,transcriber's ,notes ,inconsistent spellings 7e4g4 depolariser depolarizer7 and hyphenation 7e4g4 guttapercha gutta-percha7 are retained as in the original text4 ,minor punctuation errors are corrected without comment4 ,changes which have been made to the text 7in the case of typographical errors7 are listed at the end of the book4 ,this ,plain ,text version uses symbols from the ,,ascii character set only4 ,italic typeface is shown with surrounding underscores2 small capital typeface is shown by ,,all ,,caps2 superscript typeface is shown by a preceding caret 774 ,subscripts in chemical formulae are shown with underscores and braces1 e4g4 ,h#b,,so#d4 ,the following are used to represent other accented and special symbols3 3,a1 3,o1 3,u ,a-umlaut1 ,o-umlaut1 ,u-umlaut a a-curcumflex ,,ae1 ae upper and lower case ae-ligature 'e1 e'1 e e-acute1 e-grave1 e-circumflex oe oe-ligature battery vertical lines 7thick and thin7 box open up #c sides of rectangular 7open side up7 box open down #c sides of rectangular 7open side down7 deg4 degree symbol ,lambda sans-serif capital ,lambda rotated ,s ,s-like symbol rotated #ij deg4 ,l1 ,u1 ,v sans-serif letter shapes ,s section symbol 99 99 99 99 99 ,,electric ,,bells ,,and ,,all ,,about ,,them4 ,a ,practical ,book for ,practical ,men4 ,,with ,,more ,,than #ajj ,,illustrations4 ,,by ,s4 ,r4 ,,bottone1 ,,certificated ,,by ,,south ,,kensington 7,,late ,,of ,,the ,,collegio ,,del ,,carmine1 ,,turin1 ,,and ,,of ,,the ,,istituto ,,bellino1 ,,novara72 ,author of ,the ,dynamo1 ,electrical ,instruments for ,amateurs1 c4 ,,london3 ,,whittaker ,,co41 ,,paternoster ,,square1 ,e4,c4 #ahhi4 7,all rights reserved47 ,,preface4 ,so rapidly has the use of electric bells and similiar signalling appliances extended1 in modern houses1 offices1 hotels1 lifts1 and ships1 that every bell-fitter must have felt the need of accurate knowledge of the manner in which these instruments act and are made4 ,in the following pages the author has attempted to supply this need1 by giving full details as to the construction of batteries1 bells1 pushes1 detectors1 etc41 the mode of wiring1 testing1 connecting up1 localizing faults1 and1 in point of fact1 by directing careful attention to every case that can present itself to the electric-bell fitter4 ,,carshalton1 ,,surrey1 ,november1 #ahhh4 ,,contents4 ,,chap4 ,,page ,i4 ,,preliminary ,,considerations #a ,,ii4 ,,on ,,the ,,choice ,,of ,,batteries ,,for ,,electric ,,bell ,,work #ah ,,iii4 ,,on ,,electric ,,bells ,,and ,,other ,,signalling ,,appliances #ei ,,iv4 ,,on ,,contacts1 ,,pushes1 ,,switches1 ,,keys1 ,,alarms1 ,,and ,,relays #aji ,v4 ,,on ,,wiring1 ,,connecting ,,up1 ,,and ,,localising ,,faults #add ,,list ,,of ,,illustrations4 ,,fig4 ,,page #a4 ,direction of current in cell #i #b4 out of cell #aj #c4 ,bar and horse-shoe magnets #ad #d4 ,the ,dynamo #af #e4 ,smee cell #bh #f4 ,daniell cell #cj #g4 ,gravity cell #cb #h4 ,leclanch'e cell and parts #cd #i4 ,agglomerate cell #dj #aj4 ,judson cell #db #aa4 ,battery in box #dc #ab4 ,gent cell #dd #ac4 ,bichromate cell #dh #ad4 ,fuller cell #ej #ae4 ,cells coupled in series #ed #af4 ,parallel #eg #ag4 ,outline of electric bell #fa #ah4 ,frame of bell #fb #ai4 ,e-shaped frame #fc #bj4 ,electro-magnet1 old form #fd #bj;,a4 modern form #fe #ba4 ,magnet frame #ff #ba;,a4 ,winder #gb #bb4 ,mode of joining electromagnet wires #gc #bc4 ,armature spring #gd #bd4 ,another form #gd #be4 ,platinum tipped screw #ge #bf4 spring #gf #bg4 ,binding screws #gg #bh4 ,bell or gong #gh #bi4 ,pillar and nuts #gh #cj4 ,washers #gh #ca4 ,trembling bell #ha #cb4 ,bell action enclosed in case #hh #cc4 ,ordinary trembling bells #ij #cd4 ,single stroke bell #ia #ce4 ,continuous ring bell #id #cf4 ,release action #ie #cg4 ,continuous ringing with relay #if #ch4 ,continuous ringing action with indicator #ig #ci4 ,relay and detent lever for indicator #ig #dj4 ,callow's attachment #ii #dj;,a4 ,thorpe's arrangement #aja #da4 ,jensen bell1 section #ajb #db4 exterior #ajd #dc;,a4 ,circular bell #ajf #dc;,b4 ,mining bell #ajf #dd4 ,electric trumpet 7,binswanger's7 #ajg #de4 ,various forms of pushes #aaj #df4 ,pressel #aaa #dg4 ,pull #aab #dh4 ,bedroom pull #aac #di;,a4 ,another form #aad #di;,b4 ,floor contact1 ball form #aad #ej4 ,burglar alarm #aae #ea4 ,another form #aae #eb4 ,floor contact #aae #ec4 ,door contact #aaf #ed4 ,sash contact #aag #ee4 ,shop door contact #aag #ef;,a4 ,closed circuit system1 single #aai #ef;,b4 ,closed circuit system1 double #aai #eg4 ,modified gravity1 ,daniell #abj #eh4 ,contact for closed circuit #aba #ei4 ,thermometer alarm #abb #fj4 ,fire alarm #abc #fa;,a4 ,another form #abc #fa;,b4 in action #abc #fb4 ,binswanger's watch alarm contact #abe #fc4 ,watchman's electric tell-tale clock #abf #fd4 ,lever switch1 two-way #abh #fe4 ,morse key1 double contact #acc #ff4 ,relay #acd #fg4 ,indicator1 drop #acg #fh4 ,semaphore #ach #fi4 ,fall back #aci #gj4 ,pendulum #adj #ga4 ,coupled up #adb #gb4 ,gent's tripolar #adc #gc4 ,soldering iron and wires #adh #gd4 ,push1 interior of #aea #ge4 ,bell1 battery and push #aei #gf4 ,and earth return #afj #gg4 and two pushes #afa #gh4 two pushes and one pull #afa #gi4 ,two bells in parallel #afb #hj4 ,another mode #afb #ha4 with two-way switch #afc #hb4 ,series coupler #afc #hc4 ,bell with local battery and relay #afd #hd4 ,continuous ringing bell with wire return #afe #he4 ,bells with ,morse keys for signalling #afe #hf4 ,bells with double contact pushes for signalling #aff #hg4 ,bells with double contact with one battery only #afg #hh4 ,two-way signalling with one battery only #afh #hi4 ,complete installation of bells1 batteries1 pushes1 etc4 #afi #ij4 ,mode of getting out plan or design #agj #ia4 ,lift fitted with bells #agc #ib4 ,magneto bell3 generator #agd #ic4 ,receiver #age #id4 ,combined #agf #ie4 ,detector or galvanometer #agf ,,electric ,,bells4 ,,chapter ,i4 ,,preliminary ,,considerations4 ,s #a4 ,,electricity4--,the primary cause of all the effects which we are about to consider resides in a force known as electricity1 from the ,greek name of amber 7electron71 this being the body in which the manifestations were first observed4 ,the ancients were acquainted with a few detached facts1 such as the attractive power acquired by amber after friction2 the benumbing shocks given by the torpedo2 the aurora borealis2 the lightning flash2 and the sparks or streams of light which1 under certain conditions1 are seen to issue from the human body4 ,thales1 a ,grecian philosopher1 who flourished about #fjj years ,b4,c41 observed the former of these facts1 but nearly twenty centuries elapsed before it was suspected that any connection existed between these phenomena4 ,s #b4 ,according to the present state of our knowledge1 it would appear that electricity is a mode of motion in the constituent particles 7or atoms7 of bodies very similar to1 if not identical with1 heat and light4 ,these1 like sound1 are known to be dependent on undulatory motion2 but1 whilst sound is elicited by the vibration of a body as a whole1 electricity appears to depend1 in its manifestations1 upon some motion 7whether rotary1 oscillatory1 or undulatory1 it is not known7 of the atoms themselves4 ,however this be1 it is certain that whatever tends to set up molecular motion1 tends also to call forth a display of electricity4 ,hence we have several practical means at our disposal for evoking electrical effects4 ,these may be conveniently divided into three classes1 viz43--#ast1 mechanical2 #bnd1 chemical2 #crd1 changes of temperature4 ,among the mechanical may be ranged friction1 percussion1 vibration1 trituration1 cleavage1 etc4 ,among the chemical we note the action of acids and alkalies upon metals4 ,every chemical action is accompanied by electrical effects2 but not all such actions are convenient sources of electricity4 ,changes of temperature1 whether sudden or gradual1 call forth electricity1 but the displays are generally more striking in the former than in the latter case1 owing to the accumulated effect being presented in a shorter time4 ,s #c4 ,we may now proceed to study a few of these methods of evoking electricity1 so as to familiarise ourselves with the leading properties4 ,if we rub any resinous substance 7such as amber1 copal1 resin1 sealing-wax1 ebonite1 etc47 with a piece of warm1 dry flannel1 we shall find that it acquires the power of attracting light bodies1 such as small pieces of paper1 straw1 pith1 etc4 ,after remaining in contact with the rubbed 7or electrified7 substance for a short time1 the paper1 etc41 will fly off as if repelled2 and this apparent repulsion will be more evident and more quickly produced if the experiment be performed over a metal tray4 ,if a small pith-ball1 the size of a pea1 be suspended from the ceiling by a piece of fine cotton1 previously damped and then approached by an ebonite comb which has been briskly rubbed1 it will be vigorously attracted1 and never repelled2 but if for the cotton there be substituted a thread or fibre of very fine dry silk1 the pith-ball will be first attracted and then repelled4 ,this is owing to the fact that the damp cotton allows the electricity to escape along it3 id est1 damp cotton is a ,,conductor of electricity1 while silk does not permit its dissipation2 or1 in other words1 silk is a ,,non-,,conductor4 ,all bodies with which we are acquainted are found1 on trial1 to fall under one or other of the two heads--viz41 conductors and non-conductors4 ,nature knows no hard lines1 so that we find that even the worst conductors will permit the escape of some electricity1 while the very best conductors oppose a measurable resistance to its passage4 ,between the limits of good conductors1 on the one hand1 and non-conductors 7or insulators7 on the other1 we have bodies possessing varying degrees of conductivity4 ,s #d4 ,as a knowledge of which bodies are1 and which are not1 conductors of electricity is absolutely essential to every one aspiring to apply electricity to any practical purpose1 the following table is subjoined1 giving the names of the commoner bodies1 beginning with those which most readily transmit electricity1 or are good conductors1 and ending with those which oppose the highest resistance to its passage1 or are insulators1 or non-conductors3-- ,s #e4 ,,table ,,of ,,conductors ,,and ,,insulators4 ---------------------------------------- ---------------------------- ,quality4 ,name of ,substance4 ,relative ,resistance4 ---------------------------------------- ---------------------------- ,good ,silver1 annealed #a4 ,conductors ,copper1 annealed #a4jfc ,silver1 hard drawn #a4jhf ,copper1 hard drawn #a4jhf ,gold1 annealed #a4cfi ,gold1 hard drawn #a4cic ,aluminium1 annealed #a4ice ,zinc1 pressed #c4gda ,brass 7variable7 #e4jjj ,platinum1 annealed #f4jbb ,iron #f4dej ,steel1 soft #f4ejj ,gold and silver alloy1 #b to #a #g4bbh ,nickel1 annealed #h4bhe ,tin1 pressed #h4ghd ,lead1 pressed #ac4jej ,german silver 7variable7 #ac4ibj ,platinum-silver alloy1 #a to #b #af4baj ,steel1 hard #be4jjj ,antimony1 pressed #bc4fjj ,mercury #fb4gcj ,bismuth #hg4bcj ,graphite #ade4jjj ,nitric ,acid #igfjjj4jjj ,imperfect ,hydrochloric acid #a ,conductors ,sulphuric acid #ajcbjbj4jjj ,solutions of metallic salts varies with strength ,metallic sulphides #a ,distilled water #a #fgedbjh4jjj ,inferior ,metallic salts1 solid #a ,conductors4 ,linen ,cotton and other forms of #a ,hemp cellulose ,paper ,alcohol #a ,ether #a ,dry ,wood #a ,dry ,ice #a ,metallic ,oxides #a ,non-conductors1 ,ice1 at #be c4 #a or ,fats and oils #a ,insulators4 ,caoutchouc #ajjjjjjjjjjjj4 ,guttapercha #ajjjjjjjjjjjj4 ,dry air1 gases1 and vapours #a ,wool #a ,ebonite #acjjjjjjjjjjj4 ,diamond #a ,silk #a ,glass #a ,wax #a ,sulphur #a ,resin #a ,amber #a ,shellac #a ,paraffin #aejjjjjjjjjjj4 ---------------------------------------- ---------------------------- ,footnote #a3 ,these have not been accurately measured4 ,the figures given as indicating the relative resistance of the above bodies to the passage of electricity must be taken as approximate only1 since the conductivity of all these bodies varies very largely with their purity1 and with the temperature4 ,metals become worse conductors when heated2 liquids and non-metals1 on the contrary1 become better conductors4 ,it must be borne in mind that dry air is one of the best insulators1 or worst conductors1 with which we are acquainted2 while damp air1 on the contrary1 owing to the facility with which it deposits water on the surface of bodies1 is highly conducive to the escape of electricity4 ,s #f4 ,if the experiment described at ,s #c be repeated1 substituting a glass rod for the ebonite comb1 it will be found that the pith-ball will be first attracted and then repelled1 as in the case with the ebonite2 and if of two similar pith-balls1 each suspended by a fibre of silk1 one be treated with the excited ebonite and the other with the glass rod1 until repulsion occurs1 and then approached to each other1 the two balls will be found to attract each other4 ,this proves that the electrical condition of the excited ebonite and of the excited glass must be different2 for had it been the same1 the two balls would have repelled one another4 ,farther1 it will be found that the rubber with which the ebonite or the glass rod have been excited has also acquired electrical properties1 attracting the pith-ball1 previously repelled by the rod4 ,from this we may gather that when one body acting on another1 either mechanically or chemically1 sets up an electrical condition in one of the two bodies1 a similar electrical condition1 but in the opposite sense1 is produced in the other3 in point of fact1 that it is impossible to excite any one body without exciting a corresponding but opposite state in the other4 7,we may take1 as a rough mechanical illustration of this1 the effect which is produced on the pile of two pieces of plush or fur1 on being drawn across one another in opposite directions4 ,on examination we shall find that both the piles have been laid down1 the upper in the one direction1 the lower in the other47 ,for a long time these two electrical states were held to depend upon two distinct electricities1 which were called respectively vitreous and resinous1 to indicate the nature of the bodies from which they were derived4 ,later on 7when it was found that the theory of a single electricity could be made to account for all the phenomena1 provided it was granted that some electrified bodies acquired more1 while others acquired less than their natural share of electricity71 the two states were known as positive and negative2 and these names are still retained1 although it is pretty generally conceded that electricity is not an entity in itself1 but simply a mode of motion4 ,s #g4 ,it is usual1 in treatises on electricity1 to give a long list of the substances which acquire a positive or a negative condition when rubbed against one another4 ,such a table is of very little use1 since the slightest modification in physical condition will influence very considerably the result4 ,for example3 if two similar sheets of glass be rubbed over one another1 no change in electrical condition is produced2 but if one be roughed while the other is left polished1 this latter becomes positively1 while the former becomes negatively1 electrified4 ,so1 also1 if one sheet of glass be warmed1 while the other be left cold1 the colder becomes positively1 and the latter negatively1 excited4 ,as a general law1 that body1 the particles of which are more easily displaced1 becomes negatively electrified4 ,s #h4 ,as1 however1 the electricity set up by friction has not hitherto found any practical application in electric bell-ringing or signalling1 we need not to go more deeply into this portion of the subject1 but pass at once to the electricity elicited by the action of acids1 or their salts1 on metals4 ,here1 as might be expected from the law enunciated above1 the metal more acted on by the acid becomes negatively electrified1 while the one less acted on becomes positive4#b ,the following table1 copied from ,ganot1 gives an idea of the electrical condition which the commoner metals and graphite assume when two of them are immersed at the same time in dilute acid3-- v ,zinc4 v ,cadmium4 ,tin4 ,lead4 ,iron4 ,the portion ,nickel4 ,the portion out immersed in the ,bismuth4 of the acid fluid acid fluid4 ,antimony4 ,copper4 ,silver4 ,gold4 ,platinum4 v ,graphite4 ,footnote #b3 ,this refers1 of course1 to those portions of the metals which are out of the acid4 ,for reasons which will be explained farther on1 the condition of the metals in the acid is just the opposite to this4 ,the meaning of the above table is1 that if we test the electrical condition of any two of its members when immersed in an acid fluid1 we shall find that the ones at the head of the list are positive to those below them1 but negative to those above them1 if the test have reference to the condition of the parts within the fluid4 ,on the contrary1 we shall find that any member of the list will be found to be negative to any one below it1 or positive to any above it1 if tested from the portion ,,not immersed in the acid fluid4 ,illustration3 ,fig4 #a4 ,illustration3 ,fig4 #b4 ,s #i4 ,a very simple experiment will make this quite clear4 ,two strips1 one of copper and the other of zinc1 #a wide by #d long1 have a #ab length of copper wire soldered to one extremity of each4 ,a small flat piece of cork1 about #a long by #a square section1 is placed between the two plates1 at the end where the wires have been soldered1 this portion being then lashed together by a few turns of waxed string4 7,the plates should not touch each other at any point47 ,if this combination 7which constitutes a very primitive galvanic couple7 be immersed in a tumbler three-parts filled with water1 rendered just sour by the addition of a few drops of sulphuric or hydrochloric acid1 we shall get a manifestation of electrical effects4 ,if a delicately poised magnetic needle be allowed to take up its natural position of north and south1 and then the wires proceeding from the two metal strips twisted in contact1 so as to be parallel to and over the needle1 as shown in ,fig4 #a1 the needle will be impelled out of its normal position1 and be deflected more or less out of the line of the wire4 ,if the needle be again allowed to come to rest ,n4 and ,s4 7the battery or couple having been removed71 and then the tumbler be held close over the needle1 as in ,fig4 #b1 so that the needle points from the copper to the zinc strip1 the needle will be again impelled or deflected out of its natural position1 but in this case in the opposite direction4 ,s #aj4 ,it is a well-known fact that if a wire1 or any other conductor1 along which the electric undulation 7or1 as is usually said1 the electric current7 is passing1 be brought over and parallel to a suspended magnetic needle1 pointing north and south1 the needle is immediately deflected from this north and south position1 and assumes a new direction1 more or less east and west1 according to the amplitude of the current and the nearness of the conductor to the needle4 ,moreover1 the direction in which the north pole of the needle is impelled is found to be dependent upon the direction in which the electric waves 7or current7 enter the conducting body or wire4 ,the law which regulates the direction of these deflections1 and which is known1 from the name of its originator1 as ,ampe're's law1 is briefly as follows3-- ,s #aa4 ,if a current be caused to flow over and parallel to a freely suspended magnetic needle1 previously pointing north and south1 the north pole will be impelled to the ,,left of the entering current4 ,if1 on the contrary1 the wire1 or conductor1 be placed below the needle1 the deflection will1 under similar circumstances1 be in the opposite direction1 viz43 the north pole will be impelled to the ,,right of the entering current4 ,in both these cases the observer is supposed to be looking along the needle1 with its ,n4 seeking pole pointing at him4 ,s #ab4 ,from a consideration of the above law1 in connection with the experiments performed at ,s #i1 it will be evident that inside the tumbler the zinc is positive to the copper strip2 while1 viewed from the outside conductor1 the copper is positive to the zinc strip4#c ,footnote #c3 ,from some recent investigations1 it would appear that what we usually term the negative is really the point at which the undulation takes its rise4 ,s #ac4 ,a property of current electricity1 which is the fundamental basis of electric bell-ringing1 is that of conferring upon iron and steel the power of attracting iron and similar bodies1 or1 as it is usually said1 of rendering iron magnetic4 ,if a soft iron rod1 say about #d long by #a_/b diameter1 be wound evenly from end to end with three or four layers of cotton-covered copper wire1 say ,no4 #bj gauge1 and placed in proximity to a few iron nails1 etc41 no attractive power will be evinced2 but let the two free ends of the wire be placed in metallic contact with the wires leading from the simple battery described at ,s #i1 and it will be found that the iron has become powerfully magnetic1 capable of sustaining several ounces weight of iron and steel1 so long as the wires from the battery are in contact with the wire encircling the iron2 or1 in other words1 the soft iron is a magnet1 so long as an electric current flows round it4 ,if contact between the battery wires and the coiled wires be broken1 the iron loses all magnetic power1 and the nails1 etc41 drop off immediately4 ,a piece of soft iron thus coiled with covered or insulated wire1 no matter what its shape may be1 is termed an electro-magnet4 ,their chief peculiarities1 as compared with the ordinary permanent steel magnets or lodestones1 are1 first1 their great attractive and sustaining power2 secondly1 the rapidity1 nay1 instantaneity1 with which they lose all attractive force on the cessation of the electric flow around them4 ,it is on these two properties that their usefulness in bell-ringing depends4 ,s #ad4 ,if1 instead of using a soft iron bar in the above experiment1 we had substituted one of hard iron1 or steel1 we should have found two remarkable differences in the results4 ,in the first place1 the bar would have been found to retain its magnetism instead of losing it immediately on contact with the battery being broken2 and1 in the second place1 the attractive power elicited would have been much less than in the case of soft iron4 ,it is therefore of the highest importance1 in all cases where rapid and powerful magnetisation is desired1 that the cores of the electro-magnets should be of the very softest iron4 ,long annealing and gradual cooling conduce greatly to the softness of iron4 ,illustration3 ,fig4 #c4 ,,magnets1 showing ,lines of ,force4 ,s #ae4 ,there is yet another source of electricity which must be noticed here1 as it has already found application in some forms of electric bells and signalling1 and which promises to enter into more extended use4 ,if we sprinkle some iron filings over a bar magnet1 or a horse-shoe magnet1 we shall find that the filings arrange themselves in a definite position along the lines of greatest attractive force2 or1 as scientists usually say1 the iron filings arrange themselves in the direction of the lines of force4 ,the entire space acted on by the magnet is usually known as its field4 ,fig4 #c gives an idea of the distribution of the iron filings1 and also of the general direction of the lines of force4 ,it is found that if a body be moved before the poles of a magnet in such a direction as to cut the lines of force1 electricity is excited in that body1 and also around the magnet4 ,the ordinary magneto-electric machines of the shops are illustrations of the application of this property of magnets4 ,they consist essentially in a horse-shoe magnet1 in front of which is caused to rotate1 by means of appropriate gearing1 or wheel and band1 an iron bobbin1 or pair of bobbins1 coiled with wire4 ,the ends of the wire on the bobbins are brought out and fastened to insulated portions of the spindle1 and revolve with it4 ,two springs press against the spindle1 and pick up the current generated by the motion of the iron bobbins before the poles of the magnet4 ,it is quite indifferent whether we use permanent steel magnets or electro-magnets to produce this effect4 ,if we use the latter1 and more especially if we cause a portion of the current set up to circulate round the electro-magnet to maintain its power1 we designate the apparatus by the name of ,,dynamo4 ,illustration3 ,fig4 #d4 ,,typical ,,dynamo1 showing essential portions4 ,s #af4 ,our space will not permit of a very extended description of the dynamo1 but the following brief outline of its constructive details will be found useful to the student4 ,a mass of soft iron 7shape immaterial7 is wound with many turns of insulated copper wire1 in such a manner that1 were an electrical current sent along the wire1 the mass of iron would become strongly north at one extremity1 and south at the other4 ,as prolongations of the electro-magnet thus produced are affixed two masses of iron facing one another1 and so fashioned or bored out as to allow a ring1 or cylinder of soft iron1 to rotate between them4 ,this cylinder1 or ring of iron1 is also wound with insulated wire1 two or more ends of which are brought out in a line with the spindle on which it rotates1 and fastened down to as many insulated sections of brass cylinder placed around the circumference of the spindle4 ,two metallic springs1 connected to binding screws which form the terminals of the machine1 serve to collect the electrical wave set up by the rotation of the coiled cylinder 7or armature7 before the poles of the electro-magnet4 ,the annexed cut 7,fig4 #d7 will assist the student in getting a clear idea of the essential portions in a dynamo3--,e is the mass of wrought iron wound with insulated wire1 and known as the field-magnet4 ,n and ,s are cast-iron prolongations of the same1 and are usually bolted to the field-magnet4 ,when current is passing these become powerfully magnetic4 ,a is the rotating iron ring1 or cylinder1 known as the armature1 which is also wound with insulated wire1 ,b1 the ends of which are brought out and connected to the insulated brass segments known as the commutator1 ,c4 ,upon this commutator press the two springs ,d and ,d'1 known as the brushes1 which serve to collect the electricity set up by the rotation of the armature4 ,these brushes are in electrical connection with the two terminals of the machine ,f ,f'1 whence the electric current is transmitted where required2 the latter being also connected with the wire encircling the field-magnet1 ,e4 ,when the iron mass stands in the direction of the earth's magnetic meridian1 even if it have not previously acquired a little magnetism from the hammering1 etc41 to which it was subjected during fitting1 it becomes weakly magnetic4 ,on causing the armature to rotate by connecting up the pulley at the back of the shaft 7not shown in cut7 with any source of power1 a very small current is set up in the wires of the armature1 due to the weak magnetism of the iron mass of the field-magnet4 ,as this current 7or a portion of it7 is caused to circulate around this iron mass1 through the coils of wire surrounding the field-magnet1 this latter becomes more powerfully magnetic 7,s #ac71 and1 being more magnetically active1 sets up a more powerful electrical disturbance in the armature4 ,this increased electrical activity in the armature increases the magnetism of this field-magnet as before1 and this again reacts on the armature2 and these cumulative effects rapidly increase1 until a limit is reached1 dependent partly on the speed of rotation1 partly on the magnetic saturation of the iron of which the dynamo is built up1 and partly on the amount of resistance in the circuit4 ,,chapter ,,ii4 ,,on ,,the ,,choice ,,of ,,batteries ,,for ,,electric ,,bell ,,work4 ,s #ag4 ,if we immerse a strip of ordinary commercial sheet zinc in dilute acid 7say sulphuric acid #a part by measure1 water #af parts by measure#d71 we shall find that the zinc is immediately acted on by the acid1 being rapidly corroded and dissolved1 while at the same time a quantity of bubbles of gas are seen to collect around1 and finally to be evolved at the surface of the fluid in contact with the plate4 ,accompanying this chemical action1 and varying in a degree proportionate to the intensity of the action of the acid on the zinc1 we find a marked development of heat and electricity4 ,if1 while the bubbling due to the extrication of gas be still proceeding1 we immerse in the same vessel a strip of silver1 or copper1 or a rod of graphite1 taking care that contact does not take place between the two elements1 no perceptible change takes place in the condition of things2 but if we cause the two strips to touch1 either by inclining the upper extremities so as to bring them in contact out of the fluid like a letter ,lambda1 or by connecting the upper extremities together by means of a piece of wire 7or other conductor of electricity71 or by causing their lower extremities in the fluid to touch1 we notice a very peculiar change4 ,the extrication of bubbles around the zinc strip ceases entirely or almost entirely1 while the other strip 7silver1 copper1 or graphite7 becomes immediately the seat of the evolution of the gaseous bubbles4 ,had these experiments been performed with chemically pure metallic zinc1 instead of the ordinary impure commercial metal1 we should have found some noteworthy differences in behaviour4 ,in the first place1 the zinc would have been absolutely unattacked by the acid before the immersion of the other strip2 and1 secondly1 all evolution of gas would entirely cease when contact between the two strips was broken4 ,footnote #d3 ,in mixing sulphuric acid with water1 the acid should be added in a fine stream1 with constant stirring1 to the water1 and not the water to the acid1 lest the great heat evolved should cause the acid to be scattered about4 ,as the property which zinc possesses of causing the extrication of gas 7under the above circumstances7 has a considerable influence on the efficiency of a battery1 it is well to understand thoroughly what chemical action takes place which gives rise to this evolution of gas4 ,s #ah4 ,all acids may be conveniently regarded as being built up of two essential portions1 viz43 firstly1 a strongly electro-negative portion1 which may either be a single body1 such as chlorine1 iodine1 bromine1 etc41 or a compound radical1 such as cyanogen2 secondly1 the strongly electro-positive body hydrogen4 ,representing1 for brevity's sake1 hydrogen by the letter ,h41 and chlorine1 bromine1 iodine1 etc41 respectively by ,cl41 ,br41 and ,i41 the constitution of the acids derived from these bodies may be conveniently represented by3-- ,h ,cl ,h ,br ,h ,i ---- ---- --- ,hydrochloric#e ,hydrobromic ,hydriodic ,acid4 ,acid4 ,acid4 ,footnote #e3 ,spirits of salt4 and the more complex acids1 in which the electro-negative component is a compound1 such as sulphuric acid 7built up of #a atom of sulphur and #d atoms of oxygen1 united to #b atoms of hydrogen7 or nitric acid 7consisting of #a nitrogen atom1 #f oxygen atoms1 and #a hydrogen atom71 may advantageously be retained in memory by the aid of the abbreviations3-- ,h#b,,so#d ,,hno#f ----------- ------- ,sulphuric and ,nitric ,acid4#f ,acid4#g ,footnote #f3 ,oil of vitriol4 ,footnote #g3 ,aquafortis4 ,when zinc does act on an acid1 it displaces the hydrogen contained in it1 and takes its place2 the acid losing at the same time its characteristic sourness and corrosiveness1 becoming1 as chemists say1 neutralized4 ,one atom of zinc can replace two atoms of hydrogen1 so that one atom of zinc can replace the hydrogen in two equivalents of such acids as contain only one atom of hydrogen4 ,this power of displacement and replacement possessed by zinc is not peculiar