are almost ludicrous4 ,he wore two pairs of silk stockings1 and found that white and black silk worn together became strongly electrified4 ,when the two stockings worn on one foot were pulled off together1 and then separated1 they were found to be electrified1 and attracted each other so strongly that a force of about one pound was required to separate them4 ,the two charges1 negative and positive1 could1 however1 be separated4 ,he thought1 therefore1 that there are two electrical powers1 not one1 as ,franklin believed4 ,his belief was strengthened by examining a quire of paper through which an electric spark had passed1 and finding that the edges of the holes were bent two different ways1 as if the hole had been made in the quire by drawing two threads in contrary directions through it4 ,there was a long controversy regarding the two theories1 and neither quite gained possession of the field4 ,each contained some truth1 and each had its weak points4 ,the two had more in common than men at that time thought4 ,galvani and the ,electric ,current ,franklin had proven that there is electricity in the atmosphere1 and that lightning is an electric discharge4 ,a widespread interest in the electricity of the atmosphere followed this discovery4 ,aloisio ,galvani1 a physician in ,bologna1 ,italy1 in attempting to learn the effect of atmospheric electricity on the nerves and muscles of the human body1 made a discovery which led to the electric battery and a knowledge of electric currents4 ,having dissected a frog1 he laid it on a table on which stood an electrical machine4 ,when one of his assistants touched lightly the nerve of the thigh with the point of a knife while a spark was drawn from the electrical machine1 the muscles contracted violently1 as if they were attacked by a cramp4 ,when he held the knife by the bone handle1 there was no convulsion as there was when he held it by the steel blade4 ,he next thought it important to find out if lightning would excite contraction of the muscles4 ,he stretched and insulated a long iron wire in the open air on the housetop and1 as a storm drew near1 hung on it a dissected frog4 ,to the feet he fastened another long iron wire1 which was allowed to dip in the water in the well4 ,the result1 he said1 came about as we wished4 ,as often as the lightning broke forth1 the muscles were thrown into repeated violent convulsions1 so that always1 as the lightning lightened the sky1 the muscle contractions and movements preceded the thunder and1 as it were1 announced its coming4 ,it was best1 however1 when the lightning was strong1 or the clouds from which it broke forth were near the place of the experiment4 ,he describes his greatest experiment as follows3 ,after we had investigated the power of atmospheric electricity in storms1 our hearts burned with the desire to investigate the daily quiet electricity of the atmosphere4 ,therefore1 as the prepared frogs1 hung on an iron railing which surrounded a hanging garden on our house1 with brass hooks inserted in the spinal cord1 fell into convulsions not only when it lightened1 but when the sky was calm and clear1 ,i thought that the cause of these contractions was the changes in the electricity of the atmosphere4 ,then for hours1 yes1 even days1 ,i observed the animals1 but almost never a movement of the muscles could be seen4 ,at last1 tired with such fruitless waiting1 ,i began to press the brass hooks1 which were fastened in the spinal cord1 against the iron railing to see if such a trick would cause the muscles to contract1 and if instead of changes in the atmospheric electricity any other changes would have any influence4 ,i observed1 indeed1 vigorous contractions1 but none which could be caused by the condition of the atmosphere4 ,it was pressing the brass hook against the iron railing1 thus forming an electric battery1 that caused electricity to pass through the muscles of the frog4 ,galvani did not know that he had discovered a new source of electricity4 ,he never arrived at a correct explanation of his results1 and never knew the value of his discovery4 ,volta and the ,electric ,battery ,it was left for ,alexander ,volta to show that1 in ,galvani's experiment1 the muscles of the frog1 together with the brass hook and the iron railing1 formed an electric battery4 ,volta showed that an electric charge can be produced merely by bringing two different metals into contact4 ,he found that1 if he placed copper and zinc in sulphuric acid1 or a solution of common salt1 he could1 produce a continuous flow of electricity 7,fig4 #ah74 ,illustration3 ,,fig4 #ah--,,volta ,,explaining ,,his ,,electric ,,battery ,,to ,,napoleon ,,bonaparte ,from a painting4 ,photo by ,dubray4 ,in the beginning of the year #ahjj ,volta made the first electric battery 7,fig4 #ai74 ,it was made of copper and zinc disks placed alternately1 with a piece of wet cloth above each pair of disks4 ,with his column of disks he could obtain a strong shock2 indeed1 many shocks1 one after the other4 ,this first battery of ,volta's was a form of dry battery4 ,later ,volta devised his crown of cups1 a form of wet battery similar to some batteries in use to-day4 ,each cup contained a strip of copper and a strip of zinc in dilute sulphuric acid4 ,illustration3 ,,fig4 #ai--,,the ,,first ,,electric ,,battery ,no4 #a--;,a battery of one hundred pairs of copper and zinc disks4 ,no4 #b--,two such batteries connected4 ,by permission of the ,italian ,institute of ,graphic ,arts1 ,bergamo4 ,volta did not know the real use of the liquid in his battery1 nor that the strength of the current depends on the rate at which the metal is dissolved by the acid2 but he had discovered the electric current1 and with this discovery began a new era in electrical invention4 ,chapter ,,iv ,,faraday ,,and ,,the ,,first ,,dynamo ,michael ,faraday1 a ,london newsboy1 the son of a blacksmith1 became the inventor of the dynamo1 and prepared the way for the wonderful electrical inventions of the nineteenth century4 ,he began his career as a book-binder's apprentice1 employing his spare moments in reading the books he was binding4 ,one of these books led him to make some simple experiments in chemistry4 ,he also made an electrical machine1 first with a glass bottle1 and afterward with a glass cylinder4 ,while an apprentice he wrote to his young friend1 ,benjamin ,abbott3 ,i have lately made a few simple galvanic experiments1 merely to illustrate to myself the first principles of the science4 ,i was going to ,knight's to obtain some nickel1 and bethought me that they had malleable zinc4 ,i inquired1 and bought some--have you seen any yet8 ,the first portion ,i obtained was in the thinnest pieces possible4 ,it was1 they informed me1 thin enough for the electric stick4 ,i obtained it for the purpose of forming disks with which and copper to make a little battery4 ,the first ,i completed contained the immense number of seven pairs of plates666 and of the immense size of halfpence each666666 ,i1 sir1 ,i my own self1 cut out seven disks of the size of half pennies each6 ,i1 sir1 covered them with seven halfpence1 and ,i interposed between them seven1 or rather six1 pieces of paper soaked in a solution of muriate of soda 7common salt74 ,but laugh no longer1 dear ,a41 rather wonder at the effects this trivial power produced4 ,this tiny battery made of half pennies with zinc disks and salt solution would decompose a certain solution which ,faraday tested4 ,a larger battery made of copper and zinc disks with salt solution would decompose water from the cistern4 ,when the wires from the larger battery were put in the cistern-water he saw a dense white cloud descending from the positive wire1 and bubbles rising from the negative wire4 ,this action continued until all the white substance was taken out of the water4 ,because of his interest in science1 young ,faraday attracted the attention of a ,mr4 ,dance1 a member of the ,royal ,institution and a customer of his master1 ,mr4 ,riebau4 ,through the kindness of ,mr4 ,dance he heard four lectures by ,sir ,humphry ,davy4 ,he took notes on the lectures1 wrote them out carefully1 and added drawings of the apparatus4 ,these notes he sent to ,davy with a letter expressing the wish that he might secure employment at the ,royal ,institution4 ,in a short time1 after a warning from ,sir ,humphry that he had better stick to his business of book-binding1 that ,science is a harsh mistress1 his wish was granted1 and we find him cleaning and caring for apparatus in the ,royal ,institution and assisting ,davy in preparing for his lectures4 ,count ,rumford ,our story now takes us back to the time of the ,american ,revolution4 ,in ,america1 we find a young man of nineteen1 ,benjamin ,thompson by name1 serving as major in the ,second ,regiment of ,new ,hampshire4 ,the appointment of so young a man as major1 and his evident hold on the governor's favor1 aroused the jealousy of the older officers4 ,he was accused of being unfriendly to the cause of liberty4 ,he denied the charge1 and was acquitted by the committee of the people of ,concord4 ,a mob gathered round his house1 but he escaped4 ,driven from his refuge in his mother's home1 he fled to ,england1 leaving his wife and child4 ,appointed lieutenant-colonel in the ,british ,army1 he returned to ,america and fought against his former friends4 ,the war having ended1 he returned to ,england1 thence to the ,continent1 intending to take part in an expected war between ,austria and ,turkey4 ,a chance meeting with a ,bavarian prince1 ,maximilian1 changed the course of his life4 ,this prince1 while commanding on parade1 saw ,thompson among the spectators mounted on a fine ,english horse1 and addressed him4 ,thompson informed him that he came from serving in the ,american war4 ,the prince1 pointing to a number of his officers1 said3 ,these gentlemen were in the same war1 but against you4 ,they belonged to the ,royal ,regiment of ,deux ,ponts1 that acted in ,america under the orders of ,count ,rochambeau4 ,thompson dined with the prince and ,french officers4 ,they conversed of war and the battles in which they met4 ,the prince1 attracted to the colonel1 induced him to pass through ,munich1 and gave him a letter to his uncle1 the ,elector of ,bavaria4 ,it was in ,bavaria1 the country to which such unexpected turns of fortune led him1 that his greatest work was done4 ,he entered the service of the ,duke of ,bavaria as aide-de-camp4 ,it was his aim while in the service of the ,bavarian ,government to better the condition of the people4 ,he introduced reforms in the army1 used the soldiers to rid the country of beggars and robbers1 and took steps to provide for the infirm and find employment for the strong1 his motto being that people can best be made virtuous when first made happy4 ,a ,military ,workhouse was opened for the beggars1 and a ,house of ,industry for the poor4 ,a ,military ,academy was formed with a view to the free education of young people of talent for the public service4 ,he became absorbed in the one aim of helping the poor4 ,so thorough was his devotion to the people1 and so deeply did he win their affection1 that when he was dangerously ill a multitude of hundreds went in procession to the church to make public prayers for his recovery4 ,he saw that the poor may be helped by teaching them to save1 and in nothing is there greater need of saving than in fuel and heat4 ,in the kitchens of the ,military ,academy and the ,house of ,industry he carried out a series of experiments on the economy of fuel1 and succeeded in greatly reducing the amount of fuel needed for cooking the food4 ,he did this by using a closed fireplace1 the forerunner of the stove4 ,the closed fireplace was in reality a brick stove1 and was a great improvement over the open chimney fireplaces then in common use4 ,he made the covers of the cooking utensils double1 to save the heat1 for he had found that heat cannot escape through confined air4 ,benjamin ,thompson was knighted by ,george ,,iii41 and in #agia he was made a ,count of the ,holy ,roman ,empire1 and is known to the world of science as ,count ,rumford4 ,count ,rumford's ,experiment with the ,cannon ,while in the service of the ,duke of ,bavaria1 it became his duty to organize the field artillery4 ,to provide cannon for this purpose1 he erected a foundry and machine-shops4 ,being alert for any unusual fact relating to heat1 he observed the very high temperature produced by the boring of the cannon4 ,he was eager to learn how so much heat could be produced4 ,for this purpose he took a cannon in the rough1 as it came from the foundry1 fixed it in the machine used for boring1 and caused the cannon to be turned by horses while a blunt borer was forced against the end of the cannon4 ,he first tested the temperature of the metal itself as it turned4 ,then he surrounded the end of the cannon with water in an oblong box fitted water-tight 7,fig4 #bj74 ,illustration3 ,,fig4 #bj--;,,count ,,rumford',s ,,experiment ,,with ,,the ,,cannon1 ,,making ,,water ,,boil ,,without ,,fire ,the horses make the water boil by walking around the track2 the work the horses do is changed into heat by the friction of the drill4 ,the cannon had been turning but a short time when he found by putting his hand in the water that heat had been produced4 ,in two hours and thirty minutes the water actually boiled4 ,astonishment was expressed in the faces of the bystanders on seeing so large a quantity of water heated and actually made to boil without any fire4 ,heat1 ,count ,rumford said2 may thus be produced merely by the strength of a horse1 and1 in case of necessity1 this heat might be used in cooking victuals4 ,but no circumstance can be imagined in which there is any advantage in this method of procuring heat1 for more heat might be obtained by burning the fodder which the horse would eat4 ,the meaning of this last remark was not understood until the time of ,robert ,mayer1 about fifty years later4 ,rumford had found that the work of a horse can produce heat1 and heat1 in a steam-engine1 can do the work of a horse4 ,thus surely1 though slowly1 men were learning of the forces that move the world and do man's bidding4 ,count ,rumford1 true to his adopted land1 returned to ,london and became the founder of the ,royal ,institution in which ,faraday and his successors have achieved such marvellous results4 ,he believed that the poor can be helped in no better way than by giving them knowledge1 so that they can better their own condition4 ,for this purpose he founded the ,royal ,institution4 ,here he intended that men skilled in discovery should gain new knowledge that would add to the comfort and happiness of the people4 ,davy ,in the ,english coal-fields many accidents due to the burning of fire-damp had occurred4 ,fire-damp is caused by gas issuing from the coal4 ,on the approach of a flame this gas catches fire1 and as it burns it produces a violent wind1 driving the flame before it through the mine4 ,miners were scorched to death1 suffocated1 or buried under ruins from the roof4 ,hundreds of miners had been killed4 ,no means of lighting the mines in safety had been devised4 ,sir ,humphry ,davy1 ,professor of ,chemistry in the ,royal ,institution1 was appealed to4 ,after many experiments he devised a safe lamp1 which was a common miner's lamp enclosed in a wire gauze4 ,this proved a perfect protection from fire-damp1 and the ,davy safety lamp has been used by miners the world over for more than a century4 ,but ,davy's best work was with the electric battery4 ,some of the facts most familiar to us were discovered by him4 ,volta had contended that the contact of the metals in a battery produces a current1 that the liquid merely carries the electricity from one metal plate to the other4 ,but ,davy proved that there can be no current without chemical action4 ,whenever we put two metals in an acid or other solution that will dissolve one metal faster than the other1 and connect the metals with a wire1 an electric current is produced4 ,if we use water with silver and gold1 there is no current1 because water will not dissolve either the silver or the gold4 ,davy discovered the metal1 potassium1 by means of his electric battery4 ,potassium is found in common potash and saltpetre1 and1 when separated1 is a very soft metal4 ,the newly discovered metal aroused great interest in other countries4 ,when ,napoleon heard of it1 he inquired impetuously how it happened the discovery had not been made in ,france4 ,on being told that in ,france there had not been made an electric battery of sufficient power1 he exclaimed3 ,then let one be instantly made without regard to cost or labor4 ,his command was obeyed1 and he was called to witness the action of the new battery4 ,before any one could interfere he placed the ends of the wires under his tongue and received a shock that nearly deprived him of sensation4 ,on recovering he left the laboratory without a word1 and was never afterward heard to refer to the subject4 ,davy made many great discoveries1 but the greatest was his discovery of ,faraday4 99 99 99 99 99 ,a journey on the ,continent with ,davy was an event in the life of ,faraday1 who up to that time had never to his own recollection travelled twelve miles from ,london4 ,on this journey he met ,volta1 whom he describes as an hale elderly man1 very free in conversation4 ,he visited the ,academy del ,cimento1 in ,florence1 and wrote3 ,here was much to excite interest2 in one place was ,galileo's first telescope1 that with which he discovered ,jupiter's satellites4 ,it was a simple tube of wood and paper1 about three and a half feet long1 with a lens at each end4 ,there was also the first lens which ,galileo made4 ,it was set in a very pretty frame of brass1 with an inscription in ,latin on it4 ,faraday crossed the ,alps and the ,apennines1 climbed ,vesuvius1 visited ,rome1 and saw a glow-worm4 ,the last he thought as wonderful as the first4 ,shortly after his return to ,london he fell in love4 ,now1 ,faraday had determined that he would not be conquered by the master passion4 ,in fact1 he had written various aspersions on love1 of which the following is a sample3 ,what is the pest and plague of human life8 ,and what the curse that often brings a wife8 ',tis ,love4 ,what is't directs the madman's hot intent1 ,for which a dunce is fully competent8 ,what's that the wise man always strives to shun1 ,though still it ever o'er the world has run4 ',tis ,love4 ,but he reckoned not with his own heart4 ,it is not long until we find him writing to ,miss ,sarah ,barnard1 a bright girl of twenty-one3 ,you have converted me from one erroneous way1 let me hope you will attempt to correct what others are wrong4444 ,again and again ,i attempt to say what ,i feel1 but ,i cannot4 ,let me1 however1 claim not to be the selfish being that wishes to bend your affections for his own sake only4 ,in whatever way ,i can minister to your happiness1 either by close attention or by absence1 it shall be done4 ,do not injure me by withdrawing your friendship or punish me for aiming to be more than a friend by making me less4 ,they were married and lived in rooms at the ,royal ,institution4 ,no poet ever loved more tenderly than ,faraday4 ,truly1 science does not dry up the heart's blood4 ,at the age of seventy-one he wrote to his wife while absent from home for a few days3 ,remember me2 ,i think as much of you as is good for either you or me4 ,we cannot well do without each other4 ,but we love with a strong hope of love continuing ever4 ,faraday's ,electrical ,discoveries ,now we shall turn to ,faraday's electrical discoveries and inventions4 ,men had long known that1 in houses that have been struck by lightning1 steel objects such as knives and needles are sometimes found to be magnetized4 ,ships struck by lightning had found their compass-needles pointing south instead of north1 or wandering in direction and worthless4 ,men had wondered how an electrical discharge could magnetize steel4 ,they had tried the spark of the electrical machine with no definite result4 ,franklin1 in his experiment of magnetizing a steel needle by passing an electric spark through it1 could not tell before the spark was passed through the needle which end would be the north pole4 ,there was no seeming connection between the direction of the electric discharge and the polarity of the needle4 ,after the discovery of the electric battery1 men tried to discover a relation between the electric current and magnetism4 ,oersted and ,electromagnetism ,the first success in this direction was achieved by ,hans ,christian ,oersted1 a native of ,denmark4 ,poverty impelled his father to take him from school at the age of twelve and place him in an apothecary's shop4 ,the boy1 ,hans1 found delight in the chemical work of the apothecary4 ,his eagerness to learn and the pressure of poverty led him to neglect the usual sports of boyhood and devote his leisure time to reading and study4 ,again he entered school1 and1 though paying his way by his own work1 he graduated with honor from the ,university of ,copenhagen4 ,he was appointed ,professor of ,physics in this university1 and here he made his first great discovery in electromagnetism4 ,after working for seven years to discover a relation between current electricity and magnetism1 he made a discovery which proved to be the first step in the invention of the dynamo4 ,he was using a magnetic compass1 which is a small magnetic needle balanced on a steel point4 ,the needle points nearly north and south unless disturbed by a magnet brought near it4 ,he had tried to find if a wire through which a current is flowing would disturb the compass as a magnet does4 ,he had tried placing the wire east and west1 thinking the compass-needle would follow the wire as it does a magnet4 ,one day1 while lecturing to his students1 it occurred to him for the first time to place the wire north and south over the compass-needle4 ,he was surprised and perplexed as he did so to see the needle swing round and point nearly east and west 7,fig4 #ba74 ,on reversing the current the needle swung in the opposite direction4 ,he had discovered the magnetic action of an electric current4 ,it was learned soon afterward that a coil of wire with an electric current flowing through it acts like a magnet1 and that a current flowing around a bar of soft iron makes the iron a magnet 7,figs4 #bb and #bc74 ,illustration3 ,,fig4 #ba--,,oersted',s ,,experiment ,an electric current flowing over the compass-needle toward the north causes the needle to turn until it points nearly west4 ,by permission of ,joseph ,g4 ,branch4 ,illustration3 ,,fig4 #bb4--;,a ,,coil ,,with ,a ,,current ,,flowing ,,through ,,it ,,acts ,,like ,a ,,magnet ,the coil is picking up iron filings4 ,illustration3 ,,fig4 #bc--;,a ,,bar ,,of ,,soft ,,iron ,,with ,a ,,current ,,flowing ,,around ,,it ,,becomes ,a ,,magnet ,ampre ,the news of ,oersted's discovery aroused great interest throughout ,europe4 ,soon after its announcement in ,france1 ,andr ,marie ,ampre made a discovery of equal importance4 ,oersted had discovered electromagnetism4 ,ampre discovered electrical power or motion produced by an electrical current4 ,the youth of ,ampre was passed amid the stormy scenes of the ,french ,revolution4 ,his father had moved from his country home to ,lyons and become a justice of the peace4 ,in the destruction of the city of ,lyons during the ,reign of ,terror he lost his head under the guillotine4 ,the blow was too great for ,ampre1 then a youth of eighteen4 ,he had been a precocious child1 advanced beyond his years in all the studies of the schools4 ,but now his strong mind failed4 ,for a year he wandered about mechanically piling up heaps of sand or gazing upon the sky4 ,then his mental power returned1 and he took up with eagerness the study of botany and poetry4 ,he became a professor in the ,polytechnic ,school in ,paris1 and it was while teaching in this school that he made his great discoveries4 ,he found that two coils of wire can be made to attract or repel each other by an electric current4 ,if the current flows through the two coils in the same direction1 they attract each other 7,fig4 #bd74 ,if the current flows in opposite directions through the coils1 they repel each other 7,fig4 #be74 ,this is not very strange to us1 for we know that a coil with a current flowing through it acts just like a magnet4 ,each coil then has a north pole and a south pole4 ,if the coils are placed so that the two north poles or the two south poles are together1 they will repel each other4 ,if the north pole of one coil is near the south pole of the other1 they will attract each other4 ,illustration3 ,,fig4 #bd--,,two ,,coils ,,with ,,currents ,,flowing ,,in ,,same ,,direction ,,attract ,,each ,,other ,illustration3 ,,fig4 #be--,,two ,,coils ,,with ,,currents ,,flowing ,,in ,,opposite ,,directions ,,repel ,,each ,,other ,ampre believed that electric currents are flowing around within the earth1 and that the earth has a north and a south magnetic pole for the same reason that a coil of wire has magnetic poles2 that these poles are caused by the currents flowing around in the earth just as the poles of the coil are caused by the current flowing around in the coil4 ,we do honor to the name of ,ampre whenever we measure an electric current1 for electric currents are measured in amperes4 ,arago ,another important discovery was made by a young ,frenchman1 ,franois ,arago1 within a year of the time when ,oersted and ,ampre made their discoveries4 ,the three great discoveries of these men were made in the years #ahai and #ahbj4 ,the youth of ,arago was full of adventure4 ,he had assisted in making a survey in the ,pyrenees1 the haunt of daring robber-bands4 ,twice in his cabin he was visited by a chief of a robber-band who claimed to be a custom-house guard4 ,on the second visit he said to the robber3 ,your position is perfectly known to me4 ,i know that you are not a custom-house guard4 ,i have learned that you are the chief of the robbers of the country4 ,tell me whether ,i have anything to fear from your confederates4 ,the robber replied3 ,the idea of robbing you did occur to us2 but1 on the day that we molested an envoy from the ,french1 they would direct against us several regiments of soldiers1 and we are not so strong as they4 ,allow me to add that the gratitude which ,i owe you for the night's shelter is your surest guarantee4 ,at a later time1 when war between ,spain and ,france was threatened1 he was accused of being a spy1 and a mob was formed to put him out of the way4 ,he escaped in disguise through the midst of the mob and boarded a ,spanish ship4 ,he was carried to ,morocco1 ran the gantlet of bloodthirsty ,mussulmans in ,algiers1 escaped death by a hair's-breadth1 and through it all clung to the papers which recorded the results of the survey in the mountains1 and delivered them in safety to the office of the ,bureau of ,longitude in ,paris4 ,arago made a discovery which1 with those of ,oersted and ,ampre1 prepared the way for ,faraday's great electrical discoveries and the invention of the dynamo4 ,he found that a plate of copper whirling above or below a magnetic needle will draw the needle after it 7,fig4 #bf74 ,he could make the speed of the whirling copper plate so great that the needle would whirl rapidly1 following the copper plate4 ,faraday was the first to explain ,arago's experiment4 ,illustration3 ,,fig4 #bf--;,,arago',s ,,experiment ,when the copper plate whirls the magnet whirls also1 though it does not touch the copper plate4 ,faraday's ,first ,electric ,motor ,faraday's first electrical discovery was made soon after that of ,arago4 ,oersted had proven that an electric current acts on a magnet4 ,the magnet turns at right angles to the wire4 ,faraday saw that this is because the north pole of the magnet tries to go round the wire in one direction1 and the south pole tries to go round in the opposite direction4 ,he placed a magnet on end in a dish of mercury1 with one pole of the magnet above the mercury1 and found that the magnet would spin round a wire carrying a current4 ,when the current