Mee beo eae tose aera Ni . vrs r ; . / Hi od oI S 5 y Fi SS ‘ve fi r ' \. , Ti wk ; x ; oO y t 2 VARS MA 7 ; \- erEC c Ly cad Sik ie ee eh RN a VAN epee a me, : Stebel ete . t * ; ss ’ . ” i , a * n a * - t : ; (tr ee . oa) ae rid itr | SL ucieguhp ems a acca ee eT; - Ri Pp . : a P e Fi ; ‘ " Mervige : i Soe NST oe NSH ; y rae Bay A ; Fae ‘ . F F , te say n Pe i x : . x , , Pr a “a ; " H st N F h / t rl > a i i ; t § i’ ; " Oe 82 , note awe ry anh Smee Me ¢ tee ec - e w ~ a? ee + aw Kp Seay 1 Nahe oO Mag We E- we © we. ‘ H.C. Eggert ELECTRO=}jMF CHANICAL ANALOGIES A Thesis Cubmitted to The Faculty of sICEIGAN AGRICULTURAL COLLEGE By Earl AR: Lauffer Candidates for the Degree of Bachelor of fcience June, 1917 THESIS copil ° e ee ae em ee, OEE PREFACE It is a well established fact that most beginners in the study of electricity and the electric phenomena have considerable difficulty in comprehending the meaning and significance of electrical terns and actions or of the rea- son for these actions. In view of this fact, we have endeavored to explain, by drawing hydraulic and mechanical analogies, such terms and actions as we have been able to find references and analogies for. *we have endeavored to write tnem in such terns that the average non-technical person can easily grasvc their meaning. Especially have we endeavore: to write this so that it might be used to make things clearer for the aver- age beginner in the study of the electrical phenomena than it was for us when first attempting to grasp the meaning of abstract terns. ¥.C. Eggert Farl A..F. Lauffer BIBLIOGRAPHY Age of Electricity Benjamin 35-45, 898-299 — 1 Alternating Current Machines Sheldon, Mason, and Hausmann 60-63 Alternating Currents Houston and Kenndly 5-20, 100-108 Alternating Currents Magnusson 324-325 Cyclopedia of Engineering Part III Elements of Flectricity ol The Flectric Current 5=4 Dynamo Electric Machinery Bailey 133-136 Dynamo Machinery Hopkinson 43-42 Electrical World X ‘246-247, 258 XI 127, 198, 253 Klectrical Yorld XXI 70 XXII 103 XXIII 457, 647 XXIV 671-672, 589 LI 779 LXIV 1117 LXVI 1381 Electrical World andi Engineer ,XXXV 589 Electricity and lagnetism Jenkins 74=75 Electricity and Magnetism Houston 88-92 Electricity for tne Farm Anderson 98-102 Electricity in the Service of Man von Urbanitzky 116-118 Electricity Made Easy Houston and Kennelly 33-75 Electric Journal III 44 Electric wotor Houston and Kennelly 30-34 Electric Review and Western Electrician LXVII 522 Electric Telegraphy Houston and Kennelly 117-118 Electric Waves Franklin 1-35, 39, 45-46 Electric Wiring Clinton 11 Electro-—Dynamic itachinery Houston ana Xennelly 30-34 Elementary Electricity and Magnetism Jackson 16-18, 92-98, 825-245 Elementary Electrical Testing 33a35 Elements of Electricity Timbie 42-43 Encyclopedia of Automobile Engineering II 31-33 Engineeri:g wagazine XXIII 932 XXV 375 Experimental Science &03=-807 First Principles of Electricity ani Magnetism bigss 38-50, 89, 185-185 First Principles of Electrical Engineering Biggs 155-175 General Electric Review XIX <£64 uwOdern Views of Electricity Lodge 32-34, 54-55 Scientific American-Suprlement XL 264489 LXIV 197 LXV 6 LIX 161 LXXIII 14<é The Electric Circuit Karapetoff 65,.145-147, 185-186 The Electrician XXVIII XXXVII 614-615 795 The Electric Telepncne Houston and Kennelly 31-34 Tae Dynamo Hawkins and Vallis 3-8, 61 The wagnetic Circuit Kar apetoff 36-37 The New Physics Trowbridge 171-173, Wireless Telegraphy Collins 49-51 Wireless Telegraphy Magnusson 3 4-3 5 0) 03 Wireless Telegraphy Stanley 76-80 Wireless Telegraphy de Tunzelmann 37-44 BBO~-553 wircgless Telegraphy ani Telephony wassie and Undernill 6-10 (numbers refer to pages) oro ry S > OD Co tH 08) ry Ty FH OM He ct >) brn Q QQ } © "9 at Auimeter, battery, cry, Storece, Frearer, Circuit, Bridge, Wheatstone, Caracity, Inductarce and, in Parallel, Inszuctarce and, in Series, Charging Condensers, Chcke Coil, Circuit Frearers, Classification of Currents, Close Ccurling, Loose and, Coil, Choxe, Coupacs Leviaéticon, Condenser, Condensers, Cnzercing Converter, Retary, Coupling, Loose end Clese, Currents, Clas-ificaticn of, Cycle ani Frequency, Leviation, Cenpess, Lifference cf Fotentizl, Loubler, Electric, UCry cattery, Hlectric Loutler, INDEX nlectrical siachines, Ether Vibr:itions, Frequency, Cycle ena, Generators in Parallel, in Series, nysteresis, Inductence sand Cazacity in Farzllel, in Ceries, Insulz2tion, Loose ani Cloce Courling, wacnines, Flectric:il, wfenets, Parallel, Generators in, Inducvasce era Caracity in, Phase, Potential, Lifference cf, Resistance, Rotary Converter, Series, Generaters in, J Inductance ena Cearacit A “<< in, fQ tcrage Fattery, Systeu, Three vire, Telepréne, Three ‘Vire Cysten, Transformer, INDEX v. 3 al = oo e.tetone Eridze, wire Systen : ) ystem, Truree, O? QO) ny Cal 1 cy) Cx) €(O ELECTRO=-MECHANICAL ANALOGIES -j- Am. ETE. In measuring the strengta or tne current flowinz in 2 line use is made of what is termed an amneter or measurer of amperes. This aoes not by any mezns necessitate thzt the antire current sh2ll flow tnarougn it as an examination of Fig. 1 will snow. Tre acticn is similar to tnat of a meter in 2 water main wnere A cf Fig. 1 is txe ameter anit of Fig. 6 is tae water aeter. Only part of tn: current passes tarough the water neter. cy an examinaticn of Fig. ¢ we see that, Since pipes A ana B have Sefinite pronortions, they have a certain definite ratic to eacn otner and, therefore, the meter cen be sc calibratea as to give tne total water pas- Bing instead of merely tnet going through the meter. In ths same wey the ammeter may be calibrated to give tre full current passins in tze line at t.