edge　of　the　cutter　becomes　dull；　and　the　surface　of　the　plate　is
  indented　and　burnished；　instead　of　being　turned。　　Hence　loss　of　time
  on　the　part　of　the　workman；　and　diminished　work　on　the　part　of　the
  tool；　results　which；　considering　the　wages　of　the　one　and　the　capital
  expended　on　the　construction　of　the　other；　are　of　no　small
  importance；　for　the　prime　objects　of　all　improvement　of　tools　are；
  economy　of　time　and　economy　of　capitalto　minimize　labour　and　cost；
  and　maximize　result。
  The　defect　to　which　we　have　referred　was　almost　the　only　remaining
  imperfection　in　the　lathe；　and　Mr。　Clement　overcame　it　by　making　the
  machine　self…regulating；　so　that；　whatever　might　be　the　situation　of
  the　cutter；　equal　quantities　of　metal　should　pass　over　it　in　equal
  times；the　speed　at　the　centre　not　exceeding　that　suited　to　the　work
  at　the　circumference；while　the　workman　was　enabled　to　convert　the
  varying　rate　of　the　mandrill　into　a　uniform　one　whenever　he　chose。
  Thus　the　expedients　of　wheels；　riggers；　and　drums；　of　different
  diameters；　by　which　it　had　been　endeavoured　to　alter　the　speed　of　the
  lathe…mandrill；　according　to　the　hardness　of　the　metal　and　the
  diameter　of　the　thing　to　be　turned；　were　effectually　disposed　of。
  These；　though　answering　very　well　where　cylinders　of　equal　diameter
  had　to　be　bored；　and　a　uniform　motion　was　all　that　was　required；　were
  found　very　inefficient　where　a　Plane　surface　had　to　be　turned；　and　it
  was　in　such　cases　that　Mr。　Clement's　lathe　was　found　so　valuable。　　By
  its　means　surfaces　of　unrivalled　correctness　were　produced；　and　the
  slide…lathe；　so　improved；　became　recognised　and　adopted　as　the　most
  accurate　and　extensively　applicable　of　all　machine…tools。
  The　year　after　Mr。　Clement　brought　out　his　improved　turning…lathe；　he
  added　to　it　his　self…adjusting　double　driving　centre…chuck；　for　which
  the　Society　of　Arts　awarded　him　their　silver　medal　in　1828。　　In
  introducing　this　invention　to　the　notice　of　the　Society；　Mr。　Clement
  said；　〃Although　I　have　been　in　the　habit　of　turning　and　making
  turning…lathes　and　other　machinery　for　upwards　of　thirty…five　years；
  and　have　examined　the　best　turning…lathes　in　the　principal
  manufactories　throughout　Great　Britain；　I　find　it　universally
  regretted　by　all　practical　men　that　they　cannot　turn　anything
  perfectly　true　between　the　centres　of　the　lathe。〃　　It　was　found　by
  experience；　that　there　was　a　degree　of　eccentricity；　and　consequently
  of　imperfection；　in　the　figure　of　any　long　cylinder　turned　while
  suspended　between　the　centres　of　the　lathe；　and　made　to　revolve　by
  the　action　of　a　single　driver。　　Under　such　circumstances　the　pressure
  of　the　tool　tended　to　force　the　work　out　of　the　right　line　and　to
  distribute　the　strain　between　the　driver　and　the　adjacent　centre；　so
  that　one　end　of　the　cylinder　became　eccentric　with　respect　to　the
  other。　　By　Mr。　Clement's　invention　of　the　two…armed　driver；　which　was
  self…adjusting；　the　strain　was　taken　from　the　centre　and　divided
  between　the　two　arms；　which　being　equidistant　from　the　centre；
  effectually　corrected　all　eccentricity　in　the　work。　　This　invention
  was　found　of　great　importance　in　ensuring　the　true　turning　of　large
  machinery；　which　before　had　been　found　a　matter　of　considerable
  difficulty。
  In　the　same　year　（1828）　Mr。　Clement　began　the　making　of　fluted　taps
  and　dies；　and　he　established　a　mechanical　practice　with　reference　to
  the　pitch　of　the　screw；　which　proved　of　the　greatest　importance　in
  the　economics　of　manufacture。　　Before　his　time；　each　mechanical
  engineer　adopted　a　thread　of　his　own；　so　that　when　a　piece　of　work
  came　under　repair；　the　screw…hob　had　usually　to　be　drilled　out；　and　a
  new　thread　was　introduced　according　to　the　usage　which　prevailed　in
  the　shop　in　which　the　work　was　executed。　　Mr。　Clement　saw　a　great
  waste　of　labour　in　this　practice；　and　he　promulgated　the　idea　that
  every　screw　of　a　particular　length　ought　to　be　furnished　with　its
  appointed　number　of　threads　of　a　settled　pitch。　　Taking　the　inch　as
  the　basis　of　his　calculations；　he　determined　the　number　of　threads　in
  each　case；　and　the　practice　thus　initiated　by　him；　recommended　as　it
  was　by　convenience　and　economy；　was　very　shortly　adopted　throughout
  the　trade。　　It　may　be　mentioned　that　one　of　Clement's　ablest
  journeymen；　Mr。　Whitworth；　has；　since　his　time；　been　mainly
  instrumental　in　establishing　the　settled　practice；　and　Whitworth's
  thread　（initiated　by　Clement）　has　become　recognised　throughout　the