acts on one pole of the magnet only1 the magnet spins round the wire 7,fig4 #bg74 ,so ,faraday's first electrical discovery prepared the way for the electric motor4 ,illustration3 ,,fig4 #bg--,,one ,,pole ,,of ,a ,,magnet ,,spins ,,round ,a ,,wire ,,through ,,which ,,an ,,electric ,,current ,,flows ,an ,electric ,current ,produced by a ,magnet ,he had written in his note-book3 ,convert magnetism into electricity4 ,an electric current would magnetize iron4 ,would not a magnet produce an electric current8 ,this was his problem4 ,he connected a coil of wire to an instrument that would tell when a current was flowing1 and placed a magnet in the coil4 ,others had claimed1 and ,faraday at first believed1 that a current would flow while the magnet lay quiet within the coil4 ,but ,faraday was alert for the unexpected1 and the unexpected happened4 ,for an instant1 as he thrust the magnet into the coil1 his instrument showed that a current was flowing4 ,again1 as he drew the magnet quickly from the coil1 a current flowed1 but in the opposite direction 7,fig4 #bh74 ,from this simple experiment has grown the alternating-current machinery by which the power of ,niagara is made to light cities and drive electric cars at a distance of many miles4 ,illustration3 ,,fig4 #bh--,,when ,a ,,magnet ,,is ,,thrust ,,into ,a ,,coil ,,of ,,wire ,,it ,,causes ,a ,,current ,,to ,,flow ,,in ,,the ,,coil1 ,,but ,,the ,,current ,,flows ,,only ,,while ,,the ,,magnet ,,is ,,moving ,drawing reproduced by permission of ,joseph ,g4 ,branch4 ,a friend of ,faraday1 on learning of this discovery1 wrote the following impromptu lines3 ,around the magnet ,faraday ,was sure that ,volta's lightnings play4 ,but how to draw them from the wire8 ,he took a lesson from the heart3 ',tis when we meet1 'tis when we part1 ,breaks forth the electric fire4 ,a magnet will produce an electric current in a wire1 but only when the magnet or the wire is in motion4 ,detecting and ,measuring an ,electric ,current ,the instrument which ,faraday used to detect a current was derived from ,oersted's experiment4 ,when a current flows in a north-and-south direction over a compass-needle1 the needle swings round4 ,when the current stops flowing the needle swings back to the north-and-south position4 ,the effect on the needle is stronger if the current flows through a coil of wire and the coil is placed in a north-and-south position around the needle 7,fig4 #bi74 ,the stronger the current flowing through the coil the farther the needle will turn from the north-and-south position4 ,illustration3 ,,fig4 #bi--;,a ,,coil ,,of ,,wire ,,around ,a ,,compass-,,needle ,the needle tells when a current is flowing1 and how strong the current is4 ,the coil and the needle together are called a galvanometer1 and may be used to tell when a current is flowing1 and also to indicate the strength of the current4 ,an ,electric ,current ,produced by the ,magnetic ,field of ,another ,current ,faraday had found that a current flowing around a piece of iron will make the iron a magnet1 and that a magnet in motion will cause a current to flow in a wire4 ,it seemed to him that a second wire placed near the first should have a current produced in it without the presence of iron4 ,he wound two coils of copper wire upon the same wooden spool4 ,the wire of the two coils he separated with twine and calico4 ,one coil was connected with a galvanometer1 the other with a battery of ten cells1 yet not the slightest turning of the needle could be observed4 ,but he was not deterred by one failure4 ,he raised his battery from ten cells to one hundred cells1 but without avail4 ,the current flowed calmly through the battery wire without producing1 during its flow1 any effect upon the galvanometer4 ,during its flow was the time when an effect was expected4 ,again the unexpected happened4 ,at the instant of making contact with the battery there was a slight movement of the needle4 ,when the contact was broken1 another slight movement1 but in the opposite direction to the first 7,fig4 #cj74 ,the current in one wire caused a current to flow in the other1 but the current in the second wire continued for an instant only at the making and breaking of the contact with the battery4 ,this was the beginning of the induction-coil used to-day in wireless telegraphy4 ,illustration3 ,,fig4 #cj--;,,faraday',s ,,induction-,,coil ,starting and stopping the battery current in the primary coil causes a changing magnetic field1 and this causes a current to flow in the secondary coil4 ,drawing reproduced by permission of ,joseph ,g4 ,branch4 ,what was the secret of it8 ,simply this3 that a current in one wire will cause a current to flow in another wire near it1 but only while the current in the first wire is changing4 ,that is1 at the instant when the first wire is connected to the battery1 or its connection broken1 a current is induced in the second wire4 ,there is no battery or other source of current connected to the second wire2 but a current flows in this wire because it is near a wire in which a current is rapidly starting and stopping4 ,when these two wires are wound in coils1 together they form an induction-coil4 ,the wire which we have called the first wire forms the primary coil1 and the one we have called the second wire forms the secondary coil4 ,by repeatedly making and breaking the circuit in the primary coil we get an alternating current in the secondary coil4 ,fig4 #ca is from a photograph of some of the coils actually used by ,faraday4 ,illustration3 ,,fig4 #ca--;,,historical ,,apparatus ,,of ,,faraday ,,in ,,the ,,royal ,,institution ,some of ,faraday's transformer coils are shown here4 ,the instrument on the left in a glass case is his galvanometer4 ,faraday's ,dynamo ,to invent a new electrical machine was ,faraday's next aim4 ,arago's disk of copper whirling near a magnet had a current induced in it1 so ,faraday thought4 ,it was the action of this induced current which caused the magnet to follow the whirling disk4 ,could the current in ,arago's disk be collected and caused to flow through a wire8 ,he placed a copper disk between the poles of a magnet4 ,one galvanometer wire passed around the axis of the disk1 the other he held in contact with the edge4 ,he whirled the disk4 ,the galvanometer needle moved4 ,a current was flowing in the disk as it whirled4 ,the current from the whirling disk flowed through the galvanometer4 ,faraday had discovered the dynamo 7,fig4 #cb74 ,illustration3 ,,fig4 #cb--;,,faraday',s ,,first ,,dynamo ,a current flows in the copper disk as it whirls between the poles of the magnet4 ,by permission of ,joseph ,g4 ,branch4 ,all this work occupied but ten days in the autumn of #ahca1 though years of preparation had gone before4 ,in these ten days the foundation was laid for the induction-coil1 modern dynamo-electric machinery1 and electric lighting4 ,fig4 #cc shows the laboratory in which ,faraday did this work4 ,illustration3 ,,fig4 #cc--;,,faraday',s ,,laboratory1 ,,where ,,the ,,first ,,dynamo ,,was ,,made ,from the water-color drawing by ,miss ,harriet ,moore4 ,faraday continued to explore the field opened up before him4 ,in one experiment two small pencils of charcoal lightly touching were connected to the ends of a secondary coil4 ,a spark passed between the charcoal points when the primary circuit was closed4 ,this was the first transformer producing a tiny electric light 7,fig4 #cd74 ,illustration3 ,,fig4 #cd--,,the ,,first ,,transformer ,faraday discovered the induction-coil1 the dynamo1 and the transformer1 and he showed that1 in each of these1 it is magnetism which produces the electric current4 ,he had discovered the secret when he obtained a current by thrusting a magnet into a coil of wire4 ,the space about a magnet in which the magnet will attract iron he called the magnetic field 7,figs4 #ce and #cf74 ,in every case of magnetism causing an electric current to flow in a coil of wire1 the coil is in a magnetic field1 and the magnetic field is changing--that is1 the magnetic field is made alternately stronger and weaker1 or the coil moves across the magnetic field4 ,the point is that magnetism at rest will not produce an electric current4 ,there must be a changing magnetic field or motion4 ,in ,faraday's dynamo a copper disk whirled between the poles of a magnet and the whirling of the disk in the magnetic field caused an electric current4 ,in the modern dynamo it is the whirling of a coil of wire in a magnetic field that causes a current to flow4 ,in the induction-coil it is the change in the magnetic field that causes a current to flow in the secondary coil4 ,a coil of wire with an electric current flowing through it will attract iron like a magnet4 ,the primary coil with a current from a battery flowing through it acts in all respects like a magnet2 but as soon as the current ceases to flow the magnetic field disappears--the coil is no longer a magnet4 ,when we make and break the connection between the primary coil and the battery1 then1 we repeatedly make and destroy the magnetic field1 and this changing magnetic field causes a current to flow in the secondary coil4 ,the induction-coil is one form of transformer4 ,we shall see later how the dynamo and the transformer developed in the nineteenth century4 ,illustration3 ,,fig4 #ce--,,the ,,magnetic ,,field ,,is ,,the ,,space ,,around ,a ,,magnet ,,in ,,which ,,it ,,will ,,attract ,,iron ,the iron filings over the magnet arrange themselves along the lines of force4 ,illustration3 ,,fig4 #cf--,,magnetic ,,field ,,of ,a ,,horseshoe ,,magnet ,when a boy1 ,faraday had passed the current from his little battery through a jar of cistern-water1 and saw in the water a dense white cloud descending from the positive wire1 and bubbles arising from the negative wire4 ,something was being taken out of the water by the electric current4 ,when he tried the experiment later in his laboratory1 he found that1 whenever an electric current is passed through water1 bubbles of two gases1 oxygen and hydrogen1 rise through the water4 ,he found that if the current is made stronger the bubbles are formed faster4 ,the water in time disappears1 for it has been changed or decomposed into the two gases4 ,it was the current from a battery that would decompose water4 ,the electricity from the electrical machine would do other things that he had never seen a battery current do4 ,do the battery and the electrical machine produce different kinds of electricity1 or is electricity one and the same in whatever way it is produced8 ,this was the query that troubled him4 ,the answer to this question had been so uncertain that the effect of the voltaic battery had been termed galvanism1 while that of the friction machine retained the name electricity4 ,faraday tried many experiments in searching for an answer to this question4 ,he found that the electricity of the machine will produce the same effect as that of a battery if the machine is compelled to discharge slowly4 ,an electrical machine or a battery of ,leyden jars can be made to give out an electric current1 and this current will affect a magnetic needle in the same way that a battery current will4 ,it will magnetize steel4 ,if passed through water1 it will decompose the water into the two gases oxygen and hydrogen4 ,in short1 a current from an electrical machine or a ,leyden jar will do everything that a current from an electric battery will do4 ,faraday caused the ,leyden jar to give a current instead of a spark by connecting the two metal coatings with a wet string4 ,on the other hand1 the discharge from a powerful electric battery will produce a spark and affect the human nerves in the same way as the discharge from the electrical machine4 ,the same effects may be obtained from one as from the other4 ,in the discharge from the machine1 a small quantity of electricity is discharged under high pressure1 as water may be forced through a small opening by very high pressure4 ,the voltaic cell1 on the other hand1 furnishes a large quantity of electricity at low pressure1 as a street may be flooded by a broken water-main though the pressure is low4 ,in fact1 the quantity of electricity required to decompose a grain of water is equal to that discharged in a stroke of lightning1 while the action of a dilute acid on the one-hundredth part of an ounce of zinc in a battery yields electricity sufficient for a powerful thunder-storm4 ,many tests were made1 and the result was a convincing proof that electricity is the same whatever its source1 the different effects being due to difference in pressure and quantity4 ,but in no case1 said ,faraday1 not even in those of the electric eel and torpedo1 is there a production of electric power without something being used up to supply it4 ,faraday's professional work would have made him wealthy4 ,in one year he made #ajjj 7#ejjj71 and the amount would have increased had he sold his services at their market value4 ,but then there would have been no ,faraday the discoverer4 ,the world would have had to wait1 no one knows how long1 for the laying of the foundations of electrical industries4 ,he chose to give up wealth for the sake of discovery4 ,he gave up professional work with the exception of scientific adviser to ,trinity ,house1 the body which has charge of ,great ,britain's lighthouse service4 ,nor did he carry his discoveries to the point of practical application4 ,as soon as he discovered one principle1 he set out in pursuit of others1 leaving the practical application to the future4 ,faraday loved the beauty of nature4 ,the sunset he called the scenery of heaven4 ,he saw the beauty of electricity1 which he said lies not in its mystery1 but in the fact that it is under law and within the control of the human intellect4 ,a ,wonderful ,law of ,nature ,not long after ,faraday made his first dynamo1 ,robert ,mayer1 a physician from ,germany1 was making a voyage to the ,east ,indies which proved to be a voyage of discovery4 ,he had sailed as the ship's physician1 and after some months an epidemic broke out among the ship's company4 ,in his treatment he drew blood from the veins of the arms4 ,he was startled to see bright-red blood issue from the veins4 ,he might almost have believed that he had opened an artery by mistake4 ,it was soon explained to him by a physician who had lived long in the tropics that the blood in the veins of the natives1 and of foreigners as well1 in the tropics is of nearly the same color as arterial blood4 ,in colder climates the venous blood is much darker than the arterial4 ,he reasoned upon this curious fact for some time1 and came to the conclusion that the human body does not make heat out of nothing1 but consumes fuel4 ,the fuel is consumed in the blood1 and there the heat is produced4 ,in the tropics less heat is needed1 less fuel is consumed1 and therefore there is less change in the color of the blood4 ,when a man works he uses up fuel4 ,if a blacksmith heats a piece of iron by hammering1 the heat given to the iron and the heat produced in his body are together equal to the heat of the fuel consumed in his blood4 ,the work a man does1 as well as the heat of his body1 comes from the burning of the fuel in his blood4 ,what is true of a man is true of an engine4 ,the work the engine does1 as well as the heat it produces1 comes from the heat of the fuel in the furnace4 ,mayer found that one hundred pounds of coal in a good working engine produces the same amount of heat as ninety-five pounds in an engine that is not working4 ,in the working engine the heat of the five pounds of coal is used up in the work of running the engine1 and therefore does not heat the engine4 ,heat that is used in running the engine is no longer heat1 but work4 ,so ,mayer said the heat is not destroyed1 but only changed into work4 ,he said1 further1 that the work of running the engine may be changed again into heat4 ,mayer's theory was opposed by many scientific men of ,europe4 ,one great scientist said to him that if his theory were correct water could be warmed by shaking4 ,he remembered what the helmsman had remarked to him on the voyage to ,java1 that water beaten about by a storm is warmer than quiet sea-water2 but he said nothing4 ,he went to his laboratory1 tried the experiment1 and some weeks later returned1 exclaiming3 ,it is so6 ,it is so6 ,he had warmed water simply by shaking it4 ,these results mean that work or energy cannot be destroyed4 ,though it changes form in many ways1 it is never destroyed4 ,neither can man create energy2 he can only direct its changes as the engineer1 by the motion of his finger in opening a valve1 sets the locomotive in motion4 ,he does not move the locomotive4 ,he directs the energy already in the steam4 ,since the time of ,galileo1 men had caught now and then a glimpse of this great law4 ,galileo had stated his law of machines2 that1 when a machine does work1 a man or a horse or some other power does an equal amount of work upon the machine4 ,count ,rumford had performed his experiment with the cannon1 showing that heat is produced by the work of a horse4 ,davy had proved that1 in the voltaic battery1 something must be used up to produce the current--the mere contact of the metals is not sufficient4 ,faraday had said that in no case is there a production of electrical power without something being used up to supply it4 ,mayer stated clearly this law of energy when he said that energy cannot be created or destroyed1 but only changed from one form to another4 ,and yet inventors have not learned the meaning of this law4 ,they continue trying to invent perpetual-motion machines--machines that will produce work from nothing4 ,this is what a perpetual-motion machine would be if such a machine were possible4 ,for a machine without friction is impossible1 and friction means wasted work--work changed into heat4 ,a machine to keep itself running and supply the work wasted in friction must produce work from nothing4 ,the great law of nature is that you cannot get something for nothing4 ,whether you get work1 heat1 electricity1 or light1 something must be used up to produce it4 ,for whatever you get out of a machine you must give an equivalent4 ,this law cannot be evaded1 and from it there is no appeal4 ,chapter ,v ,,great ,,inventions ,,of ,,the ,,nineteenth ,,century ,the discoveries of ,faraday prepared the way for the great inventions of the nineteenth century4 ,by the middle of the century men knew how to control the wonderful power of electricity4 ,they did not know what electricity is1 nor do we know to-day1 though we have made some progress in that direction2 but to control it and make it furnish light1 heat1 and power was more important4 ,before the inventions of ,james ,watt made it possible to use steam-power1 factories were built near falling water1 so that water-power could be used4 ,but the steam-engine made it possible to build great factories wherever a supply of water for the boilers could be obtained4 ,cities were built around the factories4 ,cities already great became greater4 ,with the growth of cities the need of a new means of producing light and power made itself felt4 ,electricity promised to become the ,hercules that should perform the tasks of the modern world4 ,discovery gave way to invention4 ,during the second half of the nineteenth century many great inventions were made and industries were developed1 while discoveries were few until near the close of the century4 ,within this period the great industries which characterize our modern civilization1 and which arose out of the discoveries that science had made in the centuries preceding1 attained a high degree of development4 ,in this chapter we shall trace the applications of some of the discoveries with which we have now become familiar4 ,this will lead us into the field of electrical invention1 for we are dealing now with the beginning of the world's electrical age4 ,electric ,batteries ,from the time of ,volta to the time of ,faraday the only means of producing an electric current was the voltaic battery1 so called in honor of ,volta4 ,the voltaic cell is the simplest form of electric battery4 ,in this cell the zinc and copper plates are placed in sulphuric acid diluted with water4 ,as the acid eats the zinc1 hydrogen gas is formed4 ,this gas collects in bubbles on the copper plate and weakens the current4 ,the aim of inventors was to produce a steady current1 to devise a battery in which no gas would collect on the copper plate4 ,they saw the need of a battery that would give out a current of unchanging strength until the zinc or the acid was used up4 ,the first real improvement in the battery was made by ,professor ,daniell1 of ,king's ,college1 ,london4 ,in the ,daniell cell the zinc plate is in dilute sulphuric acid1 and the copper plate is in a solution of blue vitriol or copper sulphate4 ,professor ,daniell separated the two liquids by placing one of them in a tube formed of the gullet of an ox4 ,this tube dipped into the other liquid4 ,the hydrogen gas1 as it was formed by the acid acting on the zinc1 could go through the walls of the tube1 but was stopped by the copper sulphate1 and copper was deposited on the copper plate4 ,this copper deposit in no way interfered with the current1 so that the current was not weakened until the zinc plate or one of the solutions was nearly consumed4 ,a cup of porous earthenware is now used in ,daniell cells to separate the liquids 7,fig4 #cg74 ,by placing crystals of blue vitriol in the battery jar1 the solution of blue vitriol can be kept up to its full strength for a very long time4 ,the zinc in time is consumed1 and must be replaced4 ,illustration3 ,,fig4 #cg--;,a ,,daniell ,,cell ,in the gravity cell 7,fig4 #ch7 the same materials are used as in the ,daniell cell--copper in copper sulphate1 and zinc in sulphuric acid2 but there is no porous cup4 ,the solutions are kept separate by gravity1 the heavy copper sulphate being at the bottom4 ,the gravity cell has until recently been extensively used in telegraphy1 and continues in use in short-distance telegraphy and in automatic block signals4 ,the gravity and ,daniell cells are used for closed-circuit work--that is1 for work in which the current is flowing almost constantly4 ,illustration3 ,,fig4 #ch--;,a ,,gravity ,,cell ,the ,dry ,battery ,another important improvement was the invention of the dry battery4 ,you will remember that the first battery1 the one invented by ,volta1 was a form of dry battery2 but it was a very feeble battery compared with the dry batteries now in use1 so that we may call the dry battery a new invention4 ,the dry battery is falsely named4 ,there can be no battery without a liquid4 ,in the dry battery the zinc cup forming the outside of the cell is one of the plates of the cell 7,fig4 #ci74 ,the battery appears to be dry because the solution of sal ammoniac is absorbed by blotting-paper or other porous substance in contact with the zinc4 ,the inner plate is carbon1 and this is surrounded by powdered carbon and manganese dioxide--the latter to remove the hydrogen gas which collects on the carbon plate4 ,this gas weakens the current when the circuit has been closed for a short time1 but is slowly removed when the circuit is broken4 ,thus the battery is said to recover4 ,illustration3 ,,fig4 #ci--,,showing ,,what ,,is ,,in ,a ,,dry ,,battery ,the dry cell will give a strong current1 but for a short time only4 ,it recovers1 however1 if allowed to rest4 ,it can be used1 therefore1 only in open-circuit work--such as door-bell circuits1 and some forms of fire and burglar alarm4 ,a door-bell circuit is open nearly all the time1 the current flowing only while the button is being pressed4 ,some forms of wet battery work in the same way as the dry battery1 and are used like-wise for open-circuit work4 ,in these batteries carbon and zinc plates in a solution of sal ammoniac are used1 the same materials as in the dry battery4 ,the only difference is that in the dry battery the solution is absorbed by some porous substance and the battery sealed so that it appears to be dry4 ,the ,storage ,battery ,one of the greatest improvements in electric batteries is the storage battery4 ,a simple storage battery may be made by placing two strips of lead in sulphuric acid diluted with water and connecting the lead strips to a battery of ,daniell cells or dry cells4 ,in a short time one of the lead strips will be found covered with a red coating4 ,the surface of this lead strip is no longer lead but an oxide of lead1 somewhat like the rust that forms on iron4 ,if the lead strips are now disconnected from the other battery and connected to an electric bell1 the bell will ring4 ,we have here two plates1 one of lead and one of oxide of lead1 in dilute sulphuric acid4 ,this forms a storage battery4 ,the first storage battery was made of two sheets of lead rolled together and kept apart by a strip of flannel4 ,the lead strips thus separated were immersed in dilute sulphuric acid4 ,a current from another battery was passed through this cell for a long time--first in one direction1 then in the other4 ,this roughened the surface of the lead plates1 so that the battery would hold a greater charge4 ,the battery was then charged by passing a current through it in one direction only for a considerable length of time4 ,feeble cells were used for charging4 ,it took days1 and sometimes weeks1 to charge the first storage batteries4 ,then the storage battery would give out a strong current lasting for a few hours4 ,it slowly accumulated energy while being charged1 and then gave out this energy rapidly in the form of a strong electric current4 ,for this reason the storage battery was called an accumulator4 ,while charging the storage cell there was formed on the negative plate a coating of soft lead1 and on the positive plate a coating of dark-brown oxide of lead4 ,it was found better to apply these coatings to the lead plates before making up the battery4 ,later it was found that the battery would hold a still greater charge if the plates were made in the form of grids 7,fig4 #dj71 and the cavities filled with the active material--the negative with spongy lead1 and the positive with dark-brown lead oxide4 ,some excellent commercial storage batteries are made from lead plates by the action of an electric current1 very much as ,plant made his batteries4 ,fig4 #da shows one of these plates4 ,illustration3 ,,fig4 #dj--;,a ,,storage ,,battery1 ,,showing ,,the ,,grids ,illustration3 ,,fig4 #da--;,a ,,storage-,,battery ,,plate ,,made ,,from ,a ,,sheet ,,of ,,lead ,the storage battery does not store up electricity4 ,it produces a current in exactly the same way as any other battery--by the action of the acid on the plates4 ,when this action ceases it is no longer a battery1 though it may be made one again by passing a current through it in the opposite direction from that which it gives out4 ,in this it differs from the voltaic battery1 for when such a battery is run down it can be restored only by adding new solution or new plates4 ,the storage battery is especially useful for sparking in gas or gasolene motors4 ,edison has invented a storage battery that will do as much work as a lead battery of twice its weight4 ,edison's battery is intended especially for use in electric automobiles4 ,by reducing the weight of the battery which the machine must carry the weight of the truck may also be reduced4 ,in the ,edison battery the positive plates are made of a grid of nickel-plated steel containing tubes filled with pure nickel4 ,the negative plate consists of a nickel-plated steel grid containing an oxide of iron similar to common iron-rust4 ,after working a number of years on this battery and making nine thousand experiments1 ,edison thought he had it perfected1 and indeed it was a great improvement over the storage batteries that had been used--much lighter and cheaper1 and more successful in operation4 ,two hundred and fifty automobiles were equipped with it1 and it proved superior to lead batteries for this purpose4 ,but it was not to ,edison's liking4 ,he threw the machinery1 worth thousands of dollars1 on the scrap-heap1 and worked on