< time. ‘lowever, a vari- @ticn of tinis is often maae use of. Ey knowing the ratic of thes resistance in the meter itself to thet of its shunt S of Fig. 1, ani knoving that tne currents are inversely as the resistances in the line:, we may make use of what is termed the meter constzent to multirly the met-r resaing by in order to get tne full line current or, the meter can be SO arranged witn multiple scales tnat, b; resding on a cer- y tain scale when a certain shunt is used, the rezding may be had cirect. This enables us to make use of th: see meter for various strengt:is of current by merely using a daiffer- ent snunt. This vouls be analogous to bein» able to vary the size of pire A in Fig. 8, en wouli give the same re- ~2- sults in tnat case if we xnev the ratio of tne cross sec- tions of tne ricves or if the neter were equivved with mul- tiple scales. This last is an imnossibility in tre case of the actual water meter as we knox tnem tédday anl it is very doubtful if one could be so equipped witiout great trouble whicr weula not be awkward to hanile ani use. Ammeter ene ee are if ~3- CHARGING CONDENSERS, Charging is nothing more or less than c2usinzg a state of strain in the insulating medium betzeen two conductors. Suppose we teke the oculleys P and P! carrying tre endless cord C as an illustration of tne ceniuctors, the disxs at Das tre meiium, and the weie-t T as the force causing motion. Fig. 3. We wrculd then have a parallel to toe electric circuit. If we wish to insert an infinite re- Sistance it would be only necessary to clamr tne cori. This would parallel the electric circuit whicn was open or incomplete. If we take the actual circuit, we will surnose tne disks to be fixed to tzreir supports and to simc.iy im- pose friction to tne passage of ti2 cord which would be similar to the action of resistance in the electric circuit. Tne only result that couid possibly occur would be the gen- eration of heat caused by tne fricticn of tre cord as it was drawn tnrougn tne disks. However, if se suprose tne disks to be attacheia rig- ialy to tne cord an. to have an elastic suprort we would have the action of the condenser or Leyden jar while being charged. The elastic supports would then give as shown in Fiz. 4, that is tne mediun vould be wmder strain. ‘nen the force was removei the disks would srring back to tneir orig- inal position. They would nét stop just wnen it was reached however, but would go a little beyond it ana would tnen re- verse. This reversing or viorating sould be kept up for some littie time until tre position of rest waz reached -_ ~i— woich woula correspond to the aischargec condciticr of condenser. ~~ oo ar: 3 bs Gh \ ae aE qq CuCKz COIL. To protect the machinery on the line from the uamaging effect of lightning dischergee sone form of lightning arrester is used. This often takes tne form of a choke coil which mekes use of tne inauctive action of a current floxwing through a coil of wire. The coil must be made of only a fev turns of very heavy wire in order tnat the passz:e of currents of commer- cial frequency msy not be impeded. On the side of tne Coil C from wnaich the discharge is exrected, is placed 2 spark gar ©, Fig. 5, long enough so that norm2l current cannot arc across. If ve suppose our chcke coil to be a hezvy block of metal such =s an anvil, capable of transmitting rressure but, on account of its mass, not resrendirg readily tc sud- is den forces, we wovid have the acticn of the coil. If we lay as piece of soft metal on tne anvil we can trancmit pres- sure throvgn it ur te = certain limit vrithout aeformation. In tne same wey the spark gar pays no ettenticn to tre pas- sage Of ordinary currents. If, however, we sroulc strike the block 2 heavy biew, wnich would parallel the eftect of the lightning cischarge on the line, the metal would flat- ten, since the heavy biock is slow about taking ur tre orce of the blew and, according to the funcemental las, we cannot cestroy energy but can crly transforn it. Tne:e=- fore, since it cannot pass on, it must go into the -crk of deformins the metal. In the same way the nigh frequency lightning sischarge (100 000 cycles per second) cunnot go on ana, as it must go somewhere, it breaks down ths resis- tance of the srark gap anc co passes to tne ground. Or, suprose we cell our coil a very creckead, winding 5 stretch of smocth road. If an automobile cane slong the Straight road, which wcoulc represent the lins, at a reascn- able rate an. struck tnis crockea road it woulc have little Qifficulty in pessing it in safety. On “hz other hand, however, suppose the criver were "hitting it up" and struck the crookea part at a high rate of speed, wnich would cor- resrond to the hich frequency of tne lightning discharge. The chances are very strongly in favor of his going into the aitch on account of not being able to hold the road. In the same way a lightning discharge is "ditched" thrcugh the spark gap, not because it cannot follow the wire but because its high frequency builds up an oprosition in the coil which it cannot move against and, since because of its own momentum it must go somewhere, it follows the path of least resistance which is through the spark gap. Cc iss | . 