to this metal1 but is possessed also by many other bodies1 and is of very common occurrence in chemistry2 and may be roughly likened to the substitution of a new brick for an old one in a building1 or one girder for another in an arch4 ,it will be well1 therefore1 to remember that in all batteries in which acids are used to excite electricity by their behaviour along with zinc1 the following chemical action will also take place1 according to which acid is employed3-- ,hydrochloric ,acid and ,zinc1 equal ,zinc ,chloride and ,hydrogen ,gas4 #b;,h,cl ,zn ,zn,cl#b ,h#b or3-- ,sulphuric ,acid and ,zinc1 equal ,zinc ,sulphate and ,hydrogen ,gas4 ,h#b,,so#d ,zn ,zn,s,o#d ,h#b ,or we may put this statement into a general form1 covering all cases in which zinc is acted on by a compound body containing hydrogen1 representing the other or electro-negative portion of the compound by ,x3-- ,zn ,h#b,x ,zn,x ,h#b the final result being in every case the corrosion and solution of the zinc1 and the extrication of the hydrogen gas displaced4 ,s #ai4 ,we learn from the preceding statements that no electricity can be manifested in a battery or cell 7as such a combination of zinc acid and metal is called7 without consumption of zinc4 ,on the contrary1 we may safely say that the more rapidly the useful consumption of zinc takes place1 the greater will be the electrical effects produced4 ,but here it must be borne in mind that if the zinc is being consumed when we are not using the cell or battery1 that consumption is sheer waste1 quite as much as if we were compelled to burn fuel in an engine whether the latter were doing work or not4 ,for this reason the use of commercial zinc1 in its ordinary condition1 is not advisable in batteries in which acids are employed1 since the zinc is consumed in such1 whether the battery is called upon to do electrical work 7by placing its plates in connection through some conducting circuit7 or not4 ,this serious objection to the employment of commercial zinc could be overcome by the employment of chemically purified zinc1 were it not that the price of this latter is so elevated as practically to preclude its use for this purpose4 ,fortunately1 it is possible to confer1 on the ordinary crude zinc of commerce1 the power of resisting the attacks of the acid 7so long as the plates are not metallically connected2 or1 in other words1 so long as the circuit is broken71 by causing it to absorb superficially a certain amount of mercury 7quicksilver74 ,the modes of doing this1 which is technically known as amalgamating the zinc1 are various1 and1 as it is an operation which every one who has the care of batteries is frequently called upon to perform1 the following working details will be found useful3-- ,s #bj4 ,to amalgamate zinc1 it should first be washed with a strong solution of common washing soda1 to remove grease1 then rinsed in running water2 the zinc plates1 or rods1 should then be dipped into a vessel containing acidulated water 7,s #ag71 and as soon as bubbles of hydrogen gas begin to be evolved1 transferred to a large flat dish containing water4 ,while here1 a few drops of mercury are poured on each plate1 and caused to spread quickly over the surface of the zinc by rubbing briskly with an old nail-brush or tooth-brush4 ,some operators use a kind of mop1 made of pieces of rag tied on the end of a stick1 and there is no objection to this2 others recommend the use of the fingers for rubbing in the mercury4 ,this latter plan1 especially if many plates have to be done1 is very objectionable3 firstly1 on the ground of health1 since the mercury is slowly but surely absorbed by the system1 giving rise to salivation1 etc42 and1 secondly1 because any jewellery1 etc41 worn by the wearer will be whitened and rendered brittle4 ,when the entire surface of the zinc becomes resplendent like a looking-glass1 the rubbing may cease1 and the zinc plate be reared up on edge1 to allow the superfluous mercury to drain off4 ,this should be collected for future operations4 ,it is important that the mercury used for this purpose should be pure4 ,much commercial mercury contains lead and tin4 ,these metals can be removed by allowing the mercury to stand for some time in a vessel containing dilute nitric acid1 occasional agitation being resorted to1 in order to bring the acid into general contact with the mercury4 ,all waste mercury1 drainings1 brushings from old plates1 etc41 should be thus treated with nitric acid1 and finally kept covered with water4 ,sprague1 in his admirable work on electricity1 says3--,whenever the zinc shows a grey granular surface 7or rather before this71 brush it well and re-amalgamate1 remembering that a saving of mercury is no economy1 and a free use of it no waste2 for it may all be recovered with a little care4 ,keep a convenient sized jar1 or vessel1 solely for washing zinc in1 and brush into this the dirty grey powder which forms1 and is an amalgam of mercury with zinc1 lead1 tin1 etc41 and forms roughnesses which reduce the protection of the amalgamation4 ,rolled sheet zinc should always be used in preference to cast4 ,this latter is very hard to amalgamate1 and has less electro-motive power#h2 but for rods for use in porous jars1 and particularly with saline solutions1 cast-zinc is very commonly used4 ,in this case great care should be taken to use good zinc cuttings1 removing any parts with solder on them1 and using a little nitre as a flux1 which will remove a portion of the foreign metals4 ,footnote #h3 ,power to set up a current of electricity4 ,s #ba4 ,another and very convenient mode of amalgamating zinc1 specially useful where solid rods or masses of zinc are to be used1 consists in weighing up the zinc and setting aside four parts of mercury 7by weight7 for every hundred of the zinc thus weighed up4 ,the zinc should then be melted in a ladle1 with a little tallow or resin over the top as a flux4 ,as soon as melted1 the mercury should be added in and the mixture stirred with a stick4 ,it should then be poured into moulds of the desired shape4 ,this is1 perhaps1 the best mode of amalgamating cast zincs4 ,s #bb4 ,some operators recommend the use of mercurial salts 7such as mercury nitrate1 etc47 as advantageous for amalgamating2 but1 apart from the fact that these salts are generally sold at a higher rate than the mercury itself1 the amalgamation resulting1 unless a very considerable time be allowed for the mercuric salts to act1 is neither so deep nor so satisfactory as in the case of mercury alone4 ,it may here be noted1 that although the effect of mercury in protecting the zinc is very marked in those batteries in which acids are used as the exciting fluids1 yet this action is not so observable in the cases in which solutions of salts are used as exciters2 and in a few1 such as the ,daniell cell and its congeners1 the use of amalgamated zinc is positively a disadvantage4 ,s #bc4 ,if1 having thus amalgamated the zinc plate of the little battery described and figured at ,s #i1 we repeat the experiment therein illustrated1 namely1 of joining the wires proceeding from the two plates over a suspended magnetic needle1 and leave them so united1 we shall find that the magnetic needle1 which was originally very much deflected out of the line of the magnetic meridian 7north and south71 will very quickly return near to its old and normal position2 and this will be found to take place long before the zinc has been all consumed1 or the acid all neutralised4 ,of course1 this points to a rapid falling off in the transmission of the electric disturbance along the united wires2 for had that continued of the same intensity1 the deflection of the needle would evidently have remained the same likewise4 ,what1 then1 can have caused this rapid loss of power8 ,on examining 7without removing from the fluid7 the surface of the copper plate1 we shall find that it is literally covered with a coating of small bubbles of hydrogen gas1 and1 if we agitate the liquid or the plates1 many of them will rise to the surface1 while the magnetic needle will at the same time give a larger deflection4 ,if we entirely remove the plates from the acid fluid1 and brush over the surface of the copper plate with a feather or small pledget of cotton wool fastened to a stick1 we shall find1 on again immersing the plates in the acid1 that the effect on the needle is almost1 if not quite1 as great as at first2 thus proving that the sudden loss of electrical energy was greatly due to the adhesion of the free hydrogen gas to the copper plate4 ,this peculiar phenomenon1 which is generally spoken of as the polarisation of the negative plate1 acts in a twofold manner towards checking the electrical energy of the battery4 ,in the first place1 the layer of hydrogen 7being a bad conductor of electricity7 presents a great resistance to the transmission of electrical energy from the zinc plate where it is set up to the copper 7or other7 plate whence it is transmitted to the wires1 or electrodes4 ,again1 the copper or other receiving plate1 in order that the electric energy should be duly received and transmitted1 should be more electro-negative than the zinc plate2 but the hydrogen gas which is evolved1 and which thus adheres to the negative plate1 is actually very highly electro-positive1 and thus renders the copper plate incapable of receiving or transmitting the electric disturbance4 ,this state of things may be roughly likened to that of two exactly equal and level tanks1 ,z and ,c1 connected by a straight piece of tubing4 ,if ,z be full and ,c have an outlet1 it is very evident that ,z can and will discharge itself into ,c until exhausted2 but if ,c be allowed to fill up to the same level as ,z1 then no farther flow can take place between the two4 ,it is1 therefore1 very evident that to ensure anything like constancy in the working of a battery1 at least until all the zinc be consumed or all the acid exhausted1 some device for removing the liberated hydrogen must be put into practice4 ,the following are some of the means that have been adopted by practical men3-- ,s #bd4 ,roughening the surface of the negative plate1 which renders the escape of the hydrogen gas easier4 ,this mode was adopted by ,smee in the battery which bears his name4 ,it consists of a sheet of silver1 placed between two plates of zinc1 standing in a cell containing dilute sulphuric acid1 as shown at ,fig4 #e4 ,illustration3 ,fig4 #e4 ,the silver sheet1 before being placed in position1 is platinised2 that is to say1 its surface is covered 7by electro-deposition7 with a coating of platinum1 in the form of a fine black powder4 ,this presents innumerable points of escape for the hydrogen gas2 and for this reason this battery falls off much less rapidly than the plain zinc and smooth copper form4 ,a modification of ,smee's battery which1 owing to the large negative surface presented1 is very advantageous1 is ,walker's graphite cell4 ,in this we have a plate of zinc between two plates of gas-carbon 7scurf71 or graphite4 ,the surface of this body is naturally much rougher than metal sheets2 and this roughness of surface is further assisted by coating the surface with platinum1 as in the case of the ,smee4 ,the chief objection to the use of graphite is its porosity1 which causes it to suck up the acid fluid in which the plates stand1 and this1 of course1 corrodes the brass connections1 or binding screws4 ,other mechanical means of removing the hydrogen have been suggested1 such as brushing the surface of the plate1 keeping the liquid in a state of agitation by boiling or siphoning2 but the only really efficient practical means with which we are at present acquainted are chemical means4 ,thus1 if we can have present at the negative plate some substance which is greedy of hydrogen1 and which shall absorb it or combine with it1 we shall evidently have solved the problem4 ,this was first effected by ,professor ,daniell2 and the battery known by his name still retains its position as one of the simplest and best of the constant forms of battery4 ,the term constant1 as applied to batteries1 does not mean that the battery is a constancy1 and will run for ever1 but simply that so long as there is in the battery any fuel 7zinc1 acid1 etc471 the electrical output of that battery will be constant4 ,the ,daniell cell consists essentially in a rod or plate of zinc immersed in dilute sulphuric acid1 and separated from the copper or collecting plate by a porous earthen pot or cell4 ,around the porous cell1 and in contact with the copper plate1 is placed a solution of sulphate of copper1 which is maintained saturate by keeping crystals of sulphate of copper 7blue stone1 blue vitriol7 in the solution4 ,sulphate of copper is a compound built up of copper ,cu1 and of sulphur oxide ,,so#d4 ,when the dilute sulphuric acid acts on the zinc plate or rod 7,s #ah71 sulphate of zinc is formed1 which dissolves in the water1 and hydrogen is given off3-- ,zn ,h#b ,,so#d ,zn ,,so#d ,h#b4 ,zinc and sulphuric acid produce zinc sulphate and free hydrogen4 ,now this free hydrogen1 by a series of molecular interchanges1 is carried along until it passes through the porous cell1 and finds itself in contact with the solution of copper sulphate4 ,here1 as the hydrogen has a greater affinity for1 or is more greedy of1 the sulphur oxide1 ,,so#d1 than the copper is1 it turns the latter out1 takes its place1 setting the copper free1 and forming1 with the sulphur oxide1 sulphuric acid4 ,the liberated copper goes1 and adheres to the copper plate1 and1 far from detracting from its efficacy1 as the liberated hydrogen would have done1 actually increases its efficiency1 as it is deposited in a roughened form1 which presents a large surface for the collection of the electricity4 ,the interchange which takes place when the free hydrogen meets the sulphate of copper 7outside the porous cells7 is shown in the following equation3-- ,h#b ,cu ,,so#d ,h#b ,,so#d ,cu4 ,free hydrogen and copper sulphate produce sulphuric acid and free copper4 ,illustration3 ,fig4 #f4 ,,daniell ,,cell4 ,s #be4 ,the original form given to this1 the ,daniell cell1 is shown at ,fig4 #f1 in which ,z is the zinc rod standing in the porous pot ,p1 in which is placed the dilute sulphuric acid4 ,a containing vessel1 ,v1 of glazed earthenware1 provided with a perforated shelf1 ,s1 on which are placed the crystals of sulphate of copper1 serves to hold the copper sheet1 ,c1 and the solution of sulphate of copper4 ,t and ,t' are the terminals from which the electricity is led where desired4 ,in another form1 the copper sheet itself takes the form and replaces the containing vessel ,v2 and since the copper is not corroded1 but actually increases in thickness during action1 this is a decided advantage4 ,a modification1 in which the porous cell is replaced by sand or by sawdust1 is also constructed1 and known as ,minotto's cell3 this1 owing to the greater thickness of the porous layer1 offers more resistance1 and gives1 consequently1 less current4 ,by taking advantage of the greater specific gravity 7weight1 bulk for bulk7 of the solution of sulphate of copper over that of water or dilute sulphuric acid1 it is possible to construct a battery which shall act in a manner precisely similar to a ,daniell1 without the employment of any porous partition whatsoever4 ,fig4 #g illustrates the construction of one of these1 known as ,gravity ,daniells4 ,illustration3 ,fig4 #g4 ,,gravity ,,cell4 ,in this we have a plate1 disc1 or spiral of copper1 ,c1 connected by an insulated copper wire to the terminal ,t'4 ,over this is placed a layer of crystals of copper sulphate2 the jar is then filled nearly to the top with dilute sulphuric acid1 or with a strong solution of sulphate of zinc 7which is more lasting in its effects1 but not so energetic as the dilute sulphuric acid71 and on the surface of this1 connected to the other terminal1 ,t1 is allowed to rest a thick disc of zinc1 ,z4 ,speaking of these cells1 ,professor ,ayrton1 in his invaluable ,practical ,electricity1 says3--,all gravity cells have the disadvantage that they cannot be moved about2 otherwise the liquids mix1 and the copper sulphate solution1 coming into contact with the zinc plate1 deposits copper on it4 ,this impairs the action1 by causing the zinc to act electrically1 like a copper one4 ,indeed1 without any shaking1 the liquids mix by diffusion1 even when a porous pot is employed2 hence a ,daniell's cell is found to keep in better order if it be always allowed to send a weak current when not in use1 since the current uses up the copper sulphate solution1 instead of allowing it to diffuse4 ,the use of a solution of zinc sulphate to act on the zinc rod1 or plate1 is always to be preferred in the ,daniell cell1 when long duration is of more consequence than energetic action4 ,s #bf4 ,there are many other bodies which can be used in batteries to absorb the hydrogen set free4 ,of several of these we need only take a passing notice1 as the batteries furnished by their use are unfit for electric bell work4 ,of these we may mention nitric acid1 which readily parts with a portion of the oxygen 7,s #ah7 and reconverts the free hydrogen into water4 ,this acid is used as the depolarizer#i in the ,grove and in the ,bunsen cell4 ,another very energetic depolariser is chromic acid1 either in solution1 in dilute sulphuric acid1 or in the form of potassic dichromate 7bichromate of potash3 bichrome74 ,as one form of chromic cell has found favour with some bell-fitters1 we shall study its peculiarities farther on4 ,footnote #i3 ,depolarizer is the technical name given to any body which1 by absorbing the free hydrogen1 removes the false polarity of the negative plate4 ,another class of bodies which readily part with their oxygen1 and thus act as depolarisers1 are the oxides of lead and manganese4 ,this latter oxide forms the basis of one of the most useful cells for electric bell work1 namely3 the one known as the ,leclanch'e4 ,as the battery has been1 and will probably remain1 long a favourite1 the next paragraph will be devoted to its consideration4 ,s #bg4 ,the ,leclanch'e cell1 in its original form1 consists in a rod or block of gas carbon 7retort scurf3 graphite7 standing in an upright porous pot4 ,around this1 so as to reach nearly to the top of the porous cell1 is tightly packed a mixture of little lumps of graphite and black oxide of manganese 7manganic dioxide3 black wad71 the porous cell itself being placed in an outer containing vessel1 which usually takes the form of a square glass bottle4 ,a zinc rod stands in one corner of the bottle1 and is prevented from coming into actual contact with the porous cell by having an indiarubber ring slipped over its upper and lower extremities4 ,the glass containing vessel is then filled to about two-thirds of its height with a solution of ammonium chloride 7sal ammoniac7 in water1 of the strength of about #b oz4 of the salt to each pint of water4 ,this soon permeates the porous cell and reaches the mixture inside4 ,the general appearance of the ,leclanch'e cell is well shown at ,fig4 #h4 ,illustration3 ,fig4 #h4 ,in order to ensure a large surface of contact for the terminal of the carbon rod or plate1 it is customary to cast a leaden cap on the top thereof2 and1 as the porosity of the graphite1 or carbon1 is very apt to allow the fluid in the battery to creep up to and corrode the terminal1 and thus oppose resistance to the passage of electricity1 the upper end of the carbon1 before the lead cap is cast on1 is soaked for some time in melted paraffin wax1 at a temperature of #aaj deg4 ,centigrade3 that is somewhat hotter than boiling water heat4 ,this1 if left on the outside1 would prevent the passage of electricity almost entirely2 so lateral holes are drilled into the carbon before the cap is finally cast on4 ,the action that takes place in the ,leclanch'e cell may be summarised as follows3-- ,when the zinc1 ,zn1 is acted on by the ammonium chloride1 #b,,nh#d;,cl1 the zinc seizes the chlorine and forms with it zinc chloride1 ,zn,cl#b1 while the ammonium1 #b,,nh#d1 is liberated4 ,but this ammonium1 #b,,nh#d1 does not escape4 ,being electro-positive1 it is impelled towards the negative plate1 and in its passage thereto meets with another molecule of ammonium chloride1 from which it displaces the ammonium1 in this wise3 #b,,nh#d #b,,nh#d;,cl #b,,nh#d;,cl #b,,nh#d2 in other words1 this electro-positive ammonium is able1 by virtue of its electrical charge1 to displace the ammonium from the combined chloride4 ,in so doing1 it sets the liberated ammonium in an electro-positive condition1 as it was itself1 losing at the same time its electrical charge4 ,this interchange of molecules goes on 7as we saw in the case of the ,daniell's cell1 ,s #bd7 until the surface of the carbon is reached4 ,here1 as there is no more ammonium chloride to decompose1 the ammonium #b,,nh#d immediately splits up into ammonia #b,,nh#c and free hydrogen ,h#b4 ,the ammonia escapes1 and may be detected by its smell2 while the hydrogen ,h#b1 finding itself in contact with the oxide of manganese1 #b,mn,o#b1 seizes one atom of its oxygen1 ,o1 becoming thereby converted into water ,h#b,o2 while the manganese dioxide1 #b,mn,o#b1 by losing one atom of oxygen1 is reduced to the form of a lower oxide of manganese1 known as manganese sesquioxide1 ,mn#b,o#c4 ,expressed in symbols1 this action may be formulated as below3-- ,in the zinc compartment-- ,zn #b,,nh#d;,cl ,zn,cl#b #b,,nh#c ,h#b ,in the peroxide of manganese compartment-- ,h#b #b,mn,o#b ,mn#b,o#c ,h#b,o4 ,ammonia gas therefore slowly escapes while this battery is in action1 and this corrodes all the brass work with which it comes into contact1 producing a bluish green verdigris4 ,if there be not sufficient ammonium chloride in solution1 the water alone acts on the zinc3 zinc oxide is produced1 which renders the solution milky4 ,should this be the case1 more sal ammoniac must be added4 ,it is found that for every #ej grains of zinc consumed in this battery1 about #hb grains of sal ammoniac and #abd grains of manganese dioxide are needed to neutralize the hydrogen set free4 ,it is essential for the efficient working of this battery that both the manganese dioxide and the carbon should be free from powder1 otherwise it will cake together1 prevent the passage of the liquid1 and present a much smaller surface to the electricity1 than if in a granular form4 ,for this reason1 that manganese dioxide should be preferred which is known as the needle form1 and both this and the carbon should be sifted to remove dust4 ,s #bh4 ,in the admirable series of papers on electric bell fitting which was published in the ,english ,mechanic1 ,mr4 ,f4 ,c4 ,allsop1 speaking of the ,leclanch'e cell1 says3--,a severe and prolonged test1 extending over many years1 has proved that for general electric bell work the ,leclanch'e has no equal2 though1 in large hotels1 etc41 where the work is likely to be very heavy1 it may1 perhaps1 be preferable to employ a form of the ,fuller bichromate battery4 ,it is very important that the battery employed should be a thoroughly reliable one and set up in a proper manner1 as a failure in the battery causes a breakdown in the communication throughout the whole building1 whilst the failure of a push or wire only affects that portion of the building in which the push or wire is fixed4 ,a common fault is that of putting in 7with a view to economy7 only just enough cells 7when first set up7 to do the necessary work4 ,this is false economy1 as when the cells are but slightly exhausted the battery power becomes insufficient2 whereas1 if another cell or two had been added1 the battery would have run a much longer time without renewal1 owing to the fact that each cell could have been reduced to a lower state of exhaustion1 yet still the battery would have furnished the necessary power2 and the writer has always found that the extra expense of the surplus cells is fully repaid by the increased length of time the battery runs without renewal4 ,s #bi4 ,another form of ,leclanch'e1 from which great things were expected at its introduction1 is the one known as the ,agglomerate block1 from the fact that1 instead of simply placing the carbon and manganese together loosely in a porous cell1 solid blocks are formed by compressing these materials1 under a pressure of several tons1 around a central carbon core1 to which the terminal is attached in the usual manner4 ,the following are some of the compositions used in the manufacture of agglomerate blocks3-- ,no4 #a4 ,manganese dioxide #dj parts4 ,powdered gas carbon #ee ,gum lac resin #e ,no4 #b4 ,manganese dioxide 7pyrolusite7 #dj parts4 ,gas carbon 7powdered7 #eb ,gum lac resin #e ,potassium bisulphate #c ,these are to be thoroughly incorporated1 forced into steel moulds 7containing the central carbon core7 at a temperature of #ajj deg4 ,c4 7#bab deg4 ,fahr471 under a pressure of #cjj atmospheres1 say #d1ejj lbs4 to the square inch4 ,no4 #c4 ,barbier and ,leclanch'e's ,patent4 ,manganese dioxide #di parts4 ,graphite #dd ,pitch 7brai gras7 #i ,sulphur #c_/e ,water #b_/e ,the materials having been reduced to fine powder1 and the proportion of water stated having been added1 are intimately mixed together by hand or mechanically4 ,the moist mixture is moulded at the ordinary temperature1 either by a simple compressing press1 or by a press in which two pistons moving towards each other compress the block on two opposite faces2 or the mixture may be compressed by drawing1 as in the manufacture of electric light carbon4 ,after compression1 the products are sufficiently solid to be manipulated4 ,they are then put in a stove1 or oven1 the temperature of which is gradually raised to about #cej deg4 ,c4 7about #ffb deg4 ,fahr472 a temperature which is insufficient to decompose the depolarising substance 7manganese dioxide71 but sufficient to drive out first the volatile parts of the agglomerating material1 and then to transform its fixed parts in a body unattackable by the ammonia of the cell4 ,during the gradual heating1 or baking1 which lasts about two hours1 what remains of the water in the agglomerate is driven off2 then come the more volatile oils contained in the pitch1 and finally the sulphur4 ,the sulphur is added to the mixture1 not as an agglomerative1 but as a chemical re-agent 7and this is a characteristic feature in the invention71 acting on what remains of the pitch1 as it acts on all carbo-hydrides at a high temperature1 transforming it partially into volatile sulphuretted compounds1 which are expelled by the heat1 and partially into a fixed and unattackable body1 somewhat similar to vulcanite4 ,the action of the sulphur on the pitch can very well be likened to its action on caoutchouc 7which is likewise a hydro-carbon7 during the process of vulcanisation4 ,these agglomerate blocks1 however prepared1 are placed in glass or porcelain containing vessels1 as shown in ,fig4 #i1 with a rod of zinc1 separated from actual contact with the carbon by means of a couple of crossed indiarubber bands1 which serve at the same time to hold the zinc rods upright4 ,the exciting solution1 as in the case of the ordinary ,leclanch'e consists in a solution of ammonium chloride4 ,illustration3 ,fig4 #i4 ,among the various advantages claimed for the agglomerate form of ,leclanch'e over the ordinary type1 may be mentioned the following3-- #ast4--,the depolarising power of the manganese oxide is used to the best advantage1 and that1 owing to this1 the electro-motive force of the battery is kept at the same point4 #bnd4--,that1 owing to the absence of the porous cell1 there is less internal resistance in the battery and therefore more available current4 #crd4--,that the resistance of the battery remains pretty constant1 whatever work be put upon it4 #dth4--,that1 owing to the fact that the liquid comes into contact with both elements immediately1 the battery is ready for use directly on being charged4 #eth4--,that the renewal or recharging is exceedingly easy1 since the elements can be removed together1 fresh solution added1 or new depolarising blocks substituted4 ,but when this battery came to be put to the test of practical work1 it was found the block form could not be credited with all these advantages1 and that their chief superiority over the old cell consisted rather in their lower internal resistance than in anything else4 ,even this is not an advantage in the case of bell work1 except when several bells are arranged in parallel1 so that a large current is required4 ,the blocks certainly polarise more quickly than the old form1 and it does not appear that they depolarise any more rapidly4 ,probably the enormous pressure to which the blocks are subjected1 in the first two processes1 renders the composition almost impermeable to the passage of the fluid1 so that depolarisation cannot take place very rapidly4 ,another and serious objection to these blocks is that1 after a little work1 pieces break away from the blocks and settle on the zinc4 ,this sets up a short circuit1 and the zincs are consumed whether the battery is in action or not4 ,the author has had no opportunity for making any practical tests with the blocks prepared by process ,no4 #c1 but he is under the impression that the blocks would be even more friable than those prepared under greater pressure4 ,s #cj4 ,a third form of ,leclanch'e1 and one which has given considerable satisfaction1 is the one known as ,judson's ,patent4 ,this consists1 as shown at ,fig4 #aj1 in a cylinder of corrugated carbon encased in an outer coating of an insulating composition4 ,inside the cell are two or more thin carbon sheets1 cemented to the sides of the cell by ,prout's elastic glue1 or some similar compound1 so as to leave spaces1 which are filled in with granular carbon and manganese4 ,the surface of the plates is perforated1 so as to allow ready access to the exciting fluid4 ,the zinc rod1 which is affixed to the cover1 stands in the centre of the cell1 touching it at no part4 ,owing to the very large surface presented by the corrugations in the carbon1 and by the perforated carbon plates1 the internal resistance of this form of battery is very low2 hence the current1 if employed against a small outer resistance1 is large4 ,but this1 except in the case of bells arranged in parallel1 is of no great advantage4 ,illustration3 ,fig4 #aj4 ,s #ca4 ,the ordinary form of ,leclanch'e is found in market in three sizes1 viz41 ,no4 #a1 ,no4 #b1 and ,no4 #c4 ,unfortunately1 all makers do not use these numbers in the same manner1 so that while some call the smallest1 or pint size1 ,no4 #a1 others give this name to the largest1 or three-pint1 size4 ,no4 #b is always quart size1 and this is the one commonly employed4 ,when several cells are employed to work a number of bells1 it is well1 in order that they may not receive injury1 that they be enclosed in a wooden box4 ,as it is necessary that the batteries should be inspected from time to time1 boxes are specially made with doubled hinged top and side1 so that when the catch is released these fall flat2 thus admitting of easy inspection or removal of any individual cell4 ,this form of battery box is shown at ,fig4 #aa4 ,illustration3 ,fig4 #aa4 ,,battery ,,in ,,box4 ,s #cb4 ,there are certain ills to which the ,leclanch'e cells are liable that require notice here4 ,the first is creeping4 ,by creeping is meant the gradual crystallisation of the sal ammonium up the inside and round the outside of the glass containing jar4 ,there are two modes of preventing this4 ,the first consists in filling in the neck with melted pitch1 two small funnel-like tubes being previously inserted to admit of the addition of fresh sal ammoniac solution1 and for the escape of gas4 ,this mode cannot be recommended1 as it is almost impossible to remove the pitch 7in case it be required to renew the zinc1 etc47 without breaking the glass vessel4 ,the best way to remove the pitch is to place the cell in a large saucepan of cold water1 and set it on a