heroes of the telegraph-第21部分

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ess　is　now　generally　known　as　the　'Siemens…Martin；'　and　on　the　Continent　as　the　'Martin…Siemens'　process。

The　regenerative　furnace　is　the　greatest　single　invention　of　Charles　William　Siemens。　　Owing　to　the　large　demand　for　steel　for　engineering　operations；　both　at　home　and　abroad；　it　proved　exceedingly　remunerative。　Extensive　works　for　the　application　of　the　process　were　erected　at　Landore；　where　Siemens　prosecuted　his　experiments　on　the　subject　with　unfailing　ardour；　and；　among　other　things；　succeeded　in　making　a　basic　brick　for　the　lining　of　his　furnaces　which　withstood　the　intense　heat　fairly　well。

The　process　in　detail　consists　in　freeing　the　bath　of　melted　pig…iron　from　excess　of　carbon　by　adding　broken　lumps　of　pure　hematite　or　magnetite　iron　ore。　　This　causes　a　violent　boiling；　which　is　kept　up　until　the　metal　becomes　soft　enough；　when　it　is　allowed　to　stand　to　let　the　metal　clear　from　the　slag　which　floats　in　scum　upon　the　top。　　The　separation　of　the　slag　and　iron　is　facilitated　by　throwing　in　some　lime　from　time　to　time。　　Spiegel；　or　specular　iron；　is　then　added；　about　1　per　cent。　more　than　in　the　scrap　process。　　From　20　to　24　cwt。　of　ore　are　used　in　a　5…ton　charge；　and　about　half　the　metal　is　reduced　and　turned　into　steel；　so　that　the　yield　in　ingots　is　from　1　to　2　per　cent。　more　than　the　weight　of　pig　and　spiegel　iron　in　the　charge。　　The　consumption　of　coal　is　rather　larger　than　in　the　scrap　process；　and　is　from　14　to　15　cwt。　per　ton　of　steel。　　The　two　processes　of　Siemens　and　Martin　are　often　combined；　both　scrap　and　ore　being　used　in　the　same　charge；　the　latter　being　valuable　as　a　tempering　material。

At　present　there　are　several　large　works　engaged　in　manufacturing　the　Siemens…Martin　steel　in　England；　namely；　the　Landore；　the　Parkhead　Forge；　those　of　the　Steel　Company　of　Scotland；　of　Messrs。　Vickers　&　Co。；　Sheffield；　and　others。　　These　produced　no　less　than　340；000　tons　of　steel　during　the　year　1881；　and　two　years　later　the　total　output　had　risen　to　half　a　million　tons。　　In　1876　the　British　Admiralty　built　two　iron…clads；　the　Mercury　and　Iris；　of　Siemens…Martin　steel；　and　the　experiment　proved　so　satisfactory；　that　this　material　only　is　now　used　in　the　Royal　dockyards　for　the　construction　of　hulls　and　boilers。　Moreover；　the　use　of　it　is　gradually　extending　in　the　mercantile　marine。　Contemporaneous　with　his　development　of　the　open…hearth　process；　William　Siemens　introduced　the　rotary　furnace　for　producing　wrought…iron　direct　from　the　ore　without　the　need　of　puddling。

The　fervent　heat　of　the　Siemens　furnace　led　the　inventor　to　devise　a　novel　means　of　measuring　high　temperatures；　which　illustrates　the　value　of　a　broad　scientific　training　to　the　inventor；　and　the　happy　manner　in　which　William　Siemens；　above　all　others；　turned　his　varied　knowledge　to　account；　and　brought　the　facts　and　resources　of　one　science　to　bear　upon　another。　　As　early　as　1860；　while　engaged　in　testing　the　conductor　of　the　Malta　to　Alexandria　telegraph　cable；　then　in　course　of　manufacture；　he　was　struck　by　the　increase　of　resistance　in　metallic　wires　occasioned　by　a　rise　of　temperature；　and　the　following　year　he　devised　a　thermometer　based　on　the　fact　which　he　exhibited　before　the　British　Association　at　Manchester。　　Mathiessen　and　others　have　since　enunciated　the　law　according　to　which　this　rise　of　resistance　varies　with　rise　of　temperature；　and　Siemens　has　further　perfected　his　apparatus；　and　applied　it　as　a　pyrometer　to　the　measurement　of　furnace　fires。　　It　forms　in　reality　an　electric　thermometer；　which　will　indicate　the　temperature　of　an　inaccessible　spot。　　A　coil　of　platinum　or　platinum…alloy　wire　is　enclosed　in　a　suitable　fire…proof　case　and　put　into　the　furnace　of　which　the　temperature　is　wanted。　　Connecting　wires；　properly　protected；　lend　from　the　coil　to　a　differential　voltameter；　so　that；　by　means　of　the　current　from　a　battery　circulating　in　the　system；　the　electric　resistance　of　the　coil　in　the　furnace　can　be　determined　at　any　moment。　Since　this　resistance　depends　on　the　temperature　of　the　furnace；　the　temperature　call　be　found　from　the　resistance　observed。　　The　instrument　formed　the　subject　of　the　Bakerian　lecture　for　the　year　1871。

Siemens's　researches　on　this　subject；　as　published　in　the　JOURNAL　OF　THE　SOCIETY　OF　TELEGRAPH　ENGINEERS　（Vol。　I。；　p。　123；　and　Vol。　III。；　p。　297）；　included　a　set　of　curves　graphically　representing　the　relation　between　temperature　and　electrical　resistance　in　the　case　of　various　metals。