7 Ch aa Coils han) a " 0 \e) Spark Gaps Ground ro m1 il ae 3 -7- CIRCUIT ERHAKERN. As a safeguard against overload- ing the line, circuit breakers or fuses are used. The fuse denends for its action upon the heating csusea by the current as it passes threuzh the con- Gquetor. If tne current rises above « certain definite, predetermined value, the temperature of th= conductor rises above the melting point of the fuse and the fuse gives way, or ac it is termed, "blows". Witr the circuit breaker, the acticn is dependant uren the increase in strength of an electromagnet as the strength of current increases, that is, the more the current the stronger the magnet. In use we have the circuit breaker having its arm hela in place, When closed, by # latch whicr oproses the action of 4 spring waich tends te open the line, As the line becomes Overloadea an electrom2gnet becomes strong enough to draw & small trip lever which trbps tne latch and allows the spring to open the circuit. A parallel to t:is action is the acticn of a safety valve on 4 boiler. The load on the line would, in t.is cace be represented by the boiler pressure. As it becomes 3 too high for safety the safety valve rises fron its seat and allows the pressure to drop to a safe working value. The resistance to th: action of the steam may be either a spring, or a weight and lever, depending om whetner the valve is of 2 mOdern design or one of th. olger types. There is one great cdifference between the safety valve and the ordinary circuit breaker, however, and that is, that, -f- whiie the action of the safety valve is only temporary, that is, it will return to its seat as soon as tne exces- sive pressure is relieved, the acticn of the circuit btreak- er is permanent, that is, it will remain in the trippeca or Open position until some outside force operates to close it Again. We might add however, that special self setting circuit brezkers paralleling the reseating action of the safety valve can be purchased. -9- CLASSIFICATION OF CURSENTS. There are, in elec- trical terms, three kinds of currents; (1) constant or steady, (8) pulsating, ani (3) alternating. Tne first two fall under what is termed direct current or L.C. while the last fells under what is commonly known as A.C. The first may be ssid to strongly resenole the steady, normcl flow of 2 river or any other stream which does not vary perceptibly during a moderate interval of time. The second resembles the nlood flox through the ar- teries in the human boay. It varies from instant to in- stant, depending upon the tire interval since the last heart beat, but at no time does it ever cone to zero or stop. It continues always in the same direction but in varying quantities. It also resembles the flow of water from 2 pump not equipped with an air chamber. The flow is kept up by the action of the plunger, but due to the necessity of the plunger constantly reversing, a pulsating action is necessarily present. The flow does not stop in tnis case either, but it does vary from instant to instant the saac as the pulsating electric current. More current may flow at one instant than at another but, so long as the circuit is complete, the flow will contime. These two currents are found in D.C. work only. The first is probably strictly true only from a storage battery and may possibly not be absolutely true even there -~10- Owing to irregularities witcin the battery itself. Under Ordinary conuiticns the pulsating wou:d ve more liable to exist as can be easily seen by .atcning for a fev moments a meter connected in an electric line. foout the bect analogy for the elternating current ids tne ebb ana flow of ths tide in a tidal river or estu- ary. As tis tide rises the water flows up ena away from the sex, then, as ths tide reaches its maximum, it ceases, reverses ana begins to run out as ths tide falis, again re- E versing 2s the tide rises once more. In ths same way the alternating current increases, reache= a maximum, ceases for an infinitesimal instant of time, then reverses its flow, passes through zero to a maximum in th. oprvosite di- rection, again ceases ans reverses itself, to rereat the process indefinitely so long as the cause producing it ex- ists and contimues to «ect. -ll- COMPEES DEVIATION. It is an often notca fact amons surveyors and among others ec “ell that the compass dcet not always point to the true Norta: in fact it almost invariaoly deviates somewhat from the true line. This is aue to the fact tat the magnetic action of the earth is daisturbes by outsice influences ani also to the fact that t:e magnetic poles do not coincide with tne axial poles. This is squivalent to saying tnat the poles of the earth masnet are off center which in fect tiey are. Even if they were coincddent with the axial poles the compees woula still deflect ani the reason is easily Seen. Suppose ve stretch elastic bands fron poke to pole of the earth in the direction in which the magnetic force acts. Also, let us apply similer tanas tc our compass needle. Cince the lines of force arcuna = magnet are not qm Straight from role to pole but form curves, we would have the magnets surrounded by sets of curvei, elastic, roughly se be inserted in tne AD) parsllel lines. Now, if the comrsa earth's field, we wovld have the elaectic bands of the two fields interferi:ng. The earth's bands beings of course the stronger, would overcomes those of th: cozrass and woulda turn the comrass until its bance were parallel to those of the earth. Now, if an electric wire or some other strong magnet wers brousnt near tre compass, we would have still another set of elastic baraz stronger even tan t:ose of toe earth ana the result would be that the e:urth'es bands -le- woase would toni to beccsae parallel to Kee Q O ee + : S + Ls Gli.. B..0FS OI Me wi those cf the strong magnet. In reality they would not but Le) ct oO ck 5 Cu 09) ct C . am) G2 ctr ry Oo Ky each vould giv2 more or less accordizx. (uo ct ie) > Cc ) CL OQ Oo