fire until the water boils4 ,the pitch is1 by this treatment1 so far softened that the elements can be removed and the pitch scraped away with a knife4 ,illustration3 ,fig4 #ab4 ,by far the better mode is to rub round the inside and outside of the neck of the jar with tallow1 or melted paraffin wax1 to the depth of an inch or thereabouts4 ,this effectually prevents creeping and the consequent loss of current4 ,messrs4 ,gent1 of ,leicester1 have introduced a very neat modification of the ,leclanch'e cell1 with a view to obviate altogether the evils deriving from creeping4 ,this cell is illustrated at ,fig4 #ab1 and the following is the description supplied by the patentees3--,all who have had experience of batteries in which a solution of salts is used are aware of the difficulty experienced in preventing it creeping over the outside of the jar1 causing local loss1 and oftentimes emptying the jar of its solution4 ,many devices have been tried to prevent this1 but the only effectual one is our patent insulated jar1 in which a recess surrounds the top of the jar1 this recess being filled with a material to which the salts will not adhere1 thus keeping the outside of the jar perfectly clean4 ,it is specially adapted for use in hot climates1 and is the only cell in which jars may touch each other and yet retain their insulations4 ,we confidently recommend a trial of this cell4 ,its price is but little in excess of the ordinary ,leclanch'e4 ,the battery should be set up in as cool a place as possible1 as heat is very conducive to creeping4 ,it is also important that the battery should be placed as near as convenient to the bell4 ,sometimes the zincs are seen to become coated with a black substance1 or covered with crystals1 rapidly wasting away at the same time1 although doing little or no work2 a strong smell of ammonia being given off at the same time4 ,when this occurs1 it points to an electrical leakage1 or short circuit1 and this1 of course1 rapidly exhausts the battery4 ,it is of the utmost importance to the effective working of any battery that not the slightest leakage or local action should be allowed to take place4 ,however slight such loss be1 it will eventually ruin the battery4 ,this leakage may be taking place in the battery1 as a porous cell may be broken1 and carbon may be touching the zinc2 or out of the battery1 along the conducting wires1 by one touching the other1 or through partial conductivity of a damp wall1 a metallic staple1 etc41 or by creeping4 ,if loss or local action has taken place1 it is best1 after discovering and repairing the faults 7see also testing wires71 to replace the old zincs by new ones1 which are not costly4 ,s #cc4 ,there is yet a modification of the ,leclanch'e which is sometimes used to ring the large bells in hotels1 etc41 known as the ,leclanch'e reversed1 since the zinc is placed in the porous pot1 this latter being stood in the centre of the stoneware jar1 the space between the two being packed with broken carbon and manganese dioxide4 ,by this means a very much larger negative surface is obtained4 ,in the ,grenet cell1 the porous cell is replaced by a canvas bag1 which is packed full of lumps of graphite and carbon dioxide1 a central rod of carbon being used as the electrode4 ,this may be used in out-of-the-way places where porous cells are not readily obtainable1 but ,i cannot recommend them for durability4 ,s #cd4 ,the only other type of battery which it will be needful to notice in connection with bell work is one in which the depolariser is either chromic acid or a compound of chromic acid with potash or lime4 ,chromic acid consists of hydrogen united to the metal chromium and oxygen4 ,potassic dichromate 7bichromate of potash3 bichrome7 contains potassium1 chromium1 and oxygen4 ,if we represent potassium by ,k1 chromium by ,cr1 and oxygen by ,o1 we can get a fair idea of its constitution by expressing it as ,k#b;,cr#b,o#g1 by which it is shown that one molecule of this body contains two atoms of potassium united to two atoms of chromium and seven atoms of oxygen4 ,bichromate of potash readily parts with its oxygen2 and it is upon this1 and upon the relatively large amount of oxygen it contains1 that its efficiency as a depolariser depends4 ,unfortunately1 bichromate of potash is not very soluble in water2 one pint of water will not take up much more than three ounces of this salt4 ,hence1 though the solution of potassium bichromate is an excellent depolariser as long as it contains any of the salt1 it soon becomes exhausted4 ,when bichromate of potash is used in a cell along with sulphuric acid and water1 sulphate of potash and chromic acid are formed1 thus3-- ,k#b;,cr#b,o#g ,h#b,,so#d ,h#b,o ,k#b,,so#d #b;,h#b;,cr,o#d ---------------- ----------- ------ ----------- ------------- #a molecule of #a molecule #a give #a molecule #b molecules bichrome4 of molecule of of sulphuric of sulphate chromic acid4 water4 of potash4 acid4 ,from this we learn that before the potassium bichromate enters into action in the battery1 it is resolved into chromic acid4 ,chromic acid is now prepared cheaply on a large scale1 so that potassium bichromate may always be advantageously replaced by chromic acid in these batteries2 the more so as chromic acid is extremely soluble in water4 ,in the presence of the hydrogen evolved during the action of the battery 7,s #ah7 chromic acid parts with a portion of its oxygen1 forming water and sesquioxide of chromium1 ,cr#b,o#c1 and this1 finding itself in contact with the sulphuric acid1 always used to increase the conductivity of the liquid1 forms sulphate of chromium4 ,the action of the hydrogen upon the chromic acid is shown in the following equation3-- #b;,h#b;,cr,o#d #c;,h#b #e;,h#b,o ,cr#b,o#c ------------- ------ ------- ----------- #b molecules of #c molecules #e molecules #a molecule chromic of give of water4 of acid4 hydrogen4 chromium sesquioxide4 ,illustration3 ,fig4 #ac4 ,s #ce4 ,the bottle form of the bichromate or chromic acid battery 7as illustrated at ,fig4 #ac7 is much employed where powerful currents of short duration are required4 ,it consists of a globular bottle with a rather long wide neck1 in which are placed two long narrow graphite plates1 electrically connected to each other and to one of the binding screws on the top4 ,between these two plates is a sliding rod1 carrying at its lower extremity the plate of zinc4 ,this sliding rod can be lowered and raised1 or retained in any position1 by means of a set screw4 ,the zinc is in metallic connection with the other binding screw4 ,this battery 7which1 owing to the facility with which the zinc can be removed from the fluid1 is extremely convenient and economical for short experiments7 may be charged with either of the following fluids3-- ,,first ,,recipe4 ,bichromate ,solution4 ,bichromate of potash 7finely powdered7 #c oz4 ,boiling water #a pint4 ,stir with a glass rod1 allow to cool1 then add1 in a fine stream1 with constant stirring1 ,strong sulphuric acid 7oil of vitriol7 #c fluid oz4 ,the mixture should be made in a glazed earthern vessel1 and allowed to cool before using4 ,,second ,,recipe4 ,chromic ,acid ,solution4 ,chromic acid 7chromic trioxide7 #c oz4 ,water #a pint4 ,stir together till dissolved1 then add gradually1 with stirring1 ,sulphuric acid #c oz4 ,this also must not be used till cold4 ,in either case the bottle must not be more than three parts filled with the exciting fluid1 to allow plenty of room for the zinc to be drawn right out of the liquid when not in use4 ,s #cf4 ,the effects given by the above battery1 though very powerful1 are too transient to be of any service in continuous bell work4 ,the following modification1 known as the ,fuller cell1 is1 however1 useful where powerful currents are required1 and1 when carefully set up1 may be made to do good service for five or six months at a stretch4 ,the ,fuller cell consists in an outer glass or glazed earthern vessel1 in which stands a porous pot4 ,in the porous pot is placed a large block of amalgamated zinc1 that is cast around a stout copper rod1 which carries the binding screw4 ,this rod must be carefully protected from the action of the fluid1 by being cased in an indiarubber tube4 ,the amalgamation of the zinc must be kept up by putting a small quantity of mercury in the porous cell4 ,the porous cells must be paraffined to within about half an inch of the bottom1 to prevent too rapid diffusion of the liquids1 and the cells themselves should be chosen rather thick and close in texture1 as otherwise the zinc will be rapidly corroded4 ,water alone is used as the exciting fluid in the porous cell along with the zinc4 ,speaking of this form of cell1 ,mr4 ,perren-,maycock says3--,the base of the zinc is more acted on 7when bichromate crystals are used71 because the porous cells rest on the crystals2 therefore let it be well paraffined1 as also the top edge4 ,instead of paraffining the pot in strips all round 7as many operators do7 paraffin the pot all round1 except at one strip about half an inch wide1 and let this face the carbon plate4 ,if this be done1 the difference in internal resistance between the cell with paraffined pot and the same cell with pot unparaffined will be little2 but if the portion that is unparaffined be turned away from the carbon1 it will make very nearly an additional #a ohm resistance4 ,it is necessary to have an ounce or so of mercury in each porous cell1 covering the foot of the zinc2 or the zincs may be cast short1 but of large diameter1 hollowed out at the top to hold mercury1 and suspended in the porous pot4 ,the zinc is less acted on then1 for when the bichromate solution diffuses into the porous pot1 it obviously does so more at the bottom than at the top4 ,illustration3 ,fig4 #ad4 ,fig4 #ad illustrates the form usually given to the modification of the ,fuller cell as used for bell and signalling work4 ,s #cg4 ,before leaving the subject of batteries1 there are certain points in connection therewith that it is absolutely essential that the practical man should understand1 in order to be able to execute any work satisfactorily4 ,in the first place1 it must be borne in mind that a cell or battery1 when at work1 is continually setting up electric undulations1 somewhat in the same way that an organ pipe1 when actuated by a pressure of air1 sets up a continuous sound wave4 ,whatever sets up the electric disturbance1 whether it be the action of sulphuric acid on zinc1 or caustic potash on iron1 etc41 is called electromotive force1 generally abbreviated ,e4,m4,f4 ,just in the same manner that the organ pipe could give no sound if the pressure of air were alike inside and out1 so the cell1 or battery1 cannot possibly give current1 or evidence of electric flow1 unless there is some means provided to allow the tension1 or increased atomic motion set up by the electromotive force1 to distribute itself along some line of conductor or conductors not subjected to the same pressure or ,e4,m4,f4 ,in other words1 the current of electricity will always tend to flow from that body which has the highest tension1 towards the body where the strain or tension is less4 ,in a cell in which zinc and carbon1 zinc and copper1 or zinc and silver are the two elements1 with an acid as an excitant1 the zinc during the action of the acid becomes of higher potential than the other element1 and consequently the undulations take place towards the negative plate 7be it carbon1 copper1 or silver74 ,but by this very action the negative plate immediately reaches a point of equal tension1 so that no current is possible4 ,if1 however1 we now connect the two plates together by means of any conductor1 say a copper wire1 then the strain to which the carbon plate is subjected finds its exit along the wire and the zinc plate1 which is continually losing its strain under the influence of the acid1 being thus at a lower potential 7electrical level1 strain7 than the carbon1 can and does actually take in and pass on the electric vibrations4 ,it is therefore evident that no true current can pass unless the two elements of a battery are connected up by a conductor4 ,when this connection is made1 the circuit is called a closed circuit4 ,if1 on the contrary1 there is no electrical connection between the negative and positive plates of a cell or battery1 the circuit is said to be open1 or broken4 ,it may be that the circuit is closed by some means that is not desirable1 that is to say1 along some line or at some time when and where the flow is not wanted2 as1 for instance1 the outside of a cell may be wet1 and one of the wires resting against it1 when of course leakage will take place as the circuit will be closed1 though no useful work will be done4 ,on the other hand1 we may actually take advantage of the practically unlimited amount of the earth's surface1 and of its cheapness as a conductor to make it act as a portion of the conducting line4 ,it is perfectly true that the earth is a very poor conductor as compared with metals4 ,let us say1 for the sake of example1 that damp earth conducts #ajj1jjj times worse than copper4 ,it will be evident that if a copper wire #a_/bj of an inch in section could convey a given electric current1 the same length of earth having a section of #e1jjj inches would carry the same current equally well1 and cost virtually nothing1 beyond the cost of a metal plate1 or sack of coke1 presenting a square surface of a little over #gj inches in the side at each end of the line4 ,this mode of completing the circuit is known as the earth plate4 ,s #ch4 ,the next point to be remembered in connection with batteries is1 that the electromotive force 7,e4,m4,f47 depends on the nature of the elements 7zinc and silver1 zinc and carbon1 etc47 and the excitants used in the cell1 and has absolutely nothing whatever to do with their size4 ,this may be likened to difference of temperature in bodies4 ,thus1 whether we have a block of ice as large as an iceberg or an inch square1 the temperature will never exceed #cb deg4,f4 as long as it remains ice2 and whether we cause a pint or a thousand gallons of water to boil 7under ordinary conditions71 its temperature will not exceed #bab deg4,f4 ,the only means we have of increasing the ,e4,m4,f41 or tension1 or potential1 of any given battery1 is by connecting up its constituent cells in series2 that is to say1 connecting the carbon or copper plate of the one cell to the zinc of the next1 and so on4 ,by this means we increase the ,e4,m4,f4 just in the same degree as we add on cells4 ,the accepted standard for the measure of electromotive force is called a ,,volt1 and #a volt is practically a trifle less than the ,e4,m4,f4 set up by a single ,daniell's cell2 the exact amount being #a4jgi volt1 or #a-a_/ab volt very nearly4 ,the ,e4,m4,f4 of the ,leclanch'e is very nearly #a4f volt1 or nearly #a volt and #b_/c4 ,thus in ,fig4 #ae1 which illustrates #c ,leclanch'e cells set up in series1 we should get #a4f volt #a4f #a4f --------- #d4h volts as the total electromotive force of the combination4 ,illustration3 ,fig4 #ae4 ,s #ci4 ,the current1 or amplitude of the continuous vibrations kept up in the circuit1 depends upon two things3 #ast1 the electromotive force2 #bnd1 the resistance in the circuit4 ,there is a certain amount of resemblance between the flow of water under pressure and electricity in this respect4 ,let us suppose we have a constant head of water at our disposal1 and allow it to flow through a tube presenting #a inch aperture4 ,we get a certain definite flow of water1 let us say #ajj gallons of water per hour4 ,more we do not get1 owing to the resistance opposed by the narrowness of the tube to a greater flow4 ,if now we double the capacity of the exit tube1 leaving the pressure or head of water the same1 we shall double the flow of water4 ,or we may arrive at the same result by doubling the head or pressure of water1 which will then cause a double quantity of water to flow out against the same resistance in the tube1 or conductor4 ,just in the same way1 if we have a given pressure of electric strain1 or ,e4,m4,f41 we can get a greater or lesser flow or current by having less or more resistance in the circuit4 ,the standard of flowing current is called an ,,amp,e',,re2 and #a ampe're is that current which1 in passing through a solution of sulphate of copper1 will deposit #ah4ce grains of copper per hour4 ,the unit of resistance is known as an ,,ohm4 ,the resistance known as #a ohm is very nearly that of a column of mercury #a square millime'tre 7#a_/be of an inch7 in section1 and #da-a_/d inches in height2 or #a foot of ,no4 #da gauge pure copper wire1 #cc_/ajjjj of an inch in diameter1 at a temperature of #cb deg4 ,fahr41 or #j deg4 ,centigrade4 ,s #dj4 ,professor ,ohm1 who made a special study of the relative effects of the resistance inserted in the circuit1 the electromotive force1 and the current produced1 enunciated the following law1 which1 after him1 has been called ,,ohm',s ,,law4 ,it is that if we divide the number of electromotive force units 7volts7 employed by the number of resistance units 7ohms7 in the entire circuit1 we get the number of current units 7ampe'res7 flowing through the circuit4 ,this1 expressed as an equation is shown below3 ,e_/,r ,c or ,electromotive force_/,resistance ,current4 ,or if we like to use the initials of volts1 ampe'res1 and ohms1 instead of the general terms1 ,e1 ,r1 and ,c1 we may write ,v_/,r ,a1 or ,volts_/,ohms ,ampe'res4 ,from this it appears that #a volt will send a current of #a ampe're through a total resistance of #a ohm1 since #a divided by #a equals #a4 ,so also #a volt can send a current of #d ampe'res through a resistance of #a_/d of an ohm1 since #a divided by #a_/d is equal to #d4 ,we can therefore always double the current by halving the resistance2 or we may obtain the same result by doubling the ,e4,m4,f41 allowing the resistance to remain the same4 ,in performing this with batteries we must bear in mind that the metals1 carbon1 and liquids in a battery do themselves set up resistance4 ,this resistance is known as internal resistance1 and must always be reckoned in these calculations4 ,we can halve the internal resistance by doubling the size of the negative plate1 or what amounts to the same thing by connecting two similar cells in parallel2 that is to say1 with both their zincs together1 to form a positive plate of double size1 and both carbons or coppers together to form a single negative of twice the dimensions of that in one cell4 ,any number of cells thus coupled together in parallel have their resistances reduced just in proportion as their number is increased2 hence #h cells1 each having a resistance of #a ohm if coupled together in parallel would have a joint resistance of #a_/h ohm only4 ,the ,e4,m4,f4 would remain the same1 since this does not depend on the size of the plate 7see ,s #ch74 ,the arrangement of cells in parallel is shown at ,fig4 #af1 where three ,leclanch'e cells are illustrated thus coupled4 ,the following little table gives an idea of the ,e4,m4,f4 in volts1 and the internal resistance in ohms1 of the cells mostly used in electric bell work4 ,illustration3 ,fig4 #af4 ,,table ,,showing ,e4,m4,f4 ,,and ,r4 ,,of ,,batteries4 ---------------------------------------- --------------------------- ,name of ,cell4 ,capacity of ,cell4 ,electromotive ,resistance in force in ,volts4 ,ohms4 ---------------------------------------- --------------------------- ,daniell #b quarts #a4jgi #a ,gravity #b quarts #a4jgi #aj ,leclanch'e #a pint #a4fj #a4ac #b pints #a4fj #a4aj #c pints #a4fj #j4hg ,agglomerate #a pint #a4ee #j4gj #b pints #a4ee #j4fj #c pints #a4ee #j4ej ,fuller #a quart #a4hj #j4ej ---------------------------------------- --------------------------- ,from this it is evident that if we joined up the two plates of a ,fuller cell with a short wire presenting no appreciable resistance1 we should get a current of 7#a4hj divided by #j4ej7 #c4f ampe'res along the wire2 whereas if a gravity ,daniell were employed the current flowing in the same wire would only be a little over #a_/aj of an ampe're1 since #a4jgi_/aj #j4ajgi4 ,but every wire1 no matter how short or how thick1 presents some resistance2 so we must always take into account both the internal resistance 7that of the battery itself7 and the external resistance 7that of the wires1 etc41 leading to the bells or indicators7 in reckoning for any given current from any cell or cells4 ,,chapter ,,iii4 ,,on ,,electric ,,bells ,,and ,,other ,,signalling ,,appliances4 ,s #da4 ,an electric bell is an arrangement of a cylindrical soft iron core1 or cores1 surrounded by coils of insulated copper wire4 ,on causing a current of electricity to flow round these coils1 the iron becomes1 for the time being1 powerfully magnetic 7see ,s #ac74 ,a piece of soft iron 7known as the armature71 supported by a spring1 faces the magnet thus produced4 ,this armature carries at its free extremity a rod with a bob1 clapper or hammer1 which strikes a bell1 or gong1 when the armature1 under the influence of the pull of the magnet1 is drawn towards it4 ,in connection with the armature and clapper is a device whereby the flow of the current can be rapidly interrupted1 so that on the cessation of the current the iron may lose its magnetism1 and allow the spring to withdraw the clapper from against the bell4 ,this device is known as the contact breaker and varies somewhat in design1 according to whether the bell belongs to the trembling1 the single stroke1 or the continuous ringing class4 ,s #db4 ,in order that the electric bell-fitter may have an intelligent conception of his work1 he should make a small electric bell himself4 ,by so doing1 he will gain more practical knowledge of what are the requisites of a good bell1 and where defects may be expected in any he may be called upon to purchase or examine1 than he can obtain from pages of written description4 ,for this reason ,i reproduce here 7with some trifling additions and modifications7 ,mr4 ,g4 ,edwinson's directions for making an electric bell3--#aj ,how to make a bell4--,the old method of doing this was to take a piece of round iron1 bend it into the form of a horse-shoe1 anneal it 7by leaving it for several hours in a bright fire1 and allowing it to cool gradually as the fire goes out71 wind on the wire1 and fix it as a magnet on a stout board of beech or mahogany2 a bell was then screwed to another part of the board1 a piece of brass holding the hammer and spring being fastened to another part4 ,many bells made upon this plan are still offered for sale and exchange1 but their performance is always liable to variation and obstruction1 from the following causes3--,to insure a steady1 uniform vibratory stroke on the bell1 its hammer must be nicely adjusted to move within a strictly defined and limited space2 the least fractional departure from this adjustment results in an unsatisfactory performance of the hammer1 and often a total failure of the magnet to move it4 ,in bells constructed on the old plan1 the wooden base is liable to expansion and contraction1 varying with the change of weather and the humidity1 temperature1 etc41 of the room in which the bells are placed4 ,thus a damp1 foggy night may cause the wood to swell and place the hammer out of range of the bell1 while a dry1 hot day may alter the adjustment in the opposite direction4 ,such failures as these1 from the above causes alone1 have often brought electric bells into disrepute4 ,best made bells are1 therefore1 now made with metallic 7practically inexpansible7 bases1 and it is this kind ,i recommend to my readers4 ,footnote #aj3 ,amateur ,work4 ,illustration3 ,fig4 #ag4 ,illustration3 ,fig4 #ah4 ,the ,base1 to which all the other parts are fastened1 is made of #c_/d in4 mahogany or teak1 #f in4 by #d in41 shaped as shown at ,fig4 #ag1 with a smooth surface and ,french polished4 ,to this is attached the metallic base-plate1 which may be cut out of sheet-iron1 or sheet-brass 7this latter is better1 as iron disturbs the action of the magnet somewhat71 and shaped as shown in ,fig4 #ah2 or it may be made of cast-iron1 or cast in brass2 or a substitute for it may be made in wrought-iron1 or brass1 as shown in ,fig4 #ai4 ,i present these various forms to suit the varied handicrafts of my readers2 for instance1 a worker in sheet metal may find it more convenient to manufacture his bell out of the parts sketched in ,figs4 #ag1 #ah1 #bj;,a1 #ba1 #bc1 #bd;,a1 and #be2 but1 on the other hand1 a smith or engineer might prefer the improved form shown at ,fig4 #ca1 and select the parts shown at ,figs4 #bj;,a1 #bb1 #ai1 choosing either to forge the horse-shoe magnet1 ,fig4 #bj1 or to turn up the two cores1 as shown at ,fig4 #ba 7,a71 to screw into the metal base1 ,fig4 #ba ,b1 or to be fastened by nuts1 as shown at ,fig4 #ai4 ,the result will be the same in the end1 if good workmanship is employed1 and the proper care taken in fixing and adjusting the parts4 ,a tin-plate worker may even cut his base-plate out of stout block tin1 and get as good results as if the bell were made by an engineer4 ,in some makes1 the base-plate is cut or stamped out of thick sheet-iron1 in the form shown by the dotted lines on ,fig4 #ah1 and when thus made1 the part ,a is turned up at right angles to form a bracket for the magnet cores1 the opposite projection is cut off1 and a turned brass pillar is inserted at ,b to hold the contact screw1 or contact breaker 7,s #da74 ,illustration3 ,fig4 #ai4 ,illustration3 ,fig4 #bj4 ,illustration3 ,fig4 #bj ,a4 ,the ,magnet may be formed as shown at ,fig4 #bj1 or at ,fig4 #bj;,a4 ,its essential parts are3 #ast4 ,two soft iron cores 7in some forms a single core is now employed72 #bnd4 ,an iron base1 or yoke1 to hold the cores together2 #crd4 ,two bobbins wound with wire4 ,the old form of magnet is shown at ,fig4 #bj4 ,in this form the cores and yoke are made out of one piece of metal4 ,a length of round ,swedish iron is bent round in the shape of a horseshoe2 this is rendered thoroughly soft by annealing1 as explained further on4 ,it is absolutely essential that the iron be very soft and well annealed1 otherwise the iron cores retain a considerable amount of magnetism when the current is not passing1 which makes the bell sluggish in action1 and necessitates a higher battery power to make it work 7see ,s #ad74 ,two bobbins of insulated wire are fitted on the cores1 and the magnet is held in its place by a transverse strip of brass or iron secured by a wood screw passing between the two bobbins4 ,the size of the iron1 the wire1 the bobbins1 and the method of winding is the same as in the form next described1 the only difference being that the length of the iron core1 before bending to the horse-shoe form1 must be such as to allow of the two straight portions of the legs to be #b in4 in length1 and stand #a-c_/h apart when bent4 ,we may now consider the construction of a magnet of the form shown at ,fig4 #bj;,a4 ,to make the cores of such a magnet1 to ring a #b-a_/b in4 bell1 get two #b inch lengths of #e_/af in4 best ,swedish round iron1 straighten them1 smooth them in a lathe1 and reduce #a_/d in4 of one end of each to #d_/af of an in41 leaving a sharp shoulder1 as shown at ,fig4 #ba ,a4 ,next1 get a #b-;in4 length of angle iron1 drill in it two holes #a-c_/h apart1 of the exact diameter of the turned ends of the cores1 and rivet these securely in their places2 this may be done by fastening the cores or legs in a vice whilst they are being rivetted4 ,two holes should be also bored in the other flange to receive the two screws1 which are to hold the magnet to the base1 as shown at ,fig4 #ba ,b4 ,the magnet is now quite equal to the horse-shoe form1 and must be made quite soft by annealing4 ,this is done by heating it in a clear coal fire to a bright red heat1 then burying it in hot ashes1 and allowing it to cool gradually for a period of from #ab to #bd hours2 or perhaps a better guide to the process will be to say1 bury the iron in the hot ashes and leave it there until both it and they are quite cold4 ,the iron must be brought to a bright cherry red heat before allowing it to cool1 to soften it properly1 and on no account must the cooling be hurried1 or the metal will be hard4 ,iron is rendered hard by hammering1 by being rapidly cooled1 either in cold air or water1 and hard iron retains magnetism for a longer time than soft iron4 ,as we wish to have a magnet that will only act as such when a current of electricity is passing around it1 and shall return to the state of a simple piece of unmagnetised iron when the current is broken1 we take the precaution of having it of soft iron4 ,many bells have failed to act properly1 because this precaution has been neglected1 the residual 7or remaining7 magnetism holding down the armature after contact has been broken4 ,when the magnet has been annealed1 its legs should be polished with a piece of emery cloth1 and the ends filed up level and smooth4 ,if it is intended to fasten the cores into the base-plate1 this also should be annealed1 unless it be made of brass1 in which case a thin strip of soft iron should connect the back ends of the two legs before they are attached to the brass base 7an iron yoke is preferable1 as it certainly is conducive to better effects to have a massive iron yoke1 than to have a mere strip as the connecting piece74 ,it will also be readily understood and conceded that the cores should be cut longer when they are to be fastened by nuts1 to allow a sufficient length for screwing the ends to receive the nuts4 ,the length and size of the legs given above are suitable for a #b-a_/b in4 bell only2 for larger bells the size increases #a_/af of an inch1 and the length #a_/d of an inch1 for every #a_/b in4 increase in the diameter of the bell4 ,illustration3 ,fig4 #ba4 ,the ,bobbins1 on which the wire that serves to carry the magnetising current is to be wound1 next demand our attention4 ,they may be turned out of boxwood1 ebony1 or ebonite1 or out of any hard wood strong enough and dense enough to allow of being turned down thin in the body1 a very necessary requirement to bring the convolutions of wire as near the coil as possible without touching it4 ,some amateurs use the turned ends of cotton reels or spools1 and glue them on to a tube of paper formed on the cores themselves4 ,if this tube be afterwards well covered with melted paraffin wax1 the plan answers admirably1 but of course the bobbins become fixtures on the magnets4 ,there are some persons who are clever enough to make firm bobbins out of brown paper 7like rocket cases71 with reel ends1 that can be slipped off and on the magnet cores4 ,to these ,i would say1 by all means at your command1 do so if you can4 ,the size of the bobbins for a #b-a_/b in4 bell should be3 length #a-c_/d in41 diameter of heads #c_/d of an in41 the length increasing #a_/d of an in4 and the diameter #a_/h of an in4 for every additional #a_/b in4 in the diameter of the bell4 ,the holes throughout the bobbins should be of a size to fit the iron cores exactly1 and the cores should project #a_/h of an inch above the end of the bobbins when these are fitted on4 ,the wire to be wound on the bobbins is sold by all dealers in electrical apparatus4 ,it is copper wire1 covered with cotton or with silk1 to ensure insulation4 ,mention has already been made of what is meant by insulation at ,s #c1 but1 in order to refresh the reader's memory1 ,mr4 ,g4 ,edwinson's words are quoted here4 ,to insulate1 as understood by electricians1 means to protect from leakage of the electric current1 by interposing a bad conductor of electricity between two good conductors1 thus insulating#aa or detaching them from electric contact4 ,footnote #aa3 ,insula in ,latin means an island1 hence an electrified body is said to be insulated when surrounded by non-conductors1 as an island by the sea4 ,the following list will enable my readers to see at a glance the value of the substances mentioned here as conductors or insulators1 the best conductors