for six years4 ,he had then produced a battery as much better than the first as the first was better than the lead battery1 and he was content to have the new battery placed on the market4 ,the ,dynamo ,for the purpose of lighting and power the electric battery proved too costly4 ,davy produced an arc light with a battery of four thousand cells4 ,the arc was about four inches in length and yielded a brilliant light1 but as the cost was six dollars a minute it was not thought practical4 ,attempts were made early in the century to use a battery current for power1 but they failed because of the cost and the fact that no good working motor had been invented4 ,light and power were needed4 ,electricity could supply both4 ,but how overcome the difficulty of cost1 and produce an electric current from burning coal or falling water8 ,for answer man looked to the great discovery of ,faraday and his new electrical machine4 ,inventors in ,germany1 ,france1 ,england1 ,italy1 and ,america made improvements until from the disk dynamo of ,faraday there had evolved the modern dynamo4 ,electroplating and the telegraph are the only applications of the electric current that became factors in the world's industry before the dynamo1 yet in long-distance telegraphy and in electroplating to-day the dynamo is used4 ,without the dynamo1 electric lighting1 electric power1 and electric traction as developed in the nineteenth century would have been impossible2 in fact1 the dynamo with the electric motor 7which1 as we shall see1 is only a dynamo reversed7 is master of the field4 ,the way had been prepared for the application of ,faraday's discovery by ,william ,sturgeon1 an ,englishman1 and ,joseph ,henry1 an ,american4 ,sturgeon discovered that soft iron is more quickly magnetized than steel1 and found that the strength of an electromagnet can be greatly increased by making the core of a soft-iron rod and bending the rod into the form of a horseshoe 7,fig4 #db74 ,the iron rod was coated with sealing-wax and wound with a single layer of copper wire1 the turns of wire not touching4 ,this was in #ahbe1 before ,faraday discovered the principle of the dynamo4 ,illustration3 ,,fig4 #db--,,sturgeon',s ,,electromagnet ,professor ,henry still further increased the strength of the electromagnet by covering the wire with silk1 which made it possible to wind several layers of wire on the iron core1 and many times the length of wire that had been used by ,sturgeon4 ,fig4 #dc shows such a magnet4 ,one of ,henry's magnets weighed fifty-nine and a half pounds1 and would hold up a ton of iron4 ,sturgeon said3 ,professor ,henry has produced a magnetic force which completely eclipses every other in the whole annals of magnetism4 ,with ,professor ,henry's invention the electromagnet was ready for use in the dynamo4 ,fig4 #dd shows a strong electromagnet4 ,illustration3 ,,fig4 #dc--;,,an ,,electromagnet ,,with ,,many ,,turns ,,of ,,insulated ,,wire ,illustration3 ,,fig4 #dd--;,,an ,,electromagnet ,,lifting ,,twelve ,,tons ,,of ,,iron ,a moving magnet causes a current to flow in a coil1 but a magnet at rest has no effect4 ,a moving magnet is equal to a battery4 ,in ,faraday's experiments a current was induced in a coil of wire by moving a magnet in the coil or by making and breaking the circuit in another coil wound on the same iron core4 ,a current was induced in a metal disk by revolving it between the poles of a magnet4 ,in every case there was motion in a magnetic field1 or the field itself was changed4 ,a changing magnetic field is equal to a moving magnet4 ,what is needed to induce a current in a coil1 whether it be in a dynamo1 an induction-coil1 or a transformer1 is a changing magnetic field about the coil or motion of the coil in the magnetic field4 ,if fine iron filings are sprinkled over the poles of a magnet the filings arrange themselves in definite lines4 ,this is a simple experiment which any boy can try for himself4 ,faraday called the lines marked out by the iron filings lines of force 7the lines of force of a horseshoe magnet are shown in ,fig4 #cf71 because they indicate the direction in which the magnet pulls a piece of iron--that is1 the direction of the magnetic force4 ,now1 if a current is to be induced in a wire1 the wire must move across the lines of force4 ,if the wire moves along the lines marked out by the iron filings1 there will be no current4 ,when a coil rotates between the poles of a magnet1 the wire moves across the lines of force and a current is induced in the coil if the circuit is closed4 ,this is the way a current is produced in a dynamo4 ,faraday produced a current by rotating a coil between the poles of a steel magnet4 ,he made a number of such machines1 and used them with some success in producing lights for lighthouses1 but the defects of these machines were so great that the lighting of a city or the development of power on a large scale was impractical4 ,the electromagnet was needed to solve the problem4 ,siemens' ,dynamo ,the war of #ahff between ,austria and ,prussia and the certainty of a coming struggle with ,france turned the attention of ,german inventors to the use of electricity in warfare4 ,werner von ,siemens1 an artillery officer1 was improving an exploding device for mines4 ,an electric current was needed to produce a spark or heat a wire to redness in the powder4 ,faraday had used a coil of wire turning between the poles of a steel magnet to produce a current4 ,in ,england a coil turning between the poles of an electromagnet had been used1 but the electromagnet received its current from another machine in which a steel magnet was used4 ,siemens found that the steel magnet could be dispensed with1 and that a coil turning between the poles of an electromagnet could furnish the current for the electromagnet4 ,two things are needed1 then1 to make a dynamo3 an electromagnet and a coil to turn between the poles of that magnet4 ,the rotating coil1 which usually contains a soft-iron core1 is called the armature4 ,the coil will furnish current for the magnet and some to spare2 in fact1 only a small part of the current induced in the coil is needed to keep the magnet up to its full strength1 and the greater part of the current may be used for lighting or power4 ,the new machine was named by its inventor the dynamo-electric machine4 ,the name has since been shortened to dynamo4 ,the first practical problem which the dynamo solved was the construction of an electric exploding apparatus without the use of steel magnets or batteries4 ,a dynamo with ,siemens' armature is shown in ,fig4 #de4 ,illustration3 ,,fig4 #de--;,a ,,dynamo ,,with ,,siemens' ,,armature ,in his first enthusiasm the inventor dreamed of great things for the new machine1 among others an electric street railway in ,berlin4 ,but the dynamo was not yet ready4 ,the difficulty was the heating of the iron core of the armature1 caused by the action of induced currents4 ,there are induced currents in the iron core as well as in the coil1 and1 for the same reason1 the coil and the iron core within it are both moving in a magnetic field4 ,these little currents circling round and round in the iron core produce heat4 ,the rapid changing of the magnetism of the iron also heats the iron4 ,it remained for ,gramme1 in ,france1 to apply the proper remedy4 ,this remedy was an armature in which the coil was wound on an iron ring1 invented by an ,italian1 ,pacinotti4 ,gramme applied the principle discovered by ,siemens to ,pacinotti's ring1 and produced the first practical dynamo for strong currents4 ,this was in #ahfh4 ,a ring armature is shown in ,fig4 #df4 ,the first dynamo patented in the ,united ,states is shown in ,fig4 #dg4 ,this dynamo is only a curiosity4 ,illustration3 ,,fig4 #df--,,ring ,,armature ,illustration3 ,,fig4 #dg--;,,first ,,dynamo ,,patented ,,in ,,the ,,united ,,states ,intended to be used for killing whales4 ,photo by ,claudy4 ,the ,drum ,armature ,an improvement in the ,siemens armature was made four years later by ,von ,hefner-,alteneck1 an engineer in the employ of ,siemens4 ,this improvement consisted in winding on the iron core a number of coils similar to the one coil of the ,siemens armature1 but wound in different directions4 ,this is called the drum armature 7,fig4 #dh74 ,the heating of the core is prevented by building it up of a number of thin iron plates insulated from one another and by air-spaces within the core4 ,the insulation prevents the small currents from flowing around in the core4 ,the air-spaces serve for cooling4 ,the drum armature was a great improvement over both the ,siemens and the ,gramme armatures4 ,with the ,siemens one-coil armature there is a point in each revolution at which there is no current4 ,the current1 therefore1 varies during each revolution of the armature from zero to full strength4 ,in the ,gramme armature only half the wire1 the part on the outside of the ring1 receives the full effect of the magnetic field4 ,the inner half is practically useless1 except to carry the current which is generated in the outer half4 ,both these difficulties are avoided in the drum armature4 ,the dynamos of to-day are modifications of the two kinds invented by ,siemens and ,gramme4 ,many special forms have been designed for special kinds of work4 ,illustration3 ,,fig4 #dh--;,a ,,drum ,,armature1 ,,showing ,,how ,,an ,,armature ,,of ,,four ,,coils ,,is ,,wound ,edison's ,compound-,wound ,dynamo ,edison1 in his work on the electric light and the electric railway1 made some important improvements in the dynamo4 ,the armature of a dynamo is usually turned by a steam-engine4 ,edison found that much power was wasted in the use of belts to connect the engine and the dynamo4 ,he therefore connected the engine direct to the dynamo1 placing the armature of the dynamo on the shaft of the engine4 ,he also used more powerful field-magnets than had been used before4 ,his greatest improvement1 however1 was in making the dynamo self-regulating1 so that the dynamo will send out the strength of current that is needed4 ,such a dynamo will send out more current when more lights are turned on4 ,whether it supplies current for one light or a thousand1 it sends out just the current that is needed--no more1 no less4 ,it will do this if no human being is near4 ,an attendant is needed only to keep the machinery well oiled and see that each part is in working order4 ,edison brought about this improvement by his improved method of winding4 ,this method is known as compound winding4 ,to understand compound winding we must first understand two other methods of winding4 ,in the series winding 7,fig4 #di71 all the current generated in the armature flows through the coils of the field-magnet4 ,there is only one circuit4 ,the same current flows through the coils of the magnet and through the outer circuit1 which may contain lights or motors4 ,such a dynamo is commonly used for arc lights4 ,it will not regulate itself4 ,if left to itself it will give less electrical pressure when more pressure is needed4 ,it requires a special regulator4 ,illustration3 ,,fig4 #di--;,a ,,series-,,wound ,,dynamo ,in the second form of winding the current is divided into two branches4 ,one branch goes through the coils of the field-magnet4 ,the other branch goes through the line wire for use in lights or motors4 ,this is called the shunt winding 7,fig4 #ej74 ,the shunt-wound dynamo is used for incandescent lights4 ,it also requires a special regulator1 for if left to itself it gives less electrical pressure when the pressure should be kept the same4 ,illustration3 ,,fig4 #ej--;,a ,,shunt-,,wound ,,dynamo ,the compound winding 7,fig4 #ea71 which was first used by ,edison1 is a combination of the series and shunt windings4 ,illustration3 ,,fig4 #ea--;,a ,,compound-,,wound ,,dynamo ,the current is divided into two branches4 ,one branch goes only through the field-coils4 ,the other branch goes through additional coils which are wound on the field-magnet1 and also through the external circuit4 ,such a dynamo can be made self-regulating1 so that it will give always the same electrical pressure whatever the number of lamps or motors thrown into the circuit4 ,in maintaining always the same pressure it of course supplies more or less current1 according to the amount of current that is needed4 ,this is clear if we compare the flow of electric current with the flow of water4 ,open a water-faucet and notice how fast the water flows4 ,then open several other faucets connected with the same water-pipe4 ,probably the water will not flow so fast from the first faucet4 ,that is because the pressure has been lowered by the flow of water from the other faucets4 ,if we could make the water adjust its own pressure and keep the pressure always the same1 then the water would always flow at the same rate through a faucet1 no matter how many other faucets were opened4 ,this is what happens in the ,edison compound-wound dynamo4 ,turn on one #af-;candle-power carbon lamp4 ,it takes about half an ampere of current4 ,turn on a hundred lamps connected to the same wires1 and the dynamo of its own accord keeps the pressure the same1 and supplies fifty amperes1 or half an ampere for each lamp4 ,with this invention of ,edison the dynamo was practically complete1 and ready to furnish current for any purpose for which current might be needed4 ,fig4 #eb shows one of ,edison's first dynamos4 ,fig4 #ec shows a dynamo used for lighting a railway coach4 ,illustration3 ,,fig4 #eb--,,one ,,of ,,edison',s ,,first ,,dynamos ,permission of ,association of ,edison ,illuminating ,companies4 ,illustration3 ,,fig4 #ec--;,a ,,dynamo ,,mounted ,,on ,,the ,,truck ,,of ,a ,,railway ,,car ,the dynamo furnishes current for the electric lights in the car4 ,when the train is not running the current is furnished by a storage battery4 ,electric ,power ,it has been said that the nineteenth century was the age of steam1 but the twentieth will be the age of electricity4 ,before the end of the nineteenth century1 however1 electric power had become a reality1 and there remained only development along practical lines4 ,we must turn to ,oersted1 ,ampre1 and ,faraday to find the beginning of electric power4 ,in ,oersted's experiment1 motion of a magnet was produced by an electric current4 ,ampre found that electric currents attract or repel each other1 and this because of their magnetic action4 ,faraday found that one pole of a magnet will spin round a wire through which a current is flowing4 ,here was motion produced by an electric current4 ,these great scientists discovered the principles that were applied later by inventors in the electric motor4 ,a number of motors were invented in the early years of the century1 but they were of no practical use4 ,it was not until after the invention of the ,gramme and ,siemens dynamos that a practical motor was possible4 ,it was found that one of these dynamos would run as a motor if a current were sent through the coils of the armature and the field-magnet2 in fact1 the current from one dynamo may be made to run another similar machine as a motor4 ,thus the dynamo is said to be reversible4 ,if the armature is turned by a steam-engine or some other power1 a current is produced4 ,if a current is sent through the coils1 the armature turns and does work4 ,if the machine is used to supply an electric current1 it is a dynamo4 ,if used to do work--as1 for example1 to propel a street-car and for that purpose receives a current--it is a motor4 ,the same machine may be used for either purpose4 ,in practice there are some differences in the winding of the coils of dynamos and motors1 yet any dynamo can be used as a motor and any motor can be used as a dynamo4 ,this discovery made it possible to transmit power to a distance with little waste as well as to divide the power easily4 ,the current from one large dynamo may light streets and houses1 and at the same time run a number of motors in factories or street-cars at great distances apart4 ,a central-station dynamo may run the motors that propel hundreds of street-cars4 ,dynamos at ,niagara furnish current for motors in ,buffalo and other cities4 ,one great scientist1 who no doubt fore-saw the wonders of electricity which we know so well to-day1 said that the greatest discovery of the nineteenth century was that the ,gramme machine is reversible4 ,the ,first ,electric ,railway ,the electric railway was made possible by the invention of the dynamo and the discovery that the dynamo is reversible4 ,at the ,industrial ,exposition in ,berlin in #ahgi there was exhibited the first practical electric locomotive1 the invention of ,doctor ,siemens4 ,the locomotive and its passenger-coach were absurdly small4 ,the track was circular1 and about one thousand feet in length4 ,this diminutive railway was referred to by an ,american magazine as ,siemens' electrical merry-go-round4 ,but the electrical merry-go-round aroused great interest because of the possibilities it represented 7,fig4 #ed74 ,illustration3 ,,fig4 #ed--;,,first ,,electric ,,locomotive ,the current was generated by a dynamo in ,machinery ,hall1 this dynamo being run by a steam-engine4 ,an exactly similar dynamo mounted on wheels formed the locomotive4 ,the current from the dynamo in ,machinery ,hall was used to run the other as a motor and so propel the car4 ,the rails served to conduct the current4 ,a third rail in the middle of the track was connected to one pole of the dynamo and the two outer rails to the other pole4 ,a small trolley wheel made contact with the third rail4 ,the rails were not insulated1 but it was found that the leakage current was very small1 even when the ground was wet4 ,the success of this experiment aroused great interest1 not only in ,germany1 but in ,europe and ,america4 ,america's greatest inventor1 ,edison1 took up the problem4 ,edison employed no trolley line or third rail1 but only the two rails of the track as conductors1 sending the current out through one rail and back through the other4 ,of course1 this meant that the wheels must be insulated1 so that the current could flow from one rail to the other only through the coils of the motor4 ,as in ,siemens' experiment1 the motor was of the same construction as the dynamo4 ,the rails were not insulated1 and it was found that1 even when the track was wet1 the loss of electric current was not more than #e per cent4 ,edison found that he could realize in his motor #gj per cent4 of the power applied to the dynamo1 whereas the ,german inventor was able to realize only #fj per cent4 ,the improvement was largely due to the improved winding4 ,edison was the first to use in practical work the compound-wound dynamo1 and this was done in connection with his electric railway4 ,fig4 #ee shows ,edison's first electric locomotive4 ,illustration3 ,,fig4 #ee--;,,first ,,edison ,,electric ,,locomotive ,the question of gearing was a troublesome one4 ,the armature shaft of the motor was at first connected by friction gearing to the axle of two wheels of the locomotive4 ,later a belt and pulleys were used4 ,an idler pulley was used to tighten the belt4 ,when the motor was started and the belt quickly tightened the armature was burned out4 ,this happened a number of times4 ,then ,mr4 ,edison brought out from the laboratory a number of resistance-boxes1 placed them on the locomotive1 and connected them in series with the armature4 ,these resistances would permit only a small current to flow through the motor as it was starting1 and so prevent the burning-out of the armature coils4 ,the locomotive was started with the resistance-boxes in circuit1 and after gaining some speed the operator would plug the various boxes out of circuit1 and in that way increase the speed4 ,when the motor is running there is a back-pressure1 or a pressure that would cause a current to flow in the opposite direction from that which is running the motor4 ,because of this back-pressure the current which actually flows through the motor is small1 and the resistance-boxes may be safely taken out of the circuit4 ,finding the resistance-boxes scattered about under the seats and on the platform as they were a nuisance1 ,mr4 ,edison threw them aside1 and used some coils of wire wound on the motor field-magnet which could be plugged out of the circuit in the same way as the resistance-boxes4 ,this device of ,edison's was the origin of the controller1 though in the controller now used on street-cars not only is the resistance cut out as the speed of the car increases1 but the electrical connections of the motor are changed in such a way as to increase its speed gradually4 ,fig4 #ef shows ,edison's first passenger locomotive4 ,illustration3 ,,fig4 #ef--;,,edison',s ,,first ,,passenger ,,locomotive ,the news of the little electric railway at the ,industrial ,exposition in ,berlin was soon noised abroad1 and the ,german inventor received inquiries from all parts of the world1 indicating that efforts would be made in other countries to develop practical electrical railways4 ,the firm of ,siemens ,halske therefore determined to build a line for actual traffic1 not for profit1 but that ,germany might have the honor of building the first practical electric railway4 ,the line was built between ,berlin and ,lichterfelde1 a distance of about one and a half miles4 ,a horse-car seating twenty-six persons was pressed into service4 ,a motor was mounted between the axles1 and a central-station dynamo exactly like the motor was installed4 ,as in ,edison's experimental railway1 the two rails of the track were used to carry the current4 ,this electric line replaced an omnibus line1 and was immediately used for regular traffic1 and thus the electric railway was launched upon its remarkable career4 ,the first electric car used for commercial service is shown in ,fig4 #eg4 ,illustration3 ,,fig4 #eg--;,,first ,,commercial ,,electric ,,railway ,an old horse-car converted into an electric car4 ,electric ,lighting ,from the time when the night-watchman carried a lantern to the time of brilliantly lighted streets was less than a century4 ,it was a time when the rapid growth of railways and commerce brought about a rapid growth of cities1 and with the growth of cities the need of illumination4 ,factories must run at night to meet the world's demands4 ,commerce cannot stop when the sun sets4 ,the centres of commerce must have light4 ,during this time scientists were at work in their laboratories developing means for producing a high vacuum4 ,they were able to pump the air out of a glass bulb until less than a millionth part of the air remained4 ,they little dreamed that there was any connection between the high vacuum and the problem of lighting4 ,discoverers were at work bringing to light the principles now utilized in the dynamo4 ,in the fulness of time these factors were brought together to produce an efficient system of lighting4 ,for a time gas replaced the lantern of the night-watchman1 only to yield the greater portion of the field to its rival1 electricity4 ,the first efforts were in the direction of the arc light4 ,from the earliest times the light given out by an electric spark had been observed4 ,it was the aim of inventors to produce a continuous spark that should give out a brilliant light4 ,it was thought for a time that the electric battery would solve the problem1 but the cost of the battery current was too great4 ,again we are indebted to ,faraday1 for it was the dynamo that made electric lighting possible4 ,an arc light is produced by an electric current flowing across a gap between two sticks of carbon4 ,the air offers very great resistance to the flow of electric current across this gap4 ,now whenever an electric current flows through something which resists its flow1 heat is produced4 ,the high resistance of the air-gap causes such intense heat that the tips of the carbons become white hot and give out a brilliant light4 ,if examined through a smoked glass a beautiful blue arc of carbon vapor may be seen between the carbon tips4 ,if the current flows in one direction only1 one of the carbons1 the positive1 becomes hotter and brighter than the other4 ,in #ahgh the streets of ,paris were lighted with the ,jablochkoff candle1 a form of arc light supplied with current by the ,gramme machine4 ,in the same year the ,brush system of arc lighting was given to the public4 ,this was the beginning of our present system of arc lighting4 ,the electric arc is suitable for lighting streets and for large buildings1 but cannot be used for lighting houses4 ,the light is too intense4 ,one arc would furnish enough light for a number of houses if the light could be divided so that there might be just the right amount of light in each room4 ,but this is impossible with the electric arc4 ,the ,edison system of incandescent lighting was required to solve the problem of lighting houses by electricity4 ,in #ahhj the ,edison system was brought out for commercial use4 ,edison's problem was to produce a light that could be divided into a number of small lights1 and one that would require less attention than the arc light4 ,he tried passing a current through platinum wire enclosed in a vacuum4 ,this gave a fairly good light1 but was not wholly satisfactory4 ,he sat one night thinking about the problem1 unconsciously fingering a bit of lampblack mixed with tar which he had used in his telephone4 ,not thinking what he was doing1 he rolled this mixture of tar and lampblack into a thread4 ,then he noticed what he had done1 and the thought occurred to him3 ,why not pass an electric current through this thread of carbon8 ,he tried it4 ,a faint glow was the result4 ,he felt that he was on the right track4 ,a piece of cotton thread must be heated in a furnace in an iron mold1 which would prevent the thread from burning by keeping out the air4 ,then all the other elements that were in the thread would be driven out and only the carbon remain4 ,for three days he worked without sleep to prepare this carbon filament4 ,at the end of two days he succeeded in getting a perfect filament1 but when he attempted to seal it in the glass bulb it broke4 ,he patiently worked another day1 and was rewarded by securing a good carbon filament1 sealed in a glass globe4 ,he pumped the air out of this globe1 sealed it1 and sent a current through the carbon thread4 ,he tried a weak current at first4 ,there was a faint glow4 ,he increased the current4 ,the thread glowed more brightly4 ,he continued to increase the current until the slender thread of carbon1 which would crumble at a touch1 was carrying a current that would melt a wire of platinum strong enough to support a weight of several pounds4 ,the carbon gave a bright light4 ,he had found a means of causing the electric current to furnish a large number of small lights4 ,fig4 #eh is an excellent photograph of ,edison at work in his laboratory4 ,fig4 #ei shows some of ,edison's first incandescent lamps4 ,he next set out in search of the best kind of carbon for the purpose4 ,he carbonized paper and wood of various kinds--in fact1 everything he could find that would yield a carbon filament4 ,he tried the fibres of a ,japanese fan made of bamboo1 and found that this gave a better light than anything he had tried before4 ,he then began the search for the best kind of bamboo4 ,he learned that there are about twelve hundred varieties of bamboo4 ,he must have a sample of every variety4 ,he sent men into every part of the world where bamboo grows4 ,one man travelled thirty thousand miles and had many encounters with wild beasts in his search for the samples of bamboo4 ,at last a ,japanese bamboo was found that was better than any other4 ,the search for the carbon fibre had cost about a hundred thousand dollars4 ,later it was found that a squirted filament could be made that worked as well as the bamboo fibre4 ,this was made by dissolving cotton wool in a certain solution1 and then squirting this solution through a small hole into a small tank containing alcohol4 ,the alcohol causes the substance to set and harden1 and thus forms a carbon thread the size of the hole4 ,fig4 #fj shows the first commercial electric-lighting plant1 which was installed