rs w (') ct ry (D thc banas, tx strong nagnet tie leas most, until a st-te of equilibrium was reachea wren they would remain fixed unless some further disturbance occueed. The magnetic actitn of tne etrthn an. of the various electric circuits thst exist is exactly the same. When a cO1pass aprroaches a conductor, tre fiela of the compass ct pulls the co:r:iss needle around until its fieli coincides with tne combined field of tne conductor ani the sarth. Of course, the nearer the corrass is to the magnet the more Will the fiela of tne magnst credaominate in tna. combinea fiela. -~13- CONDENSER. Use is often made in electrical work of a series of thin plate: of a conducting material seperated by thin sheets of a non-conductor, the © alternate conductors being connected togetner i.e., 2, 4, 6, etc., in one group andl, 3, 5, etc., in the other. When so arranged the apparatus is termed an electrical conden- ser. Now if an electrical impluse is sent through it by connecting the two groups to opposite sides of some elec- trical generator as in Fig. 6 we find that we have an elec— tric charge on the surface of the plates or, as it is term- ed, the condenser is charged. Conversely when the electric pressure is removed, the charge is released and current flow reverses or, as we say, the condenser discharges. Suppose, now, for the electric pressure E we substi- tute a pump P and for the condenser C a cylinder containing an elastic diaphragm D. We would then have the arrangement of Fig. 7. Further, let us place valves V and V' to serve the purpose of the key K in the electric circuit. Now, if the plunger of tne pump is displace, it is evident that the diaphragm will be stretched sinee there is no way for the fluids in the pipes to get through. When the plunger reach- es the end of its stroke and reverses, the diaphragm will be at its maximum stretch and will be stretching at the maximum rate. On the other hand, when the plunger is at the middle of the stroke it will have its maximm velocity while the diaphragm will be at zero stretch and will be Changing its direction of elongation. while series connections give high pressures but smaller currents. Sometimes, too, combinations of the two connections are used. This would be equivalent to connecting uc pumps in series anu then paralleling these series sets. These cor- binaticns are used where both a larger current and a high- er voltage are desired than can te secured by eitner series or parallel connections alone. Rinaos Fig. 1/0. Pumps Pee ee ~o5e ELECTRIC DOUELER. If we take two tin cans ani place them on insulated stands as shown in Fig. lé and supose each to have a small initial charge, say C a positive ani D an equal negative, we will have the foundaticr of an electric doubler. Now if we place between them two insulated balls made of a good conductor, some of the lines of force runnimg betwe.n the cans will converge upon the balls and tne balls will have a cettain charge in- duced upon then, E being positive ani A negative. Nor if A be carried over and into CU and E te inserted into C the charges on th. balls will te given ur td the cans, the lines of force connectec with them will be transfered to the res- pective cans and there will be just that many rore lines strung between the two cans than there were at first. If this process be repeated several times it will be found treat light tnreade hung over the sides of the cans will be- gin to rise from a vertical position and stana out horizon- y tally. This shows that our metal can: have begun to snow a considerable charge. If the operati-n be rereated often enough the potential t:=t can be produced is very high. If the number of lines in the first case were only ten and Only half of them were transfered the potential would be miltiplied by one and 2 half and 2 little multiplication will snow that the tnerease will be very rapid from then on increasing as tne number of cuttings increases. In fact, Starting with these conditicns and operating uncer this Surposition, the charge after sixty repiticns will be a- cout one hundred billion times the original charge provid- ing there is no leakage through faulty insulation. A parallel to this actighb would be to suppose the lines of force to ve elastic bands capable of being cut and Treattacned. In this case it is at once evident that if we cut a certain percent of the lines the pull between the two cans will increase and thet the more tre cutting and attach- ing goes on the stronger will be this attraction. [f the cutting were to continue long enough it is also evident that tre cans would finally te under such strain that tney would be no longer able to keep their places anid vould be dravn toward eacr other. The electric action is the same except that the cans are mot drawn but tne charges on the cans are. When the charge reaches a certain value which is higher than the insulaticn of ths air can hold out against there will be a discharge in tne form of a spark from one can to tne other wrich will tend to equallize tings and put them back in tneir original state once more. Another way of producing mucn the same thing ils to make use of the metnéd shown in Fig. 13. If we Rave a hol- low conductor 5B seperated from = plate A by thse insulation Of the air ana tre point P xept at a higher charge than the plate by a small vtattery ana use the ball C to transfer the charge we may ge* practically the same results. If we touch the ball to the point we get a certain cnarge on the ball. by carrying it up into the hollow cylinder as shown at (c) we transfer the charge to the corductor as seen at es ~o5- (d). The