being arranged from the top downwards1 and the bad conductors or insulators opposed to them in similar order1 viz41 the worst conductors or best insulators being at the top3-- ,conductors4 ,insulators4 ,silver4 ,paraffin ,wax4 ,copper4 ,guttapercha4 ,iron4 ,indiarubber4 ,brass4 ,shellac4 ,all ,other ,metals4 ,varnishes4 ,metallic ,solutions4 ,sealing ,wax4 ,metallic ,salts4 ,silk and ,cotton4 ,wet ,stone4 ,dry ,clothing4 ,wet ,wood4 ,dry ,wood4 ,oil1 ,dirt and ,rust4 ,see also the more extended list given at ,s #e for a more complete and exact classification4 ,it will be seen1 on reference to the above1 that copper is a good conductor1 being excelled by silver alone in this respect2 and that silk and cotton are bad conductors4 ,when1 therefore1 a copper wire is bound round with silk or with cotton1 even if two or more strands of such a covered wire be superimposed1 since these are electrically separated by the non-conducting covering1 no escape of electricity from one strand to the other can take place1 and the strands are said to be insulated4 ,if the copper wire had been coiled naked round a bobbin1 each convolution touching its neighbour1 the current would not have circled round the whole length of the coils of wire1 but would have leapt across from one coil to the other1 and thus the desired effect would not have been obtained4 ,a similar result1 differing only in degree1 would occur if a badly insulating wire were used1 say one in which the covering had been worn in places1 or had been badly wound1 so as to expose patches of bare copper wire4 ,if the insulation of a wire be suspected1 it should be immersed in hot melted paraffin wax1 and then hung up to drain and cool4 ,the size of wire to be used on a #b-a_/b in4 bell should be ,no4 #bd ,b4 ,w4 ,g41 the size falling two numbers for each #a_/b in4 increase in the diameter of the bell4 ,in these wires the higher the number1 the finer the size1 ,no4 #f being #a_/e and ,no4 #dj being #a_/bjj of an inch in diameter4 ,silk-covered wire has an advantage over cotton-covered wire1 inasmuch as the insulating material occupies less space1 hence the convolutions of wire lie closer together4 ,this is important1 as the current has less effect on the iron if removed further from it1 the decrease being as the square of the distance that the current is removed from the wire4 ,magnets coiled with silk-covered wire admit also of better finish1 but for most purposes cotton-covered wire will give satisfaction1 especially if well paraffined4 ,this wire must be wound on the bobbins1 from end to end regularly1 with the coils side by side1 as a reel of cotton is wound4 ,this may be done on a lathe1 but a little practice will be necessary before the inexperienced hand can guide the wire in a regular manner4 ,if1 however1 the spool of wire have a metal rod passed up its centre1 and this be held in the hand at a distance of a foot or more from the bobbin on the lathe1 the wire will almost guide itself on1 providing the guiding hand be allowed to follow its course4 ,with a little care1 the wire for these little magnets may be wound entirely by hand4 ,before commencing to wind on the bobbins1 just measure off #h in4 of the wire 7not cutting it off7 and coil this length around a pencil1 to form a small coil or helix4 ,the pencil may then be withdrawn from the helix thus formed1 which serves to connect the wire with one of the points of contact4 ,this free end is to be fastened outside the bobbin by a nick in the head2 or the #a_/h in4 length1 before being formed into a helix1 may be pushed through a small hole made on the head of the bobbin1 so that #h in4 project outside the bobbin1 which projecting piece may be coiled into a helix as above described4 ,the wire should now be wound exactly as a reel of cotton is wound1 in close coils from end to end1 and then back again1 until three layers of wire have been laid on1 so that the coiling finishes at the opposite end to that at which it began4 ,to prevent this uncoiling1 it should be fastened by tying down tightly with a turn or two of strong silk4 ,the wire should now be cut from the hank1 leaving about #b in4 of free wire projecting at the finishing end of each bobbin4 ,in cases where many bobbins have to be wound1 either for bells1 for relays1 or for indicator coils1 a device similar to that illustrated at ,fig4 #ba ,a may be employed4 ,this electric bobbin winder consists in a table which can be stood on a lathe or near any other driving wheel4 ,two carriers1 ,c ,c1 somewhat similar to the back centre and poppet head of a lathe1 hollow inside1 and furnished with a spring and sliding piston spindle1 stand one at each end of this table4 ,the sliding spindle of the one carries at its extremity a pulley1 ,a1 by means of which motion can be transmitted from the band of the driving wheel4 ,the sliding spindles1 ,b ,b1 are fitted with recesses and screws1 ,h ,h ,h ,h1 by means of which the temporary wooden cores1 or the permanent iron cores1 of the bobbins can be held while the bobbins are being wound4 ,the bobbin is placed as shown at ,d2 a flat piece of metal1 ,e1 hinged at ,g1 presses against the bobbin1 owing to the spring ,f4 ,the centre figure shows details of the carrier1 ,c1 in section4 ,at the bottom is shown the spool of wire on a standard ,l4 ,the wire passes from this spot between the two indiarubber rollers1 ,m ,m1 on to the bobbin ,d4 ,illustration3 ,fig4 #ba ,a4 ,when the bobbins have been wound1 they may be slipped over the magnet cores4 ,they should fit pretty tightly2 if they do not1 a roll of paper may be put round the magnet cores1 to ensure their not slipping when the bell is at work4 ,the helix ends of the bobbins should stand uppermost1 as shown at ,fig4 #bb ,a4 ,a short length of the lower free ends of wire 7near the base or yoke7 should now be bared of their covering1 cleaned with emery paper1 twisted together tightly1 as shown at ,fig4 #bb ,b1 soldered together1 and any excess of wire cut off with a sharp pair of pliers4 ,to prevent any chance electrical leakage between this bared portion of the wire and the iron1 it should be carefully coated with a little melted guttapercha1 or ,prout's electric glue4 ,illustration3 ,fig4 #bb4 ,of course1 if the operator has any skill at winding1 he may wind both bobbins with one continuous length of wire1 thus avoiding joins1 taking care that the direction of the winding in the finished coils be as shown at ,fig4 #bb ,b2 that is to say1 that the wire from the under side of one bobbin1 should pass over to the next in the same way as the curls of the letter rotated ,s4 ,illustration3 ,fig4 #bc4 ,illustration3 ,fig4 #bd4 ,illustration3 ,fig4 #be4 ,illustration3 ,fig4 #bf4 ,illustration3 ,fig4 #bg4 ,the part that next claims our consideration is the armature1 with its fittings4 ,the armature is made out of #e_/af square bar iron1 of the best quality1 soft1 and well annealed1 and filed up smooth and true4 ,the proportionate length is shown at ,figs4 #bc and #bd2 and the size of the iron for other bells is regulated in the same ratio as that of the cores4 ,two methods of making and attaching the springs and hammers are shown4 ,fig4 #bd shows the section of an armature fitted with back spring and contact spring in one piece4 ,this is cut out of hard sheet-brass1 as wide as the armature1 filed or hammered down to the desired degree of springiness1 then filed up true on the edges4 ,it may be attached to the iron of the armature1 either by soldering1 by rivetting1 or by means of two small screws4 ,rivetting is1 perhaps1 the best mode1 as it is not liable to shake loose by the vibration of the hammer4 ,the spring at its shank end may be screwed or rivetted to the bracket4 ,mr4 ,edwinson considers this the better form of contact spring4 ,the other form is made in two pieces1 as shown at ,fig4 #bc1 where two strips of hard brass are cut off1 of the width of the armature1 and the edges filed4 ,a slot is then cut in the back end of the armature to receive the two brass strips1 and these are soldered into it4 ,the top strip is then bent back over the armature to form the contact-spring1 the other strip being soldered or rivetted to a small bracket of angle brass4 ,in either case a short rod of stout hard brass wire is rivetted or screwed into the free end of the armature1 and to the end of this rod is screwed or soldered the metal bead1 or bob1 which forms the hammer or clapper of the bell4 ,the next portion to be made is the contact pillar1 or bracket1 with its screw1 as shown at ,fig4 #be4 ,this may either be a short stout pillar of #a_/d in4 brass rod1 about #a in4 high1 tapped on one side to receive the screw1 which should be fitted with a back nut2 or it may1 as shown in the figure1 be made out of a stout piece of angle brass4 ,the exact size and length of the screw is immaterial2 it must1 however1 be long enough to reach 7when put in its place behind the contact spring7 the spring itself1 and still have a few threads behind the back nut to spare4 ,the screw should be nicely fitted to the pillar1 and the lock nut should clench it well1 as when once the adjustment of the parts is found which gives good ringing1 it is advisable that no motion should take place1 lest the perfection of ringing be interfered with4 ,some makers use a set screw at the side of the pillar wherewith to hold the contact screw2 others split the pillar and spring it against the contact screw2 but1 all things considered1 the back nut gives the greatest satisfaction4 ,when the bell is in action1 a tiny spark is produced at every make and break of contact between the contact spring and this screw4 ,this spark soon corrodes the end of the screw and the back of the spring if brass alone is used1 as this latter rusts under the influence of the spark4 ,to prevent this1 a piece of platinum must be soldered or rivetted to the spring1 at the point where the screw touches1 as shown at ,fig4 #bf1 and also at the extremity of the contact screw itself4 ,it is better to rivet the platinum than to solder it1 as the platinum is very apt to absorb the solder1 in which case it rusts quickly1 and the goodness of the contact is soon spoiled1 when the bell ceases to ring4 ,to rivet the platinum piece on to the spring1 as shown at ,fig4 #bf1 it is only needful to procure a short length of ,no4 #af platinum wire1 say #a_/h in41 then1 having drilled a corresponding hole at the desired spot in the contact spring1 put the platinum wire half way through the hole1 and give it one or two sharp blows on an anvil1 with a smooth 7pened7 hammer4 ,illustration3 ,fig4 #bh4 ,illustration3 ,fig4 #bi4 ,this will at once rivet it in its place1 and spread it sufficiently to make a good surface for contact4 ,the screw must likewise be tipped with platinum1 by having a small hole bored in the centre of its extremity1 of the same diameter as the platinum wire1 which must then be pushed in1 and rivetted by hammering the end1 and burring the sides of the screw4 ,whichever method be adopted1 care must be taken that the platinum tip on the screw and the speck on the contact spring are adjusted so as to touch exactly in their centres4 ,it will be hardly worth while for the amateur to cast or even turn up his own bells 7which are generally of the class known as clock gongs71 as these can now be procured so cheaply already nickelled 7see ,fig4 #bh74 ,the bell must be adjusted on its pillar 7see ,fig4 #bi;,a71 which is itself screwed into a hole in the base-plate1 where it is held by a nut4 ,the adjustment of the bell is effected by placing it over the shoulder of the pillar1 and then clenching it down by screwing over it one or other of the nuts shown at ,fig4 #bi4 ,the bell should clear the base1 and should be at such a height as to be struck on its edge by the hammer or clapper attached to the armature1 ,figs4 #bc and #bd4 ,we still need1 to complete our bell1 two binding screws1 which may take either of the forms shown at ,fig4 #bg2 and an insulating washer1 or collar1 made of ebonite or boxwood1 soaked in melted paraffin1 to prevent the contact pillar 7,fig4 #be7 making electrical contact with the metal base4 ,the best shape to be given to these washers is shown at ,fig4 #cj4 ,they consist in two thin circlets of wood or ebonite1 that will just not meet when dropped1 one on the one side1 and one on the other of the hole through which the shank of the contact pillar passes when set up on the base-plate4 ,if a wooden base be used below the metal base-plate1 then only one washer1 or collar1 need be used--that is1 the one above--since the screw of the pillar will pass into the wood1 and this is not a conductor4 ,if the metal base alone be used1 both washers must be employed1 and a small nut 7not so large as the washer7 used to tighten up and hold the pillar firm and immovable in its place opposite the contact spring4 ,illustration3 ,fig4 #cj4 ,having now all the parts at hand1 we can proceed to fit them together1 which is done as follows3--,the bell pillar1 with its bell attached1 is fastened by its shank into the hole shown near ,b1 ,fig4 #ag1 where it is screwed up tight by the square nut shown at ,fig4 #bi c4 ,in the same manner1 we must fasten the contact pillar1 or bracket1 shown at ,fig4 #bd ,a4 ,whichever form be used1 we must take great care that it be insulated from metallic contact with the metal base-plate by washers1 as shown at ,fig4 #cj 7similar washers must be used for the two binding screws if the whole base-plate be made in metal74 ,this being done1 the metal frame1 ,fig4 #ah1 is put in position on the wooden base1 as shown at ,fig4 #ag1 and screwed down thereto by the screws indicated at s s s4 ,the magnet may then be screwed down to the metal frame as shown4 ,the small bracket of angle brass marked ,b1 in ,figs4 #bc and #bd1 is next screwed into its place2 that is1 in such a position that the armature stands squarely facing the poles of the electro-magnet1 but not quite touching them 7say #a_/af of an inch for a #b-a_/b in4 bell74 ,in setting up this and the contact pillar1 the greatest care must be taken that the platinum tip of the contact screw1 ,fig4 #be1 should touch lightly the centre of the platinum speck at the back of the spring1 ,figs4 #bc and #bd1 shown full size at ,fig4 #bf4 ,the free ends of the helically coiled electro-magnet wires should now be inserted into short lengths of small indiarubber tubing 7same as used for feeding bottles71 the extremities being drawn through and #a in4 of the copper wire bared of its covering for the purpose of making good metallic contact with the connections4 ,one of these ends is to be soldered1 or otherwise metallically connected1 to the angle brass carrying the armature1 spring and clapper1 the other being similarly connected with the left-hand binding-screw1 shown at ,fig4 #ag4 ,another short length of wire 7also enclosed in rubber tubing7 must be arranged to connect the contact screw pillar ,fig4 #ag1 with the right-hand binding-screw4 ,when this has been done1 we may proceed to test the working of the bell by connecting up the binding screws with the wires proceeding from a freshly-charged ,leclanch'e cell4 ,if all have been properly done1 and the connections duly made1 the armature should begin to vibrate at once1 causing the bob1 or hammer1 to strike the bell rapidly2 that is1 provided the platinum tipped screw touches the platinum speck on the contact spring4 ,should this not be the case1 the screw must be turned until the platinum tip touches the platinum speck4 ,the armature will now begin to vibrate4 ,it may be that the clapper runs too near the bell1 so that it gives a harsh1 thuddy buzz instead of a clear1 ringing sound2 or1 possibly1 the clapper is set too far from the bell to strike it4 ,in either case a little bending of the brass wire carrying the clapper 7either from or towards the bell1 as the case may dictate7 will remedy the defect4 ,it is also possible that the armature itself may have been set too near1 or too far from the electro-magnet4 ,in the latter case1 the clapper will not vibrate strongly enough1 in the former the vibration will be too short1 and the clapper may even stick to the poles of the electros1 especially if these have not been carefully annealed4 ,a little bending of the spring1 to or from the magnets1 will remedy these deficiencies1 unless the distance be very much too great1 in which case the bending of the spring would take the platinum tip out of the centre of the platinum speck4 ,illustration3 ,fig4 #ca4 ,s #dc4 ,having thus constructed an efficient electric bell we may proceed to study its action and notice some of the defects to which it may be subject4 ,in the first place1 if we connect up the bell with the battery as shown in ,fig4 #ag1 viz41 the left-hand binding-screw with the wire proceeding from the carbon of the ,leclanch'e1 and the right-hand screw with the wire from the zinc1 then1 if the platinum tipped screw touches the platinum speck1 at the back of the contact spring1 a current of electricity flows from the left-hand binding-screw all round the coils of the electro-magnets1 passes along the contact spring and platinum speck1 thence to the platinum tipped screw along the short length of wire to the right-hand binding-screw1 whence it returns to the zinc element of the battery1 thus completing the circuit4 ,the current1 in thus passing around the electro-magnet cores1 converts them1 pro tem41 into a powerful magnet 7see ,s #ac72 consequently1 the armature1 with its contact spring and hammer1 is pulled towards the electro-magnets and at the same time gives a blow to the bell4 ,now1 if instead of having the platinum speck attached to a flexible spring1 it had been attached bodily to the rigid iron armature1 directly the electro-magnets felt the influence of the current1 the platinum speck would have also been pulled out of contact with the platinum screw1 therefore the electro-magnet cores would have immediately lost their magnetism 7see ,s #ac1 last five lines74 ,this would have been disadvantageous1 for two reasons3 #ast1 because the stroke of the hammer would have been very short1 and consequently the ring of the bell very weak2 and1 #bnd1 because1 as even the softest iron requires some appreciable time for the electric current to flow round it to magnetise it to its full capacity1 it would need a much greater battery power to produce a given stroke1 if the contact were so very short4 ,the use of an elastic contact spring is1 therefore1 just to lengthen the time of contact4 ,but the electro-magnets1 even when the flexible spring is used1 do actually pull the platinum speck out of contact with the platinum screw4 ,when this takes place1 the circuit is broken1 and no more current can flow round the electro-magnets1 the spring reasserts its power1 and the contact is again made between the contact screw and contact spring1 to be again rapidly broken1 each break and make contact being accompanied by a correspondingly rapid vibration of the armature1 with its attendant clapper1 which thus sets up that characteristic rapid ringing which has earned for these bells the name of trembling1 chattering1 or vibrating bells4 ,s #dd4 ,from a careful consideration of the last two sections it will be evident that the possible defects of electric bells may be classed under four heads3 viz41 #ast1 ,bad contacts2 #bnd1 ,bad adjustment of the parts2 #crd1 ,defective insulation2 #dth1 ,warpage or shrinkage of base4 ,we will consider these in the above order4 ,firstly1 then1 as to bad contacts4 ,many operators are content with simply turning the terminal wires round the base of the binding-screws4 ,unless the binding-screws are firmly held down on to the wires by means of a back nut1 a great loss is sure to occur at these points1 as the wires may have been put on with sweaty hands1 when a film of oxide soon forms1 which greatly lowers the conductivity of the junction4 ,again1 at the junction points of the wires with the contact angle brass and contact pillar1 some workmen solder the junctions1 using killed spirits as a flux4 ,a soldered contact is certainly the best1 electrically speaking1 but killed spirits1 or chloride of zinc1 should never be used as a flux in any apparatus or at any point that cannot be washed in abundance of water1 as chloride of zinc is very deliquescent 7runs to water71 rottens the wire1 and spoils the insulation of the adjacent parts4 ,if solder be used at any parts1 let resin be used as a flux4 ,even if any excess of resin remain on the work1 it does no harm and does not destroy the insulation of any of the other portions4 ,another point where bad contact may arise is at the platinum contacts4 ,platinum is a metal which does not rust easily1 even under the influence of the electric spark given at the point of contact4 ,therefore1 it is preferred to every other metal 7except1 perhaps1 iridium7 for contact breakers4 ,platinum is an expensive metal1 the retail price being about #cjs4 an ounce1 and as it is nearly twice as heavy as lead 7,lead #aa4 ,platinum #ba4e7 very little goes to an ounce4 ,for cheap bells1 therefore1 there is a great temptation to use some other white metal1 such as silver1 german silver1 platinoid1 etc4 ,the tip of the platinum screw may be tested for its being veritably platinum in the following mode3 ,touch the tip with the stopper of a bottle containing aquafortis1 so as to leave a tiny drop on the extreme point of the suspected platinum4 ,if it boils up green1 or turns black1 it is not platinum2 if it remains unaltered1 it may be silver or platinum4 ,after it has stood on the tip for a minute1 draw it along a piece of white paper1 so as to produce a streak of the acid4 ,expose the paper for a few minutes to sunlight4 ,if the streak turns violet or pinky violet1 the metal is silver2 if the paper simply shows a slightly yellowish streak1 the metal is platinum4 ,the tip of the platinum screw must be carefully dried and cleaned after this trial before being replaced4 ,secondly1 as to bad adjustment4 ,it is evident that the magnets and the armature must stand at a certain distance apart to give the best effects with a given battery power4 ,the distance varies from #a_/bd in4 in the very smallest1 to #a_/h in4 in large bells4 ,sometimes 7but only in very badly made instruments7 the armature adheres to the poles of the electro-magnet4 ,this is due to residual magnetism 7see ,s #ad71 and points to hard or unannealed iron in the cores or armature4 ,as a make-shift1 this defect may be partially remedied by pasting a thin piece of paper over that surface of the armature which faces the poles of the electro-magnets4 ,another bad adjustment is when the platinum screw does not touch fairly on the centre of the platinum speck1 but touches the spring or the solder4 ,rust is then sure to form1 which destroys the goodness of the contact4 ,to adjust the contact spring at the right distance from the platinum screw1 hold the hammer against the bell or gong4 ,the armature should now just not touch the poles of the electro-magnet4 ,now screw up the platinum screw until it clears the contact spring by about the thickness of a sheet of brown paper 7say #a_/ej of an inch74 ,let the hammer go1 and notice whether the contact spring makes good contact with the platinum screw4 ,this may be tried by the ,leclanch'e cell as well1 so as to make sure of the character of the ringing4 ,when this has been satisfactorily adjusted the back-nut or set screw may be tightened1 to insure that the vibration of the hammer shall not alter the adjustment4 ,it sometimes happens that the spring that bears the armature is itself either too strong 7or set back too far7 or too weak4 ,in the former case1 the electro-magnet cannot pull the armature with sufficient force to give a good blow2 in the latter1 the spring cannot return the armature1 with its attendant contact spring1 back to its place against the platinum screw4 ,to ascertain which of these two defects obtains1 it is only necessary1 while the bell is in action1 to press the spring lightly with a bit of wire1 first towards and then away from the electro-magnets4 ,if the ringing is improved in the first case1 the spring is too strong2 if improvement takes place in the latter case1 the spring is too weak4 ,the third source of inefficient action1 defective insulation1 is not likely to occur in a newly-made bell1 except by gross carelessness4 ,still1 it may be well to point out where electrical leakage is likely to occur1 and how its presence may be ascertained1 localized1 and remedied4 ,if the wire used to wind the electro-magnet be old1 badly covered1 or bared in several places in winding1 it probably will allow the current to short circuit1 instead of traversing the whole length of the coils4 ,if this be the case1 the magnet will be very weak3 the magnet of a #b-a_/b-;in4 bell should be able to sustain easily a #a lb4 weight attached by a piece of string to a smooth piece of #a_/b-;in4 square iron placed across its poles1 when energized by a single pint ,leclanch'e cell4 ,if it will not do this1 the insulation may be suspected4 ,if the wire has been wound on the bare cores 7without bobbins71 as is sometimes done1 bared places in the wire may be touching the iron4 ,this may be ascertained by connecting one pole of a bottle bichromate1 or other powerful battery1 with one of the wires of the electro-magnet coils1 and drawing the other pole of the battery across the clean iron faces of the electro-magnet poles4 ,if there is any leakage1 sparks will appear on making and breaking contact4 ,nothing but unwinding and rewinding with a well covered wire can remedy these defects4 ,the other points where the insulation may be defective are between the binding screws and the base1 if this be all of metal2 or between the contact spring block and the base1 and the contact pillar4 ,it is also probable 7if the connecting wires have not been covered with indiarubber tubing1 as recommended7 that leakage may be taking place between these wires and some portion of the metal work of the base or frame4 ,this must be carefully examined1 and if any point of contact be observed1 a little piece of ,prout's elastic glue1 previously heated1 must be inserted at the suspected places4 ,with regard to the binding screws1 if they stand on the wooden base1 their insulation 7unless the base be very damp indeed7 will be sufficiently good2 but if the base is entirely metallic1 then ebonite or boxwood washers must be used to insulate them from contact with the base-plate4 ,with regard to the contact spring block and the platinum screw pillar1 it is permissible that one or the other should not be insulated from the base or frame2 but one or the other must be insulated by means of ebonite or other insulating washers4 ,personally1 ,i prefer to insulate both2 but in many really good bells only the platinum screw pillar is thus insulated4 ,any such leakage can be immediately detected by holding one pole of a powerful battery against the suspected binding-screw1 or block1 or pillar1 and while in this position1 drawing the other pole across some bare iron portion of the frame or metal base4 ,sparks will appear if there is any leakage4 ,the fourth defect--that is1 warpage or shrinkage of the base--can only occur in badly-made bells1 in which the entire base is of wood4 ,a cursory examination will show whether the board is warped or swollen1 or whether it has shrunk4 ,warping or swelling will throw the electro-magnet too far from the armature1 or set the pillar out of place2 shrinkage1 on the contrary1 will bring the parts too close together and jamb the magnets1 the armature1 and the contact pillar into an unworkable position4 ,s #de4 ,before quitting the subject of the defects of bells1 it may not be out of place to mention that no bell that is set to do real work should be fitted up without a cover or case4 ,the dust which is sure to accumulate1 not to speak of damp and fumes1 etc41 will certainly militate against good contacts and good action if this important point be neglected4 ,the cover or case generally takes the form of a shallow box1 as shown at ,fig4 #cb1 and may be made from #a_/d-;in4 teak1 mahogany1 or walnut1 dovetailed together and well polished4 ,it is fastened to the base in the same manner as the sides of a ,dutch clock1 by means of studs1 hooks and eyes4 ,at the bottom of the box is cut a slot1 of sufficient width and length to admit the play of the hammer shank4 ,illustration3 ,fig4 #cb4 ,in the annexed table is given a general idea of the proportion which should be observed in the construction of bells of different sizes4 ,it must be noted that if the bells are to be used at long distances from the battery1 rather more of a finer gauge of wire must be employed to wind the magnets than that herein recommended1 unless1 indeed1 relays be used in conjunction with the bells4 ,s #df4-- ,,table ,showing proportions to be observed in the different parts of electric bells4 ---------------------------------------- --------------- ,diameter ,length of,diameter ,length ,diameter ,b4 ,w4 ,g4 of ,magnet of ,magnet of of ,bobbin of ,wire ,bell4 ,cores4 ,cores4 ,bobbin4 ,head4 on ,bobbin4 ---------------------------------------- --------------- #b-a_/b #b #e_/af #a-c_/d #c_/d #bd #c #b-a_/d #c_/h #b #g_/h #bd #c-a_/b #b-a_/b #g_/af #b-a_/d #a #bb #d #b-c_/d #a_/b #b-a_/b #a-a_/h #bb #d-a_/b #c #i_/af #b-c_/d #a-a_/d #bj #e #c-a_/d #e_/h #c #a-c_/h #ah #e-a_/b #c-a_/b #aa_/af #c-a_/d #a-a_/b #af #f #c-c_/d #c_/d #c-a_/b #a-e_/h #af #f-a_/b #d #ac_/af #c-c_/d #a-c_/d #af #g #d-a_/d #g_/h #d #a-g_/h #af #g-a_/b #d-a_/b #ae_/af #d-a_/d #b #ad #h #d-c_/d #a #d-a_/b #b-a_/h #ad #h-a_/b #e #a-a_/af #d-c_/d #b-a_/d #ad #i #e-a_/d #a-a_/h #e #b-c_/h #ad #i-a_/b #e-a_/b #a-c_/af #e-a_/d #b-a_/b #ad #aj #e-c_/d #a-a_/d #e-a_/b #b-e_/h #ad #aj-a_/b #f #a-e_/af #e-c_/d #b-c_/d #ab #aa #f-a_/d #a-c_/h #f #b-g_/h #ab #aa-a_/b #f-a_/b #a-g_/af #f-a_/d #c #aj #ab #f-c_/d #a-a_/b #f-a_/b #c-a_/h #aj ---------------------------------------- --------------- ,illustration3 ,fig4 #cc ,a4 ,illustration3 ,fig4 #cc ,b4 ,illustration3 ,fig4 #cd4 ,s #dg4 ,we can now glance at several modifications in the shape and mode of action of electric bells and their congeners4 ,taking ,figs4 #cc ,a and ,b as our typical forms of trembling bell1 the first notable modification is one by means of which the bell is made to give a single stroke only1 for each contact with the battery4 ,this form1 which is known as the single stroke bell1 lends itself to those cases in which it may be required to transmit preconcerted signals2 as also where it is desired to place many bells in one circuit4 ,fig4 #cd illustrates the construction of the single stroke bell4 ,it differs from the trembling bell in the mode in which the electro-magnet is connected up to the binding screws4 ,in the trembling bell1 ,fig4 #cc1 the circuit is completed through the platinum screw pillar1 to the binding screw marked ,z1 hence the circuit is rapidly made and broken as long as by any means contact is made with the battery1 and the binding screws ,l and ,z4 ,but in the single stroke bell1 ,fig4 #cd1 the wires from the electro-magnet are connected directly to the two binding screws ,l and ,z1 so that when contact is made with the battery1 the armature is drawn to the poles of the electro-magnet1 and kept there so long as the battery current passes4 ,by this means1 only one stroke or blow is given to the bell for each contact of the battery4 ,of course1 directly the connection with the battery is broken1 the spring which carries the armature and clapper flies back ready to be again attracted1 should connection again be made with the battery4 ,to regulate the distance of the armature from the poles of the electro-magnets1 a set screw ,q takes the place of the platinum screw in the ordinary form1 while to prevent the hammer remaining in contact with the bell 7which would produce a dull thud and stop the clear ring of the bell71 a stop 7g7 is set near the end of the armature1 or two studs