an autobiography-第93章

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In　order　to　remove　the　cause　of　these　irregularities；　I　placed　a　considerable　portion　of　the　length　of　the　pipe　which　conveyed　the　steam　from　the　boiler　to　the　engine　within　the　highly　heated　side　flue　of　the　boiler；　so　that　any　portion　of　water　in　the　liquid　form　which　might　chance　to　pass　along　with　the　steam；　might；　ere　it　reached　the　cylinder；　traverse　this　highly…heated　steam　pipe；　and；　in　doing　so；　be　converted　into　perfectly　dry　steam；　and　in　that　condition　enter　the　cylinder。　　On　carrying　this　simple　arrangement　into　practice；　I　found　the　result　to　be　in　every　way　satisfactory。　　The　active　little　steam…engine　thence…forward　performed　its　work　in　the　most　smooth　and　regular　manner。

So　far　as　I　am　aware；　this　early　effort　of　mine　at　mechanical　contrivance　was　the　first　introduction　of　what　has　since　been　termed　〃super…heated　steam〃a　system　now　extensively　employed；　and　yielding　important　results；　especially　in　the　case　of　marine　steam…engines。　Without　such　means　of　supplying　dry　steam　to　the　engines；　the　latter　are　specially　liable　to　〃break…downs；〃　resulting　from　water；　in　the　liquid　form；　passing　into　the　cylinders　along　with　the　steam。


1828。　A　Method　of　〃chucking〃　delicate　Metal…work；　in　order　that　it　may　　　　　　　be　turned　with　perfect　truth

In　fixing　portions　of　work　in　the　turning…lathe；　one　of　the　most　important　points　to　attend　to　is；　that　while　they　are　held　with　sufficient　firmness　in　order　to　be　turned　to　the　required　form；　they　should　be　free　from　any　strain　which　might　in　any　way　distort　them。　In　strong　and　ponderous　objects　this　can　be　easily　accomplished　by　due　care　on　the　part　of　an　intelligent　workman。　　It　is　in　operating　by　the　lathe　on　delicate　and　flexible　objects　that　the　utmost　care　is　requisite　in　the　process　of　chucking；　as　they　are　easily　strained　out　of　shape　by　fastening　them　by　screws　and　bolts；　or　suchlike　ordinary　means。　　This　is　especially　the　case　with　disc…like　objects。　　As　I　had　on　several　occasions　to　operate　in　the　lathe　with　this　class　of　work　I　contrived　a　method　of　chucking　or　holding　them　firm　while　receiving　the　required　turning　process；　which　has　in　all　cases　proved　most　handy　and　satisfactory。

This　method　consisted　of　tinning　three；　or；　if　need　be；　more　parts　of　the　work；　and　laying　them　down　on　a　tinned　face…plate　or　chuck；　which　had　been　heated　so　as　just　to　cause　the　solder　to　flow。　　As　soon　as　the　solder　is　cooled　and　set；　the　chuck　with　its　attached　work　may　then　be　put　in　the　lathe；　and　the　work　proceeded　with　until　it　is　completed。　　By　again　heating　the　chuck；　by　laying　upon　it　a　piece　of　red…hot　iron；　the　work；　however　delicate；　can　be　simply　lifted　off；　and　will　be　found　perfectly　free　from　all　distortion。

I　have　been　the　more　particular　in　naming　the　use　of　three　points　of　attachment　to　the　chuck　or　face…plate；　as　that　number　is　naturally　free　from　any　risk　of　distortion。　　I　have　on　so　many　occasions　found　the　great　value　of　this　simple　yet　most　secure　mode　of　fixing　delicate　work　in　the　lathe；　that　I　feel　sure　that　any　one　able　to　appreciate　its　practical　value　will　be　highly　pleased　with　the　results　of　its　employment。

The　same　means　can；　in　many　cases；　be　employed　in　fixing　delicate　work　in　the　planing…machine。　　All　that　is　requisite　is　to　have　a　clean…planed　wrought…iron　or　brass　fixing…plate；　to　which　the　work　in　hand　can　be　attached　at　a　few　suitable　parts　with　soft　solder；　as　in　the　case　of　the　turning　lathe　above　described。


1828。　A　Method　of　casting　Specula　for　Reflecting　Telescopes；　so　as　to　　　　　　　ensure　perfect　Freeness　from　Defects；　at　the　same　time　enhancing　　　　　　　the　Brilliancy　of　the　Alloy。

My　father　possessed　a　very　excellent　achromatic　spy…glass　of　2　inches　diameter。　　The　object…glass　was　made　by　the　celebrated　Ramsden。　When　I　was　about　fifteen　I　used　it　to　gaze　at　the　moon；　planets；　and　sun…spots。　　Although　this　instrument　revealed　to　me　the　general　characteristic　details　of　these　grand　objects；　my　father　gave　me　a　wonderful　account　of　what　he　had　seen　of　the　moon's　surface　by　means　of　a　powerful　reflecting　telescope　of　12　inches　diameter；　made　by　Short　that　justly　celebrated　pioneer　of　telescope　making。　　It　had　been　erected　in　a　temporary　observatory　on　the　Calton　Hill；　Edinburgh。　　These　descriptions　of　my　father's　so　fired　me　with　the　desire　to　obtain　a　sight　of　the　glorious　objects　in　the　heavens　through　a　more　powerful　instrument　than　the　spy…glass；　that　I　determined　to　try　and　make　a　reflecting　telescope　which　I　hoped　might　in　some　degree　satisfy　my　ardent　desires。