bali may then be brouznt back for ancther charge. This differs slightly from the first in trat instead of cutting a certai. percentage of the lines each time we cut a certain definite number so that the increase is at a steady rate. In the first case we hed a geometric progres- sion since the rate of increase increased as the transfer progressed while in tre lest czse we had a mathmetical pro- gression since only a definite amount was added each time and the amount was Trixed. In ti.is last- case the analogy woulda be to substitute rubber banas an the Same way as in tne first c2se but to Suppose tnem hooked over the point and capable of gliding along A. Then if tne ball had some mean@ of picking up a part of them and carrying them over to E and transfering them each time we woul. set similar results. As the trans- fer continued F wo.la be drawn over against A by the in- creased tension. In the sane way as the chirge on. & in- creased the tensicn in the air vetween would finally become so great tnat there woula be a discharge betveen the two in the form of an electric spark. Tee = = 4 sry | Penne yoo Ee | aes) Fig. Pe F aT x B te ane eee o) (a) | . P Meee] Sa ares 3 (4) ae ~23- HLECTrICAL MACHINES, riat are Kno"n as aynamos ani motors are nothing more nor les~ taan machines so constructed as to feed pover out onto a line or +o taxes power from a line ani cenvert it in- to tne work of every day life. Fig. 14. Suppose We hai 2 pump, Fig. 15, forcing water or some Otner fluia into 2 rire line at tne otner end of waich waz an hydraulic mctor or a machine of some sort capable of using the fluid in some way to perfora useful WOrk. mhis woulda parallel tne action of the generator ana motor shown in Fig. 14. The vcunr or genurator forces the medium, either weter ocr electricity, out into tne line while tne motor uses the mediur as 2 means of coimg useful work. Anotner analogy is th-= ordinary leather or rubber belt sito tne ariving ani driven pulleys of rig. 15. Ordinsrily we sneak of electricity as "generated" but tuis is in the figurative sense only. In the case of ~~ od tne leatoer bcelt we could not K of the drive pulley as mM” tc pe a "leatner cenerator". Thet wouli be absurd. te covls speas of it as a "mover of electricity" however. Wnen we Speak of "doing it electrically" or driving by electricity how many of us ever stor to think trat so0.evhers back of tae electricity ther is 2 machine which arives the elec- > + , “~ ° _ : . - * ‘ a < + - . ns V ericity in tise sans manner tnst tre drive pulley drives tne belt? In tne Sarre manner thnet trea belt arives the Sriven guy pulley the electticity drives the motor. ‘"e must have a 4) circuit in the bcelt or it cannot ict. It would be a2: ab- ( surd to try to drive = pulley by 2 belt which mer-ly touch- ei that pulley ana another without completing tns circuit and forming an endless loop as to try to arive a motor witnout comwpletins tne electric circuit either by connect- ing up te tvo or more wires or by using the ground fer 2 return Wire by whet is termed "grounaing" one siae of each of tne motor ani generator. & Anotrer point that is generally uncerstooa is that an electric machine is reversivcle. Ey t:is is weant tnat if a motor is driven it vill generate electricity and tna a gen rator will supply power if supplied vith electricity. This is what would hapreen if we had tyro engines so connectea tiat when one turned over it ~ould carry the other with it. Then if one were supplied steam it would arive tnz other ana the second vould act as a pump. Fhen, ac ee i — ain, if we feed the stzam into the second it woulda drive tos first as a pump ani we can see that the conditicns are reversed. In the Sane wey the electrical machine=> would be reversible. Theres is one significant difference however. With the engines, tney would of necessity oe coupled up so that One wouli be running backwards whichever were driveéng or ther2 would be trouble witn the valves not working. If one Were running backwards, trouga, the valve action wouli be reversea ana ther fore the engine go:lda act as 2 pump. Witn tne electric motor and generator just because the func- ) c= nN tions of the machine are reversei en. the notor runs as a generator or th: generator as a motor ioez not necessartly imply that the machine will run backward in tne dne case to what it will in the other. In sore cases this will be so but in others the direction of moticn is tre save no matter whether tne machine is bei:.z uSea as 2 generetcr or motor. Another point trat snould be notea in t'.is connection is that it is n°t slways gooi practiege to run a motor as 2 generator or vice versa s¢ the csce may be just because there is no generator cr motor 2t hand. Just because the machine is reversible is no sign that it is highly efficient in the reversed condition eny more than in the cece of the engines. A gocd enzine doe: not necessarily cake a good \ rump nor a gooi pump 3 good engine. In the sare way 2a good motor 2065 not necessarily maze a gooa generator or 2 good generator a goo motor. In fact it msy go by opposites and avery efficient motor may turn out to be a very poor ans inefficient genzrator or tn2 generator a poor motor. A ee ~59- ETHEFa VIBRATIONS. In the wireless telegraph and telephone, use is made of the known phenomena of the vibrations that are set up in the etner by the discharge of an electric spark. The recelv- er catches these vibrations on its sensitive apparatus and magnifies them so that they can be understood. Imagine the ether to be replaced by a still pond and toe receiver by a light float. Tnen if x stone or some other