are fixed on the tips of the poles of the electro-magnets4 ,the mode of adjusting this kind of bell1 so as to obtain the best effect1 differs a little from that employed in the case of the trembling bell4 ,the armature must be pressed towards the poles of the electro-magnets1 until it rests against the stop or studs4 ,a piece of wood or cork may be placed between the armature and the set screw ,q1 to retain the armature in this position1 while the rod carrying the hammer or clapper is being bent 7if required7 until the hammer just clears the bell4 ,if it touches the bell1 a thud instead of a ring is the result2 if it is set off too far1 the ring will be too weak4 ,the armature can now be released1 by removing the wood or cork1 and the set screw ,q driven forwards or backwards until the best effect is produced when tested with the battery4 ,the tension of the armature spring must be carefully looked to in these single stroke bells4 ,if it is too strong1 the blow will be weak2 if too weak1 the hammer trembles1 so that a clear single stroke is not obtainable1 as the spring chatters4 ,s #dh4 ,the continuous ringing bell is the modification which next demands our attention4 ,in this1 the ringing action1 when once started by the push1#ab or other contact maker1 having been touched1 continues either until the battery is exhausted1 or until it is stopped by the person in charge4 ,the great use of this arrangement is self-evident in cases of burglar alarms1 watchman's alarms1 etc41 as the continuous ringing gives notice that the call has not received attention4 ,the continuous ringing bell differs but little from the ordinary trembling bell4 ,the chief difference lies in the addition of an automatic device whereby contact is kept up with the battery1 even after the push contact has ceased4 ,as it is desirable for the person in charge to be able to stop the ringing at will1 without proceeding to the place where the push stands1 so it is not usual to make the continuous ringing arrangement dependent on the push1 though1 of course1 this could be done1 by causing it to engage in a catch1 which would keep up the contact1 when once made4 ,continuous ringing bells may be conveniently divided into two classes2 viz41 #ast1 those in which a device is attached to the framework of the bell2 which device1 when once upset by the first stroke of the bell1 places the bell in direct communication with the battery independent of the push or usual contact2 and #bndly1 those in which a separate device is used1 for the same purpose4 ,this latter arrangement admits of the use of an ordinary trembling bell4 ,footnote #ab3 ,a push1 of which several forms will hereafter be described and figured1 consists essentially in a spring carrying a stud1 standing directly over1 but not touching1 another stud1 fixed to a base4 ,the lower stud is connected to one terminal of battery1 the spring is connected to the bell4 ,when the spring is pressed down1 the two studs come into contact1 the current flows1 and the bell rings4 ,illustration3 ,fig4 #ce4 ,illustration3 ,fig4 #cf4 ,fig4 #ce illustrates the action of bells of the first class4 ,in the first place it will be noticed that there are three binding screws instead of two1 as in the ordinary pattern1 one marked ,c connected as usual with the carbon element of the battery2 another marked ,l1 which connects with line wire1 and a third1 ,z1 connected by means of a branch wire 7shunt wire71 proceeding from the zinc of the battery4 ,it will be seen1 that if the battery current is by means of the push caused to flow through the coils of the electro-magnets1 the armature is attracted as usual by them1 and in moving towards them1 releases and lets fall the lever contact1 which1 resting on the contact screw1 completes the circuit between ,z and ,c1 so that the bell is in direct communication with its battery1 independently of the push4 ,hence the bell continues ringing1 until the lever is replaced4 ,this can be done1 either by pulling a check string 7like a bell-pull7 attached to an eye in the lever1 or by means of a press-button and counter-spring2 as shown in ,fig4 #cf1 ,a and ,b4 ,illustration3 ,fig4 #cg4 ,illustration3 ,fig4 #ch4 ,illustration3 ,fig4 #ci4 ,in continuous ringing bells of the second class1 a detent similar to that shown at ,fig4 #ce ,d is used1 but this1 instead of being actuated by the electro-magnet belonging to the bell itself1 is controlled by a separate and entirely independent electro-magnet1 which1 as it may be wound with many coils of fine wire1 and have a specially light spring for the armature1 can be made very sensitive4 ,this second electro-magnet1 which serves only to make contact with a battery1 is known as a ,relay1 and is extensively employed in many cases where it is desired to put one or more batteries into1 or out of circuit1 from a distance4 ,the relay may be looked upon as an automatic hand1 which can be made to repeat at a distant point contacts made or broken by hand at a nearer one4 ,fig4 #cg shows this arrangement1 attached to the same base board as the bell itself4 ,on contact being made with the push1 the current enters at ,c1 circulates round the cores of the relay1 thus converting it into a magnet4 ,the armature a is thereby pulled to the magnet1 and in so doing releases the detent lever1 which falls on the contact screw1 thus at one and the same time breaking the circuit through the relay1 and making the circuit through the bell magnets ,b ,b'1 back to the battery by ,z4 ,a second modification of this mode of causing an ordinary bell to ring continuously is shown at ,fig4 #ch1 the peculiar form of relay used therewith being illustrated at ,fig4 #ci4 ,here1 the relay is placed on a separate base board of its own1 and could1 if necessary1 be thrown out of circuit altogether1 by means of a switch1#ac so that the bell can be used as an ordinary bell or continuous action at will4 ,it will be noticed that the relay has in this sketch only one core4 ,but the delicacy of the action is not impaired thereby1 as the armature1 by means of the steel spring s1 is made to form part and parcel of the magnet1 so that it becomes magnetised as well as the core1 and is attracted with more force than it would be1 if it were magnetically insulated4 ,the battery current enters by the wires ,c and ,w1 passes round the coils of the electro-magnet1 and returns by ,z4 ,in so doing it energises the electro-magnet ,e1 which immediately attracts its armature ,a4 ,the forward movement of the armature ,a1 releases the pivoted arm ,l1 to which is attached a platinum-tipped contact prong ,p4 ,this1 it will be noticed1 is in metallic connection with the pillar ,p'1 and with the base1 and1 therefore1 through the wire ,w1 with the battery4 ,when the arm ,l falls1 the contact prong completes the circuit to the bell1 through the insulated pillar ,x4 ,the relay is thus thrown out of the circuit at the same time that the bell is thrown in4 ,a device similar to those illustrated at ,fig4 #cf can be employed to reset the arm ,l4 ,footnote #ac3 ,described at ,s #fa4 ,illustration3 ,fig4 #dj4 ,a rather more complicated arrangement for continuous bell ringing is shown at ,fig4 #dj4 ,it is known as ,callow's1 and is peculiarly adapted to ringing several bells from one attachment1 etc4 ,owing to the relay in this form being wound with two sets of wires1 it takes a little more battery power2 but this disadvantage is compensated by its many good points4 ,the following description1 taken from ,f4 ,c4 ,allsop's papers in the ,english ,mechanic1 will render the working of ,callow's attachment perfectly clear4 ,when the button of the push ,p is pressed1 the current in the main circuit flows from the positive pole ,c of the battery ,d through the relay coil a1 and thence by the wire d and push ,p1 to the zinc of the battery4 ,this attracts the armature ,a of the relay ,r1 closing the local bell circuit1 the current flowing from ,c of the battery to armature ,a of the relay ,r1 through contact post p1 terminal ,l of the bell1 through bell to terminal ,z1 and thence by the wire g to the zinc of the battery4 ,part of the current also flows along the wire from the bell terminal ,l through the relay coil b and switch ,w1 to terminal ,z of the bell1 thus keeping the armature of the relay down1 after the main circuit 7through the push7 has been broken2 the bell continuing to ring until the shunt circuit is broken by moving the arm of the switch ,w over to the opposite 7or non-contact7 side4 ,the bell can also be stopped by short circuiting the relay1 which can be effected by an ordinary push4 ,it will be seen that more than one bell can be rung from the same attachment1 and the bell can1 by moving the arm of the switch ,w1 be made continuous ringing or not1 at will4 ,if the arm of the switch is moved over to the opposite side to which it is shown in the figure1 the shunt circuit of the bell through the relay is broken1 and the bell will ring only so long as the button of the push is kept in4 ,this continuous arrangement is very convenient for front doors1 etc41 where trouble is experienced in securing immediate attention to the summons4 ,instead of being taken to the switch1 as in ,fig4 #dj1 the two wires are taken to a contact piece fixed on the side of the door frame1 and so arranged that when the door is opened1 it either short circuits or breaks the shunt circuit3 thus when the push is pressed1 the bell rings until the door is opened1 the continual ringing of the bell insuring prompt attention4 ,mr4 ,h4 ,thorpe1 of #ei1 ,theobald's ,road1 ,london1 has devised a very ingenious arrangement for the continuous ringing of one or more bells for a stated period of time4 ,this is shown at ,fig4 #dj ,a4 ,it is set in action by pulling the ring outside the bottom of the core4 ,the bell or bells then start ringing1 as contact is established and kept up4 ,the novelty lies in the fact that the duration of the contact1 and consequently of the ringing1 can be accurately timed from #e seconds to #cj seconds1 by merely inserting a pin at different holes in the rod1 as shown4 ,after the bells have rung the required time the instrument automatically resets itself4 ,illustration3 ,fig4 #dj ,a4 ,s #di4 ,the modifications we are now about to consider1 differ from the ordinary bell1 either in the shape or material of the bell itself1 the relative disposition of the parts1 or some structural detail2 but not upon the introduction of any new principle4 ,the most striking is certainly the ,jensen bell1 which is shown in section at ,fig4 #da4 ,illustration3 ,fig4 #da4 ,according to ,mr4 ,jensen's system of electric bells1 the bell may take any desired form1 that of the ordinary church bell being preferred1 and the electro-magnetic apparatus is placed entirely inside the bell itself4 ,to attain this end the electro-magnetic apparatus must be compact in form4 ,a single electro-magnet has pole pieces at each end opposite to which an armature is suspended from a pivot and balanced by the hammer of the bell4 ,at the back of the armature there may be a make and break arrangement1 whereby a continuous succession of strokes is effected1 or this may be omitted1 in which case a single stroke is given when the contact with the battery is made1 or both may be effected by separate wires1 make contact with one wire1 and a single stroke is struck2 make it with the other and the current passes through the make and break and a succession of strokes is heard4 ,when the contact-breaker is used1 it is so arranged that a slight rub is caused at every stroke1 so keeping the contact clean4 ,the flexible break1 with the ingenious wiping contact1 is a great improvement over the ordinary screw1 which often becomes disarranged4 ,the form of the magnet is such that a considerable degree of magnetic force is caused by a comparatively small battery power4 ,the electro-magnetic apparatus being within the bell the latter forms a very effective and handsome shield for the former4 ,not only can the bell shield the electro-magnet from wet but the whole of the conducting wires as well4 ,the bell may be screwed to a tube through which passes the conducting wire1 which makes contact with an insulated metallic piece in the centre of the top of the bell4 ,both the wire and the contact piece are as completely shielded from the weather as if within the bell itself4 ,illustration3 ,fig4 #db4 ,the great point of departure is the discarding of the unsightly magnet box1 and the hemispherical bell 7see ,fig4 #cb71 and substituting a bell of the ,church type 7see ,fig4 #db71 and placing inside it an electro-magnet specially arranged4 ,the inventors use a single solenoidal magnet of a peculiar construction1 by which the armature is attracted by both poles simultaneously4 ,by this means less than half the usual quantity of wire is required1 thus reducing the external resistance of the circuit one half4 ,moreover the armature1 besides being magnetised by induction1 as acted on in the ordinary method of making electric bells1 is by ,messrs4 ,jensen's plan directly polarised by being in actual magnetic contact by the connection of the gimbal 7which is one piece with the armature7 with the core iron of their magnet4 ,it is thus induced to perform the largest amount of work with the smallest electro-motive force4 ,instead of the armature and clapper being in a straight line attached to a rigid spring1 which necessitates a considerable attractive power to primarily give it momentum1 in the ,jensen ,bell the armature and hammer are in the form of an inverted ,u1 and being perfectly balanced from the point of suspension1 the lines of force from a comparatively small magnetic field suffice to set this improved form of armature into instant regular vibration4 ,by using a flexible break and make arrangement instead of the usual armature spring and set screw 7at best of most uncertain action71 it is found that a much better result is attained1 and by this device the armature can be set much nearer the poles of the magnet with sufficient traverse of the hammer4 ,this is in strict accordance with the law of inverse squares1 which holds that the force exerted between two magnetic poles is inversely proportionate to the square of the distance between them1 or1 in other words1 that magnets increase proportionately in their power of attraction as they decrease in the square of the distance4 ,it will now be seen why these bells require so little battery power to ring them3 firstly1 the armature and hammer are so perfectly balanced as to offer but little resistance2 secondly1 the external resistance to the current is reduced2 and thirdly1 the best possible use is made of the electro-magnetic force at disposal4 ,s #ej4 ,the next modification which demands attention is the so-called ,circular bell4 ,this differs from the ordinary form only in having the action entirely covered by the dome4 ,except1 perhaps1 in point of appearance1 this presents no advantages to that4 ,the bells known as ,mining bells resemble somewhat in outward appearance the circular bell2 but in these mining bells the action is all enclosed in strong1 square teak cases1 to protect the movement1 as far as possible1 from the effects of the damp4 ,all the parts are1 for the same reason1 made very large and strong2 the armature is pivoted instead of being supported on a spring1 the hammer shank being long1 and furnished with a heavy bob4 ,the domes or bells are from #f inches to #ab inches in diameter1 and are generally fitted with single stroke movement1 so as to enable them to be used for signalling4 ,the hammer shank1 with its bob1 and the dome1 which stands in the centre of the case1 are the only parts left uncovered1 as may be seen on reference to ,figs4 #dc ,a and ,b1 where the exterior and interior of such a bell are shown4 ,illustration3 ,fig4 #dc ,a4 ,illustration3 ,fig4 #dc ,b4 ,illustration3 ,fig #dd4 ,s #ea4 ,in the ,electric ,trumpet1 introduced by ,messrs4 ,binswanger1 of the ,general ,electric ,company1 we have a very novel and effective arrangement of the parts of an electric bell and telephone together4 ,this instrument1 along with its battery1 line and push1 is illustrated at ,fig4 #dd1 where ,a is a hollow brass cylinder1 in which is placed an ordinary electro-magnet similar to ,figs4 #bj or #bj ,a4 ,at the front end1 near ,b1 is affixed by its edges a thin disc of sheet iron1 precisely as in the ,bell telephone1#ad and over against it1 at ,b1 is an insulated contact screw1 as in the ordinary trembling bell4 ,on the disc of sheet iron1 at the spot where the screw touches1 is soldered a speck of platinum4 ,the wires from the electro-magnet are connected1 one to the upper binding screw1 the other to the brass case of the instrument itself1 which is in metallic communication with the sheet iron disc4 ,the return wire from the contact screw is shown attached to the insulated piece1 and is fastened to another binding screw 7not visible7 on the base board4 ,when contact is made with the battery1 through the press or push1 the magnet becomes energised1 and pulls the iron disc or diaphragm towards it1 causing it to buckle inwards4 ,in doing this1 contact is broken with the screw ,b2 consequently the diaphragm again straightens out1 as the magnet no longer pulls it4 ,again contact is made2 when of course the same round of performances is continuously repeated4 ,as the plate or diaphragm vibrates many hundreds of times per second1 it sets up a distinctly musical and loud sound wave1 not unlike the note of a cornet-a-piston1 or a loud harmonium reed4 ,with a number of these trumpets1 each diaphragm being duly tuned to its proper pitch1 it would be possible to construct a novel musical instrument1 working solely by electricity4 ,the pushes need only take the form of pianoforte keys to render the instrument within the grasp of any pianoforte or organ player4 ,footnote #ad3 ,see ,electrical ,instrument ,making for ,amateurs4 ,whittaker ,co4 ,second edition4 ,s #eb4 ,sometimes the gong or dome of the ordinary bell is replaced by a coil spring1 as in the ,american clocks2 sometimes quaint forms are given to the parts covering the movement1 so as to imitate the head of an owl1 etc4 ,but bells with these changes in outward form will not present any difficulty1 either in fixing or in management1 to those who have mastered the structural and working details given in this chapter4 ,,chapter ,,iv4 ,,on ,,contacts1 ,,pushes1 ,,switches1 ,,keys1 ,,alarms1 ,,and ,,relays4 ,s #ec4 ,all the appliances which have hitherto been described1 would be utterly useless for the purposes intended1 had we not at hand some means of easily1 certainly and rapidly completing and breaking the circuit between the bell or bells1 on the one hand1 and the battery on the other4 ,this necessary piece of apparatus1 which is simply a contact maker1 receives different names1 dependent on its application4 ,when it is intended to be actuated directly by hand1 it is known as a push1 a pressel1 or pull1 according to the mode in which the contact is made4 ,at ,fig4 #de1 ,a1 ,b1 ,c1 ,d1 and ,e1 show the outward forms of various pushes1 in wood and china1 as sent out by the leading makers4 7,the ones figured are from ,messrs4 ,binswanger ,co47 ,at ,f is a sectional view of one of these pushes1 and ,g shows the interior when the cover has been removed4 ,from these two latter illustrations it will be easily understood that the push consists essentially in two pieces of metal one or both of which are springs1 and one of which is connected with one of the wires from the battery1 while the other is attached to the wire proceeding to the bell4 ,when the button is pressed the upper spring comes into contact with the lower metal spring or plate4 ,the circuit is now complete2 hence the bell rings4 ,but as soon as the finger is removed from the stud or button of the push1 the spring returns to its old place1 contact being thereby broken when the bell ceases to ring1 unless it be fitted with a continuous ringing arrangement 7see ,s #dh74 ,in fastening the leading wires to these pushes1 care must be taken that the ends of the wires be scraped1 and sand papered quite clean and bright1 bent into a loop which must be inserted under the head of the screw that holds the wire to the spring pieces2 the screws being then tightened up carefully to ensure a good grip and contact with the wires4 ,illustration3 ,fig4 #de4 ,illustration3 ,fig4 #df4 ,s #ed4 ,a pressel 7,fig4 #df7 is simply a push which instead of being made a fixture by being fastened in the wall or door1 is attached to a metallic wired line1 so that it is generally made to resemble somewhat in outward appearance the knob or tassel of the bell-pull of the last generation1 the interior arrangement is precisely similar to that of the push2 that is to say1 the pressel consists in a pear-shaped or acorn-shaped hollow wooden box1 with a projecting knob or button below4 ,this button is attached to a spring1 the tension of which keeps the knob protruding from the end of the box1 and at the same time prevents contacts with the second spring at the bottom of the box4 ,two insulated wires1 one from the battery1 the other from the bell1 are connected to separate screws at the top of the pressel4 ,one of these screws connects with the lower spring1 the other with the upper4 ,illustration3 ,fig4 #dg4 ,s #ee4 ,the pull 7,fig4 #dg71 as its name implies1 makes contact and rings the bell on being pulled4 ,the knob has a rather long shank bar1 around which is coiled a pretty stiff spring4 ,at the farther extremity is an ebonite or boxwood collar ending in a rather wider metal ring4 ,the wires from the bell and battery are connected respectively to two flat springs1 a a'1 by the screws b b'4 ,when the knob is pulled1 the metal collar touches both springs1 and the circuit is completed4 ,closely allied to the pull is a form of bedroom contact1 which combines pear-push or pressel and pull in one device4 ,this will be readily understood on reference to ,fig4 #dh4 ,another form of bedroom pull1 with ordinary rope and tassel1 consists in a box containing a jointed metal lever1 standing over a stud1 from which it is kept out of contact by a counter spring4 ,to the projecting end of the lever is attached the bell rope4 ,when this is pulled the lever touches the stud1 contact is made1 and the bell rings4 ,this is clearly shown in ,fig4 #di ,a4 ,in all these contacts1 except the door pull 7,fig4 #dg7 where the friction of the action of pulling keeps the surfaces bright1 the points of contact should be tipped with platinum4 ,another form of contact to be let in the floor of the dining-room1 within easy reach of the foot of the carver1 or other persons at the head of the table1 is shown at ,fig4 #di ,b4 ,illustration3 ,fig4 #dh4 ,illustration3 ,fig4 #di ,a4 ,illustration3 ,fig4 #di ,b4 ,mr4 ,mackenzie has introduced a very ingenious contrivance whereby the ringer may know whether the bell at the distant end has rung4 ,this is effected by inclosing in the push a device similar to that shown at ,fig4 #dc ,a4 ,that is to say1 an electro-magnet wound with wire1 and surmounted by a thin iron disc1 is placed in circuit with the line wires4 ,the ringing of the bell rapidly magnetises and demagnetises the electro-magnet1 and causes a humming sound1 which clearly indicates whether the bell is ringing or not4 ,as this device can be made very small1 compact1 and not liable to derangement1 it is of easy application4 ,s #ef4 ,the next form of contact to which our attention must be directed1 is that known as the burglar alarm1 with its variant of door-contacts1 sash-contacts1 till-contacts1 etc4 ,the burglar's pest 7as the contrivance we illustrate is called7 is one of the most useful applications of electricity for the protection of property against thieves4 ,it consists usually1 first1 of a brass plate 7,fig4 #ej71 upon which a platinum contact piece is fixed1 and second1 of a spring made of hardened brass or steel insulated from the plate2 or of a cylindrical box with a spiral spring inside 7see ,fig4 #ea74 ,it is so arranged that as long as the stud is kept pressed in1 the platinum points of contact are kept apart2 this is the position when fixed in the rebate of a closed door or window2 but as soon as opened1 the stud passes outward through the hole1 and the points of contact come together and complete the circuit of the wires in connection with the bell4 ,the bell is best to be a continuous ringing one4 ,it may be fixed in the master's bedroom1 or outside the premises in the street4 ,illustration3 ,fig4 #ej4 ,illustration3 ,fig4 #ea4 ,legge's ,window ,blind contact is an arrangement by which the blind is secured at the bottom by attaching it to a hook or button4 ,a slight pressure against the blind 7caused by anyone trying to enter after having broken a window7 sets the electric bell in motion unknown to the intruder4 ,illustration3 ,fig4 #eb4 ,illustration3 ,fig4 #ec4 ,a form of floor contact1 which may be placed under a light mat or carpet1 illustrated at ,fig4 #eb1 serves to give notice if anyone be waiting at the door1 or stepping into places which are desired to be kept private4 ,all these arrangements1 to be serviceable1 should be connected with continuous ringing bells 7see ,s #dh74 ,wherever it is likely that these arrangements may stand a long time without being called into play1 it is better to employ some form of contact in which a rubbing action 7which tends to clean the surfaces and then make a good contact7 is brought into play1 rather than a merely dotting action4 ,for this reason1 spring contacts in which the springs connected with the wires are kept apart by an insulating wedge 7shown at ,fig4 #ec7 as long as the door or window are kept closed1 are preferred4 ,in the case of windows1 strips of brass let into the frame on each side of the sash1 are thrown into contact by the springs a and a' in the sash itself1 as shown at ,fig4 #ed4 ,for shop doors and others1 where a short contact only is required1 and this only when the door is opened1 a contact such as shown at ,fig4 #ee is well adapted4 ,it consists1 as will be seen1 in a peculiarly shaped pivoted trigger a1 which is lifted forwards when the door is opened1 so that it makes contact with the spring b4 ,owing to the curved shape of the arm of the trigger1 the contact is not repeated when the door is closed4 ,illustration3 ,fig4 #ed4 ,illustration3 ,fig4 #ee4 ,s #eg4 ,in all forms of burglar or thief alarms1 the ordinary system of having the circuit broken1 until contact is made by the intruder involuntarily making contact at some point1 presents one great disadvantage2 and that is1 that if notre ami l'ennemi1 viz41 the thief or burglar1 be anything of an electrician 7and alas6 to what base uses may not even science be perverted7 he will begin by cutting all suspicious-looking wires before he attempts to set about any serious work4 ,this disadvantage may be entirely overcome by the adoption of a simple modification1 known as the closed circuit system of bell ringing4 ,for this the bells1 etc41 are continuously in contact with the batteries1 but owing to the peculiar connections1 do not ring unless the circuit is broken4 ,to render the working of such a system clear to my readers1 ,i quote the description given in the ,english ,mechanic1 by one of our leading electricians3-- ,writing on the subject of ,closed ,circuit ,bell-ringing1 ,mr4 ,perren ,maycock says3--,this is principally adopted for alarm purposes4 ,its superiority over the open circuit system lies in the fact that notice is given on opening 7breaking7 the circuit1 which is the reverse to the usual practice4 ,in the ordinary method it becomes necessary to have a contact maker1 differing in form for various purposes and situations1 which1 along with the leading wires1 must be artfully concealed4 ,all this entails great expense2 besides which one can never be sure that the contacts and wires are in proper order without actually trying each one4 ,on the other hand1 with the closed circuit system1 one has merely to place the wire in any convenient position1 it being better seen than hidden4 ,the very fact that alarm is given on breaking the contact renders the method applicable in circumstances and under conditions which would render the open method difficult and expensive1 if not impossible4 ,one can always be certain that everything is in order4 ,the modern burglar1 electrically educated as regards common practise in such matters1 would naturally make a point of cutting all wires that fall in his path4 ,from these and other obvious considerations1 it is evident how simple and yet how perfect a means of protection such a system provides4 ,i will now proceed to explain the manner of application4 ,the bell used differs from the ordinary1 only in the arrangement of its external connections4 ,illustration3 ,fig4 #ef ,a4 ,fig4 #ef ,a represents a single-alarm circuit4 ,when contact is broken externally1 there is a closed circuit in which are the battery and bell magnet coils4 ,consequently the armature is drawn away from the contact stud1 close up to the electro-magnet1 and is held so4 ,when a break occurs1 the armature flies back1 completes the local circuit1 and rings so long as the external circuit remains broken4 ,there is a switch for use when the alarm is not required4 ,illustration3 ,fig4 #ef ,b4 ,illustration3 ,fig4 #eg4 ,fig4 #ef ,b represents a case in which notice is given at two places4 ,by insulating a key as shown1 reply signalling can be carried on between the points at which the bells are placed4 ,a special gravity ,daniell modification 7,s #be7 is used for this class of work 7,fig4 #eg73 a narrow lead cylinder1 about #b in diameter1 watertight except at the bottom1 where it opens out into an inverted cone1 the surface of which is pierced with holes4 ,this stands immersed in dilute sulphuric acid4 ,a saturated solution of copper sulphate is next carefully introduced1 so as to displace the acid upwards4 ,crystals of sulphate of copper are introduced into the open end at the top of cylinder1 to fill the perforated portion at the bottom4 ,from the wooden cover of cell a thick flat ring of amalgamated zinc hangs suspended in the dilute acid4 ,care should be taken not to introduce the zinc till the two solutions have become well separated4 ,during action this becomes coppered1 while in contact with the sulphate of copper1 but it is not attacked by the acid4 ,it is1 however1 preferable to paint that portion of the lead1 which is surrounded by the acid4 ,the height of the cell is about #ad4'' ,it will be readily understood that if this latter system be employed1 special contacts1 which break contact when the pressure is removed1 must be employed for the door or window contacts4 ,a simple form is shown at ,fig4 #eh4 ,illustration3 ,fig4 #eh4 ,contacts similar to ,figs4 #ej1 #ec and #ed1 may be fitted on tills or drawers4 ,s #eh4 ,another useful application of contact is for the notification of any rise or fall of temperature beyond certain fixed limits4 ,the devices used for this purpose are known as fire alarms1 frost alarms1 and thermometer alarms4 ,the thermometer alarm is at once the most effective and trustworthy of the forms known1 as1 besides its delicacy1 it has the advantage of being able to give notice of low1 as well as of abnormally high temperature4 ,the form usually given to the electric alarm thermometer1 is well shown at ,fig4 #ei4 ,it consists in an ordinary thermometer with a wire projecting into the tube to a certain point1 say #ajj degrees4 ,the mercury in the bulb being also connected with another wire4 ,when the temperature is within the usual climatic range1 the mercury does not reach the upper wire4 ,if by reason of fire or any other abnormal heat1 the temperature rises beyond that to which the instrument is set1 the mercury rises and touches the upper wire1 contact is thus established1 and the bell rings4 ,illustration3 ,fig4 #ei4 ,by giving the thermometer the shape of a letter ,u1 it is possible