an autobiography-第51部分

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g　driven；　the　pile　in　this　respect　being　the　only　support　of　the　apparatus　A　B　C。　So　that；　besides　the　eighty　blows　per　minute　that　the　four…ton　steam　hammer　energetically　deals　out　to　the　head　of　the　pile　from　a　four　foot　fall　the　dead　weight　of　the　apparatus　constantly　acts　as　a　most　effective　〃predisposer〃　to　the　sinking　of　the　pile　into　the　ground；　the　hoisting　chain　D　being　let　slack　the　while；　so　as　to　allow　A　B　C　to　〃follow　down〃　the　pile　H；　while　the　eighty　blows　per　minute　are　incessantly　showered　on　its　head。　　The　upward　stroke　of　the　piston；　with　its　attached　hammer…block　C；　is　arrested　at　the　proper　height　not　only　by　allowing　the　steam　that　raised　it　to　escape；　but　as　soon　as　the　piston　passes　the　escape　holes　X　X；　the　confined　air　above　the　piston　at　O　rebounds；　and　so　aids　most　effectively　in　increasing　the　energy　of　the　fall　of　the　hammer…block　C　on　the　pile　head。

There　was　a　great　deal　of　curiosity　in　the　dockyard　as　to　the　action　of　the　new　machine。　　The　pile…driving　machine…men　gave　me　a　good…natured　challenge　to　vie　with　them　in　driving　down　a　pile。　　They　adopted　the　old　method；　while　I　adopted　the　new　one。　　The　resident　managers　sought　out　two　great　pile　logs　of　equal　size　and　length70　feet　long　and　18　inches　square。　　At　a　given　signal　we　started　together。　I　let　in　the　steam；　and　the　hammer　at　once　began　to　work。　The　four…ton　block　showered　down　blows　at　the　rate　of　eighty　a　minute；　and　in　the　course　of　four　and　a　half　minutes　my　pile　was　driven　down　to　the　required　depth。　　The　men　working　at　the　ordinary　machine　had　only　begun　to　drive。　　It　took　them　upwards　of　twelve　hours　to　complete　the　driving　of　their　pile！

Such　a　saving　of　time　in　the　performance　of　similar　workby　steam　versus　　manual　labourhad　never　before　been　witnessed。　The　energetic　action　of　the　steam　hammer；　sitting　on　the　shoulders　of　the　pile　high　up　aloft；　and　following　it　suddenly　down；　the　rapidly　hammered　blows　keeping　time　with　the　flashing　out　of　〃the　waste　steam　at　the　end　of　each　stroke；　was　indeed　a　remarkable　sight。　　When　my　pile　was　driven；　the　hammer…block　and　guide　case　were　speedily　re…hoisted　by　the　small　engine　that　did　all　the　labouring　and　locomotive　work　of　the　machine；　the　steam　hammer　portion　of　which　was　then　lowered　on　to　the　shoulders　of　the　next　pile　in　succession。　Again　it　set　to　work。　At　this　the　spectators　crowding　about　in　boats；　pronounced　their　approval　in　the　usual　British　style　of　〃three　cheers！〃　My　new　pile…driver　was　thus　acknowledged　as　another　triumphant　proof　of　the　power　of　steam。

The　whole　of　the　piles　for　this　great　work　were　speedily　driven　in。　The　wall　was　constructed；　and　the　docks　were　completed　in　an　unusually　short　time。　　The　success　of　my　pile…driver　was　followed　by　numerous　orders。　　It　was　used　for　driving　the　immense　piles　required　for　the　High　Level　Bridge　at　Newcastle；　the　great　Border　Bridge　at　Berwick…upon…tweed；　the　Docks　at　Tynemouth；　the　Docks　at　Birkenhead；　the　Docks　at　Grimsby；　the　new　Westminster　Bridge；　the　great　bridge　at　Kief　in　Russia；　the　bridge　at　Petersburg；　the　forts　at　Cronstadt；　the　Embarrage　of　the　Nile；　at　Yokohama　in　Japan；　and　at　other　places。　It　enabled　a　solid　foundation　to　be　laid　for　the　enormous　superstructures　erected　over　them；　and　thus　contributed　to　the　permanence　of　many　important　undertakings。