object be tnrown into tne pond, waves will be set up ana these waves will cause the float to move or vi- brate as they reach it. By this means signals could be transmitted for limited distances but, as can be easily noticed, only a very small portion of the wave set up ever affects the float. fherefore it is evident that to trans- mit messages to a greater distance a mucn more powerful source of disturbance is necessary. This explains why such s powerful electric source is necessary to affect an electric receiver only = few miles away. Suppose, however, that two or more singals were being transmittei at one and the Same time. We at once see tnat the waves will interfere ani that no intelligi- ble message can be sent. Uowever, if we add to the float a spring which will force the float to vibrate at a cer- tain preaetermined rate it is evident that waves which do not have t-is particular rate of vibration will not affect the float but tnat if es message is scent with this partic- ular wave rate it will be received in spite of the other -30- vibrations which will be automsetically discarded. This is whah is actually done in wireless work by what is called "tuning" of the receiver or sender which is, by an electrical apparatus, brought to the same rate of vibratizcn or wave length as that o8 the station with which it is desired to talk. When this is done it is easily understood that messages may be sent and received regariless of any other messezes that may be passing in the air at the Same time but with a different wave length or frequency. -~3)]- GENSRATORS IN PARALLEL. any people wonder wny we can have tvo geneators in parallel on a line ani not have them of the same capacity as far as generaticn is concerned. This is not at all nec- essary but the voltaz-= between terminals must necessarily be the sare and tiis necessity is vital to successful oper- ation. If the voltage were not th: sere it is evident thet there would not be enough resistance to the E.M.F. of the Otner machine to prevent its sending part of its current througa tne lover pressure machine ani, in adiitiom to wasting that current as far as doing any goci on the line was coneerned, render extremely probable the denagirg of the second machine. If we hadi two steam engines feeding power onto the Same shaft we would not for an instant think of saying that they mist both have the same power in order to be able to work together any more than we would say that two men pul- ling on 2a rope to move sore object must both pull with tne Sane amo nt of force in order to produce motion. Tne only es:ential’'in th. case of the engines is that the sreeas shall be the sane. ‘Vhen they are botn connected to the same shaft in the manner of a multi-cylinder engine they will of necessity run at the same rate. However, for efricient running they must be designed for tis rate. We could use two engines naving different sized cylinders and operating from tre same source of steam generation if the engines were designed for tne sane speed at full load and had a- ” = ro C7) bout toe same general characteristics threugiout the whole range from no lcai to full leaa an. get gocd results. Or, we couli have two engines having the sere or aiffcrent size cylinders anu operating at tne same or different pressures anu still get good results providing they were designed to Operate under the san2 conditions as regards speed. Now, if we compare speed to voltage, wc will se: nat we have tne same rule in effect in the parallel con- nected gersrators. Witn tre same voitege in each carte nel- ther can send current through the other wnhicn would be equi- valent to naving the higner speed engine pull the lower Speea engine along with it as it turned over. All pover must then go into the line in the same way tnat all power in the case of th le engines must go into the shaft. Thersz is no other outlet. In the ease of any number of genera- tors the sane considerations hold in exactly tre same way that they would with any number of engines or men. If all worked at the same speed they would unitedly pull the doad they were working on or put all the power onto ‘the line. If any one, or any number, trie@ tc vork at a lower or higher rate thers would be friction and power would be lost in the struggle between the units which would each be strugsling to run at tneir own varticular speed the same as it woula whth the generators in the attempt of each to put its own particular voltage out onto the line ani the consequent confusion that woulda result if there were sever- al different voltases or even two only. . " Cc “-“ w~ ao “~7 _ ~ 7 ™ a f~ wn + * : seo AL SO In CPSITS, Generators in series are commonly used where it is desirea to bocst the line voltezgée cver that waicnr coulda be Supplied by one actinz alone. This cinz2 is similer to tre conditicn we ‘youlia nave in a punpins stzetion where it was found thet the pr 6) Ssure carried would not deliver ¢:e¢ emount called for. If, hov- ever, we put in tos line somevhers, another pusp having tne Sane punpins carscity, we covla help out the main pump ana so relieve it of considerable strain that it woula otner- wise feel in trying to keep up the pressure to what it shoula be. Since the sanz amount of water must pass through all of the purrs it is evident that tney must be of the same cayacity. They need not, however, be of the sane speed. Kes If one were of half the speed but had twice the displace- ment of tn. other they would have the same capacity ani could consequently be operated in series ~itnout any trouble. If, however, they were not of the sass capacity One would either be