to notify also a fall below a certain degree1 as well as a rise beyond a certain fixed point4 ,these thermometers are specially used by nurserymen and others1 to warn them of the too great lowering of temperature1 or vice versa1 in the houses under their charge4 ,other forms of fire alarms are shown at ,fig4 #fj and #fa4 ,if a strip be built up of two thin layers of dissimilar metals riveted together1 as the two metals do not expand at the same rate1 the strip will bend to the right if heated1 and to the left if cooled4 ,in the instrument shown at ,fig4 #fj1 the application of heat causes the flexible strip carrying the contact screw1 to bend over till it touches the lower stop1 when1 of course1 the bell rings4 ,if two stops are employed instead of the lower one only1 the bell will ring when a low temperature is reached1 which causes the strip to bend in the opposite direction4 ,illustration3 ,fig4 #fj4 ,illustration3 ,fig4 #fa4 ,at ,fig4 #fa is illustrated a novel form1 in which the expansion of air causes contact to be made4 ,it consists in an air chamber hermetically closed by a corrugated metal plate ,i1 similar to that used in the aneroid barometers4 ,when the temperature rises to a certain point1 the expansion of the air in the chamber brings the metallic plate into contact with the screw1 as shown below4 ,this closes the circuit and rings the bell in the usual manner4 ,in all these fire or thermometer alarms1 the exact degree of heat at which the bell shall ring1 can be pretty accurately adjusted by means of the contact screws4 ,s #ei4 ,closely allied to these forms of contacts are the devices whereby an ordinary clock or watch can be made to arouse the over-drowsy sleeper by the ringing of an electric bell1 which in this case should be of the continuous type4 ,all these depend in their action upon some arrangement whereby when the hour hand of the clock or watch arrives at a certain given point in its travel1 it makes contact between the battery and bell4 ,in general the contact piece is attached bodily to the clock1 but in the very ingenious arrangement illustrated at ,fig4 #fb 7devised by ,messrs4 ,binswanger7 the contacts are attached to an outer case1 and as the case of the watch itself forms one point of contact1 any watch that will slip in the case1 may be set to ring the bell4 ,illustration3 ,fig4 #fb4 ,illustration3 ,fig4 #fc4 ,messrs4 ,gent1 of ,leicester1 have also perfected an electric watchman's clock1 which records the number of places the watchman in charge has visited or missed on his rounds4 ,this we illustrate at ,fig4 #fc4 ,we quote ,messrs4 ,gent's own words1 in the following description3-- ,it consists of an eight-day clock1 to which is attached a disc or table revolving upon a vertical axis and driven by the mechanism of the clock4 ,the disc is covered with a sheet of paper1 attached to it by a binding screw so that it can be removed when used and a clean sheet substituted for it4 ,each sheet of paper is divided longitudinally into hours and1 if necessary1 parts of hours1 and crosswise into as many divisions as there are places to be visited by the watchman--any number from one to twenty4 ,each division has a corresponding marker1 which indicates1 by the impression it makes upon the paper1 the time the watchman visits the place connected with that marker4 ,wires are carried from the terminals of the clock1 one to the battery1 and one to each press-button fixed at the points intended to be visited by the watchman2 another wire is carried from each press-button to the other end of the battery4 ,the action is very simple3 when the button is pressed in the current passes through a coil carrying an armature and contact breaker with a point at the end of a long arm2 a hammer-like motion is given to the pointer1 and a distinct perforation made in the card4 ,it is usual to have the press-button in a box locked up1 of which the watchman only has the key4 ,the clock may be in the office or bedroom of the manager or head of the establishment1 who can thus1 from time to time1 satisfy himself of the watchman's vigilance4 ,the record should be examined in the morning1 and replaced by a clean sheet of card4 ,this clock received the special mention of ,her ,majesty's ,commissioners in ,lunacy1 and has been adopted by some of the largest asylums in the country4 ,we have recently made an important improvement by adding a relay for every marker1 thus enabling a local battery of greater power to be used for actuating the markers4 ,this has made no alteration in the appearance of the clock1 as the relays are contained within the cornice at the top of the clock case4 ,s #fj4 ,by means of a float1 it is possible to give notice of the height of water in a tank1 a reservoir1 or even of the state of the tide4 ,in these cases all that is needed is a float with an arm1 having a suitable contact attached1 so that when the water rises to the level of the float and lifts it1 it causes the contact piece to complete the circuit through a set screw4 ,or the float may be attached to an arm having a certain play in both directions1 i4e41 up and down1 within which no contact is made1 as the arm has a contact piece on either side1 which can touch either an upper or a lower contact screw1 according to whether the tide is low or high1 or whether the lock or tank is nearly empty or too full4 ,illustration3 ,fig4 #fd4 ,s #fa4 ,sometimes it is convenient to be able to ring an ordinary trembling bell continuously1 as when a master wishes to wake a member of his family or a servant2 or again1 to cut a given bell or bells out of circuit altogether4 ,the arrangements by which this can be effected1 are known as switches4 ,of switches there are two kinds1 namely1 plugswitches or interruptors1 and lever switches4 ,the former consists essentially in two stout plates of brass affixed to a base board of any insulating material4 ,these brass plates are set parallel to each other1 a short distance apart1 and the centre of the facing edge is hollowed out to take a brass taper plug4 ,a binding or other screw is fixed to each brass plate1 to connect up to the leading wires4 ,when the plug is in its socket1 the circuit between the two plates 7and consequently between the battery and bell1 etc47 is complete2 when the plug is out1 the contact is broken4 ,this form of switch is subject to work out of order1 owing to the fact that the taper plug gradually widens the hole1 so that the contact becomes uncertain or defective altogether4 ,by far the better form of switch is the lever switch1 as shown at ,fig4 #fd4 ,this consists in a movable metal lever or arm1 which is held by a strong spring in contact with the upper binding screw4 ,it can be made to slide over to the right or left of the centre1 at its lower or free end1 as far as the binding screws or studs shown1 which act at once as stops and point of connection to wires4 ,when the arm or lever is in the centre no contact is made but if it be pushed over to the right1 it slides on a brass strip let into and lying flush with the base4 ,contact is thus made between the upper binding screw and the left-hand screw4 ,if there is another brass strip on the left-hand side 7as shown in the figure71 contact may be made with another bell1 etc41 by sliding the arm to the left2 or again1 if no metal strip be placed on the left side the contact may be broken by pushing the arm towards the left-hand stud4 ,s #fb4 ,a key is another form of contact1 by means of which a long or short completion of circuit can be made by simply tapping on the knob4 ,it is particularly useful when it is desired to transmit signals1 either by ringing or otherwise4 ,it consists1 as may be seen at ,fig4 #fe1 of a lever or arm of brass1 pivoted at its centre1 furnished with a spring which keeps the portion under the knob out of contact with the stud in the front of the base-board4 ,as both the stud and the lever are connected to binding screws communicating with the battery and bell1 etc41 it is evident that on depressing the key the circuit with the bell will be completed for a longer or shorter period1 varying with the duration of the depression4 ,hence1 either by using preconcerted signals of short and long rings to signify certain common words1 such as a long ring for ,no1 and a short one for ,yes1 or by an adaptation of the ordinary ,morse code1 intelligible conversation can be kept up between house and stable1 etc41 etc41 by means of a key and a bell4 ,as ,mr4 ,edwinson has given much time to the elucidation of this system of bell signalling1 ,i cannot do better than quote his instructions1 as given in ,amateur ,work3-- ,for this purpose preconcerted signals have been agreed upon or invented as required1 and these have been found to be irksome and difficult to remember1 because constructed without any reference to a definite plan4 ,we may1 however1 reduce bell signals to a definite system1 and use this system or code as a means to carry on conversation at a distance as intelligently as it can be done by a pair of telegraph instruments4 ,in fact1 the ,morse telegraph code can be easily adopted for use with electric bells of the vibrating or trembling type1 and its alphabet1 as appended below1 easily learnt4 ,the letters of the alphabet are represented by long strokes and short strokes on the bell1 as here shown4-- ,a 4- ,b -444 ,c -4-4 ,d -44 ,e 4 ,f 44-4 ,g --4 ,h 4444 ,i 44 ,j 4--- ,k -4- ,l 4-44 ,m -- ,n -4 ,o --- ,p 4--4 ,q --444 ,r 4-4 ,s 444 ,t - ,u 44- ,v 444- ,w 4-- ,x -44- ,y -4-- ,z --44 ,ch ---- 3,a 7ae7 4-4- 3,o 7oe7 ---4 3,u 7ue7 44-- #a 4---- #b 44--- #c 444-- #d 4444- #e 44444 #f -4444 #g --444 #h ---44 #i ----4 #j ----- ,it will be noticed that the strokes to represent a letter do not in any case exceed four1 and that all the figures are represented by five strokes of varying length to each figure4 ,stops1 and other marks of punctuation1 are represented by six strokes1 which are in their combination representations of two or three letters respectively1 as shown below3-- ,comma 717 by ,a ,a ,a or 4-4-4- ,full stop 747 ,i ,i ,i 444444 ,interrogation 787 ,u ,d 44--44 ,hyphen 7-7 ,b ,a -4444- ,apostrophe 7'7 ,w ,g 4----4 ,inverted commas 77 ,a ,f 4-44-4 ,parenthesis 77 ,k ,k -4--4- ,semi-colon 727 ,k ,ch 4----- ,surprise 767 ,n ,ch -4---- ,colon 737 ,i ,ch 44---- ,in sending signals to indicate stops1 no regard must be had to the letters which they represent2 these are only given as aids to memory1 and are not to be represented separately on the bell4 ,bell signals must be given with a certain amount of regularity as to time2 indeed1 to carry on a conversation in this way it is necessary to be as punctilious in time as when playing a piece of music on a piano1 if the signals are to be understood4 ,the dots of the signal should therefore be represented in time by one1 and the dashes by two1 whilst the spaces between words and figures where a stop does not intervene should be represented by a pause equal to that taken by a person counting three1 the space between a word and a stop being of the same duration4 ,to make this more clear ,i give an example4 ,the mistress signals to her coachman3-- ,g ,e ,t ,t ,h ,e --4 4 - - 4444 4 #bba #a #b #c #b #aaaa #a #c ,c ,a ,r ,r ,i ,a ,g ,e -4-4 4- 4-4 4-4 44 4- --4 4 #baba #ab #aba #aba #aa #ab #bba #a #c ,r ,e ,a ,d ,y 4-4 4 4- -44 -4-- #aba #a #ab #baa #babb ,the coachman replies3-- ,r ,e ,a ,d ,y 4-4 4 4- -44 -4-- #aba #a #ab #baa #babb ,when the mistress is ready she signals3-- ,b ,r ,i ,n ,g ,t ,h ,e -444 4-4 44 -4 --4 - 4444 4 #baaa #aba #aa #ba #bba #c #b #aaaa #a #c ,c ,a ,r ,r ,i ,a ,g ,e -4-4 4- 4-4 4-4 44 4- --4 4 #baba #ab #aba #aba #aa #ab #bba #a ,and the coachman replies with a single long ring to signify that he understands4 ,it will be found convenient to have an answering signal from the receiving end of the line to each word separately4 ,this must be sent in the pause after each word1 and consists of the short signal ,e 4 when the word is understood1 or the double short signal ,i 44 when the word is not understood4 ,a negative reply to a question may be given by the signal for ,n -41 and an affirmative by the signal for ,,ae 4-4-2 other abbreviations may be devised and used where desired4 ,the code having been committed to memory1 it will be quite easy to transpose the words and send messages in cypher when we wish to make a confidential communication2 or the bells may be muffled under a thick cloak1 and thus1 whilst the measured beats are heard by the person for whom the signal is intended1 others outside the room will not be annoyed by them4 ,illustration3 ,fig4 #fe4 ,s #fc4 ,at ,s #dh1 we noticed that a device known as a ,relay is a convenient1 if not an essential mode of working continuous ringing bells4 ,here we will direct our attention to its structural arrangement1 and to its adaptations4 ,let us suppose that we had to ring a bell at a considerable distance1 so far indeed that a single battery would not energise the electro-magnets of an ordinary bell1 sufficiently to produce a distinct ring4 ,it is evident that if we could signal1 ever so feebly1 to an attendant at the other end of the line to make contact with another battery at the distant end of the line to his bell1 by means1 say1 of a key similar to that shown at ,fig4 #fe1 we should get a clear ring1 since this second battery1 being close to the bell1 would send plenty of current to energise the bell's magnets4 ,but this would require a person constantly in attendance4 ,now the relay does this automatically2 it relays another battery in the circuit4 ,the manner in which it effects this will be rendered clear1 on examination of ,fig4 #ff4 ,here we have an armature ,a attached to a light spring1 which can play between an insulated stop ,c1 and a contact screw ,b4 ,the play of this armature can be regulated to a nicety by turning the screws ,b or ,c4 ,these two screws are both borne by a double bent arm 7of metal7 affixed to the pillar ,d4 ,this pillar is separated from the rest of the frame by an insulating collar or washer of ebonite1 so that no current can pass from ,e to ,d1 unless the armature be pulled down so as to make contact with the contact screw ,b4 ,just under the armature1 stands the electro-magnet ,g1 which when energised can and does pull down the armature ,a4 ,it will be readily understood that if we connect the wires from the electro-magnet ,g1 to the wires proceeding from the battery and push 7or other form of contact7 at the distant station1 the electro-magnet1 being wound with a large quantity of fine wire1 will become sufficiently magnetized to pull the armature down through the small space intervening between ,c and ,b2 so that if the screws ,d and ,e are connected respectively to the free terminals of a battery and bell coupled together at the nearer station1 this second battery will be thrown into circuit with the bell1 and cause it to ring as well and as exactly as if the most skilful and most trustworthy assistant were in communication with the distant signaller4 ,every tap1 every release of the contact1 7be it push1 key1 or switch7 made at the distant end1 will be faithfully reproduced at the nearer end1 by the motion of the armature ,a4 ,for this reason we may use a comparatively weak battery to work the relay1 which in its turn brings a more powerful and local battery into play1 for doing whatever work is required4 ,in cases where a number of calls are required to be made simultaneously from one centre1 as in the case of calling assistance from several fire engine stations at once1 a relay is fixed at each station1 each connected with its own local battery and bell4 ,the current from the sending station passes direct through all the relays1 connecting all the local batteries and bells at the same time4 ,this is perhaps the best way of ringing any number of bells from one push or contact1 at a distant point4 ,ordinary trembling bells1 unless fitted with an appropriate contrivance1 cannot well be rung if connected up in series4 ,this is owing to the fact that the clappers of the bells do not all break or make contact at the same time1 so that intermittent ringing and interruptions take place4 ,with single stroke bells1 this is not the case1 as the pulling down of the armature does not break the contact4 ,illustration3 ,fig4 #ff4 ,illustration3 ,fig4 #fg4 ,illustration3 ,fig4 #fh4 ,s #fd4 ,we now have to consider those contrivances by means of which it is possible for an attendant to know when a single bell is actuated by a number of pushes in different rooms1 etc41 from whence the signal emanates4 ,these contrivances are known as indicators4 ,indicators may be conveniently divided into #c classes1 viz43--#ast1 indicators with mechanical replacements2 #bnd1 those with electrical replacements2 and #crdly1 those which are self replacing4 ,of the former class we may mention two typical forms1 namely1 the ordinary fall back indicator1 and the drop indicator4 ,all indicators depend in their action on the sudden magnetisation of an electro-magnet by the same current that works the electric bell at the time the call is sent4 ,to understand the way in which this may be effected1 let the reader turn to the illustration of the ,relay 7,fig4 #ff71 and let him suppose that the pillar ,d1 with its accompanying rectangle ,b ,c1 were removed1 leaving only the electro-magnet ,g1 with its frame and armature ,a4 ,if this armature holds up a light tablet or card1 on which is marked the number of the room1 it is evident that any downward motion of the armature1 such as would occur if the electro-magnet were energised by a current passing around it1 would let the tablet fall1 so as to become visible through a hole cut in the frame containing this contrivance4 ,it is also equally evident that the card or tablet would require replacing by hand1 after having once fallen1 to render it capable of again notifying a call4 ,fig4 #fg shows the working parts of one of these drop indicators1 as sent out by ,messrs4 ,binswanger4 ,in another modification1 known as ,thorpe's ,semaphore ,indicator1 we have a most ingenious application of the same principle in a very compact form4 ,in this 7,fig4 #fh71 the electro-magnet is placed directly behind a disc-shaped iron armature1 on which is painted or marked the number of the room etc4 7in this case #d72 this armature is attached by a springy shank to the drop bar1 shown to the left of the electro-magnet4 ,in front of the armature is a light metal disc1 also pivoted on the drop bar4 ,this engages in a catch above1 when pushed up so as to cover the number4 ,when pushed up1 the spring of the armature retains it in its place so that the number is hidden4 ,when the current passes around the electro-magnet1 the armature is pulled toward it1 and thus frees the covering disc1 which therefore falls1 and displays the number4 ,the ordinary form of fall back indicator 7a misnomer1 by the way1 since the indicator falls forwards7 is well illustrated at ,fig #fi4 ,here we have an ordinary electro-magnet ,a1 with its wires w w' standing over an armature ,b attached to a spring ,c1 which bears on its lower extremity1 a toothed projection which serves to hold up the short arm of the bent lever ,d1 which supports the number plate ,e4 ,when the electro-magnet ,a is energised by the current1 it pulls up the armature ,b1 which releases the detent ,d from the tooth ,c2 the number plate therefore falls forwards1 as shown by the dotted lines1 and shows itself at the aperture ,e'1 which is in front of the indicator frame4 ,to replace the number out of sight1 the attendant pushes back the plate ,e1 till it again engages the bent lever ,d in the tooth ,c4 ,this replacement of the number plate1 which the attendant in charge is obliged to perform1 gives rise to confusion1 if through carelessness it is not effected at once1 as two or more numbers may be left showing at one time4 ,for this reason1 indicators which require no extraneous assistance to replace them1 are preferred by many4 ,indicators with electrical replacements meet in part the necessities of the case4 ,this form of indicator consists usually of a permanent bar magnet pivoted near its centre1 so that it can hang vertically between the two poles of an electro-magnet placed at its lower extremity4 ,the upper extremity carries the number plate1 which shows through the aperture in the frame4 ,this bar magnet is made a trifle heavier at the upper end1 so that it must rest against either the one or other pole of the electro-magnet below4 ,if the north pole of the bar magnet rests against the right hand pole of the electro-magnet when the number does not show1 we can cause the bar magnet to cross over to the other pole1 and display the number by sending a current through the electro-magnet in such a direction as to make its right hand pole a north pole1 and its left hand a south pole4 ,this is because the two north poles will repel each other1 while the south will attract the north4 ,on being once tilted over1 the bar magnet cannot return to its former position1 until the person who used the bell sends a current in the opposite direction 7which he can do by means of a reversing switch71 when the poles of the electro-magnet being reversed1 the bar magnet will be pulled back into its original position4 ,indicators of this class1 owing to the fact that their replacement depends on the polarity of the bar magnet1 are also known as polarised indicators4 ,illustration3 ,fig4 #fi4 ,s #fe4 ,for general efficiency and trustworthiness1 the pendulum indicator2 as shown at ,fig4 #gj1 is unsurpassed4 ,it consists of an electro-magnet with prolongation at the free end on which is delicately pivoted a soft iron armature4 ,from the centre of this armature hangs1 pendulum fashion1 a light brass rod carrying a vane of fluted silver glass1 or a card with a number on it1 as may be found most convenient4 ,this vane or card hangs just before the aperture in the indicator frame4 ,stops are usually placed on each side of the pendulum rod to limit the swing4 ,when the electro-magnet is magnetised by the passage of the current1 the armature is pulled suddenly on one side1 and then the pendulum swings backwards and forwards in front of the aperture for some minutes before it comes to rest4 ,when fitted with silver fluted glass1 the motion of the vane is clearly visible even in badly lighted places4 ,as the pendulum1 after performing several oscillations1 comes to rest by itself in front of the aperture1 this indicator requires no setting4 ,messrs4 ,binswanger fit these indicators with double core magnets1 and have a patented adjustment for regulating the duration of the swings of the pendulum1 which may be made to swing for two or three minutes when the circuit is completed by pressing the push2 it then returns to its normal position1 thus saving the servant the trouble of replacing the drop4 ,illustration3 ,fig4 #gj4 ,messrs4 ,gent1 of ,leicester1 have also patented a device in connection with this form of indicator1 which we give in the patentee's own words3--,the objection so frequently urged against the use of ,electric ,bells1 that the servants cannot be depended upon to perform the operation of replacing the signals1 cannot any longer apply1 for the pendulum signals require no attention whatever4 ,it consists of an electro-magnet having forks standing up in which ,v openings are made4 ,an armature of soft iron1 with a piece of thin steel projecting at each end lies suspended at the bottom of the ,v opening1 a brass stem carrying the signal card is screwed into the armature1 the action being1 that when a current is allowed to pass through the electro-magnet the armature with the pendulum is drawn towards it and held there until the current ceases to pass1 when it instantly looses its hold of the armature1 which swings away and continues to oscillate for two or three minutes1 so that if the servant happens to be out of the way1 it may be seen on her return which pendulum has been set in motion4 ,the ,pendulum ,indicator we have recently patented is entirely self-contained4 ,the magnet has its projecting poles riveted into the brass base which carries the flag4 ,the flag is constructed as ,fig4 #gj1 but swings in closed bearings1 which prevents its jerking out of its place1 and enables us to send it out in position ready for use4 ,it will be seen this patented improvement makes all screws and plates as formerly used for securing the parts unnecessary4 ,it will be seen at once that this is simplicity itself1 and has nothing about it which may by any possibility be put out of order1 either by warping or shrinking of the case or carelessness of attendants4 ,illustration3 ,fig4 #ga4 ,there is only one point that needs further notice with regard to these pendulum indicators1 and that is1 that since the rapid break and make contact of the ringing bell interferes somewhat with the proper action of the indicator magnet1 it is always advisable to work the indicator by means of a relay 7fixed in the same frame7 and a local battery4 ,this is shown in ,fig4 #ga1 where a second pair of wires attached to ,c and ,c1 to the extreme right of the indicator frame1 are brought from the same battery to work the indicator and contained relay4 ,it is not advisable1 however1 with the pendulum indicator1 to use the same battery for the indicator2 the relay should throw a local battery into the indicator circuit4 ,in ,fig4 #ga six pushes are shown to the left of the indicator frame4 ,these1 of course1 are supposed to be in as many different rooms4 ,illustration3 ,fig4 #gb4 ,we close this chapter with an engraving of a very compact and neat form of drop indicator devised by ,messrs4 ,gent1 and called by them a ,tripolar ,indicator4 ,it consists1 as the name implies1 of a single magnet1 having one end of the iron core as one pole1 the other end extending on each side like a ,v1 forming1 as it were1 three poles4 ,though but one bobbin is used1 the effect is very powerful4 ,there are no springs or other complications1 so that the arrangement is adapted for ship use1 as are also those represented at ,figs4 #fg and #fh4 ,pendulum and fall-back indicators1 as well as polarised indicators1 owing to the delicacy of the adjustments1 are unfitted for use on board ship1 or in the cabs of lifts1 where the sudden jolts and jerks are sure to move the indicators1 and falsify the indications4 ,the tripolar indicator is illustrated at ,fig4 #gb4 ,,chapter ,v4 ,,on ,,wiring1 ,,connecting ,,up1 ,,and ,,localising ,,faults4 ,s #ff4 ,however good may be the bells1 indicators1 batteries1 etc41 used in an electric bell installation1 if the wiring be in any wise faulty1 the system will surely be continually breaking down1 and giving rise to dissatisfaction4 ,it is therefore of the highest importance that the workman1 if he value his good name1 should pay the greatest attention to ensure that this part of his work be well and thoroughly done4 ,this is all the more necessary1 since while the bells1 batteries1 relays1 pushes1 etc41 are easily got at for examination and repair1 the wires1 when once laid1 are not so easily examined1 and it entails a great deal of trouble to pull up floor boards1 to remove skirtings etc41 in order to be able to overhaul and replace defective wires or joints4 ,the first consideration of course1 is the kind and size of wire fitted to carry the current for indoor and outdoor work4 ,now this must evidently depend on three points4 #ast1 ,the amount of current 7in ampe'res7 required to ring the bell4 #bnd1 ,the battery power it is intended to employ4 #crd1 ,the distance to which the lines are to be carried4 ,from practical experience ,i have found that it is just possible to ring a #b-a_/b bell with #a_/b an ampe're of current4 ,let us consider what this would allow us to use1 in the way of batteries and wire1 to ring such a bell4 ,the electro-motive force of a single ,leclanche' cell is1 as we have seen at ,s #ch1 about #a4f volt1 and the internal resistance of the quart size1 about #a4a ohm4 ,no4 #bj gauge copper wire has a resistance of about #a4b ohm to the pound1 and in a pound 7of the cotton covered wire7 there are about #fj yards4 ,supposing we were to use #fj yards of this wire1 we should have a wire resistance of #a4b ohm1 an internal resistance of #a4a ohm1 and a bell resistance of about #j4a of an ohm1 altogether about #b4d ohms4 ,since the ,e4,m4,f4 of the cell is #a4f volt1 we must divide this by the total resistance to get the amount of current passing4 ,that is to say3-- ,ohms4 ,volts4 ,ampe'res4 #b4d7 #a4fj 7#j4ff1 or about #b_/c of an ampe're2 just a little over what is absolutely necessary to ring the bell4 ,now this would allow nothing for the deterioration in the battery1 and the increased resistance in the pushes1 joints1 etc4 ,we may safely say1 therefore1 that no copper wire1 of less diameter than ,no4 #ah gauge 7#dh_/ajjj of an inch diameter7 should be used in wiring up house bells1 except only in very short circuits of two or three yards1 with one single bell in circuit2 and as the difference in price between ,no4 #ah and ,no4 #bj is very trifling1 ,i should strongly recommend the bell-fitter to adhere to ,no4 #ah1 as his smallest standard size4 ,it would also be well to so proportion the size and arrangement of the batteries and wires1 that1 at the time of setting up1 a current of at least one ampe're should flow through the entire circuit4 ,this will allow margin for the weakening of the battery1 which takes place after it has been for some months in use4 ,as a guide as to what resistance a given length of copper wire introduces into any circuit in which it may be employed1 ,i subjoin the following table of the ,birmingham wire gauge1 diameter in #a1jjjths of an inch1 yards per lb41 and resistance in ohms per lb4 or #ajj yards1 of the wires which the fitter is likely to be called upon to employ3-- ---------------------------------------- -------------------- ,table of ,resistance and lengths per lbs4 #ajj yards of cotton covered copper wires4 ---------------------------------------- -------------------- ,birmingham ,diameter in ,yards ,ohms4 ,ohms4 per ,wire ,gauge4 #ajjjth of per lb4 per lb4 #ajj yards4 an inch4 ---------------------------------------- ---------------- ,no4 #ab #ajj #i #j4jcdb #j4jjch #ad #hj #ae #j4jhej #j4jjid #af #fb #bd #j4bbci #j4jbdi #ah #dh #da #j4fijj #j4jgff #bj #da #ei #a4bajj #j4accc #bb #cb #aji #c4ajjj #j4cddd ---------------------------------------- -------------------- ,s #fg4 ,whatever gauge wire be selected1 it must be carefully insulated1 to avoid all chance contact with nails1 staples1 metal pipes or other wires4 ,the best insulation for wires employed indoors is gutta-percha1 surrounded with a coating of cotton wound over it1 except only in cases when the atmosphere is excessively dry4 ,in these1 as the gutta-percha is apt to crack1 india-rubber as the inner coating is preferable4 ,if ,no4 #ah wire be used1 the thickness of the entire insulating coating should be thick enough to bring it up to ,no4 #aj gauge1 say a little over #a_/ajth inch in diameter4 ,there is one point that will be found very important in practice1 and that is to have the cotton covering on the wires leading to the bells of a different colour from that on the return wires2 in other words1 the wires starting from the zinc poles of the battery to the bells1 indicators1 relays1 etc41 should be of a different colour from that leading from the carbon poles to the bells1 etc4 ,attention to this apparently trifling matter1 will save an infinite amount of trouble in connecting up1 repairing1 or adding on fresh branch circuits4 ,for outdoor work1 wire of the same gauge 7,no4 #ah7 may generally be used1 but it must be covered to the thickness of #a_/aj with pure gutta-percha1 and over this must be wound tape served with ,stockholm tar4 ,wires of this description1 either with or without the tarred tape covering1 may be obtained from all the leading electricians' sundriesmen4 ,many firms use copper wire tinned previous to