I　accordingly　searched　for　the　requisite　practical　instruction　in　the　pages　of　the　Encyclopedia　Britannica；　and　in　other　books　that　professed　to　give　the　necessary　technical　information　on　the　subject。　　I　found；　however；　that　the　information　given　in　booksat　least　in　the　books　to　which　I　had　access　was　meagre　and　unsatisfactory。　　Nevertheless　I　set　to　work　with　all　earnestness；　and　began　by　compounding　the　requisite　alloy　for　casting　a　speculum　of　8　inches　diameter。　　This　alloy　consisted　of　32　parts　of　copper；　15　parts　of　grain　tin；　and　1　part　of　white　arsenic。　These　ingredients；　when　melted　together；　yielded　a　compound　metal　which　possessed　a　high　degree　of　brilliancy。　　Having　made　a　wooden　pattern　for　my　intended　8…inch　diameter　speculum；　and　moulded　it　in　sand；　I　cast　this　my　first　reflecting　telescope　speculum　according　to　the　best　book　instructions。　　I　allowed　my　casting　to　cool　in　the　mould　in　the　slowest　possible　manner；　for　such　is　the　excessive　brittleness　of　this　alloy　（though　composed　of　two　of　the　toughest　of　metals）　that　in　any　sudden　change　of　temperature；　or　want　of　due　delicacy　in　handling　it；　it　is　very　apt　to　give　way；　and　a　fracture　more　or　less　serious　is　sure　to　result。　　Even　glass；　brittle　though　it　be；　is　strong　in　comparison　with　speculum　metal　of　the　above　proportions；　though；　as　I　have　said；　it　yields　the　most　brilliant　composition。

Notwithstanding　the　observance　of　all　due　care　in　respect　of　the　annealing　of　the　casting　by　slow　cooling；　and　the　utmost　care　and　delicate　handling　of　it　in　the　process　of　grinding　the　surface　into　the　requisite　curve　and　smoothness　suitable　to　receive　the　final　polish；　I　was　on　more　than　one　occasion　inexpressibly　mortified　by　the　sudden　disruption　and　breaking　up　of　my　speculum。　　Thus　many　hours　of　anxious　care　and　labour　proved　of　no　avail。　　I　had　to　begin　again　and　proceed　da　capo。　　I　observed；　however；　that　the　surplus　alloy　that　was　left　in　the　crucible；　after　I　had　cast　my　speculum；　when　again　melted　and　poured　out　into　a　metal　ingot　mould；　yielded　a　cake　that；　brittle　though　it　might　be；　was　yet　strong　in　comparison　with　that　of　the　speculum　cast　in　the　sand　mould；　and　that　it　was　also；　judging　from　the　fragments　chipped　from　it；　possessed　of　even　a　higher　degree　of　brilliancy。

The　happy　thought　occurred　to　me　of　substituting　an　open　metal　mould　for　the　closed　sand　one。　　I　soon　had　the　metal　mould　ready　for　casting。　It　consisted　of　a　base　plate　of　cast　iron；　on　the　surface　of　which　I　placed　a　ring　or　hoop　of　iron　turned　to　fully　the　diameter　of　the　intended　speculum；　so　as　to　anticipate　the　contraction　of　the　alloy。　The　result　of　the　very　first　trial　of　this　simple　metal　mould　was　most　satisfactory。　　It　yielded　me　a　very　perfect　casting：　and　it　passed　successively　through　the　ordeal　of　the　first　rough　grinding；　and　eventually　through　the　processes　of　polishing；　until　in　the　end　it　exhibited　a　brilliancy　that　far　exceeded　that　of　the　sand　mould　castings。

The　only　remaining　difficulty　that　I　had　to　surmount　was　the　risk　of　defects　in　the　surface　of　the　speculum。　　These　sometimes　result　from　the　first　splash　　of　the　melted　metal　as　it　is　poured　into　the　ring　mould。　The　globules　sometimes　got　oxidised　before　they　became　incorporated　with　the　main　body　of　the　inflowing　molten　alloy：　and　dingy　spots　in　the　otherwise　brilliant　alloy　were　thus　produced。　　I　soon　mastered　this；　the　only　remaining　source　of　defect；　by　a　very　simple　arrangement。　In　place　of　pouring　the　melted　alloy　direct　into　the　ring　mould；　I　attached　to　the　side　of　it　what　I　termed　a　〃pouring　pocket；〃　which　communicated　with　an　opening　at　the　lower　edge　of　the　ring；　and　by　a　self…acting　arrangement　by　which　the　mould　plate　was　slightly