pumping water faster than the other coulda taxe it or else would be pumping water out of the line faster than the other could force it in. Consequently it would be pumping egainst a vacuum for a part of the time. In the ease of two or more generators in serédes on the line we have tne condition that they must all be de- slgenea to deliver the szems current since the total line current must flow throusn all of them in successicn. They necad not, however, be of thse same preseure so lonz as they “7 4 » can put the sane strength of current through tleir respec- ¢ trex tive arnatures. If one or tie other proauced a stronger current, tne other woulc imnediately cegin to draw current out ani to act as a motor ani of course woulc be useless as fer as incressing tre line voltege was concerned. The fact that tre voltage is not the sexe makes not the least ypar- ticle of difference ery more than it wo:ld in tre case of the pumps if each individual pump requirca 2 different pressure to produce the sare purping caracity. The fact that thers are & nunwer cf generators in the line hz3 no ef8ect upon tre propositi-n providines they are dbuilt to give the sane current to the line. In actual use the gen- eraetors wo.la not be bunched togetner in one building nec- essarily but wo vla be scattered so as tc get tne best re- sults by increxsing the pressure where it showed the great- er inclinaticn to drop below that waich was allowable on thet particular line. ~35- HYSTERESIS, In the actual magnetisaticn andi demagnetisation of iron as it occurs under the acticn of the reversinz current in th. field of sn electric machine, it will be found that the actual mag- netisation cf ths iron lags benina the current which pro- duces it, caused by what is termed the hysteresis of the iron or its tendency to renain in one state of nagnetisation indefinitely unless affected by some outside cause. The curve showing the r-lation voetween the force causing the magnetisation and the magnetisation produced would be the hysteresis loop as shown in Fig. 17. Suppose, now, we had a body of considerable mass and inertia which was hela in a central position on a smooth plane by springs capable of acting either under tension or CO. pression. This arrangement is shown in Fig. 18. I1f we were to impose upon this body a force F, we would cause the body to be disrlaced a certain distance from its central po position. If the force were now removed, however, the body would .ot at once return to its central position owimg to the friction between it and the plane upon whicn it rests, but would still hav: a cer&ain displacement D remaining which would call for a negative force F' to overcome the friction in order to bring the body back to its central po- sition. If tn2 curve showing the relation between the force and the displacement were to be plotted we would have a figure similar to the hysteresis loop of Fig. 17 showing that tnis action is similar to that of the iron under the | ' i ) ah ‘mb steresis Loop We Soa > Magnetic flux density. H—Magnet field intensity, Fig. 17. -35- action of the alternating magnetising current of tr. ma netic field. 27 IGNITION. The use Of the electric sc2rk for the ieniticn of the charge in the cylitder of a gas engine is a simrcle phenomenon commonly known to nearly everybody. It is usually, in fect nearly always, accouplishea by the use of a spark gar and condenser in some form or other, the condenser storing uv tre el-ctric- ity over a comraratively long period ana then releasing it Suddenly througn the gap in the form of a spark. Parallels to tne action of tne condenser and spark gap are feirly common. Since man first began to think he has more or less conciously tried to fina ways an. means of multipiying nis muscuia:r powers, of storing up energy over 2 long period, ana Of using tnis stored un energy to do work trrourn a short pcricd. For tnis purpose there are txo great devices; mass- velocity anu sprinz deflection. The charging of a conden- ser is similar to the deflecticn of a spring, wnile the creation of 2 magnetic field bears a strong resemblance to tae acccsleration in the mass-velocity. The mechanical spring device whic: mathmatically, most resentles the con- denser, is an air chamber into which more air can be forced by increasing the pressure. The amount of air © is provor- ticnal to tne pressure P and tne energy stored in it is pro- portional to tre square of the pressure, so long az tzc alr Temeins in the gaseous state and the comrressicn is at a constant temperature. -35— The ordinary expressions denoting the amount of en- ergy storec ur in each of thse four mediums; mass-velocity, spring, magnetic inductien, and electrest2tic capacity are in order; (1) uv*/2 (2) Gp®/2 (3) LI%/z (4) cE®/2 wnere iv mass G quantity V velocity P pressure L induc&ance C cap=city I current K EMP. It will be seen tnat the first and third ani likewise the Second an.