The　mechanical　principles　on　which　the　efficiency　of　the　steam　pile…driver　chiefly　depends　are　as　simple　as　I　believe　they　are　entirely　novel　and　original。　　The　shoulder　of　the　pile　acts　as　the　sole　supporter　of　the　ponderous　mass　of　the　hammer…block；　cylinder；　and　guide…box。　　This　heavy　weight　acts　as　a　predisposing　agency　to　force　the　pile　down；　while　the　momentum　given　by　the　repeated　fall　of　the　hammer；　at　eighty　blows　the　minute；　brings　the　constant　dead　weight　into　full　action。　　I　am　not　aware　of　any　other　machine　in　which　such　a　combination　of　mechanical　forces　is　employed。

Another　very　effective　detail　consisted　in　employing　the　waste　steam　in　the　upper　part　of　the　cylinder　for　the　purpose　of　acting　as　a　buffer　to　resist　any　undue　length　of　the　upward　stroke　of　the　piston。　But　for　this　the　cylinder　covers　might　have　been　knocked　off。　The　elastic　buffer　of　waste　steam　also　acted　as　a　help　to　the　downward　blow　of　the　hammer…block。　　The　simplicity　and　effectiveness　of　these　arrangements　formif　I　may　be　allowed　to　say　soa　happy　illustration　of　my　〃Definition　of　Engineering；〃　the　application　of　common　sense　in　the　use　of　materials。

The　folding…up　steam　pipe　with　which　the　steam　was　conveyed　from　the　boiler　to　the　cylinder　at　all　heights；　and　the　way　in　which　the　folding　joints　accommodated　themselves　to　the　varying　height　of　the　cylinder；　was　another　of　my　happy　thoughts。　　In　fact；　this　invention；　like　most　others；　was　the　result　of　a　succession　of　happy　thoughts。　The　machine　in　its　entirety　was　the　result　of　a　number　of　common…sense　contrivances；　such　as　I　generally　delight　in。　　At　all　events；　this　most　effective　and　novel　machine　was　a　special　favourite　with　me。

I　may　mention；　before　concluding　this　branch　of　my　subject；　that　pile…driving　had　before　been　conducted　on　what　I　might　term　the　artillery　or　cannon…ball　principle。　　A　small　mass　of　iron　was　drawn　slowly　up；　and　suddenly　let　down　on　the　head　of　the　pile　at　a　high　velocity。　　This　was　destructive；　not　impulsive　action。　　Sometimes　the　pile　was　shivered　into　splinters；　without　driving　it　into　the　soil；　in　many　cases　the　head　of　the　pile　was　shattered　into　matches；　and　this　in　spite　of　a　hoop　of　iron　about　it　to　keep　the　layers　of　wood　together。　　Yet　the　whole　was　soon　beat　into　a　sort　of　brush。　Indeed；　a　great　portion　of　the　men's　time　was　consumed　in　〃reheading〃　the　piles。　　On　the　contrary；　I　employed　great　mass　and　moderate　velocity。　The　fall　of　the　steam　hammer…block　was　only　three　or　four　feet；　but　it　went　on　at　eighty　blows　the　minute；　and　the　soil　into　which　the　pile　was　driven　never　had　time　to　grip　or　thrust　it　up　an　impediment　well　known　to　ordinary　pile…drivers。　　At　the　end　of　the　driving　by　my　steam　hammer；　the　top　of　the　pile　was　always　found　neat　and　smooth；　indeed　more　so　than　when　the　driving　began。

I　may　again　revert　to　my　interview　with　the　Lords　of　the　Admiralty　on　the　occasion　of　my　first　meeting　them　at　Devonport。　　I　was　residing　at　the　hotel　where　they　usually　took　up　their　quarters　while　making　their　annual　visitation　of　the　dockyard。　　I　was　honoured　with　an　invitation　to　confer　with　Sir　George　Cockburn；　Mr。　Sidney　Herbert；　and　Captain　Brandreth　on　a　subject　of　considerable　importance；　namely；　the　proving　of　chain　cables　and　anchors　required　for　the　Royal　Navy。　　The　question　was　mooted　as　to　whether　or　not　some　permanent　injury　was　done　to　both　by　the　test　strains　to　which　they　were　submitted　before　being　put　on　board　ship。　　This　was　a　subject　of　vital　importance。　　The　members　of　the　Board　requested　me　to　act　as　one　of　a　committee　to　inquire　into　the　subject。　　I　felt　much　gratified　by　the　invitation　and　gladly　accepted　it。