on the steamship ,columbia in #ahhj4 ,illustration3 ,copyright1 #aijd1 by ,byron1 ,n4 ,y4 ,,fig4 #eh--;,,edison1 ,,america',s ,,greatest ,,inventor1 ,,at ,,work ,,in ,,his ,,laboratory ,illustration3 ,copyright1 #aijd1 by ,william ,j4 ,hammer ,,fig4 #ei--;,,edison',s ,,famous ,,horseshoe ,,paper-,,filament ,,lamp ,,of #ahgj ,illustration3 ,,fig4 #fj--;,,first ,,commercial ,,edison ,,electric-,,lighting ,,plant2 ,,installed ,,on ,,the ,,steamship ,,columbia ,,in ,,may1 #ahhj ,the carbon thread in the incandescent light is heated to a white heat1 and because it is so heated it gives out light4 ,in air such a tiny thread of white-hot carbon would burn in a fraction of a second4 ,the carbon must be in a vacuum1 and so the air is pumped out of the light bulb with a special kind of air-pump invented not long before ,edison began his work on the electric light4 ,this pump is capable of taking out practically all the air that was in the bulb4 ,perhaps a millionth part of the original air remains4 ,a great invention is never completed by one man4 ,it was to be expected that the electric light would be improved4 ,a number of kinds of incandescent light have been devised1 using different kinds of filaments and adapted to a variety of uses4 ,the original ,edison carbon lamp1 however1 continues in use1 being better adapted to certain purposes than the newer forms4 ,the mercury vapor light deserves mention as a special form of arc light4 ,in the ordinary arc light the arc is formed of carbon vapor1 and the light is given out from the tips of the white-hot carbons4 ,in the mercury vapor light the light is given out from the mercury vapor which forms the arc4 ,this arc may be of any desired length1 and yields a soft1 bluish-white light which is a near approach to daylight4 ,the ,telegraph ,the need of some means of giving signals at a distance was early felt in the art of war4 ,flag signals such as are now used by the armies and navies of the world were introduced in the middle of the seventeenth century by the ,duke of ,york1 admiral of the ,english fleet1 who afterward became ,james ,,ii4 of ,england4 ,other methods of communicating at a distance were devised from time to time1 but the distance was only that at which a signal could be seen or a sound heard4 ,no means of communicating over very long distances was possible until the magnetic action of an electric current was discovered4 ,when ,oersted's discovery was made known men began to think of signalling to a distance by means of the action of an electric current on a magnetic needle4 ,a current may be sent over a very long wire1 and it will deflect a magnetic needle at the other end4 ,the movements of the needle may be controlled by opening and closing the circuit1 and a system of signals or an alphabet may be arranged4 ,a number of needle telegraphs were invented1 but they were too slow in action4 ,two other great inventions were needed to prepare the way for the telegraph4 ,one was the electromagnet in the form developed by ,professor ,henry1 a horseshoe magnet with many turns of silk-covered wire around the soft-iron core1 so that a very feeble current will produce a magnet strong enough to move an armature of soft iron4 ,the magnet has this strength because the current flows so many times around the iron core4 ,another need was that of a battery that could be depended on to give a constant current for a considerable length of time4 ,this need was met by the ,daniell cell4 ,the electromagnet made the telegraph possible4 ,the locomotive made it a necessity4 ,without the telegraph it would be impossible to control a railway system from a central office4 ,a train after leaving the central station would be like a ship at sea before the invention of the wireless telegraph4 ,nothing could be known of its movements until it returned4 ,the need of a telegraph was keenly felt in ,america when the new republic was extended to the ,pacific ,coast4 ,an ,english statesman said1 after the ,united ,states acquired ,california1 that this marked the end of the great ,american ,republic1 for a people spread over such a vast area and separated by such natural barriers could not hold together4 ,he did not know that the iron wire of the telegraph would bind the new nation firmly together4 ,the ,morse telegraph system now in use throughout the civilized world was made possible by the work of ,sturgeon and ,henry4 ,sturgeon's electromagnet might have been used for telegraphy through very short distances1 but ,henry's magnet1 with its coils of many turns of insulated wire1 was needed for long-distance signalling4 ,in one of the rooms of the ,albany ,academy1 ,professor ,henry caused an electromagnet to sound a bell when the current was transmitted through more than a mile of wire4 ,this might be called the first electromagnetic telegraph4 ,but the application to actual practice was made by ,morse1 and the man who first makes the practical application of a principle is the true inventor4 ,in #ahcb1 on board the packet-ship ,sully1 ,samuel ,f4 ,b4 ,morse1 an ,american artist1 forty-one years of age1 was returning from ,europe4 ,in conversation a ,doctor ,jackson referred to the electrical experiments of ,ampre1 which he had witnessed while in ,europe1 and1 in reply to a question1 said that electricity passes instantaneously over any known length of wire4 ,the thought of transmitting words by means of the electric current at once took possession of the artist's mind4 ,after many days and sleepless nights he showed to friends on board the drawings and notes he had made of a recording telegraph4 ,in ,new ,york1 in a room provided by his brothers1 he gave himself up to the working-out of his idea1 sleeping little and eating the simplest food4 ,receiving an appointment as professor in the ,university of the ,city of ,new ,york1 he moved to one of the buildings of that university and continued his experiments in extreme poverty1 and at times facing starvation1 as his salary depended on the tuition fees of his pupils4 ,a story told by one of his pupils describes his condition at the time4 ,i engaged to become one of ,morse's pupils4 ,he had three others4 ,i soon found that the professor had little patronage4 ,i paid my fifty dollars2 that settled one quarter's tuition4 ,i remember1 when the second was due1 my remittance from home did not come as expected1 and one day the professor came in and said1 courteously3 ',well1 ,strother1 my boy1 how are we off for money8' ',why1 professor1 ,i am sorry to say ,i have been disappointed2 but ,i expect a remittance next week4' ',next week6' he repeated1 sadly2 ',i shall be dead by that time4' ',dead1 sir8' ',yes2 dead by starvation6' ,i was distressed and astonished4 ,i said1 hurriedly3 ',would ten dollars be of any service8' ',ten dollars would save my life2 that is all it would do4' ,the money was paid1 all the student had1 and the two dined together4 ,it was ,morse's first meal in twenty-four hours4 ,the ,morse telegraph sounder 7,fig4 #fa7 consists of an electromagnet and a soft-iron armature4 ,when no current is flowing the armature is held away from the magnet by a spring4 ,when the circuit is closed a current flows through the coils of the magnet and the armature is attracted1 causing a click4 ,when the circuit is broken the spring pulls the armature away from the magnet1 causing another click4 ,the circuit is made and broken by means of a key at the other end of the line4 ,in ,morse's first instrument 7,fig4 #fb7 the armature carried a pen1 which was drawn across a ribbon of paper when the armature was attracted by the magnet4 ,if the pen was held by the magnet for a very short time1 a dot was made2 if for a longer time1 a dash4 ,the pen was soon discarded1 and the message taken by sound only4 ,the ,morse alphabet now in use was devised by a ,mr4 ,vail1 who assisted ,morse in developing the telegraph4 ,the thought occurred to ,mr4 ,vail that he could get help from a printing-office in deciding the combinations of dots and dashes that should be used for the different letters4 ,the letters requiring the largest spaces in the type-cases are the ones that occur most frequently1 and for these letters he used the simplest combinations of dots and dashes4 ,illustration3 ,,fig4 #fa--;,a ,,telegraph ,,sounder ,illustration3 ,,fig4 #fb--,,morse',s ,,first ,,telegraph ,,instrument ,a pen was attached to the pendulum and drawn across the strip of paper by the action of the electromagnet4 ,the lead type shown in the lower right-hand corner was used in making electrical contact when sending a message4 ,the modern instrument shown in the lower left-hand corner is the one that sent a message around the world in #ahif4 ,photo by ,claudy4 ,morse repeatedly said that1 if he could make his telegraph work through ten miles1 he could make it work around the world4 ,this promise of long-distance telegraphy he fulfilled by the use of the relay4 ,the relay works in the same way as the sounder4 ,the current coming over a long line may be too feeble to produce a click that can be easily heard1 yet strong enough to magnetize the coils of the relay and cause the armature to close another circuit4 ,this second circuit includes the sounder and a battery in the same station as the sounder1 which we shall call the local battery4 ,the relay simply acts as a contact key1 and closes the circuit of the local battery4 ,thus the current from the local battery flows through the sounder and produces a loud click4 ,sometimes a relay is used to control a second very long circuit4 ,at the farther end of the second circuit may be a sounder or a second relay which controls a third circuit4 ,any number of circuits may be thus connected by means of relays4 ,this is a form of repeating system used for telegraphing over very long distances4 ,fig4 #fc shows a circuit with relay and sounder4 ,illustration3 ,,fig4 #fc--;,a ,,telegraphic ,,circuit ,,with ,,relay ,,and ,,sounder ,in the telegraphic circuit only one connecting wire is needed4 ,the earth1 being a good conductor of electricity1 is used as part of the circuit4 ,it is necessary1 therefore1 to make a ground connection at each end of the line1 the instruments being connected between the line wire and the earth4 ,for long-distance telegraphy a current from a dynamo is used instead of a battery current4 ,fig4 #fd shows a simple telegraphic circuit4 ,illustration3 ,,fig4 #fd--;,a ,,simple ,,telegraphic ,,circuit ,two keys are shown at ,k ,k1 and two switches at ,s ,s4 ,when one key is to be used the switch at that station must be open1 and the switch at the other station closed4 ,a telegraphic message travels with the speed of light1 for the speed of electricity and the speed of light are the same4 ,a telegraphic signal would go more than seven times around the earth in one second if it travelled on one continuous wire4 ,the relays that must be used1 however1 cause some delay4 ,in #ahce ,morse's experimental telegraph was completed1 and in #ahcg it was exhibited to the public1 but seven years more passed before a line was established for public use4 ,aid from ,congress was necessary4 ,going to ,washington1 ,morse exhibited his instrument in the halls of the ,capitol1 sending messages through ten miles of wire wound on a reel4 ,the invention was ridiculed1 but the inventor did not despair4 ,a bill for an appropriation to establish a telegraphic line between ,washington and ,baltimore passed the ,house by a small majority4 ,the last day of the session came4 ,ten o'clock at night1 two hours before adjournment1 and the ,senate had not acted4 ,a senator advised ,morse to go home and think no more of it1 saying that the ,senate was not in sympathy with his project4 ,he went to his hotel1 counted his money1 and found that he could pay his bill1 buy his ticket home1 and have thirty-seven cents left4 ,all through his work he had firmly believed that a ,higher ,power was directing his work1 and bringing to the world1 through his invention1 a new and uplifting force2 and so when all seemed lost he did not lose heart4 ,in the morning a friend1 ,miss ,ellsworth1 called and offered her congratulations that the bill had been passed by the ,senate and thirty thousand dollars appropriated for the telegraph4 ,being the first to bring the news of his success1 ,mr4 ,morse promised her that the first message over the new line should be hers4 ,in about a year the line was completed1 and ,miss ,ellsworth dictated the now famous message3 ,what hath ,god wrought6 ,soon afterward the ,democratic ,convention1 in session in ,baltimore1 received a telegraphic message from ,senator ,silas ,wright1 in ,washington1 declining the nomination for the ,vice-,presidency1 which had been tendered him4 ,the convention refused to accept a message sent by telegraph1 and sent a committee to ,washington to investigate4 ,the message was confirmed1 and ,morse and his telegraph became famous4 ,fig4 #fe shows the first telegraph instrument used for commercial work4 ,illustration3 ,,fig4 #fe--;,,first ,,telegraph ,,instrument ,,used ,,for ,,commercial ,,work ,photo by ,claudy4 ,the desire to telegraph across the ocean came with the introduction of the telegraph on land4 ,bare wires in the air with glass insulators at the poles are used for land telegraphy1 but bare wires in the water could not be used1 for ocean water will conduct electricity4 ,something was needed to cover the wire1 protect it from the water1 and prevent the escape of the electric current4 ,just when it was needed such a substance was discovered4 ,in #ahdc1 when ,morse was working on his telegraph1 it was found that the juice of a certain kind of tree growing in the ,malayan ,archipelago formed a substance somewhat like rubber but more durable1 and especially suited to the insulation of wires in water4 ,this substance is gutta-percha4 ,ocean cables are made of a number of copper wires1 each wire covered with gutta-percha1 the wires twisted together and protected with tarred rope yarn and an outer layer of galvanized iron wires4 ,the earth is used for the return circuit1 as in the land telegraph4 ,duplex ,telegraphy ,the telegraph was a success1 but many improvements were yet to be made4 ,economy of construction was the thing sought for4 ,to make one wire do the work of two was accomplished by the invention of the duplex system4 ,in duplex telegraphy two messages may be sent in opposite directions over the same wire at the same time4 ,let us take a look at some of the methods by which this is accomplished4 ,one method with a long name but very simple in its working is the differential system 7,fig4 #ff74 ,in the differential system the current from the home battery divides into two branches passing around the coils of the electromagnet in opposite directions4 ,now if these two branches are so arranged that the currents flowing through them are equal1 the relay will not be magnetized1 because one current would tend to make the end ,a a north pole1 and the other current would tend to make the same end a south pole4 ,the result is that the relay coil is not magnetized1 and does not attract the armature4 ,but the current from the distant battery comes over one of these branches only1 and will magnetize the relay4 ,hence1 with a similar arrangement at the second station1 two messages may be sent at the same time in opposite directions4 ,illustration3 ,,fig4 #ff--;,,how ,,two ,,messages ,,are ,,sent ,,over ,,one ,,wire ,,at ,,the ,,same ,,time ,another method not quite so simple in principle is the bridge method4 ,when the key at station ,a 7see ,fig4 #fg7 is closed1 the current from the battery at station ,a divides at ,c1 and if the resistances #a and #b are equal1 and the resistance #c is equal to the resistance of the line1 no current will flow through the sounder4 ,but if a current comes over the line from the distant station this current divides at ,d1 and a part goes through the sounder1 causing it to click4 ,the sounder is not affected1 therefore1 by the current from the home battery1 but is affected by the current from the distant battery4 ,therefore1 a message may be sent and another received at the same time4 ,if there is a similar arrangement at the other station1 two messages may travel over the line in opposite directions at the same time4 ,illustration3 ,,fig4 #fg--;,,how ,,two ,,messages ,,are ,,sent ,,over ,,one ,,wire ,,at ,,the ,,same ,,time4 ,,bridge ,,method ,the differential method is used in land telegraphy1 the bridge method almost exclusively in submarine telegraphy4 ,the next step was a quadruplex system1 by means of which four messages may be transmitted over one wire at the same time4 ,the first quadruplex system was invented by ,edison in #ahgd1 and in four years it saved more than half a million dollars4 ,other systems have been invented which make it possible to send even a larger number of messages at one time over a single wire4 ,the ,telephone ,the idea of talking by telegraph began to grow in the minds of inventors soon after the ,morse instrument came into use4 ,the sound of the voice causes vibrations in the air4 7,this is simply shown in the string telephone4 ,this telephone is made by stretching a thin membrane1 such as thin sheepskin1 or gold-beaters' skin1 over a round frame of wood or metal4 ,two such instruments are connected by a string1 the end of the string being fastened to the middle of the stretched membrane4 ,the sound of the voice causes this membrane to vibrate4 ,as the membrane moves rapidly back and forth1 it pulls and releases the string1 and so causes the membrane at the other end to vibrate and give out the sound4 ,this is the actual carrying of the sound vibrations along the string47 ,in the telephone it is not sound vibrations but an electric current that travels over the line wire4 ,the telephone message1 therefore1 travels with the speed of electricity1 not with the speed of sound4 ,if it travelled with the speed of sound in air1 a message spoken in ,chicago would be heard in ,new ,york one hour later2 but we know that a message spoken in ,chicago may be heard in ,new ,york the instant it is spoken4 ,the telephone1 like the telegraph1 depends on the electromagnet4 ,the thought of inventors at first was to make the vibrations of a thin membrane1 caused by the sound of the voice1 open and close a telegraphic circuit4 ,an electromagnet at the other end of the line would cause a thin membrane with a piece of soft iron attached to it to vibrate1 just as the magnet in the telegraph receiver pulls and releases the soft-iron armature as the circuit is made and broken4 ,the thin membrane caused to vibrate in this way would give out the sound4 ,a telephone on this principle was invented by ,philip ,reis1 a schoolmaster in ,germany4 ,the transmitter was carved out of wood in the shape of a human ear1 the thin membrane being in the position of the ear-drum4 ,musical sounds and even words were transmitted by this telephone1 but it could never have been successful as a practical working telephone4 ,the membrane in the receiver would vibrate with the same speed as the membrane in the transmitter1 but sound depends on something more than speed of vibration4 ,the ,bell telephone1 as known to-day1 began with a study of the human ear4 ,alexander ,graham ,bell was a teacher of the deaf4 ,his aim was to teach the deaf to use spoken language1 and for this purpose he wished to learn the nature of the vibrations caused by the voice4 ,his plan was to cause the ear itself to trace on smoked glass the waves produced by the different letters of the alphabet1 and to use these tracings in teaching the deaf4 ,accordingly1 a human ear was mounted on a suitable support1 the stirrup-bone removed1 leaving two bones attached1 and a stylus of wheat straw attached to one of the bones4 ,the ear-drum1 caused to vibrate by the sound1 moved the two small bones and the pointer of straw1 so that when he sang or talked to the ear delicate tracings were made on the glass4 ,this experiment suggested to ,mr4 ,bell that a membrane heavier than the ear-drum would move a heavier weight4 ,if the ear-drum1 no thicker than tissue-paper1 could move the bones of the ear1 a heavier membrane might vibrate a piece of iron in front of an electromagnet4 ,he was at the same time devising a telegraph for transmitting messages by means of musical sounds4 ,in this telegraph he was using an electromagnet in the transmitter and another electromagnet in the receiver4 ,he attached the soft-iron armature of each electromagnet to a stretched membrane of gold-beaters' skin1 expecting that the sound of his voice would cause the membrane of the transmitter to vibrate1 and that1 by means of the electromagnets1 the membrane of the receiver would be made to vibrate in the same way 7,fig4 #fh74 ,at first he was disappointed1 but after making some changes in the armatures a distinct sound was heard in the receiver4 ,later the membrane was discarded1 and a thin iron disk used with better effect4 ,illustration3 ,,fig4 #fh--;,,first ,,bell ,,telephone ,,receiver ,,and ,,transmitter ,the receiver is on the left in the picture4 ,a thin membrane of gold-beaters' skin tightly stretched and fastened with a cord can be seen on the end of the transmitter and of the receiver4 ,an electromagnet is also shown over each membrane4 ,this thin membrane1 with a piece of soft iron attached1 was used in place of the soft-iron disk of the modern receiver4 ,the story of ,bell's struggles might seem like the repetition of the life story of many another great inventor4 ,he knew that he had discovered something of great value to the world4 ,he devoted his time to the perfecting of the telephone1 neglecting his professional work and finally giving it up1 that he might give his whole time to his invention4 ,he was forced to endure poverty and ridicule4 ,he was called a crank who says he can talk through a wire4 ,men said his invention could never be made practical4 ,even after he succeeded in finding a few purchasers and some of the telephones were in actual use1 people were slow to adopt it4 ,the idea of talking at a piece of iron and hearing another piece of iron talk seemed like a kind of witchcraft4 ,in the telephone we see another use of the electromagnet4 ,a very thin iron disk near the poles of an electromagnet forms the telephone receiver 7,fig4 #fi74 ,an electric current travels over the telephone wire4 ,if the current grows stronger1 the magnet is made stronger and pulls the disk toward it4 ,if the current grows weaker1 the magnet becomes weaker and does not pull so hard on the disk4 ,the disk then springs back from the magnet4 ,if these changes take place rapidly the disk moves back and forth rapidly and gives out a sound4 ,the sound of the voice at the other end of the line sets the disk in the mouthpiece vibrating4 ,the vibrations of this disk cause the changes in the electric current flowing over the line-wire1 and the changes in the electric current cause the disk of the receiver to vibrate in exactly the same way as the disk at the mouthpiece4 ,thus the words spoken into the mouthpiece may be heard at the receiver4 ,illustration3 ,,fig4 #fi--;,a ,,telephone ,,receiver ,the transmitter used by ,bell was like the receiver4 ,two receivers from the common telephone connected by two wires may be used as a telephone without batteries4 ,fig4 #gj shows a complete telephone made of two receivers connected by two wires4 ,the disk in one receiver which is now used as a transmitter is made to vibrate by the sound of the voice4 ,now when a piece of iron moves back and forth in a magnetic field it strengthens and weakens the field4 ,so the magnetic field in the transmitter is rapidly changed by the movement of the iron disk4 ,now we have found that whenever a coil of wire is in a changing magnetic field a current is induced in the coil4 ,the small coil in the transmitter1 therefore1 has a current induced in it4 ,we have also found that when the magnetic field is made stronger the induced current flows in one direction1 and when the field is made weaker the current flows in the opposite direction4 ,since the field in the transmitter is made alternately stronger and weaker1 the current in the coil flows first in one direction1 then in the opposite direction--that is1 we have an alternating current4 ,this alternating current1 of course1 flows over the line-wire and through the coil in the receiver4 ,in the receiver the alternating current will alternately strengthen and weaken the magnetic field1 and as it does so the pull of the magnet on the iron disk is strengthened and weakened4 ,the iron disk in the receiver1 therefore1 vibrates in exactly the same way as the disk in the transmitter1 and so gives out a sound just like that which is acting on the transmitter4 ,illustration3 ,,fig4 #gj--,,two ,,receivers ,,used ,,as ,a ,,complete ,,telephone ,in the ,blake transmitter1 which is now commonly used1 the disk moves a pencil of carbon which presses against another pencil of carbon4 ,this varies the pressure between the two pencils of carbon4 ,a battery current flows through the two carbons1 and as the pressure of the carbons changes the strength of the current changes4 ,when the carbons are pressed together more closely the current is stronger4 ,when the pressure is less the current is weaker4 ,we have1 then1 a varying current through the carbons4 ,this current flows through the primary coil of an induction-coil1 the secondary being connected to the line-wire4 ,now a current of varying strength in the primary induces an alternating current in the secondary4 ,we have1 then1 an alternating current flowing over the line-wire4 ,this alternating current acts on the magnetic field of the receiver in the way described before1 causing the disk in the receiver to vibrate and give out the sound4 ,for long-distance work a carbon-dust transmitter 7,fig4 #ga7 is used4 ,in this there are many granules of carbon1 so that instead of two carbon-points in contact there are many4 ,this makes the transmitter more sensitive4 ,illustration3 ,,fig4 #ga--;,,carbon-,,dust ,,transmitter ,the strength of current required for the telephone is very small4 ,to transmit a telephone message requires less than a hundred-millionth part of the current required for a telegraphic message4 ,the work done in lifting the telephone receiver a distance of one foot1 if changed into an alternating current1 would be sufficient to keep up a sound in the receiver for a hundred thousand years4 ,because of its extreme sensitiveness the telephone requires a complete wire circuit4 ,the earth cannot be used for the return circuit1 as in the case of the telegraph4 ,disturbances in the earth1 vibration1 leakage currents from trolley lines1 and so forth1 would interfere seriously with the action of the telephone4 ,when the telephone was invented it was commonly remarked that it could not take the place of the telegraph in commerce1 for the latter gave the merchant some evidence of a business transaction1 while the telephone left no sign4 ,there was a time when men feared to trust each other1 but now large business deals are made by telephone2 products of the farm1 the factory1 and the mine are bought and sold in immense quantities without a written contract or even the written evidence of a telegram4 ,thus the telephone has developed a spirit of business honor4 ,the ,phonograph ,the phonograph grew out of the telephone4 ,it is said to be the only one of ,edison's inventions that came by accident1 yet only a man of genius would have seen the meaning of such an accident4 ,he was singing into the mouthpiece of a telephone when the vibrations of the disk caused a fine steel point to pierce one of his fingers held just behind the disk4 ,this set him to thinking4 ,if the sound of his voice could cause the disk to vibrate with force enough to pierce the skin1 would it not make impressions on tin-foil1 and so make a record of the voice that could be reproduced by passing the point rapidly over the same impressions8 ,he gave his assistants the necessary instructions1 and soon the first phonograph was made4 ,this disk in the phonograph is set in vibration by sound vibrations in