« fourth areclose parallels. There is one ting that shoula be noted in t-is connection, however, and that ie that no energy can be stored in any one or all of the four mediums without the action of some active outside el- ement. | In sore resrects a megnetic field may be saic to re- Sermble a spring, particularly if the medium opposing the action ig in the form of an sir gap. bLines of force in air resemble rubber bands which tend to snortan, collapse and disaprear, losing their ehergy as tne coercive force is re- moved. The presence of iron in the magnetic circuit in- creases the magnetic inauctance and so stores up more ener- gy. Ey increasing the bron ana at the same time reducing the air gap more and more energy may be stored up but at the same time there is no gain in the released energy. The -39- greatest release of stored energy is when tnat air gap is used whicrn gives tre greatest range from maximum to tue Te- Sidual fluxes. For ignition purposes it is net desirable to use 80 small an air g=2p on account of the slowing up effect of the iron. In this sense, if it is without iron, an inductive coil or spark coil resembles a spring such as an archer's bow, so stiff tnat it requires considerable pull to deflect it even a small amount or like a spring without any great stiffness ani with great flexibility if there is a large a- mount of iron ani no svark gap. An intermediate degree of stiffness trat gives a large defléction for a given pull ana has a large returning moment is nearest like the spark coil with a properly provortioned amount of iron and length of sp2rk gap. -40- INDICTANCE AND CAPACITY IN PARALL@™L. If we con= nect up @ parallel circuit with a condenser in one branch and an in- ductance coil in the other as in Fig. 19 we find that the amount of current that will flow in the two branches will vary with the freanuency of the curr:nt. If the frequency is low most of tec current will go through the inductance coll ana, in fact, if tne frequency ig zero so that we nave direct current all of it will flow througn the inductance. If the frequency is high, however, most of it will pass througn the other branch of the circuit. In between, then, the e will be & point where the amount passing in each branch will ve exactly the same. This point is called the critical. frequency znd it will be found that at this fre- quency the pressure in the branches will be out of all pro- portion to tnat in th. line and may even build up so high as to disrupt the instruments. Suppose we take the arrangement of scoring a::d weignt shown in Fig. cO. If *s move tne handle very slovly the scring S will not be affected ani the moticn will be trans- ferred to the weignt ¥. If we move the handle rapidly, now- ever, ta. inertia of the weight will hold it staticnary and the spring will take ur the motion. If the criticel fre- quency is found ana the handle moved back aiid fortn at this motion of the cb rate it vill be found after a time that th handle will be ve:y small in comvarison to that of tne le- ver ends. If, now, the motion of th. handle were to be -4i- stopped altcgether, the motion of the spring and weight whuld go on for some little time on the momentum they had gained before the stoppage of the active outsiac force. If, however, the motion of tne hanile be kept up, the add- ed force will, in time, be so great tnat tne mechanism will os beyond control ana someting will have to give. In the electric circuit this action is the same. Tne induction builds ur 2 high pressure which it will trans- fer to the condenser if it has a chance ang@ the condenser will promptly return it, to receive it again on the return. Now, if the outsiae force is at the same time adiing more force it is easily seen that, after a short interval of time, toe force built up between the inductance ana the capacity will be much aigher than tne outside pressure and will keep on crowing just as long as the line keevs feeding im more and more current and keeps the condenser and coil passing tre force back ana forth between themselves. od deans Inductance aT ie Spring § pe re Pye A ee ae a ae A ep) aE rx Om ~40- INEUCTACs Anu CAPACITY Iu fCralts. It is common knowledge a- mong giectrical pecorle tnat if en electric current te sent 4c througn an inductance coil a current in ths directicn oppo- sing the current flow tends “cc sercecir. Talis acticn is in addition to tnt csused by any resistanc= thet the circuit may posses. Fig. eal. Survose we teke es an illustration of tnis a vump hanaling water ana connectsd to = chamber having in it a oeavy veigit whica i8 free to move with tne water but Which will not let any water rass it. SChovn in Fig. go. As the piston P moves, it forces the water into the cham- ber containing the *signt “ ani causes it to move. At low frequency of tre piston P, it is evident thet t:..c inertia of the weiz.t will net enter in any great degree into the resisting force but that as tne rate of motion of the pis- ‘ton increases, tne force will have to overcore not only the resistance cf the rires to the flox, put the inertia of the Welght ag vell ana, finelly, at high speeds, the inertia of the mass will be the predos.inating factor. }- Or, take the case of the spring S carrying a weight W and having one end fixed as in a vise. Fig. 62. When the sprinz is bent very slowly to 2nd fro most of the force Will go into the bending of the svring. At high speed the foree will go into ove rco:.ing the. inertia of the weight. There will be an int=rzmediate speed, however, where the in- ertia of the veigkt will beni the srring and the outside force will nerely have to surprly the force necessary to Overcone the cutsiie resistence. In the electric circuit, the cutsice force would he the A.C. current. At lov frequency most of it woulda have to be msed in overcesing the resistance of the circuit but at risn fresuency it wculd heave to overecie what is teraed the counter EF.A.F. set up in the inducticn coil of Fig. «l. Inductance are a oe aD eB ~44— INSULATION, In tne electrical fieli we fina that jf some meins i¢ not sade use Of te keey the current from straying from tic patna we wisn it to follcw we can de little. To prevent this xe mixe use of sone substance that will net cenduct electricity vwnaicn we c2ll an insulstor. Ctrictly sreaking, thers is ne such thing in nature