The　electric　pyrometer；　which　is　perhaps　the　most　elegant　and　original　of　all　William　Siemens's　inventions；　is　also　the　link　which　connects　his　electrical　with　his　metallurgical　researches。　　His　invention　ran　in　two　great　grooves；　one　based　upon　the　science　of　heat；　the　other　based　upon　the　science　of　electricity；　and　the　electric　thermometer　was；　as　it　were；　a　delicate　cross…coupling　which　connected　both。　　Siemens　might　have　been　two　men；　if　we　are　to　judge　by　the　work　he　did；　and　either　half　of　the　twin…career　he　led　would　of　itself　suffice　to　make　an　eminent　reputation。

The　success　of　his　metallurgical　enterprise　no　doubt　reacted　on　his　telegraphic　business。　　The　making　and　laying　of　the　Malta　to　Alexandria　cable　gave　rise　to　researches　on　the　resistance　and　electrification　of　insulating　materials　under　pressure；　which　formed　the　subject　of　a　paper　read　before　the　British　Association　in　1863。　　The　effect　of　pressure　up　to　300　atmospheres　was　observed；　and　the　fact　elicited　that　the　inductive　capacity　of　gutta…percha　is　not　affected　by　increased　pressure；　whereas　that　of　india…rubber　is　diminished。　　The　electrical　tests　employed　during　the　construction　of　the　Malta　and　Alexandria　cable；　and　the　insulation　and　protection　of　submarine　cables；　also　formed　the　subject　of　a　paper　which　was　read　before　the　Institution　of　Civil　Engineers　in　1862。

It　is　always　interesting　to　trace　the　necessity　which　directly　or　indirectly　was　the　parent　of　a　particular　invention；　and　in　the　great　importance　of　an　accurate　record　of　the　sea…depth　in　which　a　cable　is　being　laid；　together　with　the　tedious　and　troublesome　character　of　ordinary　sounding　by　the　lead…line；　especially　when　a　ship　is　actually　paying　out　cable；　we　may　find　the　requirements　which　led　to　the　invention　of　the　'bathometer；'　an　instrument　designed　to　indicate　the　depth　of　water　over　which　a　vessel　is　passing　without　submerging　a　line。　The　instrument　was　based　on　the　ingenious　idea　that　the　attractive　power　of　the　earth　on　a　body　in　the　ship　must　depend　on　the　depth　of　water　interposed　between　it　and　the　sea　bottom；　being　less　as　the　layer　of　water　was　thicker；　owing　to　the　lighter　character　of　water　as　compared　with　the　denser　land。　　Siemens　endeavoured　to　render　this　difference　visible　by　means　of　mercury　contained　in　a　chamber　having　a　bottom　extremely　sensitive　to　the　pressure　of　the　mercury　upon　it；　and　resembling　in　some　respects　the　vacuous　chamber　of　an　aneroid　barometer。　Just　as　the　latter　instrument　indicates　the　pressure　of　the　atmosphere　above　it；　so　the　bathometer　was　intended　to　show　the　pull　of　the　earth　below　it；　and　experiment　proved；　we　believe；　that　for　every　1；000　fathoms　of　sea…water　below　the　ship；　the　total　gravity　of　the　mercury　was　reduced　by　1/3200　part。　　The　bathometer；　or　attraction…meter；　was　brought　out　in　1876；　and　exhibited　at　the　Loan　Exhibition　in　South　Kensington。　　The　elastic　bottom　of　the　mercury　chamber　was　　supported　by　volute　springs　which；　always　having　the　same　tension；　caused　a　portion　of　the　mercury　to　rise　or　fall　in　a　spiral　tube　of　glass；　according　to　the　variations　of　the　earth's　attraction。　　The　whole　was　kept　at　an　even　temperature；　and　correction　was　made　for　barometric　influence。　　Though　of　high　scientific　interest；　the　apparatus　appears　to　have　failed　at　the　time　from　its　very　sensitiveness；　the　waves　on　the　surface　of　the　sea　having　a　greater　disturbing　action　on　its　readings　than　the　change　of　depth。　　Siemens　took　a　great　interest　in　this　very　original　machine；　and　also　devised　a　form　applicable　to　the　measurement　of　heights。　　Although　he　laid　the　subject　aside　for　some　years；　he　ultimately　took　it　up　again；　in　hopes　of　producing　a　practical　apparatus　which　would　be　of　immediate　service　in　the　cable　expeditions　of　the　s。s。　Faraday。

This　admirable　cable　steamer　of　5；000　tons　register　was　built　for　Messrs。　Siemens　Brothers　by　Messrs。　Mitchell　&　Co。；　at　Newcastle。　　The　designs　were　mainly　inspired　by　Siemens　himself；　and　after　the　Hooper；　now　the　Silvertown；　she　was　the　second　ship　expressly　built　for　cable　purposes。　　All　the　latest　improvements　that　electric　science　and　naval　engineering　could　suggest　were　in　her　united。　　With　a　length　of　360　feet；　a　width　of　52　feet；　and　a　depth　of　36　feet　in　the　hold；　she　was　fitted　with　a　rudder　at　each　end；　either　of　which　could　be　locked　when　desired；　and　the　other　brought　into　play。　　Two　screw　propellers；　actuated　by　a　pair　of　compound　engines；　were　the　means　of　driving　the　vessel；　and　they　were　placed　at　a　slight　angle　to　each　other；　so　that　when　the　engines　were　worked　in　opposite　directions　the　Faraday　could　turn　completely　round　in　her　own　length。　　Moreover；　as　the　ship　could　steam　forwards　or　backwards　with　equal　ease；　it　became　unnecessary　to　pass　the　cable　forward　bef