the air in the same way as the disk in the telephone transmitter4 ,attached to the disk is a needle-point which1 of course1 vibrates with the disk4 ,if a cylinder with a soft surface is turned rapidly under the steel point as it vibrates1 impressions are made in the cylinder corresponding to the movements of the disk4 ,the cylinder must move forward as it turns1 so that its path will be a spiral4 ,if1 now1 the stylus is placed at the starting-point and the cylinder turned rapidly the stylus will move rapidly up and down as it goes over the indentations in the cylinder1 and so cause the metal disk to vibrate and give out a sound like that received at first4 ,in the earliest phonographs the cylinder was covered with tin-foil4 ,later the so-called wax records came into use4 ,these cylinders are not made of wax1 but of very hard soap4 ,fig4 #gb shows an instrument in which the sound of the voice caused a pencil-point to trace a wavy line on a cylinder4 ,this instrument may be called a forerunner of the phonograph4 ,fig4 #gc shows ,edison's first phonograph with a modern instrument placed beside it for comparison4 ,illustration3 ,,fig4 #gb--,,the ,,phonautograph1 ,a ,,forerunner ,,of ,,the ,,phonograph ,illustration3 ,,fig4 #gc ,,edison',s ,,first ,,phonograph ,,and ,a ,,modern ,,instrument ,photo by ,claudy4 ,gas-,engines ,cannons are the oldest gas-engines4 ,indeed1 the principle of the cannon is the same as that of the modern gas-engine1 the piston in the engine taking the place of the cannon-ball4 ,the power in each case is obtained by explosion--in the cannon the explosion of powder1 in the engine the explosion of a mixture of air and gas4 ,powder-engines with pistons were proposed in the seventeenth century1 and some were actually built1 but it proved too difficult to control them1 and the idea of the gas-engine was abandoned for more than a hundred years4 ,the discovery of coal-gas near the close of the eighteenth century gave a new impetus to the gas-engine4 ,john ,barber1 an ,englishman1 built the first actual gas-engine4 ,he used gas distilled from wood1 coal1 or oil4 ,the gas1 mixed with the proper proportion of air1 was introduced into a tank which he called the exploder4 ,the mixture was fired and issued out in a continuous stream of flame against the vanes of a paddle-wheel1 driving them round with great force4 ,in #ahjd ,lebon1 a ,french engineer1 was assassinated1 and the progress of the gas-engine set back a number of years1 for this engineer had proposed to compress the mixture of gas and air before firing1 and to fire the mixture by an electric spark4 ,this is the method used in gas-engines to-day4 ,the first practical working gas-engine was invented by ,lenoir1 a ,frenchman1 in #ahfj4 ,from this time to the end of the century the gas-engine developed rapidly1 receiving a new impulse from the increasing demand for the motor-car4 ,the engine of the ,german inventors1 ,otto and ,langen1 brought out in #ahgf1 marked the beginning of a new era4 ,the greater number of engines used in automobiles to-day are of the kind known as the ,otto cycle1 or four-cycle1 engine4 ,this engine is called four-cycle because the piston makes four strokes for every explosion4 ,there is one stroke to admit the mixture of gas and air to the cylinder1 another to compress the gas and air1 at the beginning of the third stroke the explosion takes place1 and in the fourth stroke the burned-out gases are driven out of the cylinder4 ,the working of the four-cycle gas-engine is made clear in ,figs4 #gd1 #ge1 #gf1 and #gg4 ,illustration3 ,,fig4 #gd--;,,first ,,stroke4 ,,gas ,,and ,,air ,,admitted ,,to ,,the ,,cylinder ,illustration3 ,,fig4 #ge--,,second ,,stroke4 ,,mixture ,,of ,,gas ,,and ,,air ,,compressed ,illustration3 ,,fig4 #gf--,,third ,,stroke4 ,,the ,,mixture ,,is ,,exploded ,,and ,,expands1 ,,driving ,,the ,,piston ,,forward ,illustration3 ,,fig4 #gg--;,,fourth ,,stroke1 ,,exhaust4 ,,the ,,burned-,,out ,,mixture ,,of ,,gas ,,and ,,air ,,expelled ,,from ,,the ,,cylinder ,,the ,,four-,,cycle ,,gas-,,engine ,in such a gas-engine the power is applied to the piston only in one stroke out of every four1 while in the steam-engine the power is applied at every stroke4 ,it would seem1 therefore1 that a steam-engine would do more work than a gas-engine for the same amount of heat1 but such is not the case2 in fact1 a good gas-engine will do about twice as much work as a good steam-engine for the same amount of fuel4 ,the reason is that the steam-engine wastes its heat4 ,heat is given to the condenser1 to the iron of the boiler1 to the connecting pipes and the air around them1 while in the gas-engine the heat is produced in the cylinder by the explosion and the power applied directly to the piston-head4 ,more than this1 a steam-engine when at rest wastes heat2 there must be a fire under the boiler if the engine is to be ready for use on short notice4 ,when a gas-engine is at rest there is no fire1 nothing is being used up1 and yet the engine can be started very quickly4 ,a gas-engine can be made much lighter than a steam-engine of the same horse-power4 ,the automobile and the flying-machine require very light engines4 ,without the gas-engine the automobile would have remained imperfect and crude1 while the flying-machine would have been impossible4 ,in a two-cycle gas-engine there is an explosion for every two strokes of the piston1 or one explosion for every revolution of the crank-shaft4 ,during one stroke the mixture of gas and air on one side of the piston is compressed and a new mixture enters on the opposite side of the piston4 ,at the end of this stroke the compressed mixture is exploded1 and power is applied to the piston during about one-fourth of the next stroke4 ,during the remainder of the second stroke the burned-out gas escapes1 and the fresh mixture passes over from one side of the piston to the other ready for compression4 ,the two-cycle engine is simpler in construction than the four-cycle1 having no valves4 ,it also has less weight per horse-power4 ,the cylinder of a two-cycle engine is shown in ,fig4 #gh4 ,illustration3 ,,fig4 #gh--,,two-,,cycle ,,gas-,,engine4 ,,crank ,,and ,,connecting-,,rod ,,are ,,enclosed ,,with ,,the ,,piston ,a steam-engine is self-starting4 ,the engineer has only to turn the steam into the cylinder1 but the gas-engine requires to be turned until at least one explosion takes place1 for until there is an explosion of gas and air in the cylinder there is no power4 ,a gas-engine may have a number of cylinders4 ,four-cylinder and six-cylinder engines are common4 ,in a four-cylinder1 four-cycle engine1 while one cylinder is on the power stroke the next is on the compression stroke1 the third on the admission stroke1 and the fourth on the exhaust stroke4 ,fig4 #gi shows the ,selden explosion buggy propelled by a gas-engine4 ,this machine was the forerunner of the modern automobile4 ,illustration3 ,,fig4 #gi--,,selden ,,explosion ,,buggy4 ,,forerunner ,,of ,,the ,,modern ,,automobile ,the ,steam ,locomotive ,late in the eighteenth century a mischievous boy put some water in a gun-barrel1 rammed down a tight wad1 and placed the barrel in the fire of a blacksmith's forge4 ,the wad was thrown out with a loud report1 and the boy's play-mate1 ,oliver ,evans1 thought he had discovered a new power4 ,the prank with the gun-barrel set young ,evans thinking about the power of steam4 ,it was not long until he read a description of a ,newcomen engine4 ,in the ,newcomen engine1 you will remember1 it was the pressure of air1 not the pressure of steam1 that lifted the weight4 ,evans soon set about building an engine in which the pressure of steam should do the work4 ,he is sometimes called the ,watt of ,america1 for he did in ,america much the same work that ,watt did in ,scotland4 ,evans built the first successful non-condensing engine--that is1 an engine in which the steam1 after driving the piston1 escapes into the air instead of into a condenser4 ,the non-condensing engine made the locomotive possible1 for a locomotive could not conveniently carry a condenser4 ,evans made a locomotive which travelled very slowly4 ,he said1 however3 ,the time will come when people will travel in stages moved by steam-engines from one city to another1 almost as fast as birds can fly1 fifteen or twenty miles an hour4 ,the inventor who made the first successful locomotive was ,george ,stephenson1 and it is worth noting that one of his engines1 the ,rocket1 possessed all the elements of the modern locomotive4 ,he combined in the ,rocket the tubular boiler1 the forced draft1 and direct connection of the piston-rod to the crank-pin of the driving-wheel4 ,the ,rocket was used on the first steam railway 7the ,stockton ,darlington1 in ,england71 which was opened in #ahbe4 ,there had been other railways for hauling coal by means of horses over iron tracks1 and other locomotives that travelled over an ordinary road2 but this was the first road on which a steam-engine pulled a load over an iron track1 the first real railroad4 ,fig4 #hj shows the ,rocket and two other early locomotives4 ,illustration3 ,,fig4 #hj--,,some ,,early ,,locomotives ,the one on the right is ,stephenson's ,rocket4 ,photo by ,claudy4 ,in order to build a railroad between ,liverpool and ,manchester for carrying both passengers and freight it was necessary to secure an act of ,parliament4 ,stephenson was compelled to undergo a severe cross-examination by a committee of ,parliament1 who feared there would be great danger if the speed of the trains were as high as twelve miles an hour4 ,he was asked3 ,have you seen a railroad that would stand a speed of twelve miles an hour8 ,yes4 ,where8 ,any railroad that would bear going four miles an hour4 ,i mean to say that if it would bear the weight at four miles an hour it would bear it at twelve4 ,do you mean to say that it would not require a stronger railway to carry the same weight at twelve miles an hour8 ,i will give an answer to that4 ,i dare say every person has been over ice when skating1 or seen persons go over1 and they know that it would bear them better at a greater velocity than it would if they went slower2 when they go quickly the weight1 in a measure1 ceases4 ,would not that imply that the road must be perfect8 ,it would1 and ,i mean to make it perfect4 ,for seven miles the road must be built over a peat bog into which a stone would sink to unknown depths4 ,to convince the committee1 however1 and secure the act of ,parliament was more difficult than to build the road4 ,but ,stephenson was one of the men who do things because they never give up1 and the road was built4 ,how a ,locomotive ,works ,to understand how a locomotive works1 let us consider how the steam is produced1 how it acts on the piston1 and how it is controlled4 ,the steam is produced in a locomotive in exactly the same way that steam is produced in a tea-kettle4 ,now everybody knows that a quart of water in a tea-kettle with a wide bottom placed on a stove will boil more quickly than the same amount of water in a tea-pot with a narrow bottom4 ,the greater the heating-surface--that is1 the greater the surface of heated metal in contact with the water--the more quickly the water will boil and the more quickly steam can be produced4 ,in a locomotive the aim is to use as large a heating-surface as possible4 ,this is done by making the fire-box double and allowing the water to circulate in the space between the inner and outer parts1 except underneath2 also by placing tubes in the boiler through which the heated gases and smoke from the fire must pass4 ,an ordinary locomotive contains two hundred or more of these tubes4 ,the water surrounds these tubes1 and is therefore in contact with a very large surface of heated metal4 ,in some engines the water is in the tubes1 and the heated gases surround the tubes4 ,the steam as it enters the cylinder should be dry--that is1 it should not contain drops of water4 ,this is accomplished by allowing the steam from the boiler to pass into a dome above the boiler4 ,here the steam1 which is nearly dry1 enters a steam-pipe leading to the cylinder 7,fig4 #ha74 ,the steam is admitted to the cylinder by means of a slide-valve4 ,from the diagram it can easily be seen that the valve admits steam first on one side of the piston1 then on the other4 ,it can also be seen that the valve closes the admission-port1 and so cuts off the steam before the piston has made a full stroke4 ,the steam that is shut up in the cylinder continues to expand and act on the piston4 ,at the same time the valve opens the exhaust-port1 allowing the steam to escape from the other side of the piston2 but it closes this port before the piston has quite finished the stroke4 ,the small quantity of steam thus shut up acts like a cushion to prevent the piston striking the end of the cylinder with too great force4 ,the exhaust-steam escapes through a blast-pipe into the chimney1 drives the air before it up the chimney1 and thus makes a greater draft of air through the fire-box4 ,this is called the forced draft4 ,the escape of the exhaust-steam causes the puffing of the locomotive just after starting4 ,after the engine is under way the engineer partly shuts off the steam by means of the reversing lever and the puffing is less noticeable4 ,illustration3 ,,fig4 #ha--;,,how ,a ,,locomotive ,,works ,the arrows show the course of the steam4 ,the action of the steam may be summed up as follows3 #a4 ,steam admitted to the cylinder 7admission74 #b4 ,valve closes admission-port 7cut-off74 #c4 ,steam shut up in the cylinder expands1 acting on the piston 7expansion period74 #d4 ,valve opens exhaust-port to allow used steam to escape 7exhaust74 ,the devices for controlling the steam are the throttle-valve and the valve-gear4 ,the throttle-valve is at the entrance to the steam-pipe in the steam-dome4 ,this valve is opened and closed by means of a rod in the engineer's cab4 ,stephenson's link-motion valve-gear is used on most locomotives4 ,the forward rod in the diagram is in position to act upon the valve-rod through the lever ,l4 ,suppose the reversing-lever is drawn back to the dotted line2 then the forward rod will be raised and the backward rod will come into position to act on the lever ,l4 ,if this is done while the locomotive is at rest the valve is moved through one-half a complete stroke4 ,in the diagram the steam enters the cylinder on the right of the piston4 ,after this movement of the valve the steam would enter on the left side of the piston4 ,in the present position the locomotive would move forward1 but if the valve is changed so as to admit steam to the left of the piston while the connecting-rod is in the position shown then the engine will move backward4 ,thus the direction can be controlled by the engineer in the cab4 ,of course1 this can be done while the engine is in motion4 ,the forward rod and the backward rod are each moved by an eccentric on the axle of the front driving-wheel4 ,the two eccentrics are in opposite positions on the axle4 ,an eccentric acts just like a crank1 causing the rod to move forward and backward as the axle turns1 and of course this motion is given to the valve-rod through the lever4 ,when the link is set midway between the forward and the backward rod the valve cannot move4 ,when the link is raised or lowered part way the valve makes a short stroke1 and less steam is admitted to the cylinder than with a full stroke4 ,in starting the locomotive the valve is set to make a full stroke4 ,when the train is under headway the valve is set for a short stroke to economize steam4 ,the valve-gear and the throttle-valve together take the place of the governor in the stationary engine1 but while the governor acts automatically these are controlled by the engineer4 ,in reality a locomotive is two engines1 one on either side1 connected to the same driving-wheels4 ,but the two piston-rods are connected to the driving-wheels at points which are at right angles with each other1 so that when the crank on one side is at the end of a stroke--the dead centre--that on the other side is on the quarter1 either above or below the axle1 ready for applying the greatest turning force4 ,the expansion-engine was designed to use more of the power of the steam than can be done in the single-cylinder engine4 ,in the double expansion-engine the steam expands from one cylinder into another4 ,the second cylinder must be larger in diameter than the first4 ,in the triple expansion-engine the steam expands from the second cylinder into a third1 still larger4 ,the second and third cylinders use a large part of the power that would be wasted with only one cylinder4 ,the ,turbine ,one of the great inventions relating to steam-power is the steam-turbine4 ,the water-turbine is equally useful in relation to water-power4 ,the water-turbine and the steam-turbine work in very much the same way1 the difference being due to the fact that steam expands as it drives the engine1 while water drives it by its weight in falling1 or by its motion as it rushes in a swift stream or jet against the blades of the turbine4 ,the first steam-engine1 that of ,hero in the time of ,archimedes1 was a form of turbine 7,fig4 #hb74 ,it was driven by the reaction of the steam as it escaped into the air4 ,the common lawn-sprinkler1 that whirls as the water rushes through it1 is a water-turbine that works in the same way4 ,barker's ,mill is the name applied to a water-turbine that works like the lawn-sprinkler4 ,as the water rushes out of the opening it pushes against the air4 ,it cannot push against the air without pushing back at the same time4 ,never yet has any person or object in nature been able to push in one direction only4 ,it cannot be done4 ,if you push a cart forward you push backward against the ground at the same time4 ,if there were nothing for you to push back against your forward push would not move the cart a hair's-breadth4 ,if you doubt this1 try to push a cart when you are standing on ice so slippery that you cannot get a foothold4 ,it is the backward push of the water in the lawn-sprinkler and the backward push of the steam in ,hero's engine that cause the machine to turn4 ,illustration3 ,,fig4 #hb--;,,hero',s ,,engine ,the turbines in common use for both water and steam power have curved blades4 ,the reason for curving the blades can best be seen by referring to an early form of water-wheel4 ,the best water-turbine is only an improved form of water-wheel4 ,the first water-wheels had flat blades1 and these answered very well so long as only a low power was needed and it was not necessary to save the power of the water4 ,it was found1 however1 that there was a great waste of power in the wheel with flat blades4 ,one inventor proposed to improve the wheel by curving the blades in such a way that the water would glide up the curve and then drop directly downward 7,fig4 #hc74 ,the water then gives up practically all of its power to the wheel and falls from the wheel4 ,it would have no power to move a second wheel4 ,in this way he used practically all the power of the water4 ,to save the power of the water by making all of the water strike the wheel at high speed the channel was made narrow just above the wheel1 forming a mill-race4 ,this applies to the undershot wheel4 ,in the overshot wheel 7,fig4 #hd7 the power depends on the weight of the water and on its height4 ,the water runs into buckets attached to the wheel1 and1 as it falls in these buckets1 turns the wheel4 ,the undershot wheel and the mill-race represent a common form of turbine1 that form in which the steam or the water is forced in a jet against a set of curved blades4 ,fig4 #he shows a steam-turbine run by a jet of steam4 ,in the water-turbine there are two sets of blades4 ,one set rotates1 the other remains fixed4 ,the use of the fixed blades is to turn the water and drive it in the right direction against the moving blades4 ,in some forms of turbine there are more than two sets of blades4 ,the steam1 as it passes through1 gives up some of its power to each set of blades until1 after passing the last set1 it has given up nearly all its power4 ,the action of the steam in this turbine is somewhat like that in the expansion-engine1 in which the steam gives up a portion of its power in each cylinder4 ,fig4 #hf is from a photograph of a modern steam-turbine1 and ,fig4 #hg is a drawing of the same turbine showing the course of the steam4 ,fig4 #hh is a turbine that runs a large dynamo4 ,illustration3 ,,fig4 #hc--;,,an ,,undershot ,,water-,,wheel ,,with ,,curved ,,blades ,illustration3 ,,fig4 #hd--;,,an ,,overshot ,,water-,,wheel ,illustration3 ,,fig4 #he--;,,de ,,laval ,,steam-,,turbine ,driven by a jet of steam striking the blades4 ,illustration3 ,,fig4 #hf--;,a ,,modern ,,steam-,,turbine ,,with ,,top ,,casing ,,raised ,,showing ,,blades ,illustration3 ,,fig4 #hg--;,,diagram ,,of ,,turbine ,,shown ,,in ,,fig4 #hf ,the arrows show the course of the steam4 ,illustration3 ,,fig4 #hh--;,a ,,steam-,,turbine ,,that ,,runs ,a ,,dynamo ,,generating #ad1jjj ,,electrical ,,horse-,,power ,the steam enters through the large pipe at the left4 ,in #ahig1 as the battle-ships of the ,british fleet were assembled to celebrate the ,diamond jubilee of ,queen ,victoria1 a little vessel a hundred feet long darted in and out among the giant ships1 defied the patrol-boats whose duty it was to keep out intruders1 and raced down the lines of battle-ships at the then unheard-of speed of thirty-five knots an hour4 ,it was the ,turbinia1 fitted with the ,parsons turbine4 ,this event marked the beginning of the modern turbine4 ,it also marked the beginning of a revolution in steam propulsion4 ,the ,parsons turbine does not use the jet method1 but the steam enters near the centre of the wheel and flows toward the rim1 passing over a number of rows of curved blades4 ,the ,parsons turbine is used on the fastest ocean liners4 ,the ,lusitania1 one of the fastest steamships in the first decade of the twentieth century1 has two sets of high and low pressure turbines with a total of #fh1jjj horse-power4 ,the windmill is a form of turbine driven by the air4 ,as the air rushes against the blades of the windmill1 it forces them to turn4 ,if the windmill were turned by some mechanical power1 it would drive the air back1 and we should have a blower4 ,this is what we have in the electric fan1 a small windmill driven by an electric motor so that it drives the air instead of being driven by it4 ,the blades of the windmill and the electric fan are shaped very much like the screw propeller4 ,the screw propeller1 driven by an engine1 would drive the water back if the ship were firmly anchored1 just as the fan drives the air4 ,but it cannot drive the water back without pushing forward on the ship at the same time1 and this forward push propels the ship4 ,it is difficult to attain what is now regarded as high speed with a single screw4 ,with engines in pairs and two lines of shafting higher power can be used4 ,the best steamers1 therefore1 are fitted with the twin-screw propeller4 ,some large steamers have three and some four screws4 ,the screw propellers of turbine steamships are made of small diameter1 that they may rotate at high speed without undue waste of power4 ,by the use of turbine engines and twin-screw propellers1 the weight of the machinery has been greatly reduced4 ,the old paddle-wheels1 with low-pressure engines1 developed only about two horse-power for each ton of machinery4 ,the turbine1 with the twin-screw propeller1 develops from six to seven horse-power for every ton of machinery4 ,the modern steamer1 with all its machinery and coal for an ,atlantic voyage1 weighs no more than the engines of the old paddle-wheel type and coal would weigh for the same horse-power4 ,the steam-turbine and the twin-screw propeller have made rapid ocean travel possible4 ,chapter ,,vi ,,the ,,twentieth-,,century ,,outlook ,we have seen that the latter half of the nineteenth century was a time of invention4 ,it was a time when the great discoveries of many centuries bore fruit in great inventions4 ,it was thought by some scientists that all the great discoveries had been made1 and that all that remained was careful work in applying the great principles that had been discovered4 ,so far was this from being true that in the last ten years of the nineteenth century discoveries were made more startling1 if possible1 than any that had preceded4 ,the nineteenth century not only brought forth many great inventions1 but handed down to the twentieth century a series of discoveries that point the way to still greater inventions4 ,air-,ships ,for centuries men sailed over the water at the mercy of the wind4 ,the sailing vessel is helpless in a storm4 ,early in the nineteenth century they learned to use the power of steam for ocean travel1 and the wind lost its terrors4 ,late in the eighteenth century men learned to sail through the air in balloons even more at the mercy of the wind than the sailing vessels on the ocean4 ,more than a hundred years later they learned to propel air-ships in the teeth of the wind4 ,the nineteenth century saw the mastery of the water4 ,the twentieth is witnessing the mastery of the air4 ,the first balloon ascension was made in #aghc1 two men being carried over ,paris by what ,benjamin ,franklin called a bag of smoke4 ,the balloon was a bag of oiled silk open at the bottom4 ,in the middle of the opening was a grate in which bundles of fagots and sheaves of straw were burned4 ,the heated air filled the balloon1 and as the heated air was lighter than the air around it the balloon could rise and carry a load4 ,beneath the grate was a wicker car for the men4 ,they were supplied with straw and fagots with which to feed the fire4 ,when they wanted to rise higher they added fuel to heat the air in the balloon4 ,when they wished to descend they allowed the fire to die out1 so that the air in the balloon would cool4 ,they could not guide the balloon1 but drifted with the wind4 ,that great philosopher ,benjamin ,franklin1 who saw the ascension1 said that the time might come when the balloon could be made to move in a calm and guided in a wind4 ,in the second ascension bags of sand were taken as ballast1 and the car was suspended from a net which enclosed the balloon4 ,in this second ascension hydrogen gas was used in place of heated air4 ,the greatest height ever reached by a human being is about seven miles4 ,this height was first reached in #ahfb by two balloonists who nearly lost their lives in the adventure4 ,at a height of nearly six miles one of the men became unconscious4 ,the other tried to pull the valve-cord to allow the gas to escape1 but found that the cord was out of his reach4 ,his hands were frozen1 but he climbed out of the car into the netting of the balloon1 secured the cord in his teeth1 returned to the car1 and threw the weight of his body on the cord4 ,this opened the valve and the balloon descended4 ,those who go to great heights now provide themselves with tanks of compressed oxygen4 ,then when the air becomes so thin and rare that breathing is difficult they can breathe from the oxygen tanks4 ,a captive balloon in war serves as an observation tower from which to observe the enemy4 ,it is connected to the ground by a cable4 ,this cable is wound on a drum carried by the balloon wagon4 ,the balloon can be lowered or raised by winding or unwinding the cable4 ,the gas-bag is sometimes made of oiled silk1 sometimes of two layers of cotton cloth with vulcanized rubber between4 ,the cotton cloth gives the strength needed1 and the rubber makes the bag gas-tight4 ,the most convenient gas for filling balloons is heated air1 but the air cools rapidly and loses its lifting power4 ,coal-gas furnished by city gas-plants is sometimes used4 ,this gas will lift about thirty-five pounds for every thousand cubic feet4 ,a balloon holding thirty-five thousand cubic feet of coal gas will easily lift the car and three persons4 ,the lightest gas is hydrogen4 ,this gas will lift about seventy pounds for every thousand cubic feet4 ,hydrogen is made by the action of sulphuric acid and water on iron4 ,if a bit of iron is thrown into a mixture of sulphuric acid and water bubbles of hydrogen gas will rise through the liquid4 ,this gas will burn if a lighted match is brought near4 ,a balloon without propelling or steering apparatus is not an air-ship4 ,it may be raised by throwing out ballast or lowered by letting out gas1 but further than this the aeronaut has no control over its movements4 ,the balloon moves with the wind4 ,no breeze is felt1 for balloon and air move together4 ,to the aeronaut the balloon seems to be in a dead calm4 ,it is only when he catches sight of houses and trees and rivers darting past below that he realizes that the balloon is moving4 ,if a balloon has a propelling apparatus it may move against the wind1 or it may outspeed the wind4 ,a balloon with propelling and steering apparatus is called a dirigible balloon1 which means a balloon that can be guided4 ,figs4 #hi and #ij are from photographs of a dirigible used in the ,british army4 ,such a balloon is usually long and pointed like a spindle or a cigar4 ,it is built to cut the air1 just as a rowboat built for speed is long and pointed so that it may cut the water4 ,the propeller acts like an electric fan4 ,an electric fan drives the air before it1 but the air pushes back on the fan just as much as the fan pushes forward on the air1 and if the fan were suspended by a long cord it would move backward4 ,so the large fan or screw propeller on an air-ship drives the air backward1 and the air reacts and drives the ship forward4 ,in the same way the screw-propeller of an ocean liner drives the vessel forward by the reaction of the water4 ,illustration3 ,,fig4 #hi--;,,british ,,army ,,air-,,ship ,,nulli ,,secundus ,,ready ,,for ,,flight ,illustration3 ,,fig4 #ij--;,,basket1 ,,motor1 ,,and ,,propeller ,,of ,,the ,,british ,,army ,,air-,,ship ,,nulli ,,secundus ,a balloon rises for the same reason that wood floats on water4 ,the wood is lighter than water1 and the water holds it up4 ,the balloon is lighter than air and the air pushes it up4 ,the upward push of the air is just equal to the weight of the air that would fill the same space the balloon fills4 ,the balloon can support a load that makes the whole weight of the balloon and its load together equal to the weight of the air that would fill the same space4 ,for the balloon to rise the load must be somewhat lighter than this4 ,a balloon may be made lighter than air by filling it with heated air or coal-gas4 ,hydrogen1 however1 is used in the better balloons and in air-ships of the lighter than air type4 ,the air-ship must1 of course1 use a very light motor4 ,a steam-engine cannot be made light enough4 ,neither can an electric motor1 if we add the weight of the storage battery that would be required4 ,air-ships have been propelled by both steam-engines and electric motors1 but with low speed because of the weight of the engine or motor4 ,the only successful motor for this purpose is the gasolene motor1 which is a form of gas-engine using gas formed by the evaporation of gasolene4 ,the first air-ship that could be controlled and brought back to the starting-point was made in ,france1 in #ahhe1 by ,captain ,renard1 of the ,french army4 ,it was a cigar-shaped balloon1 with a screw propeller run by an electric motor of eight horse-power4 ,the ship attained a speed of thirteen miles an hour4 ,a more successful air-ship was that built by ,santos ,dumont4 ,with this ship1 in #aija1 he won a prize of #bj1jjj1 which had been offered to the builder of the first air-ship that would sail round the ,eiffel ,tower in ,paris from the ,aerostatic ,park of ,vaugirard1 a distance of about three miles1 and return in half an hour4 ,the balloon part of this air-ship was #aab-a_/b feet long and #ai-a_/b feet in diameter1 holding about #fdjj cubic feet of gas4 ,the car was built of pine beams no larger in section than two fingers and weighing only #aaj pounds4 ,this car could be taken apart and put in a trunk4 ,a gasolene automobile motor was used1 and thus it is seen that the automobile aided in solving the problem of sailing through the air4 ,it was the automobile that led to the construction of light and powerful gasolene motors4 ,the car and motor were suspended from the balloon by means of piano wires1 which at a short distance were invisible1 so that the man in the car appeared in some mysterious way to follow the balloon4 ,the ship was turned to the left or right by means of a rudder4 ,it was made to ascend or descend by shifting the weight of a heavy rope that hung from the car1 thus inclining the ship upward or downward4 ,count ,zeppelin1 of ,germany1 constructed a much larger dirigible balloon than that of ,santos ,dumont4 ,the balloon of the first ,zeppelin air-ship was #cij feet in length1 with a diameter of about #ci feet4 ,it was divided into seventeen sections1 each section being a balloon in itself4 ,these sections serve the same purpose as the water-tight compartments of a battle-ship4 ,an accident to one section would not mean the destruction of the entire ship4 ,within the balloon is a framework of aluminum rods extending from one end to the other and held in place by aluminum rings twenty-four feet apart4 ,the balloon contains about #ajh1jjj cubic feet of gas1 and it costs about #bejj to fill it4 ,one filling of gas will last about three weeks4 ,there are two cars1 each about ten feet long1 five feet wide1 and three feet deep4 ,the cars are connected by a narrow passageway made of aluminum wires and plates1 making a walking distance of #cbf feet--longer than the decks of many ocean steamers4 ,a sliding weight of #cjj kilograms 7about #fjj pounds7 serves the same purpose as the guide-ropes in the ,santos ,dumont air-ship4 ,by moving this weight forward or backward the ship is raised or lowered at the bow or stern1 and thus caused to glide up or down4 ,anchor-ropes are carried for use in landing4 ,the ship is propelled by four screws1 and guided by a number of rudders placed some in front and some in the rear4 ,the first ,zeppelin air-ship carried four passengers4 ,the work of ,dumont and ,zeppelin has led the great powers to manufacture dirigible balloons for use in time of war4 ,fig4 #ia shows one of the ,zeppelin air-ships sailing over a lake4 ,illustration3 ,,fig4 #ia--;,a ,,zeppelin ,,air-,,ship ,a larger air-ship1 the ,deutschland1 built later by ,count ,zeppelin1 was the first air-ship to be used for regular passenger service4 ,the ,deutschland is shown in ,fig4 #ib4 ,the ,deutschland carried the crew and twenty passengers4 ,it operated for a time as a regular passenger air-ship between ,friedrichshafen and ,dsseldorf1 a distance of three hundred miles4 ,the ,deutschland was wrecked in a storm on ,june #bh1 #aiaj1 but it was successfully operated long enough to give ,germany the honor of establishing the first air-ship line for regular passenger service4 ,this is an honor perhaps equally as great as that of establishing the first commercial electric railway1 which also belongs to ,germany4 ,an ,american army air-ship is shown in ,fig4 #ic4 ,illustration3 ,,fig4 #ib--;,,count ,,zeppelin',s ,,deutschland1 ,,the ,,first ,,air-,,ship ,,in ,,regular ,,passenger ,,service ,illustration3 ,copyright by ,pictorial ,news ,co4 ,,fig4 #ic--,,the ,,baldwin ,,air-,,ship ,,used ,,in ,,the ,,united ,,states ,,army ,the ,aeroplane ,the aeroplane is a later development than the dirigible balloon4 ,the aeroplane is heavier than air4 ,so is a bird and so is a kite4 ,what supports a kite or a bird as it soars8 ,every boy knows that the strings of a kite must be attached so that the kite is inclined and catches the wind underneath4 ,then the wind lifts the kite4 ,in still air the kite will not fly unless the boy who holds the string runs very fast and so causes an artificial breeze to blow against the kite4 ,in much the same way a hovering bird is held aloft by the wind4 ,in a dead calm the bird must flap its wings to keep afloat4 ,if the kite string is cut the kite tips over and drops to the earth because it has lost its balance4 ,the lifting power of the wind is well shown in the man-lifting kites which are used in the ,british army service4 ,in a high wind a large kite is used in place of a captive balloon4 ,it is a box-kite made of bamboo and carries a passenger in a car1 the car running on the cable which attaches the kite to the ground4 ,now suppose a kite with a motor and propeller in place of a string and a boy to run with it1 and that the kite is able to balance itself1 then it will sail against a wind of its own making and you have a flying-machine heavier than air4 ,the first aeroplane that would fly under perfect control of the operator was built by the ,wright brothers at ,dayton1 ,ohio4 ,when they were boys1 ,bishop ,wright gave his two sons1 ,orville and ,wilbur1 a toy flyer4 ,from that time on the thought of flying through the air was in their minds4 ,a few years later the death of ,lilienthal1 who was killed by a fall with his glider in ,germany1 stirred them1 and they took up the problem in earnest4 ,they read all the writings of ,lilienthal and became acquainted with ,mr4 ,octave ,chanute1 an engineer of ,chicago who had made a successful glider4 ,they soon built a glider of their own1 and experimented with it each summer on the huge sand-dunes of the ,north ,carolina coast4 ,a glider is an aeroplane without a propeller4 ,with it one can cast off into the air from a great height and sail slowly to the ground4 ,before attempting to use a motor and propeller1 the ,wrights learned to control the glider perfectly4 ,they had to learn how to prevent its being tipped over by the wind1 and how to steer it in any direction4 ,this took years of patient work4 ,but the problem was conquered at last1 and they attached a motor and propeller to the glider1 and had an air-ship under perfect control and with the speed of an express-train4 ,their flyer of #aije1 which made a flight of twenty-four miles at a speed of more than thirty-eight miles an hour1 carried a twenty-five-horse-power gasolene motor1 and weighed1 with its load1 #ibe pounds4 ,figs4 #id and #ie show the ,wright air-ship in flight4 ,fig4 #ig shows the mechanism4 ,illustration3 ,,fig4 #id--;,,in ,,full ,,flight ,illustration3 ,copyright1 #aijh1 by ,pictorial ,news ,co4 ,,fig4 #ie--,,wright ,,air-,,ship ,,in ,,flight ,rear view1 showing propellers4 ,illustration3 ,,fig4 #ig--,,the ,,seat ,,and ,,motor ,,of ,,the ,,wright ,,aeroplane ,photo by ,pictorial ,news ,co4 ,how the ,wright ,aeroplane ,is ,kept ,afloat ,the ,wright aeroplane is balanced by a warping or twisting of the planes #a and #b1 which form the supporting surfaces 7,fig4 #if74 ,if left to itself the machine would tip over like a kite when the string is cut and drop edgewise to the ground4 ,suppose the side ,r starts to fall4 ,the corners a and e are raised by the operator while b and f are lowered1 thus twisting the planes1 as shown in the dotted lines of the figure4 ,the side ,r then catches more wind than the side ,l4 ,the wind exerts a greater lifting force on ,r than on ,l1 and the balance is restored4 ,the twist is then taken out of the machine by the operator4 ,a ship when sailing on an even keel presents true unwarped planes to the wind4 ,illustration3 ,,fig4 #if--;,,how ,,the ,,wright ,,air-,,ship ,,is ,,kept ,,afloat ,this picture represents a glider4 ,the motor-driven aeroplane is balanced by the warping of the planes in the same way as the glider4 ,the twisting is brought about by a pull on the rope #c1 which is attached at d and c1 and passes through pulleys at g and h4 ,when the rope is pulled toward the left the right end is tightened and slack is paid out at the left end4 ,this pulls down the corner d1 and raises e4 ,the corner a is raised by the post which connects a and e4 ,the rope #d1 passing from a to b through pulleys at m and n1 is thus drawn toward a and pulls down the corner b4 ,thus a is raised and b is lowered4 ,at the same time rope #d turns the rear rudder to the left1 as shown by the dotted lines1 thus forcing the side ,r against the wind4 ,of course1 if the left side of the machine starts to fall1 the rope #c is pulled toward the right1 and all the movements take place in the opposite direction4 ,the ropes are connected to a lever1 by which the operator controls the warping of the planes4 ,these movements are possible because the joints are all universal1 permitting movement in any direction4 ,in whatever position the planes may be set1 they are held perfectly rigid by the two ropes1 together with others not shown in the figure4 ,the machine is guided up or down by the front horizontal rudder4 ,when the aeroplane swings round a curve the outer wing is raised because it moves faster than the inner wing1 and therefore has greater lifting force4 ,thus the aeroplane banks its own curves4 ,the ,wright flying-machine is called a biplane because it has two principal planes1 one above the other4 ,a number of successful flying-machines have been built with only one plane1 and these are called monoplanes4 ,a monoplane that early became famous is that of ,blriot 7,fig4 #ih74 ,the ,blriot monoplane was the first flying-machine to cross the ,english ,channel4 ,this machine is controlled by a single lever mounted with a ball-and-socket coupling1 so that it can move in any direction4 ,when on the ground it is supported by three wheels like bicycle wheels1 so that it does not require a track for starting1 but can start anywhere from level ground4 ,the ,wright and the ,blriot represent the two leading types of early successful flying-machines4 ,illustration3 ,copyright by ,m4 ,brauger1 ,paris ,,fig4 #ih--,,the ,,bl,,riot ,,monoplane ,submarines ,successful navigation beneath the surface of the water1 though not carried to the extent imagined by ,jules ,verne1 was a reality at the beginning of the twentieth century4 ,instead of twenty thousand leagues under the sea1 less than a hundred leagues had been accomplished1 but no one can foretell what the future may have in store4 ,the principal use of the submarine is in war4 ,it is a diving torpedo-boat1 and acts under cover of water1 as the light artillery on land is secured behind intrenchments4 ,the weapon used by the submarine is the torpedo4 ,the torpedo is itself a small submarine able to propel itself1 and if started in the water toward a certain object1 to go under water straight to the mark4 ,it carries a heavy charge either of guncotton or dynamite1 which explodes when the torpedo strikes a solid object1 such as a battle-ship4 ,the first torpedo was intended to be steered from the shore by means of long tiller-ropes1 and to be propelled by a steam-engine or by clockwork4 ,the ,whitehead fish torpedo1 invented in #ahff1 is self-steering4 ,at the head of the torpedo is a pointed steel firing-pin4 ,when the torpedo strikes a ship or any rigid object this steel pin is driven against a detonator cap which is in the centre of the charge of dynamite4 ,the blow causes the cap to explode1 and the explosion of the cap explodes the dynamite4 ,the torpedo is so arranged that it cannot explode until it is about thirty yards away from the ship from which it is fired4 ,the steel pin cannot strike the cap until a small collar has been revolved off by a propeller fan1 and this requires a distance of about thirty yards4 ,the screw propeller is driven by compressed air4 ,a valve which is worked by the pressure of the water keeps the torpedo at any depth for which the valve is set4 ,the torpedo contains many ingenious devices for bringing it quickly to the required depth and keeping it straight in its course4 ,one of these devices is the gyroscope1 which will be described under the head of spinning tops4 ,whitehead torpedoes are capable of running at a speed of over thirty-seven miles an hour for a range of two thousand yards and hitting the mark aimed at almost as accurately as a gun4 ,the submarine boat carries a number of torpedoes1 and has one torpedo-tube near the forward end from which to fire the torpedoes4 ,it would be very difficult for one submarine to fight another submarine1 for the submarine when completely submerged is blind4 ,it could not see in the water to find its enemy4 ,the torpedo-boat-destroyer is able to destroy a submarine by means of torpedoes1 shells full of high explosives1 or quick-firing guns4 ,advantage must be taken of the moment when the submarine comes to the surface to get a view of her enemy4 ,one of the great enemies of the submarine will probably be the air-ship1 for while the submarine when under water cannot be seen from a ship on the surface1 it can1 under favorable conditions1 be seen from a certain height in the air4 ,most submarines use a gasolene motor for surface travel1 and an electric motor run by a storage battery for navigation below the surface4 ,the best submarines can travel at the surface like an ordinary boat1 or awash--that is1 just below the surface--with only the conning tower projecting above the water1 or they can travel completely submerged4 ,the rising and sinking of the submarine depend on the principle of ,archimedes4 ,the upward push of the water is just equal to the weight of the water displaced4 ,if the water displaced weighs more than the boat1 then the upward push of the water is greater than the weight of the boat and the boat rises4 ,however1 the boat can be made to dive when its weight is just a little less than the weight of the water displaced4 ,this is done by means of horizontal rudders which may be inclined so as to cause the boat to glide downward as its propeller drives it forward4 ,the magnetic compass is not reliable in a submarine with a hull made of steel4 ,the electric motor used for propelling the boat under water also interferes with the action of the compass1 because of its magnetic field4 ,the gyroscope1 which we shall describe later1 is not affected by magnetic action1 and may take the place of the compass4 ,water ballast is used1 and when the submarine wishes to dive1 water is admitted into the tanks until the boat is nearly heavy enough to sink of its own weight4 ,it is then guided downward by the horizontal rudder4 ,the submarine is driven by a screw propeller1 and some submarines are lowered by means of a vertical screw4 ,just as a horizontal screw propels a vessel forward1 so a vertical screw will propel it downward4 ,when the submarine wishes to rise1 it may do so by the action of its rudder1 or the water may be pumped out of its tanks1 when the water will raise it rapidly4 ,a submarine which is kept always a little lighter than water will rise to the surface in case of accident to its machinery4 ,figs4 #ii1 #ajj1 and #aja are from photographs of ,united ,states submarines4 ,illustration3 ,,fig4 #ii--,,the ,,plunger ,photo by ,pictorial ,news ,co4 ,illustration3 ,,fig4 #ajj--,u4 ,s4 ,,submarine ,,shark ,,ready ,,for ,a ,,dive ,photo by ,pictorial ,news ,co4 ,illustration3 ,,fig4 #aja--;,,first ,,submarine ,,constructed ,,in ,,united ,,states4 ,,it ,,went ,,to ,,the ,,bottom ,,with ,,seven ,,men1 ,,who ,,were ,,drowned ,photo by ,pictorial ,news ,co4 ,there is one kind of submarine built for peaceful pursuits which deserves mention4 ,it is the ,argonaut1 invented by ,simon ,lake4 ,this remarkable boat crawls along the bottom of the sea1 but not at a very great depth4 ,it is equipped with divers' appliances1 and is used in saving wreckage4 ,divers can go out through the bottom of the boat1 walk about on the sea bottom1 and when through with their work re-enter the boat2 all the while boat and men are1 perhaps1 a hundred feet below the surface4 ,the divers' compartment1 from which the divers go out into the water1 is separated by an air-tight partition from the rest of the boat4 ,compressed air is forced into this compartment until the pressure of the air equals the pressure of the water outside4 ,then the door in the bottom is opened1 and the air keeps the water out4 ,the men in their diving-suits can then go out and in as they please4 ,for every boat there is a depth beyond which it must not go4 ,the penalty for going beyond this depth is a battered-in vessel1 for the pressure increases with the depth4 ,every time the depth is increased thirty-two feet the pressure is increased fifteen pounds on every square inch4 ,beyond a certain depth the vessel cannot resist the pressure4 ,submarines have been made strong enough to withstand the pressure at a depth of five thousand feet1 or nearly a mile4 ,most submarines1 however1 cannot go deeper than a hundred and fifty feet4 ,air is supplied to the occupants of the boat either from reservoirs containing compressed air or oxygen1 or by means of chemicals which absorb the carbon dioxide produced in breathing and restore the needed quantity of oxygen to the air4 ,while the men in the boat cannot see in the water1 they can see objects on the surface of the water1 even when their boat is several feet below the surface1 by means of the periscope4 ,this is an arrangement of lenses and mirrors in a tube bent in two right angles1 which projects a short distance above the surface and can be turned in any direction 7,fig4 #ajb74 ,thus the boat1 while itself nearly invisible1 can have a clear view of the battle-ship which it is about to attack4 ,illustration3 ,,fig4 #ajb--;,,how ,,men ,,in ,a ,,submarine ,,see ,,when ,,under ,,the ,,water ,some ,spinning ,tops that ,are ,useful ,every one knows that a top will stand upright only when it is spinning4 ,most tops when spinning will stand very rough treatment without being upset4 ,the whip-top will stand a severe lashing4 ,spin a top upright and give it a knock4 ,it will go round in a circle in a slanting position1 and after a time will right itself4 ,if the top is struck toward the south it will not bow toward the south but toward the east or west4 ,in throwing a quoit1 the quoit must be given a spinning motion or the thrower cannot be certain how it will alight4 ,a coin thrown up with a spinning motion will not turn over4 ,the quoit and the coin are like the top4 ,they will not turn over easily when spinning4 ,for the same reason a rifle bullet is set spinning by the spiral grooves in the bore of the gun1 and it goes straight to its mark4 ,with a smooth-bore gun that does not set the bullet spinning the gunner cannot be sure of his aim4 ,it took a long time to discover that the spinning top is a useful machine4 ,it is useful because of its steady motion1 because it is difficult to turn over4 ,it was discovered by ,newton long ago that every moving object tries to keep on in the direction in which it is moving4 ,a moving object always requires some force to change its direction4 ,the spinning top is a beautiful illustration of this principle4 ,the top that is most useful is the gyroscope top 7,fig4 #ajc74 ,it is mounted on pivots so arranged that the top can turn in any direction within the frame that supports it4 ,if the top is set spinning one may turn the frame in any direction1 but the top does not change direction4 ,the axis of the top will point in the same direction all the while the top is spinning1 no matter how the supporting frame is moved about4 ,the top will spin on a string4 ,if attached inside a box the box can be made to stand on one corner while the top is spinning4 ,illustration3 ,,fig4 #ajc--;,a ,,top ,,that ,,spins ,,on ,a ,,string ,this top1 which is so hard to upset1 has been used in ships to prevent the ship being rolled by the waves4 ,a large fly-wheel is mounted in the middle of the vessel on a horizontal axle4 ,a fly-wheel is only a large top4 ,it spins with a steady motion1 and because of its larger size it is very much harder to overturn than a toy top4 ,the fly-wheel in the ship resists the rolling force of the waves and steadies the ship1 so that even with high waves the rolling can scarcely be felt4 ,the waves do not so readily break over the ship when thus steadied by the revolving wheel4 ,the gyroscope is also used in some forms of torpedo to give the torpedo steady motion4 ,by means of a spring released by a trigger the gyroscope within the torpedo is set spinning before the torpedo enters the water4 ,the gyroscope keeps its direction unchanged1 and as the torpedo turns one way or the other the gyroscope acts upon one or the other of two valves connected with the compressed-air chambers from which the screws of the torpedo are driven4 ,the air thus set free by the gyroscope drives a piston-rod connected with a rudder in such a way as to right the torpedo4 ,the torpedo goes through the water with a slightly zigzag motion1 but never more than two feet out of the line in which it was aimed4 ,the ,monorail-,car ,another use of the gyroscope is in the monorail-car4 ,to make a car run on a single rail1 with its weight above the rail1 was impossible until the use of the gyroscope was discovered4 ,in the monorail-car invented by ,brennan 7,fig4 #ajd7 there are two gyroscopes1 each weighing fifteen hundred pounds1 driven at a speed of three thousand revolutions a minute by an electric motor4 ,each gyroscope wheel with its motor is mounted in an air-tight casing from which the air is pumped out4 ,the wheel will run much more easily in a vacuum than in air1 for the air offers very great resistance to its motion4 ,the wheels are placed one on each side of the car with their axles horizontal4 ,when the car starts to fall the spinning gyroscopes right it much as a spinning top rights itself if tipped to one side by a blow4 ,if the wind tips the car to the left the gyroscopes incline to the right until the car is again upright4 ,if the load is heavier on the right side the car inclines itself toward the left just as a man leans to the left when carrying a load on his right shoulder4 ,in rounding a curve the car leans to the inside of the curve just as a bicycle rider does1 and as a railway train is made to do by laying the outer rail of the curve higher than the inner rail4 ,two gyroscopes spinning in opposite directions are necessary to keep the car from falling when rounding a curve4 ,illustration3 ,,fig4 #ajd--;,a ,,car ,,that ,,runs ,,on ,,one ,,rail ,louis ,brennan's full-size monorail4 ,the gyroscope may be used in place of a compass4 ,if it is set spinning in a north and south direction it will continue to spin in a north and south direction1 no matter how the ship may turn4 ,it is even more reliable than the compass1 for it is not affected by magnetic action4 ,possibly some of the great inventions yet to be made will be new uses of the spinning top4 ,liquid ,air and the ,greatest ,cold ,for a long time after men had learned the use of the furnace and could produce great heat1 the greatest cold known was that of the mountain-top4 ,men wondered what would happen if air could be made colder than the frost of winter1 but knew not how to bring about such a result4 ,they wondered what things could be frozen that remain liquid or gaseous even in the cold of winter4 ,the first artificial cold was produced by a mixture of salt and ice1 such as we now use in an ice-cream freezer4 ,in time men learned other ways of producing great cold and even to manufacture ice in large quantities4 ,the cold of liquid air is far greater than that of ice or even a freezing mixture of salt and ice4 ,liquid air is simply air that is so cold that it becomes a liquid just as steam when cooled forms water4 ,steam has only to be cooled to the temperature of boiling water1 while air must be cooled to #cad degrees below zero on the ,fahrenheit scale4 ,if it were possible for us to live in such a climate1 and the world were cooled to the temperature of liquid air1 we should have a curious world4 ,watch-springs might be made out of pewter1 bells of tin1 and piano wires of solder1 for these metals are made stronger by the extreme cold of liquid air4 ,there would be no air to breathe4 ,oceans and rivers would be frozen solid1 and the air would form a liquid ocean about thirty-five feet deep4 ,this ocean of liquid air would be kept boiling a long time by the heat of the ice beneath it1 for ice is hot compared with liquid air4 ,the ice would cool as it gave up its heat to the liquid air and in time become as