  mechanical　world。　　To　carry　out　his　idea；　Clement　invented　his
  screw…engine　lathe；　with　gearing；　mandrill；　and　sliding…table
  wheel…work；　by　means　of　which　he　first　cut　the　inside　screw…tools
  from　the　left…handed　hobsthe　reverse　mode　having　before　been
  adopted；while　in　shaping　machines　he　was　the　first　to　use　the
  revolving　cutter　attached　to　the　slide　rest。　　Then；　in　1828；　he　fluted
  the　taps　for　the　first　time　with　a　revolving　cutter；other　makers
  having　up　to　that　time　only　notched　them。　　Among　his　other　inventions
  in　screws　may　be　mentioned　his　headless　tap；　which；　according　to　Mr。
  Nasmyth；　is　so　valuable　an　invention；　that；　〃if　he　had　done　nothing
  else；　it　ought　to　immortalize　him　among　mechanics。　　It　passed　right
  through　the　hole　to　be　tapped；　and　was　thus　enabled　to　do　the　duty　of
  three　ordinary　screws。〃　　By　these　improvements　much　greater　precision
  was　secured　in　the　manufacture　of　tools　and　machinery；　accompanied　by
  a　greatly　reduced　cost　of　production；　the　results　of　which　are　felt
  to　this　day。
  Another　of　Mr。　Clement's　ingenious　inventions　was　his　Planing
  Machine；　by　means　of　which　metal　plates　of　large　dimensions　were
  planed　with　perfect　truth　and　finished　with　beautiful　accuracy。　　There
  is　perhaps　scarcely　a　machine　about　which　there　has　been　more
  controversy　than　this；　and　we　do　not　pretend　to　be　able　to　determine
  the　respective　merits　of　the　many　able　mechanics　who　have　had　a　hand
  in　its　invention。　　It　is　exceedingly　probable　that　others　besides
  Clement　worked　out　the　problem　in　their　own　way；　by　independent
  methods；　and　this　is　confirmed　by　the　circumstance　that　though　the
  results　achieved　by　the　respective　inventors　were　the　same；　the
  methods　employed　by　them　were　in　many　respects　different。　　As　regards
  Clement；　we　find　that　previous　to　the　year　1820　he　had　a　machine　in
  regular　use　for　planing　the　triangular　bars　of　lathes　and　the　sides
  of　weaving…looms。　　This　instrument　was　found　so　useful　and　so
  economical　in　its　working；　that　Clement　proceeded　to　elaborate　a
  planing　machine　of　a　more　complete　kind；　which　he　finished　and　set　to
  work　in　the　year　1825。　　He　prepared　no　model　of　it；　but　made　it　direct
  from　the　working　drawings；　and　it　was　so　nicely　constructed；　that
  when　put　together　it　went　without　a　hitch；　and　has　continued　steadily
  working　for　more　than　thirty　years　down　to　the　present　day。
  Clement　took　out　no　patent　for　his　invention；　relying　for　protection
  mainly　on　his　own　and　his　workmen's　skill　in　using　it。　　We　therefore
  find　no　specification　of　his　machine　at　the　Patent　Office；　as　in　the
  case　of　most　other　capital　inventions；　but　a　very　complete　account　of
  it　is　to　be　found　in　the　Transactions　of　the　Society　of　Arts　for
  1832；　as　described　by　Mr。　Varley。　　The　practical　value　of　the　Planing
  Machine　induced　the　Society　to　apply　to　Mr。　Clement　for　liberty　to
  publish　a　full　description　of　it；　and　Mr。　Varley's　paper　was　the
  result。*
  ＇footnote。。。
  Transactions　of　the　Society　for　the　Encouragement　of　Arts；　vol。　xlix。
  p。157。
  。。。＇
  It　may　be　briefly　stated　that　this　engineer's　plane　differs　greatly
  from　the　carpenter's　plane；　the　cutter　of　which　is　only　allowed　to
  project　so　far　as　to　admit　of　a　thin　shaving　to　be　sliced　off；the
  plane　working　flat　in　proportion　to　the　width　of　the　tool；　and　its
  length　and　straightness　preventing　the　cutter　from　descending　into
  any　hollows　in　the　wood。　　The　engineer's　plane　more　resembles　the
  turning…lathe；　of　which　indeed　it　is　but　a　modification；　working　up
  on　the　same　principle；　on　flat　surfaces。　　The　tools　or　cutters　in
  Clement's　machine　were　similar　to　those　used　in　the　lathe；　varying　in
  like　manner；　but　performing　their　work　in　right　lines；the　tool
  being　stationary　and　the　work　moving　under　it；　the　tool　only
  travelling　when　making　lateral　cuts。　　To　save　time　two　cutters　were
  mounted；　one　to　cut　the　work　while　going；　the　other　while　returning；
  both　being　so　arranged　and　held　as　to　be　presented　to　the　work　in　the
  firmest　manner；　and　with　the　least　possible　friction。　　The　bed　of　the
  machine；　on　which　the　work　was　laid；　passed　under　the　cutters　on
  perfectly　true　rollers　or　wheels；　lodged　and　held　in　their　bearings
  as　accurately　as　the　best　mandrill　could　be；　and　having　set…screws
  acting　against　their　ends　totally　preventing　all　end…motion。　　The
  machine　was　bedded　on　a　massive　and　solid　foundation　of　masonry　in
  heavy　blocks；　the　support　at　all　points　being　so　complete　as
  effectually　to　destroy　all　tendency　to　vibration；　wi