being insulated4 ,this tinning serves two good purposes1 #ast1 the copper wire does not verdigris so easily2 #bndly1 it is more easily soldered4 ,on the other hand1 a tinned wire is always a little harder1 and presents a little higher resistance4 ,whenever wires are to be joined together1 the ends to be joined must be carefully divested of their covering for a length of about three inches1 the copper carefully cleaned by scraping and sand-papering1 twisted tightly and evenly together1 as shown in ,fig4 #gc ,a1 and soldered with ordinary soft solder 7without spirits71 and a little resin or composite candle as a flux4 ,a heavy plumber's soldering iron1 or even a tinman's bit1 is not well adapted for this purpose1 and the blowpipe is even worse1 as the great heat melts and spoils the gutta-percha covering4 ,the best form of bit1 is one made out of a stout piece of round copper wire #a_/d thick with a nick filed in its upper surface for the wire to lie in 7see ,fig4 #gc ,b74 ,this may be fastened into a wooden handle1 and when required heated over the flame of a spirit lamp4 ,when the soldering has been neatly effected1 the waste ends a and b of the wire should be cut off flush4 ,the wire must then be carefully covered with warm ,prout's elastic or softened gutta-percha1 heated and kneaded round the wire with the fingers 7moistened so as not to stick7 until the joint is of the same size as the rest of the covered wire4 ,as a further precaution1 the joints should be wrapped with a layer of tarred tape4 ,let me strongly dissuade the fitter from ever being contented with a simply twisted joint4 ,although this may and does act while the surfaces are still clean1 yet the copper soon oxidises1 and a poor non-conducting joint is the final result4 ,that'll do will not do for electric bell-fitting4 ,illustration3 ,fig4 #gc4 ,s #fh4 ,whenever possible1 the wiring of a house1 etc41 for bell work1 should be done as soon as the walls are up and the roof is on4 ,the shortest and straightest convenient route from bell to battery1 etc41 should always be chosen where practicable to facilitate drawing the wire through and to avoid the loss of current which the resistance of long lengths of wire inevitably entails4 ,the wires should be run in light zinc tubes nailed to the wall4 ,in joining up several lengths of tubing1 the end of one piece of tube should be opened out considerably of a trumpet shape for the other piece to slip in2 and the end of this latter should also be slightly opened out1 so as not to catch in the covering of any wire drawn through it4 ,the greatest care must be exercised in drawing the wires through the tubes or otherwise1 that the covering be not abraded1 or else leakage at this point may take place4 ,in cases where tubes already exist1 as in replacing old crank bells by the electric bells1 the new wires can be drawn through the tubes1 by tying the ends of the new wire to the old wire1 and carefully pulling this out1 when it brings the new wire with it4 ,or if the tubes are already empty1 some straight stout wire may be run through the tubes1 to which the new wires may be attached1 and then drawn through1 using1 of course1 every possible precaution to avoid the abrasion of the insulating covering of the wire1 which would surely entail leakage and loss of current4 ,all the old fittings1 cranks1 levers1 etc41 must be removed1 and the holes left1 carefully filled with dowels or plaster4 ,in those cases where it is quite impossible to lay the wires in zinc or wooden tubes 7as in putting up wires in furnished rooms already papered1 etc471 the wires may be run along the walls1 and suspended by staples driven in the least noticeable places2 but in no case should the two wires 7go and return7 lie under the same staple1 for fear of a short circuit4 ,it must be borne in mind that each complete circuit will require at least two wires1 viz41 the one leading from the battery to the bell1 and the other back from the bell to the battery2 and these until connection is made between them by means of the contact 7pull1 push1 or key7 must be perfectly insulated from each other4 ,in these cases1 as far as possible1 the wires should be laid in slots cut in the joists under the floor boards1 or1 better still1 as tending to weaken the joists less1 small holes may be bored in the joists and the wires passed through them2 or again1 the wires may be led along the skirting board1 along the side of the doorpost1 etc41 and when the sight of the wires is objectionable1 covered with a light ornamental wood casing4 ,when the wires have been laid and the position of the pushes1 etc41 decided upon1 the blocks to which these are to be fastened must be bedded in the plaster4 ,these blocks may be either square or circular pieces of elm1 about #c inches across1 and #a inch thick1 bevelled off smaller above1 so as to be easily and firmly set in the plaster4 ,they may be fastened to the brickwork by two or three brads1 at such a height to lie level with the finished plaster4 ,there must of course be a hole in the centre of the block1 through which the wires can pass to the push4 ,when the block has been fixed in place1 the zinc tube1 if it does not come quite up to the block1 should have its orifice stopped with a little paper1 to prevent any plaster1 etc41 getting into the tube4 ,a little care in setting the block will avoid the necessity of this makeshift4 ,a long nail or screw driven into the block will serve to mark its place1 and save time in hunting for it after the plastering has been done4 ,when the blocks have been put in their places1 and the plastering1 papering1 etc41 done1 the wires are drawn through the bottom hole of the push 7after the lid or cover has been taken off71 ,fig4 #gd1 and a very small piece of the covering of the wire having been removed from each wire1 and brightened by sand papering1 one piece is passed round the shank of the screw connected with the lower spring1 shown to the right in ,fig4 #gd1 and the other round the shank of the screw connected to the upper spring1 shown to the left in the ,fig4 ,the screws must be loosened to enable the operator to pass the wire under their heads4 ,the screws must then be tightened up to clench the wire quite firmly4 ,in doing this1 we must guard against three things4 ,firstly1 in pulling the wire through the block1 not to pull so tightly as to cut the covering against the edge of the zinc tube4 ,secondly1 not to uncover too much of the wire1 so as to make contact between the wires themselves either at the back of the push1 or at any other part of the push itself4 ,thirdly1 to secure good contact under the screws1 by having the ends of the wires quite clean1 and tightly screwed down4 ,illustration3 ,fig4 #gd4 ,s #fi4 ,in all cases where the wires have to be taken out of doors1 such as is necessitated by communication from house to outhouses1 stables1 greenhouses1 etc41 over head lines 7,no4 #ah gauge1 gutta-percha tape and tar covering7 should be used4 ,where overhead lines are not admissible1 either as being eyesores1 or otherwise1 the wires may be laid in square wooden casings of this section box open up1 the open part of which must be covered by a strip of wood laid over it4 ,the wood must have been previously creosoted1 in the same manner as railway sleepers4 ,this mode admits of easy examination4 ,iron pipes must1 however1 be used if the lines have to pass under roads1 etc41 where there is any heavy traffic4 ,and it must be borne in mind that however carefully the iron pipes1 etc41 be cemented at the joints1 to make them watertight1 there will always be more electrical leakage in underground lines than in overhead ones4 ,in certain rare cases it may be needful to use iron wires for this purpose instead of copper2 in this case1 as iron is six or seven times a worse conductor than copper1 a much heavier wire must be employed to get the same effect4 ,in other words1 where iron wire is used1 its section must be not less than seven times that of the copper wire which it replaces4 ,s #gj4 ,it is always preferable1 where great distance 7and1 consequently1 greater expense7 do not preclude it1 to use wire for the leading as well as for the returning circuit4 ,still1 where for any reason this is not practicable1 it is perfectly admissible and possible to make a good return circuit through the earth1 that is to make the damp soil carry the return current 7see ,s #cg74 ,as recommended at the section just quoted1 this earth circuit must have at each extremity a mass of some good conductor plunged into the moist ground4 ,in towns1 where there are plenty of water mains and gas mains1 this is a matter of no difficulty1 the only point being to ensure good contact with these masses of metal4 ,in other places a hole must be dug into the ground until the point of constant moisture is reached2 in this must be placed a sheet of lead or copper1 not less than five square feet surface1 to which the earth wires are soldered1 the hole then filled in with ordinary coke1 well rammed down to within about six inches of the surface1 and then covered up with soil well trodden down4 ,in making contact with water or gas pipes1 care must be taken to see that these are main pipes1 so that they do lead to earth1 and not to a cistern or meter only1 as1 if there are any white or red lead joints the circuit will be defective4 ,to secure a good contact with an iron pipe1 bare it1 file its surface clean1 rub it over with a bit of blue stone 7sulphate of copper7 dipped in water2 wipe it quite dry1 bind it tightly and evenly round with some bare copper wire 7also well cleaned71 ,no4 #af gauge4 ,bring the two ends of the wire together1 and twist them up tightly for a length of three or four inches4 ,now heat a large soldering bit1 put some resin on the copper wire1 and solder the wire1 binding firmly down to the iron pipe4 ,do likewise to the projecting twist of wire1 and to this twist solder the end of the return wire4 ,on no account should the two opposite earth wires be soldered to water mains and gas mains at the same time1 since it has been found that the different conditions in which these pipes find themselves is sufficient to set up a current which might seriously interfere with the working of the battery proper4 ,sometimes there is no means of getting a good earth except through the gas main3 in this case we must be careful to get to the street side of the meter1 for the red lead joints will prevent good conductivity being obtained4 ,in out of the way country places1 if it is possible to get at the metal pipe leading to the well of a pump1 a very good earth can be obtained by soldering the wires to that pipe1 in the same manner as directed in the case of the water main4 ,the operator should in no case be contented with a merely twisted joint1 for the mere contact of the two metals 7copper and iron7 sets up in the moist earth or air a little electric circuit of its own1 and this speedily rusts through and destroys the wires4 ,the following suggestions1 by ,messrs4 ,gent1 on the subject of wiring1 are so good1 that we feel that we shall be doing real service to the reader to quote them here in full3-- #ast4--,the description of wire to be used4 ,it is of the utmost importance that all wires used for electric bell purposes be of pure copper and thoroughly well insulated4 ,the materials mostly employed for insulating purposes are indiarubber1 gutta-percha1 or cotton saturated with paraffin4 ,for ordinary indoor work1 in dry places1 and for connecting doors and windows with burglar alarms1 or for signalling in case of fire1 indiarubber and cotton covered wires answer well2 but for connecting long distances1 part or all underground1 or along walls1 or in damp cellars or buildings1 gutta-percha covered wire is required1 but it should be fixed where it will not be exposed to heat or the sun1 or in very dry places1 as the covering so exposed will perish1 crack1 and in time fall off4 ,this may be1 to some extent1 prevented by its being covered with cotton2 but we recommend for warm or exposed positions a specially-prepared wire1 in which rubber and compound form the insulating materials1 the outside being braided or taped4 ,for ordinary house work1 we refer to lay a wire of ,no4 #ah or #bj copper1 covered to ,no4 #ad or #aa with gutta-percha1 and an outer covering of cotton1 which we called the 'battery' wire1 this being the wire which conveys the current from the battery to every push1 etc41 no matter how many or in what position4 ,the reason for selecting this kind is1 that with the gutta-percha wires the joints may be more perfectly covered and made secure against damp4 ,this is of the utmost importance in the case of 'battery wires1' as the current is always present and ready to take advantage of any defect in the insulation to escape to an adjoining wire1 or to 'earth1' and so cause a continuous waste of current4 ,the wires leading from the pushes to the signalling apparatus or bell we call the 'line' wires4 ,in these1 and the rest of the house wires1 the perfect covering of the joints is important4 ,for line wires we usually prefer ,no4 #ah or #bj copper1 covered with indiarubber1 and an outer coating of cotton1 well varnished4 ,in joining the 'battery wires1' the place where the junction is to be made must be carefully uncovered for the distance of about an inch2 the ends of the wire to be joined1 well cleaned1 and tightly twisted together2 with the flame of a spirit lamp or candle the joint must be then heated sufficiently to melt fine solder in strips when held upon it1 having first put a little powdered resin on the joint as a flux2 the solder should be seen to run well and adhere firmly to the copper wire4 ,a piece of gutta-percha should then be taken and placed upon the joint while warm1 and with the aid of the spirit lamp and wet fingers1 moulded round until a firm and perfect covering has been formed4 ,on no account use spirits in soldering4 ,with the line wire1 it is best1 as far as possible1 to convey it all the way from the push to the signal box or bell in one continuous length4 ,of course1 when two or more pushes are required to the same wire1 a junction is unavoidable4 ,the same process of joining and covering1 as given for the battery wire1 applies to the line wire4 ,where many wires are to be brought down to one position1 a large tube may be buried in the wall1 or a wood casing fixed flush with the plaster1 with a removable front4 ,the latter plan is easiest for fixing and for making alterations and additions4 ,for stapling the wires1 in no case should the wires be left naked4 ,when they pass along a damp wall1 it is best to fix a board and loosely staple them4 ,in no case allow more than one wire to lie under the same staple1 and do not let the staples touch one another4 ,in many cases1 electric bells have been an incessant annoyance and complete failure1 through driving the staples tight up to the wires1 and several wires to the same staple1--this must not be done on any account4 ,a number of wires may be twisted into a cable1 and run through a short piece of gutta-percha tube1 and fastened with ordinary gas hooks where it is an advantage to do so4 ,in running the wires1 avoid hot water pipes1 and do not take them along the same way as plumber pipes4 ,underground wires must be laid between pieces of wood1 or in a gas or drain pipe1 and not exposed in the bare earth without protection1 as sharp pieces of stone are apt to penetrate the covering and cause a loss2 in fact1 in this1 as in every part of fixing wires1 the best wire and the best protection is by far the cheapest in the end4 ,the copper wire in this case should not be less than ,no4 #af ,b4,w4,g41 covered with gutta-percha1 to ,no4 #i or #aj ,b4,w4,g41 and preferably an outer covering of tape or braid well tarred4 ,outside wire1 when run along walls and exposed to the weather1 should be covered with rubber and compound1 and varnished or tarred on an outer covering of tape or braid4 ,hooks or staples must be well galvanised to prevent rusting1 and fixed loosely4 ,if the wire is contained within an iron pipe1 a lighter insulation may be used3 but the pipe must be watertight4 ,in a new building1 wires must be contained within zinc or copper bell tubes4 ,a #c_/h inch tube will hold two wires comfortably4 ,the tubes should be fixed to terminate in the same positions in the rooms as ordinary crank bell levers1--that is1 about three feet from the floor4 ,at the side of the fireplace a block of wood should be fixed in the wall before any plaster is put on1 and the end of the tube should terminate in the centre of the same4 ,a large nail or screw may be put in to mark the place1 so that the end of the tube may be found easily when the plastering is finished4 ,bend the tube slightly forward at the end1 and insert a short peg of wood to prevent dirt getting into the tube4 ,do the same at the side of1 or over the bed in bedroom4 ,if the tubes are kept clean1 the wires may be easily drawn up or down as the case may require4 ,the best way is to get a length of ordinary copper bell wire1 ,no4 #af1 sufficient to pass through the tube1 and having stretched it1 pass it through and out at the other end4 ,here have your coils of insulated wire1 viz41 one battery wire1 which is branched off to every push1 and one line wire1 which has to go direct to the indicator or bells1 and having removed a short portion of the insulation from the end of each1 they are tied to the bare copper wire and drawn through4 ,this is repeated wherever a push is to be fixed throughout the building4 ,in making connection with binding screws or metal of any kind1 it is of the utmost importance that everything should be perfectly clean4 ,joints in wire1 whether tinned or untinned1 must be soldered and covered4 ,we cannot impress this too earnestly on fixers4 ,never bury wires in plaster unprotected1 and in houses in course of erection1 the tubes only should be fixed until the plastering is finished1 the wires to be run in at the same time that the other work is completed4 ,illustration3 ,fig4 #ge4 ,s #ga4 ,the wires having been laid by any of the methods indicated in the preceding five sections1 the fixer is now in a position to connect up4 ,no two houses or offices will admit of this being done in exactly the same way2 but in the following sections most of the possible cases are described and illustrated1 and the intelligent fixer will find no difficulty1 when he has once grasped the principle1 in making those trifling modifications which the particular requirements may render necessary4 ,the first and simplest form1 which engages our attention1 is that of a single bell1 battery1 and push1 connected by wire only4 ,this is illustrated at ,fig4 #ge4 ,here we see that the bell is connected by means of one of the wires to the zinc pole of the battery1 the push or other contact being connected to the carbon pole of the same battery4 ,a second wire unites the other screw of the push or contact with the second binding screw of the bell4 ,there is no complete circuit until the push is pressed1 when the current circulates from the carbon or positive pole of the battery1 through the contact springs of the push1 along the wire to the bell1 and then back again through the under wire to the zinc or negative pole of the battery4#ae ,it must be clearly understood that the exact position of battery1 bell1 and push is quite immaterial4 ,what is essential is1 that the relative connections between battery1 bell1 and push be maintained unaltered4 ,fig4 #gf shows the next simplest case1 viz41 that in which a single bell and push are worked by a single cell through an earth return 7see ,s #gj74 ,here the current is made to pass from the carbon pole of the battery to the push1 thence along the line wire to the bell4 ,after passing through the bell1 it goes to the right-hand earth-plate ,e1 passing through the soil till it reaches the left-hand earth-plate ,e1 thence back to the zinc pole of the battery4 ,it is of no consequence to the working of the bell whether the battery be placed between the push and the left-hand earth-plate1 or between the bell and the right-hand earth-plate2 indeed1 some operators prefer to keep the battery as near to the bell as possible4 ,at ,fig4 #gg is shown the mode by which a single battery and single bell can be made to ring from two 7or more7 pushes situated in different rooms4 ,here it is evident that1 whichever of the two pushes be pressed1 the current finds its way to the bell by the upper wire1 and back home again through the lower wire2 and1 even if both pushes are down at once1 the bell rings just the same1 for both pushes lead from the same pole of the battery 7the carbon7 to the same wire 7the line wire74 ,footnote #ae3 ,it must be borne in mind that the negative element is that to which the positive pole is attached1 and vice versa 7see ss4 #h and #i74 ,illustration3 ,fig4 #gf4 ,illustration3 ,fig4 #gg4 ,in ,fig4 #gh1 we have a slight modification of the same arrangement1 a front-door pull contact being inserted in the circuit2 and here1 in view of the probably increased resistance of longer distance1 two cells are supposed to be employed instead of one1 and these are coupled up in series 7,s #dj71 in order to overcome this increased resistance4 ,illustration3 ,fig4 #gh4 ,the next case which may occur is where it is desired to ring two or more bells from one push4 ,there are two manners of doing this4 ,the first mode is to make the current divide itself between the two bells1 which are then said to be in parallel4 ,this mode is well illustrated both at ,figs4 #gi and #hj4 ,as in these cases the current has to divide itself among the bells1 larger cells must be used1 to provide for the larger demand2 or several cells may be coupled up in parallel 7,s #dj74 ,at ,fig4 #gi is shown the arrangement for two adjoining rooms2 at ,fig4 #hj1 that to be adopted when the rooms are at some distance apart4 ,if1 as shown at ,fig4 #ha1 a switch similar to that figured in the cut ,fig4 #fd be inserted at the point where the line wires converge to meet the push1 it is possible for the person using the push to ring both bells at once1 or to ring either the right-hand or the left-hand bell at will1 according to whether he turns the arm of the switch-lever on to the right-hand or left-hand contact plate4 ,illustration3 ,fig4 #gi4 ,illustration3 ,fig4 #hj4 ,illustration3 ,fig4 #ha4 ,the second mode of ringing two or more bells from one push is that of connecting one bell to the other1 the right-hand binding screw of the one to the left-hand binding screw of the next1 and so on1 and then connecting up the whole series of bells to the push and battery1 as if they were a single bell4 ,this mode of disposing the bells is called the series arrangement4 ,as we have already noticed at ,s #fc1 owing to the difference in the times at which the different contact springs of the various bells make contact1 this mode is not very satisfactory4 ,if the bells are single stroke bells1 they work very well in series2 but1 to get trembling bells to work in series1 it is best to adopt the form of bell recommended by ,mr4 ,f4 ,c4 ,allsop4 ,he says3 ,perhaps the best plan is to use the form of bell shown at ,fig4 #hb1 which1 as will be seen from the figure1 governs its vibrations1 not by breaking the circuit1 but by shunting its coils4 ,on the current flowing round the electro-magnet1 the armature is attracted1 and the spring makes contact with the lower screw4 ,there now exists a path of practically no resistance from end to end4 ,the current is therefore diverted from the magnet coils1 and passes by the armature and lower screw to the next bell1 the armature falling back against the top screw1 and repeating the previous operation so long as the circuit is closed4 ,thus1 no matter how many bells there be in the series1 the circuit is never broken4 ,this form of bell1 however1 does not ring so energetically as the ordinary form1 with a corresponding amount of battery power4 ,illustration3 ,fig4 #hb4 ,illustration3 ,fig4 #hc4 ,fig4 #hc illustrates the mode in which a bell1 at a long distance1 must be coupled up to work with a local battery and relay4 ,the relay is not shown separately1 but is supposed to be enclosed in the bell case4 ,here1 on pressing the push at the external left-hand corner1 the battery current passes into the relay at the distant station1 and out at the right-hand earth-plate ,e returning to the left-hand earth-plate ,e4 ,in doing this1 it throws in circuit 7just as long as the push is held down7 the right-hand local battery1 so that the bell rings by the current sent by the local battery1 the more delicate relay working by the current sent from the distant battery4 ,illustration3 ,fig4 #hd4 ,illustration3 ,fig4 #he4 ,at ,fig4 #hd1 we have illustrated the mode of connecting up a continuous ringing bell1 with a wire return4 ,of course1 if the distance is great1 or a roadway1 etc41 intervene1 an overhead line and an earth plate may replace the lines shown therein1 or both lines may be buried4 ,it is possible1 by using a ,morse key 7,fig4 #fe7 constructed so as to make contact in one direction when not pressed down1 and in the other when pressed down1 to signal from either end of a circuit1 using only one line wire and one return4 ,the mode of connecting up for this purpose is shown at ,fig4 #he4 ,at each end we have a battery and bell1 with a double contact ,morse key as shown1 the ,morse key at each end being connected through the intervention of the line wire through the central stud4 ,the batteries and bells at each station are connected to earth plates1 as shown4 ,suppose now we depress the ,morse key at the right-hand station4 ,since by so doing1 we lift the back end of the lever1 we throw our own bell out of circuit1 but make contact between our battery and the line wire4 ,therefore the current traverses the line wire1 enters in the left-hand ,morse key1 and1 since this is not depressed1 can1 and does1 pass into the bell1 which therefore rings1 then descends to the left-hand earth-plate1 returning along the ground to the battery from whence it started at the right-hand ,e4 ,if1 on the contrary1 the left-hand ,morse key be depressed1 while the right-hand key is not being manipulated1 the current traverses in the opposite direction1 and the right-hand bell rings4 ,instead of ,morse keys1 double contact pushes 7that is1 pushes making contact in one direction when not pressed1 and in the opposite when pressed7 may advantageously be employed4 ,this latter arrangement is shown at ,fig4 #hf4 ,illustration3 ,fig4 #hf4 ,it is also possible1 as shown at ,fig4 #hg1 to send signals from two stations1 using but one battery 7which1 if the distance is great1 should be of a proportionate number of cells71 two bells1 and two ordinary pushes4 ,three wires1 besides the earth-plate or return wire1 are required in this case4 ,the whole of the wires1 except the return1 must be carefully insulated4 ,suppose in this case we press the right-hand button4 ,the current flows from the battery along the lower wire through this right-hand push and returns to the distant bell along the top wire1 down the left-hand dotted wire back to the battery1 since it cannot enter by the left-hand press1 which1 not being pushed1 makes no contact4 ,the left-hand bell therefore rings4 ,if1 on the other hand1 the left-hand push be pressed1 the current from the carbon of the battery passes through the left-hand push1 traverses the central line wire1 passes into the bell1 rings it1 and descends to the right-hand earth plate ,e1 traverses the earth circuit till it reaches the left-hand earth plate ,e1 whence it returns to the zinc pole of the battery by the lower dotted line4 ,illustration3 ,fig4 #hg4 ,fig4 #hh shows how the same result 7signalling in both directions7 may be attained1 using only two wires1 with earth return1 and two ,morse keys4 ,the direction of the current is shown by the arrows4 ,both wires must be insulated and either carried overhead or underground1 buried in tubes4 ,fig4 #hi shows the proper mode of connecting the entire system of bells1 pushes1 etc41 running through a building4 ,the dotted lines are the wires starting from the two poles of the battery 7which should consist of more cells in proportion as there is more work to do71 the plain lines being the wires between the pushes and the bell and signalling box4 ,in this illustration a door-pull is shown to the extreme left4 ,pendulum indicators are usually connected up as shown in this figure1 except that the bell is generally enclosed in the indicator case4 ,the wire1 therefore1 has to be carried from the left-hand screw of the indicator case direct to the upper dotted line1 which is the wire returning to the zinc pole of the battery4 ,n4,b4--,when the wires from the press-buttons are connected with the binding-screw1 of the top of or inside of the indicator case1 the insulating material of the wires1 at the point where connection is to be made1 must be removed1 and the wires carefully cleaned and tightly clamped down4 ,illustration3 ,fig4 #hh4 ,illustration3 ,fig4 #hi4 ,when it is desired to connect separate bells to ring in other parts of the building1 the quickest way is to take a branch wire out of the nearest battery wire 7the wire coming from the carbon pole71 and carry it to the push or pull1 from thence to the bell1 and from the bell back to the zinc of the battery4 ,s #gb4 ,we should advise the fixer always to draw out a little sketch of the arrangement he intends to adopt in carrying out any plan1 as any means of saving useless lengths of wire1 etc41 will then easily be seen4 ,in doing this1 instead of making full sketches of batteries1 he may use the conventional signs battery for each cell of the battery1 the thick stroke meaning the carbon1 the thin one the zinc4 ,pushes may be represented by 7471 earth-plates by ,e and pulls1 switches1 c41 as shown in the annexed cut1 ,fig4 #ij1 which illustrates a mode of connecting up a lodge with a house1 continuous bells being used1 in such a way that the lodge bell can be made to ring from the lodge pull1 the house bell ringing or not1 according to the way the switch 7shown at top left-hand corner7 is set4 ,as it is set in the engraving1 only the lodge bell rings4 ,illustration3 ,fig4 #ij4 ,s #gc4 ,there are still two cases of electric bell and signal fitting1 to which attention must be directed4 ,the first is in the case of ships4 ,here all the connections can be made exactly as in a house1 the only exception to be made being that the indicators must not be of the pendulum1 or other easily displaced type2 but either of the form shown at ,fig4 #fg or #fh1 in which the electro-magnet has to lift a latch to release the fall or drop1 against a pretty stiff spring4 ,besides being thus firmly locking1 so as not to be affected by the ship's motion1 all the wood work should be soaked in melted paraffin wax1 the iron work japanned1 and the brass work well lacquered1 to protect all parts from damp4 ,the second case requiring notice is that of lifts4 ,every well-appointed lift should be fitted with electric bells and indicators4 ,in the cab of the lift itself should be placed an electric bell1 with as many double contact pushes and indicators as there are floors to be communicated with4 ,at the top and at the bottom of the left shaft1 as near to the landing side as possible1 must be set two stout wooden blocks 7oak1 elm1 or other non-perishable wood74 ,from top to bottom of the shaft must then be stretched1 in the same manner as a pianoforte is strung1 on stout metal pins1 with threading holes and square heads1 as many ,no4 #ab or #ad bare copper wires as there are floors or landings1 and two more for the battery and return wire respectively4 ,care must be taken that these wires are strung perfectly parallel1 and that they are stretched quite taut1 but not strained1 otherwise they will surely break4 ,to the top of the cab1 and in connection in the usual manner by wires with the bell