cold as the liquid air itself4 ,liquid air has been shipped thousands of miles in a double walled tin can1 the space between the two walls being filled with felt4 ,the felt protects the liquid air from the heat of the air without4 ,the liquid air evaporates slowly1 and escapes through a small opening at the top4 ,professor ,dewar1 a successor of ,faraday in the ,royal ,institution1 invented the ,dewar bulb1 by means of which the evaporation of the liquid air is prevented4 ,this bulb is a double-walled flask4 ,in the space between the two walls of the flask is a vacuum4 ,now a vacuum is the best possible protection against heat4 ,if we were to take a bottle full of air and pump out from the bottle all except about a thousandth of a millionth of the air it contained at first we should have such a vacuum as that of the ,dewar bulb4 ,with such a vacuum around it ice could be kept from melting for many days even in the hottest weather1 for no heat can go through a vacuum4 ,but the greatest cold is not the cold of liquid air4 ,liquid hydrogen is so cold that it freezes air4 ,when a flask of liquid hydrogen is opened there is a small snow-storm of frozen air in the mouth of the flask4 ,but even this is not the greatest cold4 ,the liquid hydrogen may be frozen1 forming a hydrogen snow whose temperature is #dce degrees below zero4 ,this is nearly equal to the cold of the space beyond the earth's atmosphere1 which is the greatest possible cold4 ,the ,electric ,furnace and the ,greatest ,heat ,the greatest heat that has yet been produced artificially is that of the electric arc4 ,the exact temperature of the electric arc is not known with certainty4 ,it is known1 however1 that the temperature of the hottest part of the arc is not less than #fejj degrees ,fahrenheit4 ,when we compare this with the temperature of the hottest coal furnace1 which is about #djjj degrees1 we can very easily understand that something is likely to happen at the temperature of the electric arc that could not happen in an ordinary furnace4 ,if an electric arc is enclosed by something that will hold the heat in we have an electric furnace1 and any substance placed in the furnace may be made nearly as hot as the arc itself4 ,in the electric furnace any substance1 whether found in nature or prepared artificially1 may be melted or vaporized4 ,it was ,henri ,moissan1 ,professor of ,chemistry at the ,sorbonne in ,paris1 who made the first great discoveries in the use of the electric furnace and produced the first artificial diamonds4 ,the study of diamonds led ,moissan to believe that in nature they are formed by the cooling of a melted mixture of iron and carbon4 ,he could prepare such a mixture with his electric furnace1 he thought1 and so make diamonds like those of the diamond mines4 ,so1 with an electric furnace having electrodes as large as a man's wrist1 a mixture of iron and charcoal in a carbon crucible1 and a glass tank filled with water1 ,moissan set out to change the charcoal to diamonds4 ,at a temperature of more than six thousand degrees the iron and charcoal were melted together4 ,for a time of from three to six minutes the mixture was in the intense heat4 ,then the covering of the furnace was removed and the crucible with the melted mixture dropped into the tank of water4 ,with some fear this was done for the first time1 for it was not known what would happen when such a hot object was dropped into cold water4 ,but no explosion occurred1 only a violent boiling of the water1 a fierce blazing of the molten mass1 and then a gradual change of color from white to red and red to black4 ,with boiling acids and other chemicals the refuse was removed1 and the fragments that remained were found to be diamonds1 small1 it is true1 so small that they could be seen only with the aid of a microscope1 but giving promise of greater things to come4 ,the outer crust of iron held the melted charcoal under enormous pressure while it slowly cooled and formed the diamond crystals4 ,the process of manufacturing diamonds is illustrated in ,figs4 #aje1 #ajf1 and #ajg4 ,illustration3 ,,fig4 #aje--,,manufacturing ,,diamonds--,,first ,,operation ,preparing the furnace4 ,charcoal and iron ore placed in a crucible and subjected to enormous heat electrically4 ,illustration3 ,,fig4 #ajf--,,manufacturing ,,diamonds--,,second ,,operation ,the furnace at work4 ,illustration3 ,,fig4 #ajg--,,manufacturing ,,diamonds--,,third ,,operation ,plunging the crucible into cold water4 ,observe the white-hot carbon just removed from the furnace4 ,the electric furnace has made possible the preparation of substances unknown before1 and the production in large quantities at low cost of substances that before were too costly for general use4 ,one of the best known of these substances is aluminum4 ,with the discovery of the electric-furnace method of extracting aluminum from its ores1 the price of aluminum fell from one hundred and twenty-four dollars per pound to twelve cents per pound4 ,among the many uses of the electric furnace we may mention the preparation of calcium carbide1 which is used in producing the acetylene light2 carborundum1 a substance almost as hard as diamond2 and phosphorus1 which is used in making the phosphorus match4 ,it is used also to some extent in the manufacture of glass1 and1 in some cases1 for extracting iron from its ores4 ,the ,wireless ,telegraph ,a ship in a fog is struck by another ship4 ,the water rushes in1 puts out the fires in the boilers1 the engines stop1 the ship is helpless in mid-ocean in the darkness of the night4 ,but the snapping of an electric spark is heard in one of the cabins4 ,soon another vessel steams alongside4 ,the life-boats are lowered and every person is saved4 ,the call for help had gone out over the sea in every direction for two hundred miles4 ,another ship had caught the signal and hastened to the rescue1 and the world realized that the wireless telegraph had robbed the sea of its terrors4 ,without the curious combination of magnets1 wires1 and batteries on the first ship no signal could have been sent1 and without such a combination on the second ship the signal would have passed unheeded4 ,how was this combination discovered1 and how does it work8 ,faraday1 as we have seen1 discovered the principle of the induction-coil4 ,with the induction-coil a powerful electric spark can be produced4 ,the friction electrical machine was known long before the time of ,faraday4 ,franklin proved that a stroke of lightning is like a spark from an electrical machine1 only more powerful4 ,these great discoverers did not know1 however1 that an electric spark sends out something like light which travels in all directions4 ,they did not know it1 because they had no eyes to see this strange light4 ,i will tell you a fable to make the meaning clear4 ,there once lived a race of blind men4 ,not one of them could see4 ,they built houses and cities1 railroads and steamships1 but they did everything by touch and sound4 ,when they met they touched each other and spoke1 and each man knew his friend by the sound of his voice4 ,one day a wise man among them said he believed there was something besides the sound of the voice with which they could make signals to each other4 ,another wise man thought upon this matter for some time and brought forth a proof that there is something called light1 though no man could see it4 ,another1 wiser and more practical1 invented an eye which any man could carry about with him and see the light when he turned it in the direction from which the light was coming4 ,thereafter each man carried a light that flashed like the flashing of a firefly4 ,each man also carried an eye1 and each could see his friend as well as hear the sound of his voice4 ,the fable is true4 ,the light which no man had seen we now call electric waves4 ,the eye with which any one can perceive this light is the receiving instrument of the wireless telegraph4 ,the strange light flashed out whenever an electric spark passed from an electrical machine1 a ,leyden jar1 an induction-coil1 or as lightning in the clouds1 but for hundreds of years this light was unseen4 ,the human eye could not see it1 and no artificial eye that would catch electric waves had been invented4 ,a man in ,england1 ,james ,clerk-,maxwell1 first proved that there is such a light4 ,heinrich ,hertz1 a ,german1 first made an eye that would catch the waves from the electric spark1 and the man who first perfected an eye with which one could catch the electric waves at a great distance and improved the instruments for sending out such waves was ,marconi4 ,the fable is true1 for electric waves are like the light from the sun4 ,they go through space in all directions as light does4 ,they will not merely go through air1 but through what we call empty space1 or a vacuum1 as light will4 ,if we think of waves somewhat like water waves1 but not exactly like them1 rushing through space1 we have about as good a picture of electric waves as we can well form in our minds4 ,as the light of a lamp goes out in all directions1 so do the electric waves go out in all directions from the place where the electric spark passes4 ,since these waves go through what we call empty space1 we must think of something in that space and that it is not really empty4 ,examine an incandescent electric lamp4 ,the bulb was full of air when the carbon thread was placed in it4 ,the air was then pumped out until only about a millionth part remained4 ,the bulb was then sealed at the tip and made air-tight4 ,we say the space inside is a vacuum4 ,if the bulb is broken there is a loud report as the air rushes in4 ,is the bulb really empty after the air is pumped out8 ,is anything left in the bulb around the carbon thread8 ,turn on the electric current and the carbon thread becomes white hot4 ,the light from the white-hot carbon thread goes out through the vacuum4 ,there is nothing in the vacuum that we can see or feel or handle1 but something must be there to carry the light from the carbon thread4 ,the light of the sun comes to the earth through ninety-three million miles of space4 ,is there anything between the earth and the sun through which this light can pass8 ,light1 we know1 is made up of waves1 and we cannot think of waves going through empty space4 ,there must be something between the sun and the earth4 ,that something through which the light of the sun comes to the earth we call the ether4 ,it is the ether that carries the light across the vacuum in the light bulb as well as from the sun to the earth4 ,electric waves used in wireless telegraphy go through this same ether4 ,the light of the sun is made up of the same kind of waves1 and we do not think it strange because it is so common4 ,it is true we do not see light waves1 but they affect our eyes so that by means of them we can see objects and perceive the flashing of a light4 ,so with the wireless receiving instrument we do not see the electric waves1 but we perceive the flashing of the strange light4 ,electric waves and light travel with the same speed--#ahf1jjj miles in a second4 ,a wireless message will go around the earth in about one-seventh of a second4 ,electric waves will go through a brick wall as readily as sunlight will go through a glass window1 but that is not so strange as it may seem4 ,red light will not go through blue glass4 ,blue glass holds back the red light1 but lets the blue light go through4 ,so the brick wall holds back common light1 but allows the light which we call electric waves to go through4 ,some waves on water are longer than others4 ,so electric waves are longer than light waves4 ,that is the only difference between them4 ,in fact1 the light of the sun is made up of very short electric waves4 ,these short waves affect our eyes1 but the longer electric waves do not4 ,we are daily receiving the wireless-telegraph waves from the sun1 which we call light4 ,electric waves used in wireless telegraphy vary from about six hundred feet to two miles in length1 while the longest light waves that affect our eyes are only one thirty-three-thousandth of an inch in length4 ,the sensitive part of the ,marconi receiving apparatus is the coherer4 ,the first coherer was made in #ahij by ,prof4 ,edward ,branly1 of the ,catholic ,university of ,paris4 ,very fine metal filings were enclosed in a tube of ebonite and connected in a circuit with a battery and a galvanometer4 ,the filings have so high a resistance that no current flows4 ,the waves from an electric spark1 however1 affect the filings so that they allow the current to flow4 ,the electric waves are said to cause the filings to cohere--that is1 to cling together more closely4 ,it is a peculiar form of electric welding4 ,branly discovered that a slight tapping of the tube loosens the filings and stops the flow of the current4 ,all that was needed for wireless telegraphy was at hand4 ,men knew how to produce electric waves of any desired length4 ,they knew how they would act4 ,a sensitive receiver had been discovered4 ,there was needed the practical man who should combine the parts1 improve details1 and apply the wireless telegraph to actual use4 ,this was the work of ,guglielmo ,marconi4 ,in #ahid1 at the age of twenty1 ,marconi began his experiments on his father's estate1 the ,villa ,grifone1 ,bologna1 ,italy4 ,fig4 #ajh is from a photograph of ,marconi and his wireless sending and receiving instruments4 ,illustration3 ,,fig4 #ajh--,,marconi ,,and ,,his ,,wireless-,,telegraph ,,sending ,,and ,,receiving ,,instruments ,to ,marconi1 telegraphing through space without wires appears no more wonderful than telegraphing with wires4 ,in the wire telegraph electric waves1 which we then call an electric current1 follow a wire somewhat as the sound of the voice goes through a speaking-tube4 ,in the wireless telegraph the electric waves go out through space without any wire to guide them4 ,the light and heat waves of the sun travel to us through millions of miles of space without requiring any conducting wire4 ,that electric waves should go though space in the same way that light does is no more wonderful than that the waves should follow all the turns of a wire4 ,the sending instrument used by ,marconi includes an induction-coil1 one side of the spark-gap being connected to the earth and the other to a vertical wire 7,fig4 #aji74 ,there must be a battery of ,leyden jars in the circuit of the secondary coil4 ,the induction-coil may be operated by a storage battery or dynamo4 ,the vertical wire1 or antenna1 is to the sending instrument what the sounding-board is to a violin4 ,it is needed to increase the strength of the waves4 ,in the wireless telegraph some wires must be used4 ,it is called wireless because the stations are not connected by wires4 ,the antenna for long-distance work consists of a network of overhead wires4 ,when the key is pressed a rapid succession of sparks passes across the spark-gap4 ,the antenna1 or overhead wire1 is thus made to send out electric waves4 ,by pressing the key for a longer or shorter time1 a longer or shorter series of waves may be produced and a correspondingly longer or shorter effect on the receiver4 ,in this manner the dots and dashes of the ,morse alphabet may be transmitted4 ,illustration3 ,,fig4 #aji--;,,diagram ,,of ,,wireless-,,telegraph ,,sending ,,apparatus ,at the receiving station there are two circuits4 ,one includes a coherer1 a local battery1 and a telegraph relay 7,fig4 #aaj74 ,the other circuit1 which is opened and closed by the relay1 includes a recording instrument and a tapper4 ,one end of the coherer is connected to the earth and the other to a vertical wire like that used for the transmitter4 ,the electric waves weld the filings in the coherer1 and this closes the first circuit4 ,the relay then closes the second circuit1 the recording instrument records a dot or a dash1 and the tapper strikes the coherer and breaks the filings apart ready for another stream of electric waves4 ,illustration3 ,,fig4 #aaj--;,,diagram ,,of ,,marconi ,,wireless-,,telegraph ,,receiving ,,apparatus ,the second circuit described in the text is not shown here4 ,the relay and the second circuit would take the place of the electric bell4 ,in the circuit as shown here the electric waves would cause the coherer to close the circuit and ring the bell4 ,with this arrangement it was possible to work only two stations at one time4 ,though stations were to be established in all the cities of ,great ,britain1 only one message could be sent at one time1 and all stations but one must keep silence1 because a second series of waves would mingle with the first and confusion would result4 ,marconi's next effort was to make it possible to send any number of messages at one time4 ,this led to his system of tuning the sending and receiving instruments4 ,with this system the receiving instrument will take a message only from a sending instrument with which it is in tune4 ,it is possible1 therefore1 for any number of wireless-telegraph stations to operate at the same time1 the waves crossing one another in all directions without interfering1 each receiver responding to the waves intended for it4 ,an ocean steamer can1 with the tuned system1 send one message and receive another from a different station at the same time4 ,marconi's ambition was to send a wireless message across the ,atlantic4 ,quietly he made his preparation1 building at ,poldhu1 ,cornwall1 ,england1 a more powerful transmitter than had yet been used4 ,at noon on the #abth of ,december1 #aija1 he sat in a room of the old barracks on ,signal ,hill1 near ,st4 ,johns1 ,newfoundland1 waiting for a signal from ,england4 ,his assistants at the ,poldhu station were to telegraph across the ocean the letter ,s at certain times each day4 ,on the table was the receiving apparatus1 made very sensitive1 and including a telephone receiver4 ,a wire led out of the window to a huge kite1 which the furious wind held four hundred feet above him4 ,one kite and a balloon used for supporting the antenna had been carried out to sea4 ,he held the telephone receiver to his ear for some time4 ,the critical time had come for which he had worked for years1 for which his three hundred patents had prepared the way1 and for which his company had erected the costly power station at ,poldhu4 ,calmly he listened1 his face showing no sign of emotion4 ,suddenly there sounded the sharp click of the tapper as it struck the coherer4 ,after a short time ,marconi handed the telephone receiver to his assistant4 ,see if you can hear anything1 he said4 ,a moment later1 faintly and yet distinctly1 came the three little clicks1 the dots of the letter ,s tapped out an instant before in ,england4 ,marconi's victory was won4 ,a flying-machine can be equipped with a wireless-telegraph outfit1 so that a man can telegraph while flying through the air4 ,two men are needed1 one to operate the flying-machine1 the other to send the telegraphic messages4 ,this has been done with the ,wright machine and with some dirigible balloons4 ,of course1 the wireless instruments on the flying-machine cannot be connected to the ground4 ,instead of the ground connection there is a second antenna4--one antenna on each side of the spark-gap4 ,while in the ordinary wireless instruments the discharge surges back and forth between the antenna and the earth1 in the flying-machine wireless the discharge surges back and forth between the two antenn4 ,in the ,wright machine1 when equipped for wireless telegraphy1 the two antenn are placed one under the upper plane1 the other under the lower plane of the flying-machine4 ,more power is required for the wireless than for the wire telegraph4 ,in the wire telegraph about one-hundredth horse-power is required to send a message one hundred and twenty miles4 ,to send a message the same distance with the wireless requires about ten horse-power1 or a thousand times as much as with the wire telegraph4 ,this is because in the wireless telegraph the waves go out in all directions1 and much of the power is wasted4 ,in the wire telegraph the electric waves are directed along the wire and very little of the power is wasted4 ,for the same reason a person's voice can be heard a long distance through a speaking-tube4 ,the speaking-tube guides the sound and prevents it from scattering somewhat as the wire guides the electric waves4 ,the overhead wires of a wireless-telegraph station send out a dark light while a message is being sent4 7,see frontispiece47 ,standing near the station on a dark night one can see nothing1 but can hear only the terrific snapping of the electric discharge4 ,the camera1 however1 shows that light goes out from the wires4 ,it is light of shorter waves than any that the eye can perceive1 but the sensitive film of the photographic plate makes it known to us4 ,the ,wireless ,telephone ,in sending a message by the wire telegraph the current flows over the line wire when the key is pressed4 ,when the key is released the current stops4 ,the circuit is made and broken for every dot or dash4 ,this we may call an interrupted current4 ,now we have seen that the attempt to invent a wire telephone using an interrupted current failed4 ,while one is talking over the wire telephone a current 7alternating7 must be flowing over the line wire4 ,the sound of the voice does not make and break the circuit1 but changes the strength of the current4 ,this alternating current is wonderfully sensitive4 ,it can vary in the rate at which it alternates or the number of alternations per second to correspond to sound of every pitch4 ,it varies in strength to correspond to all the variations in the voice1 and reproduces in the receiver not merely the words that are spoken but the quality of the voice1 so that the voice of a friend can be recognized by telephone almost as well as if talking face to face4 ,the same things are true of the wireless telegraph and telephone4 ,instead of an electric current1 let us say a stream of electric waves4 ,then we may say of the wireless everything that we have said of the wire telegraph and telephone4 ,in sending a message by wireless telegraph the stream of electric waves flows when the key is pressed and stops when the key is released4 ,we have an interrupted stream of electric waves4 ,but an interrupted stream of waves cannot be used for a wireless telephone any more than an interrupted current can be used for a wire-telephone4 ,there must be a constantly flowing stream of electric waves1 and these waves must be changed in strength and form by the sound of the voice4 ,fig4 #aaa shows a wireless-telephone receiver in which light is used to carry the message4 ,the light acts on the receiver in such a way as to reproduce the sound4 ,illustration3 ,,fig4 #aaa--,,receiver ,,of ,,bell',s ,,photophone ,an early idea in wireless telephony4 ,in the wireless-telegraph receiver the interrupted stream of electric waves makes and breaks the circuit of an electric battery4 ,the wireless-telephone receiver must not make and break a circuit1 but it must be sensitive to all the changes in the electric waves4 ,one such receiver is the audion1 which we shall now describe4 ,the audion was invented by ,dr4 ,lee de ,forest4 ,de ,forest had taken the degree of ,doctor of ,philosophy at ,yale ,university1 having written his thesis for that degree on the subject of electric waves4 ,he then entered the employ of the ,western ,electric ,company in ,chicago1 and while in this position worked at night in his room on experiments with electric waves4 ,here he found that a gas flame is sensitive to electric waves 7,fig4 #aab74 ,if a gas flame is made part of the circuit of an electric battery1 which includes also an induction-coil connected to a telephone receiver1 then when a stream of electric waves comes along there is a click in the receiver4 ,the waves change the resistance of the flame1 and so change the strength of the current4 ,the flame is a simple audion4 ,it is the heated gas in the flame that responds to the electric waves4 ,illustration3 ,,fig4 #aab--;,a ,,gas ,,flame ,,is ,,sensitive ,,to ,,electric ,,waves ,if instead of a gas flame an incandescent-light bulb is used having a metal filament1 and on either side of the filament a small strip of platinum1 a more sensitive receiver is obtained4 ,this is the audion1 which is the distinguishing feature of the ,de ,forest wireless telegraph and wireless telephone4 ,the metal filament is made white hot by the current from a storage battery4 ,the vacuum in the bulb is about the same as that of the ordinary incandescent electric light4 ,a very small quantity of gas is therefore left in the bulb4 ,the electrified particles of gas respond more freely to electric waves in this bulb than in the gas flame4 ,the ,de ,forest wireless telephone was adopted for use in the ,united ,states ,navy shortly before the cruise around the world in #aijh4 ,every ship in the navy was equipped with the wireless telephone1 enabling the ,admiral to talk with the officers of any vessel up to a distance of thirty-five miles4 ,the wireless telephone in use on a battle-ship is shown in ,fig4 #aac4 ,illustration3 ,,fig4 #aac--;,,captain ,,ingersoll ,,on ,,board ,,the ,u4 ,s4 ,,battle-,,ship ,,connecticut ,,using ,,the ,,wireless ,,telephone ,wonders of the ,alternating ,current ,before the days of the electric current1 men used the power of falling water4 ,the mill or factory using the water-power was placed beside the fall4 ,the water turned a great wheel1 to which was connected the machinery of the mill1 ,it was not until the invention of the dynamo and motor that water-power could be used at a great distance4 ,if a hundred years ago a man had said that the time would come when a waterfall could turn the wheels of a mill a hundred miles away he would have been laughed at4 ,yet this very thing has come to pass4 ,indeed1 one waterfall may turn the wheels of many factories1 run street-cars1 and light cities up to a distance of a hundred miles and even more4 ,the power of the falling water goes out over slender copper wires from a great dynamo near the fall to the motors in the factories and street-cars4 ,the falling water of ,niagara has about five million horse-power4 ,about the hundredth part of this power is now being used4 ,the water1 falling in a wheel-pit #ada feet deep1 turns a great dynamo weighing #hg1jjj pounds with a speed of #bej turns per minute4 ,a number of such dynamos are used supplying an alternating current at a pressure of #bb1jjj volts1 the current alternating or changing direction twenty-five times per second4 ,such a pressure is too high for the motors and electric lights1 but the current is carried at high pressure to the place where it is to be used and there transformed to a current of low pressure4 ,in carrying a current over a long line1 there is less loss if the current is carried at high pressure4 ,with an alternating current this can be done and the current changed by means of a transformer to a current of low pressure4 ,a transformer is simply two coils of wire wound on an iron core4 ,the simplest transformer is the form used by ,faraday when he discovered electromagnetic induction4 ,if instead of making and breaking a circuit that flows only in one direction as ,faraday did1 we cause an alternating current to flow through one of the coils1 which we may call the primary1 each time the current changes direction in the primary the magnetic field is reversed--that is1 the end of the coil which was the north pole becomes the south pole4 ,this rapidly changing magnetic field induces a current in the secondary coil4 ,each time the magnetic field of the primary coil is reversed the current in the secondary changes direction4 ,thus an alternating current in the primary induces an alternating current in the secondary4 ,one of these coils is of fine wire1 which is wound a great many times around the iron4 ,the other is of coarser wire wound only a few times around the iron4 ,suppose the current is to be changed from high pressure to low pressure4 ,then the high-pressure current from the line is made to flow through the coil of many turns1 and a current of low pressure