On　discussing　the　subject　with　these　gentlemen　that　evening；　I　found　that　Sir　George　Cockburn　entertained　an　ingenious　theory　in　support　of　his　apprehensions　as　the　effect　of　〃over…proof〃　straining　of　cables　and　anchors。　　It　was　that　they　were　originally　in　the　condition　of　a　strong　man　who　had　to　lift　some　heavy　weight；　requiring　him　to　exert　his　muscular　strength　to　the　utmost；　and；　although　he　might　perform　the　feat；　it　was　at　the　cost　of　a　permanent　injury；　and　that　he　might　never　be　able　to　lift　the　same　weight　again。　　This；　however　true　it　might　be　with　regard　to　flesh　and　bone　structures；　was　scarcely　true　with　respect　to　mechanical　agencies。　　I　proposed　a　simple　experiment　with　chain　cables；　which；　it　occurred　to　me；　would　show　quite　a　different　resultnamely；　that　the　capability　of　resisting　the　severest　proof…strain　would　rise　rather　than　fall　at　each　successive　proof　of　the　same　chain　cable。

To　test　the　correctness　of　my　supposition；　we　had　a　first…class　chain　cable　put　into　the　proof　machine；and　subjected　it　to　such　a　strain　as　to　break　it　again　and　again；　until　at　last　it　was　divided　almost　into　single　links。　　As　I　expected；　the　proof　or　breaking　strain　kept　rising　and　rising　as　each　successive　remaining　portion　of　the　cable　was　torn　asunder；　thus　showing　that　no　injury　to　the　natural　tenacity　of　the　chain　had　resulted　from　the　increased　proofs　to　which　it　had　been　subjected；　and　that　the　last　broken　links　had　been　much　more　resisting　than　the　first。　　The　same　class　of　demonstrative　experiments　was　made　with　anchors；　and　other　wrought…iron　work　used　in　the　service。　The　Admiralty　officers　were　much　gratified　with　the　result；　as　removing　a　groundless　but　very　natural　apprehension；　heightened；　no　doubt；　by　the　suggestions　that　had　been　made　to　the　Admiralty；　that　their　standard　proof　strain　was　not　only　too　high　in　itself；　but　produced　permanent　damage　to　what　at　the　outset　was　of　the　toughest　iron。　My　system　of　continued　proof…straining　was；　in　fact；　another　exemplification　of　the　〃Survival　of　the　Fittest〃！

A　very　interesting　truth　came　out　in　the　course　of　our　experiments。　It　was　that　the　chief　cause　of　failure　in　the　links　of　chain　cables　arose；　not　so　much　from　their　want　of　tenacity；　or　from　the　quality　of　the　iron；　but　from　some　defective　welding　in　the　making　of　the　links。　To　get　at　this　truth；　many　excellent　cables　as　received　from　the　contractors；　as　well　as　veteran　ones　that　had　held　great　ships　riding　at　anchor　in　terrible　gales；　were　pulled　asunder　link　by　link　by　an　intentional　destructive　strain　by　the　proving　machine。　An　exact　account　was　taken　of　the　nature　of　the　fracture　of　each。　The　result　was　that　in　eight　cases　out　of　ten；　the　fracture　was　found　to　result　from　a　defectively　welded　part　of　the　chain…link。　The　practically　trained　eye　could　see　the　scoria　which　indicates　the　defective　welding。　　Though　long　unseen；　it　was　betrayed　at　once　when　the　link　was　torn　open　by　the　proof　strain。

My　services　on　this　committee　proved　a　source　of　great　enjoyment　to　me。　I　had　frequent　occasion　to　visit　the　dockyards　and　workshops；　accompanied　by　Captain　Brandreth；　surveyor…general　of　the　Admiralty　landworks；Mr。　Thomas　Lloyd；　engineer…in…chief　of　the　Admiralty；　and　Mr。　Jeremiah　Owen；　chief　of　the　metal　material　required　in　the　equipment　o