and indicator 7which1 as in the case of ships1 must be of the locking type1 lest the jolts of the cab disturb their action7 must be attached a number of spoonbill springs1 which press against the naked wires running down the shaft4 ,the shape of these springs 7which should be of brass7 at the part where they press against the bare wires1 is similar to that of the spoon break of a bicycle4 ,some operators use rollers at the end of the spring instead of spoonbills1 but these latter rub the wires and keep up good contact1 while the rollers slip over the wires and do not keep them clean4 ,by means of these springs1 the current from the batteries1 which are best placed either at the top of the lift itself1 or in one of the adjacent rooms 7never at the bottom of the shaft1 owing to the damp which always reigns there71 can be taken off and directed where it is desired1 precisely as if the batteries were in the cab itself4 ,it is usual 7though not obligatory7 to use the two wires furthest from the landing as the go and return battery wires1 and from these1 through the other wires1 all desired communication with the landings can be effected4 ,to obtain this end1 it will be necessary to furnish every landing with a double contact push and bell1 and each bell and push must be connected up to the shaft wires in the following mode3-- ,a wire must be led from the lower contact spring of the double contact push1 to the main battery carbon wire in the shaft4 ,a second wire is led from the upper contact stop of the double contact push to the bell1 and thence to the main battery zinc wire on the shaft4 ,lastly1 a third wire is taken from the upper contact spring of the push and connected to that particular wire in the shaft which by means of the spoonbill springs connects the particular push and indicator in the cab1 destined to correspond with it4 ,it will be seen that with the exception of using the rubbing spoonbill springs and return wires in the shaft1 this arrangement is similar to that illustrated at ,fig4 #hg4 ,illustration3 ,fig4 #ia4 ,a glance at ,fig4 #ia will render the whole system of wiring and connecting up with lifts and landing1 perfectly clear4 ,in connecting the branch lines to the main bare copper wires in the shaft1 in order that the spoonbill springs should not interfere with them1 they 7the ends of the branch wires7 must be bent at right angles1 like a letter ,l1 and the upright portion soldered neatly to the back of the shaft wire4 ,any solder which may flow over to the front of the wire must be carefully scraped off to prevent any bumps affecting the smooth working of the contact springs4 ,it will be evident on examination of ,fig4 #ia1 that if any of the pushes on the landings be pressed1 the circuit is completed between the battery at the top1 through the two battery wires to the bell and one of the indicators to the cab1 and1 on the other hand1 that if a push be pressed in the cab1 a corresponding bell on the landing will be rung1 precisely as in ,fig4 #hg4 ,some fitters employ a many-stranded cable to convey the current to and from the battery to the cab and landing1 instead of the system of stretched wires herein recommended2 but this practice cannot be advocated1 as the continual bending and unbending of this cable1 repeated so frequently every day1 soon breaks the leading wires contained in the cable4 ,s #gd4 ,in many cases where a call bell alone is required1 the battery may be entirely dispensed with1 and a small dynamo 7,s #ae7 employed instead4 ,the entire apparatus is then known as the magneto-bell1 and consists essentially of two parts1 viz41 the generator1 ,fig4 #ib1 and the bell1 ,fig4 #ic4 ,the generator or inductor consists of an armature1 which by means of a projecting handle and train of wheels can be revolved rapidly between the poles of a powerful magnet2 the whole being enclosed in a box4 ,the current produced by the revolution of the armature is led to the two binding screws at the top of the box4 ,by means of two wires1 or one wire and an earth circuit1 the current is led to the receiver or bell case1 ,fig4 #ic4 ,here1 there are usually two bells1 placed very near one another1 and the armature attached to the bell clapper is so arranged between the poles of the double-bell magnets1 that it strikes alternately the one and the other1 so that a clear ringing is kept up as long as the handle is being turned at the generator4 ,illustration3 ,fig4 #ib4 ,illustration3 ,fig4 #ic4 ,illustration3 ,fig4 #id4 ,if a combined generator and bell be fitted at each end of a line1 it becomes possible to communicate both ways2 one terminal of each instrument must be connected to the line1 and the other terminal on each to earth4 ,a combined generator and bell is shown at ,fig4 #id4 ,these instruments are always ready for use1 require no battery or press-buttons4 ,the generator1 ,fig4 #ib1 will ring seven bells simultaneously1 if required1 so powerful is the current set up2 and by using a switch any number of bells1 placed in different positions1 can be rung1 by carrying a separate wire from the switch to the bell4 ,illustration3 ,fig4 #ie4 ,s #ge4 ,our work would not be complete unless we pointed out the means necessary to detect faults in our work4 ,in order to localise faults1 two things are requisite3 first1 a means of knowing whether the battery itself is working properly1 that is to say1 giving the due amount of current of the right pressure1 or ,e4,m4,f42 secondly1 a means of detecting whether there is leakage1 or loss of current1 or break of circuit in our lines4 ,fortunately1 the means of ascertaining these data can be all combined in one instrument1 known as a linesman's galvanometer or detector1 of which we give an illustration at ,fig4 #ie4 ,it will be remembered 7,s #aj7 that if a current be passed over or under a poised magnetic needle1 parallel to it1 the needle is immediately deflected out of the parallel line1 and swings round to the right or left of the current1 according to the direction of the current2 likewise that the needle is deflected farther from the original position as the current becomes stronger4 ,the deflections1 however1 are not proportionate to the strength of the current1 being fairly so up to about #be to #cj degrees of arc out of the original position1 but being very much less than proportionate to the current strength as the needle gets farther from the line of current2 so that a current of infinite strength would be required to send the needle up to #ij deg4 ,on this principle the detector is constructed4 ,it consists of a lozenge-shaped magnetic needle1 suspended vertically on a light spindle1 carrying at one end a pointer1 which indicates on a card1 or metal dial1 the deflection of the needle4 ,behind the dial is arranged a flat upright coil of wire 7or two coils in many cases7 parallel to the needle1 along which the current to be tested can be sent4 ,the needle lies between the front and back of the flat coil4 ,the whole is enclosed in a neat wooden box1 with glazed front to show the dial1 and binding screws to connect up to the enclosed coil or coils4 ,if the coil surrounding the needle be of a few turns of coarse wire1 since it opposes little resistance to the passage of the current1 it will serve to detect the presence of large quantities of electricity 7many ampe'res7 at a low pressure2 this is called a quantity coil4 ,if1 on the other hand1 the coil be one of fine wire1 in many convolutions1 as it requires more pressure1 or ,e4,m4,f41 or intensity to force the current through the fine high-resistance wire1 the instrument becomes one fitted to measure the voltage or pressure of the current1 and the coil is known as the intensity4 ,if both coils are inserted in the case1 so that either can be used at will1 the instrument is capable of measuring either the quantity of electricity passing1 or the pressure at which it is sent1 and is then known as a quantity and intensity detector4 ,no two galvanometers give exactly the same deflection for the same amount of current1 or the same pressure2 the fitter will therefore do well to run out a little table 7which he will soon learn by heart7 of the deflection his instrument gives with #a1 #b1 #c1 #d1 #e and #f ,leclanch'e's coupled in parallel1 when connected with the quantity coil4 ,he will find the smaller sizes give less current than the larger ones4 ,in testing the deflections given by the intensity coil1 he must remember to couple his cells in series1 as he will get no increase in tension or pressure by coupling up in parallel4 ,in either case the cells should be new1 and freshly set up1 say1 within #bd hours4 ,as some of my readers may like to try their skill at constructing such a detector1 ,i transcribe the directions given in ,amateur work by ,mr4 ,edwinson3-- ,s #gf4 ,such an instrument1 suitable for detecting the currents in an electric bell circuit1 may be made up at the cost of a few shillings for material1 and by the exercise of a little constructive ability4 ,we shall need1 first of all1 a magnetised needle2 this can be made out of a piece of watch spring4 ,procure a piece of watch spring two inches long1 soften it by heating it to redness1 and allowing it to cool gradually in a bed of hot ashes2 then file it up to the form of a long lozenge1 drill a small hole in the centre to receive the spindle or pivot1 see that the needle is quite straight1 then harden it by heating it again to a bright red and plunging it at once into cold water4 ,it now has to be magnetised4 ,to do this1 rub it on a permanent horse-shoe1 or other magnet1 until it will attract an ordinary sewing needle strongly1 or wrap it up in several turns of insulated line wire1 and send many jerky charges of electricity from a strong battery through the wire4 ,when it has been well magnetised1 mount it on a spindle of fine hard wire1 and secure it by a drop of solder4 ,we will next turn our attention to the case1 bobbin1 or chamber in which the needle has to work4 ,this may be made out of cardboard entirely1 or the end pieces may be made of ivory or ebonite1 or it may be made out of thin sheet brass2 for our purpose we will choose cardboard4 ,procure a piece of stout cardboard #d-c_/d inches long by #b inches wide1 double it to the form of a ,t3andstickor match-box1 and pierce it in exactly opposite sides1 and in the centre of those sides with holes for the needle spindle4 ,now cut another piece of stout1 stiff cardboard #b-c_/d inches long by #c_/d inch wide1 and cut a slit with a sharp knife to exactly fit the ends of the case or body already prepared4 ,the spindle holes must now be bushed with short lengths of hard brass or glass bugles1 or tubing1 made to allow the spindle free movement1 and these secured in position by a little melted shellac1 sealing-wax1 or glue4 ,the needle must now be placed in the case1 the long end of the spindle first1 then the short end in its bearing2 then1 whilst the case with the needle enclosed is held between the finger and thumb of the left hand1 we secure the joint with a little glue or with melted sealing-wax4 ,the end-pieces are now to be put on1 glued1 or sealed in position1 and set aside to get firm1 whilst we turn our attention to other parts4 ,the case1 #e inches by #d inches by #b inches in depth1 may be improvised out of an old cigar-box1 but is best made of thin mahogany or teak1 nicely polished on the outside1 and fitted with a cover sliding in a groove1 or hinged to form the back of the instrument4 ,the binding screws should be of the pattern known as the telegraph pattern1 fitted with nuts1 shown at ,fig4 #bg4 ,a small brass handle to be fitted to the top of the instrument1 will also be handy4 ,a circular piece of smooth cardboard #c-a_/d inches in diameter1 with a graduated arc1 marked as shown in ,fig4 #ie1 will serve the purpose of a dial1 and a piece of thin brass1 bent to the form of box open down1 will be required as a needle guard4 ,the face of the dial may be a circular piece of glass1 held in a brass ogee1 or a hole the size of the dial may be cut in a piece of thin wood2 this1 glazed on the inside with a square of glass1 may be made to form the front of the instrument over the dial4 ,an indicating needle will also be required for an outside needle2 this is usually made of watch spring1 and nicely blued2 but it may be made of brass or any other metal1 one made of aluminium being probably the best on account of its lightness4 ,it must be pierced with a hole exactly in the centre1 so as to balance it as the beam of scales should be balanced1 and should one end be heavier than the other it must be filed until they are equal4 ,we will now turn our attention to the coil4 ,procure sixpennyworth of ,no4 #cf silk-covered copper wire and wind three layers of it very evenly on the coil case or bobbin1 being careful in passing the needle spindle not to pinch it or throw it out of truth4 ,when this has been wound on1 it will be found that one end of the wire points to the left and the other end to the right4 ,these are destined to be connected to the under side of the binding screws shown on the top of ,fig4 #ie4 ,we therefore secure them to their respective sides with a touch of sealing wax1 and leave enough wire free at the ends to reach the binding screws--say1 about #f inches4 ,it is handy to have an additional coil for testing strong currents1 and as this may be combined in one instrument at a trifle additional cost1 we will get some line wire 7,no4 #bb7 and wind six or eight turns of it around the coil outside the other wire2 one end of this wire will be attached to an additional binding screw placed between the others1 and the other end to left binding screw shown4 ,the coil thus prepared may now be mounted in position4 ,pierce the board dial and the wood at its back with a hole large enough for the needle spindle to pass through from the back to the centre of the dial4 ,see that the thick end of the inside needle hangs downwards1 then place the coil in the position it is intended to occupy1 and note how far the needle spindle protrudes on the face of the dial4 ,if this is too long1 nip off the end and file it up taper and smooth until it will work freely in a hole in the needle guard1 with all parts in their proper places4 ,this being satisfactory1 secure the coil in its place by sealing wax1 or1 better still1 by two thin straps of brass1 held by screws at each end1 placed across the coil4 ,now clean the free ends of the coil wires1 insert them under the nuts of the binding screws1 fix the indicating needle on the end of the spindle outside1 and see that it hangs in a vertical position with the inside needle when the instrument is standing on a level surface4 ,secure it in this position1 screw on the needle guard1 fasten on the glass face1 and the instrument will be complete4 ,s #gg4 ,provided thus with an efficient detector1 the fitter may proceed to test his work4 ,in cases of new installations1 take the wire off the carbon binding screw of the battery and attach it to one screw of the galvanometer 7on the intensity coil side71 next attach a piece of wire from the other binding screw of the galvanometer 7the central one7 so as to place the galvanometer in circuit4 ,there should be no movement of the needle1 and in proportion to the deflection of the needle1 so will the loss or waste be4 ,if loss is going on1 every means must be used to remedy it4 ,it is of the utmost importance to the effective working of the battery and bells that not the slightest leakage or local action should be allowed to remain4 ,however slight such loss may be1 it will eventually ruin the battery4 ,let damp places be sought out1 and the wires removed from near them4 ,bad or injured coverings must also be looked for1 such as may have been caused by roughly drawing the wires across angular walls1 treading on them1 or driving staples too tightly over them4 ,two or more staples may be touching1 or two or more wires carelessly allowed to lie under one staple4 ,the wire may have been bared in some places in passing over the sharp edges of the zinc tube4 ,the backs of the pushes should be examined to see if too much wire has been bared1 and is touching another wire at the back of the push-case itself4 ,or the same thing may be taking place at the junction with the relays or at the indicator cases4 ,should the defect not be at any of these places1 the indicator should next be examined1 and wire by wire detached 7not cut7 until the particular wire in which the loss is going on has been found4 ,this wire should then be traced until the defect has been discovered4 ,in testing underground wires for a loss or break1 it will be necessary first to uncouple the distant end1 then to disconnect the other end from the instruments1 and attach the wire going underground to the screw of the galvanometer4 ,a piece of wire must then be taken from the other screw of the detector to the carbon end of the battery1 and a second wire from the zinc end of the battery to the earth plate or other connection4 ,proceeding to that part of the wire where the injury is suspected1 the wire is taken up1 and a temporary earth connection having been made 7water main1 gas pipe1 etc471 and by means of a sharp knife connected with this latter1 the covering of the suspected wire penetrated through to the wire1 so as to make a good connection between this suspected wire and the temporary earth plates4 ,if1 when this is done1 the needle is deflected fully1 the injury is farther away from the testing end1 and other trials must be made farther on1 until the spot is discovered4 ,wherever the covering of the wire has been pierced for testing1 it must be carefully recovered1 finished off with ,prout's elastic glue1 or gutta-percha1 and made quite sound4 ,the connections with the earth plates very frequently give trouble1 the wires corrode or become detached from the iron pipes etc41 and then the circuit is broken4 ,s #gh4 ,when the fitter is called to localise defects which may have occurred in an installation which has been put up some time1 before proceeding to work let him ask questions as to what kind of defect there is1 and when and where it evinces itself4 ,if all the bells have broken down1 and will not ring1 either the battery or the main go and return wires are at fault4 ,let him proceed to the battery1 examine the binding screws and connected wires for corrosion4 ,if they are all right1 let the batteries themselves be tested to see if they are giving the right amount of current4 ,this should be done with the quantity coil of the detector4 ,should the battery be faulty1 it will be well to renew the zincs and recharge the battery1 if the porous cell be still in good condition2 if not1 new cells should be substituted for the old ones4 ,should the battery be all right1 and still none of the bells ring1 a break or bad contact1 or short circuit in the main wires near the battery may be the cause of the mischief4 ,if some bell rings continuously1 there must be a short circuit in the push or pushes somewhere2 the upper spring of one of the pushes may have got bent1 or have otherwise caught in the lower spring4 ,pulls are very subject to this defect4 ,by violent manipulations on the part of mischievous butcher or baker boys1 the return spring may be broken1 or so far weakened as not to return the pull into the off position4 ,if1 the batteries being in good order1 any bell rings feebly1 there is either leakage along its line1 or else bad contact in the push or in the connections of the wires to and from the push4 ,there should be platinum contacts at the ends of the push springs2 if there are not1 the springs may have worked dirty at the points of contact1 hence the poor current and poor ringing4 ,it is seldom that the bells themselves1 unless1 indeed1 of the lowest quality1 give any serious trouble4 ,still the set screw may have shaken loose 7which must then be adjusted and tightened up71 or the platinum speck has got solder on its face and therefore got oxidised4 ,this may be scraped carefully with a penknife until bright4 ,or1 purposely or inadvertently1 no platinum is on the speck at all1 only the solder4 ,a piece of platinum foil should be soldered on the spot1 if this is so4 ,or again 7and this only in very bad bells71 the electro-magnets being of hard iron1 may have retained a certain amount of permanent magnetism1 and pull the armature into permanent contact with itself4 ,this can be remedied by sticking a thin piece of paper 7stamp paper will do7 over the poles of the magnet1 between them and the armature4 ,in no case should the fitter cut or draw up out of tubes1 etc41 any wire or wires1 without having first ascertained that the fault is in that wire2 for1 however carefully joints are made1 it is rare that the jointed places are so thoroughly insulated as they were before the cutting and subsequent joining were undertaken4 ,to avoid as much as possible cutting uselessly1 let every binding screw be examined and tightened up1 and every length of wire1 which it is possible to get at1 be tested for continuity before any slashing at the wires1 or furious onslaughts on the indicator be consummated4 ,in conclusion1 ,i beg to record my thanks for the very generous assistance which ,i have received in the compilation of the foregoing pages from the electrical firms of ,messrs4 ,blakey ,emmot1 ,binswanger1 ,gent1 ,judson1 ,jensen1 and ,thorpe4 ,,addendum4 ,,the ,,gassner ,,battery4 ,since the compilation of the foregoing pages1 a dry battery1 known by the above name1 has found great favour with electric-bell fitters4 ,its peculiarity consists in the zinc element forming the outside cell4 ,in this is placed the carbon1 which is separated from the zinc by a thick paste or jelly made of gypsum and oxide of zinc4 ,the cell can be placed in any position1 works as well on its side as upright1 is not subject to creeping1 has an ,e4,m4,f4 of about #a4e volt1 with an internal resistance of only #j4be ohm in the round form1 and #j4f in the flat form4 ,the ,gassner dry battery polarizes much less quickly than the ordinary ,leclanch'e4 ,the only defects at present noticeable1 are the flimsy connections1 and the fact that the outer cases being metal must be carefully guarded from touching one another4 ,this can be effected by enclosing in a partitioned wooden box4 ,,index4 ,a4 ,acid1 ,chromic1 #cc1 #df ---- ,hydrobromic1 #bj ---- ,hydrochloric1 #bj ---- ,hydriodic1 #bj ---- ,nitric1 #bj ---- ,sulphuric1 #bj ,action in ,bichromate1 #dg ---- ,dotting1 #aaf ---- of electric bell1 #ha ---- ,leclanch'e1 #ce ---- ,relay1 #acd ---- ,rubbing1 #aaf ---- of zinc on acids1 #ba ,agglomerate block1 #ch ---- ,cell1 #ch ---- ,compo1 #ch ,alarms1 ,burglar1 #aac ---- ,fire1 #abc ---- ,frost1 #aba ---- ,thermometer1 #abb ---- ,thief1 #aac ---- ,watch1 #abd ,amber1 #a ,ampe're1 #ee ,ampe're's law1 #aa ,annealing iron1 #ac ,arrangement of bells for lifts1 #aga ---- ,ships1 #agj ,attraction1 #c ,b4 ,batteries1 #ah ,battery agglomerate1 #ci ,battery1 ,bichromate1 #dh ---- ,bunsen1 #cc ---- ,chromic acid1 #df ---- ,daniell's1 #bi ---- ,gassner 7addendum71 #ahf ---- ,gent's1 #dd ---- ,gravity1 #ca ---- ,modified1 #abj ---- ,grenet1 #df ---- ,grove1 #cc ---- ,judson's1 #da ---- ,leclanch'e1 #cc ---- ,reversed1 #df ---- ,minotto1 #ca ---- ,smee's1 #bg ---- ,walker's1 #bg ,bell action1 case for1 #hh ,blocks1 wooden1 #aej ,bobbins1 electric bell1 #fg ,box for batteries1 #dc ,brushes1 dynamo1 #ag ,c4 ,cable1 many stranded1 #agd ,case for bell action1 #hh ,cells in parallel1 #eg ---- series1 #ec ,charging fluid1 recipes1 #dh ---- ,fuller1 #di ,circuits1 closed1 #eb1 #aah ---- ,of bells complete in house1 #afh ---- ,for signalling1 #afg ---- ,in both directions1 #afh ,circuits of bells with ,morse key1 #afe ,in parallel1 #afa ,series1 #afb ,with relay1 #afd ,single bell and wire1 #aei ,earth1 #afj ,two pushes1 #afa ,push and pull1 #afa ,open1 #eb ,closed circuit system1 #aah ,code for signalling1 #acj ,coil spring1 #ajh ,conductors1 #c ,connecting up1 #add1 #aei ,contacts1 burglar alarm1 #aac ,door1 #aaf ,drawer1 #aba ,floor1 #aac ,for closed circuits1 #aba ,mackenzie's humming1 #aac ,shop door1 #aaf ,till1 #aba ,watch alarm1 #abd ,window sash1 #aaf ,corrugated carbons1 #da ,creeping in cells1 #dc ,to remedy1 #dd ,callow's attachment1 #ii ,current1 #ed ,to ring bell1 #ade ,d4 ,daniell's cell1 #bi ,action in1 #bi ,deflection of needle1 #i1 #aa ,detector or galvanometer1 to make1 #agh ,detent lever1 #id ,door contact1 #aaf ,dotting action1 #aaf ,drawing out plans1 #afi ,dynamo1 #ae ,armature1 #af ,brushes1 #ag ,commutator1 #ag ,dynamo1 ,cumulative effects1 #ag ,field magnets1 #af ,e4 ,earth1 #eb ,plate1 #ec ,return1 #aec ,electric bell1 action of1 #ha ,armature1 #gd ,base1 #fa ,bobbins1 #fg ,contact screw1 #ge ,continuous1 #ib ,circular bell1 #ajf ,gong1 #gg ,how to make1 #fj ,in lifts1 #aga ,ships1 #agj ,jensen's1 #aja ,joining ,e4 ,m4 wire1 #gc ,magnets1 #fc ,magneto1 #agd ,mining1 #ajf ,paraffining1 #fi ,platinum tip1 #gf ,putting together1 #gh ,single stroke1 #ia ,spring1 #gd ,thorpe's1 #ajj ,trembling1 #ha1 #ij ,winding wire on1 #ga ,wire for1 #fi ,trumpet1 #ajg ,electricity1 sources of1 #b ,electrodes1 #bf ,electro-motive force1 #ea ,electron1 #a ,e4,m4,f41 #ea ,excitation1 #f ,f4 ,faults to detect1 #ahb ,fire alarms1 #abc ,floor contacts1 #aac ,frost alarms1 #aba ,fuller charging1 #di ,g4 ,galvanometer1 #agf ,gas evolved1 #ah ,gassner battery 7addendum71 #ahf ,generator 7magneto71 #agd ,gent's battery1 #dd ,glue1 ,prout's elastic1 #adh ,graphite1 #bg ,gravity battery1 #ca ,daniell battery1 #ca ,modified1 #abj ,grenet battery1 #df ,grove battery1 #cc ,gutta-percha1 #adh ,i4 ,indicator1 #ace ,automatic1 #ach ,drop1 #acf ,electric replacement1 #acf ,gent's1 #adj ,tripolar1 #adc ,mechanical replacement1 #acf ,mode of coupling up1 #adb ,pendulum1 #aci ,polarised1 #aci ,self replacing1 #acf ,semaphore1 #acf ,inductor1 #agd ,insulation1 #fh ,insulators1 #d ,internal resistance1 #ef ,interior of push1 #aea ,iron1 importance of soft1 #fe ,yoke1 #ff ,j4 ,jensen's bell1 #aja ,joining wires to push1 #aea ,judson's cell1 #da ,k4 ,key1 ,morse1 #abi ,l4 ,leakage1 #eb ,leclanch'e cell1 #cc reversed1 #df ,legge's contact1 #aae ,lever switches1 #abh ,lifts1 bells for1 #aga ,localising faults1 #add1 #age ,lodge bell1 #afi ,m4 ,magnetic field1 #ad ,magneto bells1 #age ,electric machines1 #ad1 #ae ,magnets1 #ac ,magnets producing electricity1 #ad ,magnetisation of iron1 #ab ,steel1 #ac ,manganese oxide1 #cc ,minotto cell1 #ca ,modified gravity battery1 #abj ,morse key1 #abi ,musical instrument1 novel1 #ajh ,n4 ,negative electricity1 #g ,non-conductors1 #c ,novel musical instrument1 #ajh ,o4 ,ohm1 #ee ,ohm's law1 #ee ,open circuit1 #eb ,overhead lines1 #aeb ,p4 ,paraffin1 #fi1 #agj ,percha1 gutta1 #adh ,plans1 drawing out1 #afi ,platinum1 riveting1 #gf ,platinum1 use of1 #gf ,plug switches1 #abh ,polarisation1 #bf ,positive electricity1 #g ,proportions of bell parts1 table of1 #hi ,pressels1 #aaa ,prout's elastic glue1 #adh ,pulls1 #aaa ,push1 #ib1 #aea1 #aji ,interior of1 #aea ,joining wires to1 #aea ,r4 ,relay1 #if1 #acc ,action of1 #acd ,repulsion1 #c ,resinous electricity1 #g ,resistance of wire1 table of1 #adf ,return current1 #aec ,riveting platinum1 #gf ,rubbing action1 #aaf ,s4 ,ships1 bells for1 #agj ,shop door contact1 #aaf ,signalling by bells1 #acj ,code1 #acj ,silver platinised1 #bg ,single cell1 #i ,sizes of ,leclanch'e's1 #db ,smee's cell1 #bg ,spring coil1 #ajh ,standard size of wires1 #adf ,switches1 lever1 #abh ,plug1 #abh ,t4 ,table of batteries1 ,e4,m4,f4 and ,r41 #eh ,conductors and insulators1 #d1 #fh ,metals in acid1 #h ,table of ,proportions of bell parts1 #hi ,wire resistance1 etc41 #adf ,testing new work1 #ahb ,old1 #ahc ,thermometer alarms1 #abb ,thorpe's ,ball1 #ajj ,u4 ,use of platinum1 #gf ,v4 ,vitreous electricity1 #g ,volt1 #ec ,w4 ,walker's cell1 #bg ,watchman's clock1 #abd ,water level indicator1 #abg ,washer1 insulating1 #gg ,window sash contact1 #aaf ,wiping contact1 #ajb ,wire covering1 #adg ,in iron pipes1 #aeb ,in wooden boxes1 #aeb ,iron1 #aeb ,joining1 #adh ,to push1 #aea ,laying in tubes1 #adi ,leading1 #adg1 #aej ,overhead1 #aeb ,resistance1 table of1 #adf ,return1 #adg1 #aej ,soldering iron1 #adh ,tinned1 #adg ,underground1 #aeb ,wiring1 general instructions1 #aee ,up1 #add ,z4 ,zinc1 amalgamated1 #bb ,blacking1 #de ,consumption1 #ba ,commercial1 #ai ,pure1 #ai ,,william ,,rider ,,and ,,son1 ,,printers1 ,,london4 99 99 99 99 99 ,small crown #hvo1 cloth4 ,with many ,illustrations4 ,,whittaker',s ,,library ,,of ,,arts1 ,,sciences1 ,,manufactures ,,and ,,industries4 ,,management ,,of ,,accumulators ,,and ,,private ,,electric ,,light ,,installations4 ,a ,practical ,handbook by ,sir ,,david ,,salomons1 ,bart41 ,m4 ,a4 #dth ,edition1 ,revised and ,enlarged1 with #cb ,illustrations4 ,cloth #cs4 ,to say that this book is the best of its kind would be a poor compliment1 as it is practically the only work on accumulators that has been written4--,electrical ,review4 ,,electrical ,,instrument-,,making ,,for ,,amateurs4 ,a ,practical ,handbook4 ,by ,s4 ,r4 ,,bottone1 ,author of ,the ,dynamo1 c4 ,with #fj ,illustrations4 ,second ,edition4 ,cloth #cs4 ,,electric ,,bells4 ,by ,s4 ,r4 ,,bottone4 ,with numerous ,illustrations4 ,,in ,,preparation4 ,,the ,,protection ,,of ,,buildings ,,from ,,lightning4 ,a ,treatise on the ,theory of ,lightning ,conductors from a ,modern ,point of ,view4 ,being the substance of two lectures delivered before the ,society of ,arts in ,march1 #ahhh4 ,by ,,oliver ,j4 ,,lodge1 ,,ll4,d41 ,d4,sc1 ,f4,r4,s41 ,professor of ,physics in ,university ,college1 ,liverpool4 ,published with various amplifications and additions1 with the approval of the ,society of ,arts4 ,,electrical ,,influence ,,machines3 ,containing a full account of their historical development1 their modern ,forms1 and their ,practical ,construction4 ,by ,j4 ,,gray1 ,b4,sc4 ,,electrical ,,engineering ,,in ,,our ,,workshops4 ,a ,practical ,handbook4 ,by ,,sydney ,f4 ,,walker4 ,ready ,shortly 99 99 99 99 99 ,transcriber's ,note ,page #ab3 changed guage to gauge 7444 cotton-covered copper wire1 say ,no4 #bj gauge 4447 ,page #ce3 changed change to charge 7444 losing at the same time its electrical charge 4447 ,page #ee3 changed guage to gauge 7444 #a foot of ,no4 #da gauge pure copper wire 4447 ,page #fd3 changed exaet to exact 7444 of the exact diameter of the turned ends of the cores 4447 ,page #gc3 moved comma ,rivetting1 is to ,rivetting is1 7,rivetting1 is perhaps1 the best mode 4447 ,page #ha3 added hyphen 7444 along the short length of wire to the right-hand binding-screw 4447 ,page #hc3 changed head to heads 7444 the possible defects of electric bells may be classed under four heads3 4447 ,page #ib3 changed its to it 7444 until it rests against the stop or studs47 ,page #ajb3 changed contract-breaker to contact-breaker 7,when the contact-breaker is used1 4447 ,page #ajc3 changed instead to ,instead 7,instead of the armature and clapper 4447 ,page #acb3 in the ,morse code for ,,bring ,,the1 the code for ,h has been corrected from two dots to four dots4 ,page #acf3 changed eletro-magnet to electro-magnet 7444 if the electro-magnet were energised 4447 ,page #acg3 changed idicator to indicator 7since the indicator falls forwards7 ,page #adf3 changed arrangment to arrangement 7the size and arrangement of the batteries and wires7 ,page #adf3 added comma nails1 7444 chance contact with nails1 staples1 metal pipes or other wires 4447 ,page #agi3 changed carboard to cardboard 7444 for our purpose we will choose cardboard47 ,page #agi3 changed ,tanstickor to ,t3andstickor 7444 double it to the form of a ,t3andstickor match-box1 4447 ,page #ahe3 suspected typo 7unchanged7 ,emmot should perhaps be ,emmott 7444 the electrical firms of ,messrs4 ,blakey ,emmot1 4447 ,page #ahf3 changed ,leclanche' to ,leclanch'e 7444 polarizes much less quickly than the ordinary ,leclanch'e47 ,page #ahg3 changed two instances of ,amp'ere to ,ampe're in the index 7,ampe're1 #ee _/ ,ampe're's law1 #aa7