is given out from the coil of few turns4 ,by changing the number of turns of wire in the coils we can make the pressure whatever we please4 ,if the pressure or voltage of the secondary coil is less than that of the primary1 we have a step-down transformer4 ,on the other hand1 if we send the current from the line wire through the coil of few turns1 then we get a higher voltage from the secondary coil than that of the line wire1 and we have a step-up transformer4 ,the ,niagara current is stepped down from #bb1jjj volts to #bbj volts for use in motors4 ,an electric lamp may be lighted though not connected to any battery or dynamo1 but connected only to a coil of wire 7,fig4 #aad74 ,more than this1 the coil may be insulated so that no current can enter it from any other coil or wire1 and yet the lamp can be lighted4 ,this can be done only by means of an alternating current4 ,if the coil to which the lamp is connected is held in the magnetic field of an alternating current1 then another alternating current is induced in the coil1 and this second current flows through the lamp4 ,illustration3 ,,fig4 #aad--;,,incandescent ,,electric ,,lamp ,,lighted ,,though ,,not ,,connected ,,to ,,any ,,battery ,,or ,,dynamo ,we have already learned that a changing magnetic field induces a current in a coil4 ,now the coil through which an alternating current is flowing has a changing magnetic field all around it1 and if the lamp-coil is brought into this changing magnetic field an alternating current will flow through the coil and the lamp4 ,the insulation on the lamp-coil does not prevent the magnetic field from acting1 though it does prevent a current from entering the coil4 ,the current is induced in the coil itself1 and does not enter it from any outside source4 ,the transformer works in the same way1 the only difference being that in the transformer the two coils are on the same iron core4 ,but in the transformer the two coils are insulated so that no current can flow from one coil to the other4 ,when an alternating current and transformers are used1 the current that lights the lamps in the houses or on the streets is not the current from the dynamo4 ,it is a new current induced in the secondary coil of the transformer by the magnetic field of the primary coil4 ,a peculiar transformer which produces an alternating current that changes direction millions of times in a second has been made by ,nikola ,tesla4 ,this current will do many wonderful things which no ordinary current will do4 ,it will light a room or run a motor without connecting wires4 ,it has produced an electric discharge sixty-five feet in length 7,figs4 #aae and #aaf74 ,though this current is caused to flow by a pressure of millions of volts1 it may be taken with safety through the human body4 ,strange as it may seem1 the safety of this current is due to the high pressure and the rapidity with which it changes direction4 ,while the current used at ,sing ,sing in executing criminals has a pressure of about twenty-five hundred volts1 a current having a pressure of a million volts and alternating hundreds of thousands or millions of times per second is harmless2 ,with such a current the human body may become a live wire1 and an electric lamp to be lighted held in one hand while the other hand grasps the wire from the transformer4 ,illustration3 ,,fig4 #aae--;,,an ,,electric ,,discharge ,,at ,a ,,pressure ,,of #ab1jjj1jjj ,,volts1 ,a ,,current ,,of #hjj ,,amperes ,,in ,,the ,,secondary ,,coil ,illustration3 ,,fig4 #aaf4--;,,an ,,electric ,,discharge ,,sixty-,,five ,,feet ,,in ,,length ,x-,rays and ,radium ,a strange light which passes through the human body as readily as sunlight through a window was discovered by ,prof4 ,wilhelm ,konrad ,roentgen1 of the ,university of ,wrzburg4 ,this light1 which ,professor ,roentgen named ,x-rays1 is given out when an electric discharge at high pressure passes through a certain kind of glass tube from which the air has been pumped out until there is a nearly perfect vacuum4 ,x-rays were discovered by accident4 ,professor ,roentgen was working at his desk with one of the glass tubes when he was called to lunch4 ,he laid the tube with the electric discharge passing through it on a book4 ,returning from lunch he took a photographic plate-holder which was under the book and made some outdoor exposures with his camera4 ,on developing the plates a picture of a key appeared on one of them4 ,he was greatly puzzled at first1 but after a search for the key found it between the leaves of the book4 ,the strange light from the electric discharge in the glass tube had passed through the book and the hard-rubber slide of the plate-holder and made a shadow-picture of the key on the photographic plate4 ,he tried the strange light in many ways1 and found that it would go through many objects4 ,it would even go through the human body1 so that shadow-pictures of the bones and organs of the body could be obtained4 ,in ,fig4 #aag is shown a physician using ,x-rays4 ,fig4 #aah is an ,x-ray photograph of the eye4 ,illustration3 ,,fig4 #aag--;,a ,,physician ,,examining ,,the ,,bones ,,of ,,the ,,arm ,,by ,,means ,,of ,x-,,rays ,illustration3 ,,fig4 #aah--,x-,,ray ,,photograph ,,of ,,the ,,eye ,the eye is above and to the left of the larger black circle4 ,the smaller black circle is a shot which has lodged back of the eye4 ,not long after the discovery of ,x-rays it was discovered that light very much like the ,x-rays is given out by certain minerals4 ,one of the most interesting and the best known of these is radium4 ,radium gives out a light somewhat like ,x-rays that will go through copper and other metals4 ,it does many other strange things4 ,it gives out heat as well as light2 so much heat1 in fact1 that it is always about five degrees warmer than the air around it4 ,it continues to give out heat at such a rate that a pound of radium will melt a pound of ice every hour4 ,it can probably keep this up for at least a thousand years4 ,if this heat could be used in running an engine1 a hundred pounds of radium would run a one-horse-power engine without stopping for many hundred years4 ,the power of ,niagara might be replaced by the power of radium if an engine that could use this power were invented4 ,fig4 #aai is from a photograph made with radium4 ,illustration3 ,,fig4 #aai--,,photograph ,,made ,,with ,,radium ,a purse containing a coin4 ,the strange light from the radium goes through the purse and the slide of the plate-holder and makes a shadow-picture4 ,the great inventor of the future may be able to use the heat of radium or some new power now unknown4 ,we have seen how1 through the toil of many years and the labors of many men1 the great inventions of our age have come into being4 ,it may be that we are now witnessing other great inventions in the making4 ,,appendix ,,brief ,,notes ,,on ,,important ,,inventions ,aerial ,navigation ,first air balloon--,montgolfier ,brothers1 ,france1 #aghc4 ,first balloon ascension--,rozier1 ,france1 #aghc4 ,first gas balloon--,charles1 ,france1 #aghc4 ,first crossing of the ,english ,channel in a balloon--,blanchard1 #aghe4 ,first successful dirigible balloon--,la ,france1 ,renard and ,krebs1 ,france1 #ahhd4 ,first successful motor-driven aeroplane--,wright ,brothers1 ,united ,states2 date of patent1 #aijf4 ,first crossing of the ,english ,channel by an aeroplane--,blriot1 #aiji4 ,first air-ship in regular passenger service--,count ,zeppelin1 ,germany1 #aiaj4 ,agriculture ,plough with cast-iron mold-board and iron shares--,james ,small1 ,scotland1 #aghd4 ,grain-threshing machine--,andrew ,meikle1 ,england1 #aghh4 ,mc,cormick reaper1 first practical grain-harvesting machine--,cyrus ,h4 ,mc,cormick1 ,united ,states1 #ahca4 ,self-raker for harvesters--,mc,cormick1 #ahde4 ,inclined platform and elevator in the reaper1 to enable men binding the grain to ride with the machine--,j4 ,s4 ,marsh1 ,united ,states1 #aheh4 ,barbed-wire fence introduced--,united ,states1 #ahfa4 ,self-binder1 first automatic grain-binding device for the reaper--,jacob ,behel1 ,united ,states1 #ahfd4 ,sulky plough--,b4 ,slusser1 ,united ,states1 #ahfh4 ,twine-binder for harvesters--,m4 ,l4 ,gorham1 ,united ,states1 #ahgc4 ,improved self-binding reaper--,lock and ,wood1 ,united ,states1 #ahgc4 ,barbed-wire machine--,glidden and ,vaughn1 ,united ,states1 #ahgd4 ,rotary disk cultivator--,mallon1 ,united ,states1 #ahgh4 ,steam-plough--,w4 ,foy1 ,united ,states1 #ahgi4 ,combined harvester and thresher--,matteson1 ,united ,states1 #ahhf4 ,automobile mower--,deering ,harvestor ,company1 ,united ,states1 #aija4 ,automobile ,first steam-automobile--,cugnot1 ,france1 #agfi4 ,first chain transmission of power in an automobile--,gurney1 ,england1 #ahbi4 ,application of gas-engine to road vehicles1 beginning of the modern motor-car--,gottlieb ,daimler and ,carl ,benz working independently1 ,germany1 #ahhf4 ,daimler's invention consisted of a two-cylinder air-cooled motor4 ,it was taken up in #ahhi1 by ,panhard and ,levassor1 of ,paris1 who began immediately the construction of the motor-car4 ,this was the beginning of the motor-car industry4 ,bicycle ,first bicycle--,branchard and ,magurier1 ,france1 #aggi4 ,rear-driven chain safety bicycle--,george ,w4 ,marble1 ,united ,states1 #ahhd4 ,bicycles first equipped with pneumatic tires--#ahij4 ,electrical ,inventions ,william ,gilbert1 ,england1 #aedj-afjc1 called the father of magnetic philosophy1 first to use the terms electric force1 electric attraction1 magnetic pole4 ,first electrical machine1 a machine for producing electricity by friction--,otto von ,guericke1 ,germany1 about #afha4 ,discovery of conductors and insulators--,stephen ,gray1 ,england1 #afif-agcf4 ,first to discover that electric charges are of two kinds--,cisternay du ,fay1 ,france1 #afih-agci2 ,du ,fay was also the first to attempt an explanation of electrical action4 ,he supposed that electricity consists of two fluids which are separated by friction1 and which neutralize each other when they combine4 ,this theory was more fully set forth by ,robert ,symmer4 ,leyden jar--,discovered first by ,von ,kleist in #agde4 ,the same discovery was made and the ,leyden jar brought to the attention of the public in #agdf by ,pieter van ,musschenbroek in ,holland4 ,lightning-rod--,benjamin ,franklin1 #agcb4 ,electroplating--,luigi ,brugnatelli1 ,italy1 #ahje4 ,voltaic arc1 a powerful arc light produced with a battery current--,sir ,humphry ,davy1 ,england1 #ahjh4 ,storage battery--,ritter1 ,germany1 #ahjc4 ,platinum wires were dipped in water and a battery current passed through4 ,hydrogen collected on one wire and oxygen on the other4 ,if the platinum wires were disconnected from the battery and connected with each other by a conductor1 the two wires acted like the plates of a battery1 and a current would flow for a short time in the new circuit4 ,electromagnetism discovered--,h4 ,c4 ,oersted1 ,denmark1 #ahai4 ,galvanometer1 a coil of wire around a magnetic needle for measuring the strength of an electric current--,schweigger1 ,germany1 #ahbj4 ,motion of magnet produced by an electric current--,m4 ,faraday1 ,england1 #ahba4 ,thermo-electricity1 an electric current produced by heating the junction of two unlike metals--,discovered by ,professor ,seebeck ,england1 #ahba4 ,principles of electrodynamics1 motion produced by an electric current--,ampre1 ,france4 ,announced in #ahbc4 ,law of electric circuits1 ,ohm's law1 current strength equals electromotive force divided by resistance of the circuit--,george ,s4 ,ohm1 ,germany4 ,proven by experiment in #ahbf2 mathematical proof published in #ahbg4 ,magneto-electric induction1 induction of electric currents by means of a magnetic field--,m4 ,faraday1 ,england1 #ahca4 ,electric telegraph--,prof4 ,s4 ,f4 ,b4 ,morse1 ,united ,states1 #ahcb4 ,first telegram sent in #ahdd--,morse4 ,constant electric battery--,j4 ,p4 ,daniell1 ,england1 #ahcf4 ,first electric motor-boat--,jacobi1 ,russia1 #ahci4 ,induction-coil--,rhumkorff1 ,germany1 #ahea4 ,duplex telegraph1 first practical system--,stearns1 ,united ,states1 about #ahee-ahfj4 ,storage battery1 lead plates in sulphuric acid--,gaston ,plant1 ,france1 #ahei4 ,telephone1 make-and-break system1 first electrical transmission of speech--,philip ,reiss1 ,germany1 #ahfj4 ,atlantic cable laid--,cyrus ,w4 ,field1 #ahff4 ,dynamo1 armature coil rotates in the field of an electromagnet1 armature supplies current for the electromagnet as well as for the external circuit--,william ,siemens1 ,germany1 #ahff4 ,gramme ring armature for dynamo--,gramme1 ,france1 #ahfh4 ,theory that light consists of electromagnetic waves--,clerk-,maxwell1 ,england1 #ahgc4 ,quadruplex telegraph1 sending four messages over one wire at the same time--,edison1 #ahgc4 ,siphon recorder for submarine telegraph1 sensitive to very feeble currents--,sir ,william ,thomson1 ,england1 #ahgd4 ,telephone1 varying current1 first practical working telephone--,alexander ,graham ,bell1 ,united ,states1 #ahgf4 ,electric candle1 beginning of present arc light--,paul ,jablochkoff1 ,russia1 #ahgf4 ,telephone transmitter of variable resistance--,emil ,berliner and ,edison working independently1 ,united ,states1 #ahgg4 ,edison used carbon contacts1 ,berliner used metal contacts4 ,brush system of arc lighting--#ahgh4 ,incandescent electric lamp with carbon filament--,edison1 #ahgh4 ,first electric locomotive--,siemens1 ,germany1 #ahgi4 ,blake telephone transmitter--,blake1 ,united ,states1 #ahhj4 ,storage battery1 lead grids filled with active material--,faure1 ,france1 #ahha4 ,electric ,welding--,elihu ,thompson1 ,united ,states1 #ahhf4 ,electric ,waves discovered by experiment--,heinrich ,hertz1 ,germany1 #ahhh4 ,coherer for receiving electric ,waves--,edward ,branly1 ,france1 #ahij4 ,x-rays--,discovered by ,prof4 ,w4 ,c4 ,roentgen1 ,germany2 announced to the public in #ahie4 ,wireless telegraphy--,g4 ,marconi1 ,italy1 #ahif4 ,nernst electric light1 a clay capable of conducting electricity when heated is used2 it becomes incandescent without a vacuum--,walter ,nernst1 ,germany1 #ahig4 ,radium discovered by ,madame ,curie1 ,france1 #ahih4 ,explosives ,gunpowder--,inventor and date unknown4 ,guncotton--,schnbein1 ,germany1 #ahde4 ,nitroglycerine--,sobrero1 #ahdg4 ,explosive gelatine--,a4 ,nobel1 ,france1 #ahfc4 ,dynamite--,a4 ,nobel1 ,france1 #ahff4 ,smokeless powder--,vielle1 ,france1 #ahff4 ,firearms and ,ordnance ,spirally grooved rifle barrel--,koster1 ,england1 #afbj4 ,breech-loading shot-gun--,thornton and ,hall1 ,united ,states1 #ahaa4 ,the revolver2 a device for combining a number of long barrels so as to rotate upon a spindle by the act of cocking the hammer--,samuel ,colt1 ,united ,states1 #ahcf4 ,breech gun-lock1 interrupted thread--,chambers1 ,united ,states1 #ahdi4 ,magazine gun--,walter ,hunt1 ,united ,states1 #ahdi4 ,breech-loading rifle--,maynard1 ,united ,states1 #ahea4 ,iron-clad floating batteries first used in ,crimean ,war--#ahee4 ,breech-loading ordnance--,wright and ,gould1 ,united ,states1 #aheh4 ,revolving turret for floating batteries--,theodore ,timby1 ,united ,states1 #ahfb4 ,first iron-clad floating battery propelled by steam3 the ,monitor--,john ,ericsson1 ,united ,states1 #ahfb4 ,gatling gun--,dr4 ,r4 ,j4 ,gatling1 ,united ,states1 #ahfb4 ,automatic shell-ejector for revolver--,w4 ,c4 ,dodge1 ,united ,states1 #ahfe4 ,torpedo--,whitehead1 ,united ,states1 #ahff4 ,disappearing gun-carriage--,moncrief1 ,england1 #ahfh4 ,rebounding gun-lock--,l4 ,hailer1 ,united ,states1 #ahgj4 ,magazine rifle--,lee1 ,united ,states1 #ahgi4 ,hammerless gun--,greener1 ,united ,states1 #ahhj4 ,gun silencer1 to be attached to barrel of gun2 gun can be fired without noise--,maxim1 #aiji4 ,gas ,used for ,light and ,power ,gas first used for illuminating purposes--,william ,murdoch1 ,england1 #agib4 ,first street gas-lighting in ,england--,f4 ,a4 ,winsor1 #ahad4 ,gas-meter--,s4 ,clegg1 ,england1 #ahae4 ,water-gas1 prepared by passing steam over white-hot anthracite coal--,first produced in ,england in #ahbc4 ,illuminating water-gas--,lowe1 ,united ,states1 #ahge4 ,gas-engine1 #d-;cycle1 beginning of modern gas-engine--,otto and ,langen1 ,germany1 #ahgg4 ,incandescent gas-mantle--,carl ,a4 von ,welsbach1 ,austria1 #ahhg4 ,iron and ,steel ,blast-furnace1 beginning of iron industry--,belgium1 #acdj4 ,use of coke in blast-furnace--,abram ,darby1 ,england1 about #agbj4 ,puddling iron--,henry ,cort1 ,england1 #aghc-hd4 ,process of making malleable-iron castings--,lucas1 ,england1 #ahjd4 ,hot-air blast for iron furnaces--,j4 ,b4 ,neilson1 ,scotland1 #ahbh4 ,the galvanizing of iron--,henry ,craufurd1 ,england1 #ahcg4 ,process of making steel1 blowing air through molten pig-iron to burn out carbon1 then adding spiegel iron2 first production of cheap steel--,sir ,henry ,bessemer1 ,england1 #ahee4 ,regenerative furnace1 a gas-furnace in which gas and air are heated before being introduced into the furnace1 giving an extremely high temperature--,william ,siemens1 ,england1 #ahef4 ,open-hearth process of making steel--,siemens-,martin1 ,england1 #ahef4 ,nickel steel1 much stronger than ordinary steel1 used for armorplate--,schneider1 ,united ,states1 #ahhi4 ,mining ,miners' safety-lamp--,sir ,humphry ,davy1 ,england1 #ahae4 ,compressed-air rock-drill--,c4 ,burleigh1 ,united ,states1 #ahff4 ,diamond rock-drill1 a tube of cast-steel with a number of black diamonds set at one end4 ,the machine cuts a circular groove1 leaving a core inside the tube4 ,this core is brought to the surface with a rod1 and the powdered rock is washed out by water forced down the tube and flowing up the sides of the hole4 ,the drill does not have to stop for cleaning out--,herman1 ,united ,states1 #ahed4 ,photography ,first photographic picture1 not permanent--,thomas ,wedgewood1 ,england1 #agia4 ,daguerreotype1 first developing process--,louis ,daguerre1 ,france1 #ahci4 ,first photographic portraits1 daguerreotype process--,prof4 ,j4 ,w4 ,draper1 ,united ,states1 #ahci4 ,collodion process in photography--,scott ,archer1 ,england1 #ahdi4 ,photographic roll films--,melhuish1 ,england1 #ahed4 ,dry-plate photography--,dr4 ,j4 ,m4 ,taupenot1 #ahee4 ,photographic emulsion1 bromide of silver in gelatine1 basis of present rapid photography--,r4 ,l4 ,maddox1 ,england1 #ahga4 ,hand photographic camera for plates--,william ,schmid1 ,united ,states1 #ahha4 ,printing ,first printing with movable types in ,europe and first printing-press--,guttenberg1 ,germany1 about #adde4 ,screw printing-press--,blaew1 ,germany1 #afbj4 ,first newspaper of importance--,london ,weekly ,courant1 #afbe4 ,stereotyping1 making plates from casts of the type after it is set up--,william ,ged1 ,scotland1 #agca4 ,first practical steam rotary printing-press1 paper printed on both sides1 #ahjj impressions per hour--,frederick ,koenig1 ,germany1 #ahad4 ,printing from curved stereotype plates--,h4 ,cowper1 ,england1 #ahae4 ,hoe's lightning press1 #bjjj impressions per hour--,r4 ,hoe1 ,united ,states1 #ahdg4 ,printing from a continuous web1 paper wound in rolls1 both sides printed at once--,william ,bullock1 ,united ,states1 #ahfe4 ,straightline newspaper perfecting press1 prints #ajj1jjj eight-page papers per hour--,goss ,company1 ,united ,states4 ,linotype machine4 ,the operator uses a keyboard like that of a typewriter4 ,the machine sets the matrices which correspond to the type1 casts the type in lines from molten metal1 delivers the lines of type on a galley1 and returns the matrices to their appropriate tubes4 ,it does the work of five men setting type in the ordinary way--,othmar ,mergenthaler1 ,united ,states1 #ahij4 ,steam ,navigation ,first steamboat in the world--,papin1 ,river ,fulda1 ,germany1 #agje4 ,first steamboat in ,america--,john ,fitch1 ,delaware ,river1 #aghc4 ,first passenger steamboat in the world1 the ,clermont--,robert ,fulton1 ,hudson ,river1 #ahjg4 ,first steamer to cross the ,atlantic1 the ,savannah1 built at ,new ,york--,first voyage across the ,atlantic1 #ahai4 ,the screw propeller first used on a steamboat--,john ,ericsson1 ,united ,states1 about #ahcf4 ,compound engines adopted for steamers--#ahef4 ,first turbine-steamer1 the ,turbinia--,parsons1 #ahie4 ,first mercantile steam-turbine ship1 the ,king ,edward--,denny and ,brothers1 ,england1 #aija4 ,steam ,used for ,power and ,land ,transportation ,first steam-engine with a piston--,denys ,papin1 ,france1 #afij4 ,first practical application of the power of steam1 pumping water--,thomas ,savery1 ,england1 #afih4 ,double-acting steam-engine and condenser--,james ,watt1 ,scotland1 #aghb4 ,steam-locomotive first used to haul loads on a railroad--,richard ,trevethick1 ,england1 #ahjd4 ,first passenger steam railway1 the ,stockton ,darlington--,george ,stephenson1 ,england1 #ahbe4 ,first steam-locomotive in the ,united ,states1 the ,stourbridge ,lion--#ahbi4 ,link motion for locomotives--,george ,stephenson1 ,england1 #ahcc4 ,steam-whistle1 adopted for use on locomotives--,george ,stephenson1 #ahcc4 ,steam-hammer--,james ,nasmyth1 ,scotland1 #ahdb4 ,steam-pressure gauge--,bourdon1 ,france1 #ahdi4 ,corliss engine--,g4 ,h4 ,corliss1 ,united ,states1 #ahdi4 ,first practical steam-turbine--,c4 ,a4 ,parsons1 ,england1 #ahhd4 ,textile ,industries ,flying shuttle1 first important invention in weaving1 leading to modern weaving machinery--,john ,kay1 ,england1 #agcc4 ,spinning-jenny--,james ,hargreaves1 ,england1 #agfc4 ,power loom--,james ,cartwright1 ,england1 #aghe4 ,cotton-gin1 for separating the seeds from the fibre1 gave a new impetus to the cotton industry4 ,the production of cotton increased in five years from #ce1jjj to #aee1jjj bales--,eli ,whitney1 ,united ,states1 #agib4 ,pattern loom1 for the weaving of patterns--,m4 ,j4 ,jacquard1 ,france1 #ahja4 ,application of steam to the loom--,william ,horrocks1 ,england1 #ahjc4 ,knitting-machine--,brunel1 ,england1 #ahaf4 ,sewing-machine--,elias ,howe1 ,united ,states1 #ahdf4 ,mercerized cotton--,john ,mercer1 ,england1 #ahej4 ,process of making artificial silk--,h4 de ,chardonnet1 ,france1 #ahhh4 ,wood-,working ,circular wood-saw--,miller1 ,england1 #aggg4 ,wood-planing machine--,samuel ,benthem1 ,england1 #agia4 ,wood-mortising machine--,m4 ,j4 ,brunel1 ,england1 #ahja4 ,band wood-saw--,newberry1 ,england1 #ahjh4 ,lathe for turning irregular wood forms--,thomas ,blanchard1 ,united ,states1 #ahai4 ,improved planing-machine--,william ,woodworth1 ,united ,states1 #ahbh4 ,miscellaneous ,first fireproof safe--,richard ,scott1 ,england1 #ahja4 ,steel pen1 quill pen used up to this time--,wise1 ,england1 #ahjc4 ,first life-preserver--,john ,edwards1 ,england1 #ahje4 ,calculating machine--,charles ,babbage1 ,england1 #ahbb4 ,first friction matches--,john ,walker1 ,united ,states1 #ahbg4 ,flint and steel were used for starting fires before matches were invented4 ,first portable steam fire-engine--,brithwaite and ,ericsson1 ,england1 #ahcj4 ,vulcanizing of rubber--,charles ,goodyear1 ,united ,states1 #ahci4 ,pneumatic tire--,r4 ,w4 ,thompson1 ,england1 #ahde4 ,time-lock for safes--,savage1 ,united ,states1 #ahdg4 ,match-making machinery--,a4 ,l4 ,denison1 ,united ,states1 #ahej4 ,american machine-made watches--,united ,states1 #ahej4 ,safety matches--,lundstrom1 ,sweden1 #ahee4 ,sleeping-car--,woodruff1 ,united ,states1 #ahef4 ,printing-machine for the blind1 origin of the typewriter--,alfred ,e4 ,beach1 ,united ,states1 #ahef4 ,cable-car--,e4 ,a4 ,gardner1 ,united ,states1 #aheh4 ,driven well1 an iron tube with the end pointed and perforated driven into the ground--,col4 ,n4 ,w4 ,green1 ,united ,states1 #ahfa4 ,passenger elevator--,e4 ,g4 ,otis1 ,united ,states1 #ahfa4 ,first practical typewriter--,c4 ,l4 ,sholes1 ,united ,states1 #ahfa4 ,railway air-brake1 use of air-pressure in applying brakes to the wheels of a car4 ,a strong spring presses the brake against the wheels4 ,air acts against the spring and holds the brake away from the wheels4 ,to apply the brake1 air is allowed to escape1 reducing the pressure and allowing the spring to act--,george ,westinghouse1 ,united ,states1 #ahfi4 ,store-cash carrier--,dr4 ,brown1 ,united ,states1 #ahge4 ,roller flour-mills--,f4 ,wegman1 ,united ,states1 #ahge4 ,kinetoscope1 moving-picture machine--,edison1 #ahic4 ,,index ,aeroplane1 #ahd4 ,air-pressure1 #bc4 ,air-pump1 #bj4 ,air-ships1 #agc4 ,air thermometer1 #ac4 ,alternating current1 wonders of1 #bbe4 ,amber1 #h4 ,ampre1 #fg1 #aaa4 ,arago1 #fi4 ,archimedes1 #a1 #ab2 inventions of1 #g4 ,archimedes' principle1 #f1 #ab4 ,arc light1 #abj4 ,armature1 #aja1 #ajc1 #ajd4 ,balloons1 #agd4 ,barometer1 mercury1 #ai1 #be2 water1 #bc4 ,battle of ,syracuse1 #b4 ,bell1 ,alexander ,graham1 #ada4 ,blake transmitter1 #adf4 ,blriot1 #aij4 ,boyle1 #bc4 ,branly1 #bad4 ,cannon experiment1 ,rumford's1 #ei4 ,cog-wheels1 first used1 #h4 ,coherer1 #bad4 ,colors in sunlight1 #ca4 ,condenser in steam-engine1 #dj4 ,conductors1 electrical1 #dd4 ,controller1 #aaf4 ,daniell cell1 #hi1 #abg4 ,davy1 #ef1 #fa1 #if4 ,de ,forest1 #bbd4 ,diamonds1 manufacturing1 #bjf4 ,drum armature1 #ajd4 ,dry battery1 #ia4 ,du,fay1 #de4 ,dumont1 #agi4 ,duplex telegraphy1 #acf4 ,dynamo1 #ee1 #gi1 #ha1 #if1 #ii1 #ajj1 #aje1 #aaa2 series wound1 #aje2 shunt wound1 #ajg2 compound wound1 #ajh4 ,edison1 #ie1 #aje1 #aad1 #aba4 ,electrical machine1 #bc1 #dd1 #de1 #hc4 ,electric battery1 #ec1 #fb1 #hd1 #hi4 ,electric charge1 two kinds1 #de4 ,electric current1 #ej1 #fi1 #gc1 #gd1 #hb1 #if2 magnetic action of1 #ff1 #fh2 produced by a magnet1 #gb4 ,electric furnace1 #bje4 ,electricity1 #h1 #ej2 theories of1 #di2 speed of1 #acc4 ,electric lighting1 #ig1 #aah4 ,electric motor1 #ga1 #ig1 #aaa4 ,electric power1 #aaa4 ,electric railway1 #aab4 ,electric waves1 #bab4 ,electromagnet1 #ajj1 #abf1 #adc4 ,electromagnetism1 #fe4 ,faraday1 #ee1 #fc1 #ajj1 #aaa2 electrical discoveries1 #fd4 ,force-pump1 #h4 ,franklin1 #dc1 #de1 #df1 #fe4 ,galileo1 #i1 #fc2 experiment with falling shot1 #ab4 ,galvani1 #ej4 ,galvanometer1 #gd1 #ge4 ,gas-engines1 #aej4 ,glider1 #ahf4 ,governor1 fly-ball1 #db4 ,gramme-ring armature1 #ajc4 ,gravitation1 #cj4 ,gravity cell1 #ia4 ,gray1 ,stephen1 #dd4 ,guericke1 #bj1 #ce4 ,gyroscope1 #bjj4 ,heat1 #ei4 ,henry1 ,joseph1 #ig1 #abg4 ,hero1 #h1 #afd2 engine1 #afd4 ,hiero1 ,king of ,syracuse1 #a1 #f4 ,horse-power1 #dj4 ,hydraulic press1 #bf4 ,incandescent light1 #aba4 ,indicator1 #da4 ,induction-coil1 #gf1 #hb1 #ii4 ,induction1 electrical1 #gd4 ,insulators1 #dd4 ,inventions of the ancient ,greeks #g2 of the nineteenth century1 #hh4 ,kite experiment1 ,franklin's1 #df4 ,kites1 #bg4 ,leyden jar1 #dc4 ,lightning-rod1 #dh4 ,lines of force1 #ii4 ,liquid air1 #bjc4 ,locomotive1 electric1 #aad2 steam1 #aee4 ,magdeburg1 #ba4 ,magnetic field1 #hj1 #ii4 ,magnets1 #h1 #acj4 ,marconi1 #bae4 ,mayer1 ,robert1 #fa1 #he4 ,mercury vapor light1 #abe4 ,microscope1 #ah4 ,miner's safety lamp1 #fa4 ,monorail car1 #bja4 ,morse1 #abh4 ,napoleon1 #fb4 ,newcomen1 #cd1 #cf4 ,newcomen's engine1 #cf4 ,newton1 #bg4 ,niagara1 #bbg4 ,oersted1 #fe1 #ga1 #aaa1 #abf4 ,papin1 #ce4 ,papin's engine1 #ce4 ,pascal1 #be4 ,pendulum clock1 #aj1 #ab4 ,perpetual motion impossible1 #hg4 ,phonograph1 #adg4 ,principle of ,work1 #ai4 ,prism1 #ca4 ,pump1 #h1 #ai4 ,radium1 #bcb4 ,reis1 ,philip1 #ada4 ,relay1 #acj4 ,roentgen1 #bcb4 ,royal institution1 #ef1 #fa4 ,rumford1 #eg1 #ei4 ,rumford's cannon experiment1 #ei4 ,safety-lamp1 #fb4 ,screw propeller1 #aga4 ,siemens1 #ajj4 ,spinning tops1 #aii4 ,steam-engine1 #h1 #be1 #cd4 ,steam locomotive1 #aee4 ,steam pressure1 #bc4 ,stephenson1 #aef4 ,storage battery1 #ic4 ,sturgeon1 #ig1 #abg4 ,submarines1 #aij4 ,suction-pump1 #h4 ,symmer1 ,robert1 #di4 ,telegraph1 #if1 #abf2 wireless1 #bjh4 ,telephone1 #adj2 wireless1 #bba4 ,telescope1 invention of1 #ae2 ,newton's1 #cb4 ,tesla1 #bca4 ,thermometer1 air1 #ac4 ,torpedo1 #aib4 ,torricelli1 #ai1 #ce4 ,transformer1 #hj1 #hb1 #ii1 #bbg4 ,turbine1 #afc4 ,university of ,padua1 #ac4 ,university of ,pisa1 #aj1 #ab4 ,valve-gear1 #cg1 #afb4 ,volta1 #ec1 #fc1 #hi4 ,voltaic battery1 #ec1 #hi4 ,water-clock1 #h1 #bi4 ,water-wheel1 #afe4 ,watt1 ,james1 #cd4 ,watt's engine1 #ch4 ,wireless telegraph1 #bjh4 ,wright aeroplane1 #ahh4 ,x-rays1 #bcb4 ,zeppelin1 #ahj4 ,,the ,,end