absolute　proof　at　all；　it　is　only　rendered　highly　probable　by　a　series
  of　inductive　and　deductive　reasonings。
  I　suppose　your　first　action；　assuming　that　you　are　a　man　of　ordinary
  common　sense；　and　that　you　have　established　this　hypothesis　to　your　own
  satisfaction；　will　very　likely　be　to　go　off　for　the　police；　and　set
  them　on　the　track　of　the　burglar；　with　the　view　to　the　recovery　of　your
  property。　　But　just　as　you　are　starting　with　this　object；　some　person
  comes　in；　and　on　learning　what　you　are　about；　says；　〃My　good　friend；
  you　are　going　on　a　great　deal　too　fast。　　How　do　you　know　that　the　man
  who　really　made　the　marks　took　the　spoons？　　It　might　have　been　a　monkey
  that　took　them；　and　the　man　may　have　merely　looked　in　afterwards。〃　　You
  would　probably　reply；　〃Well；　that　is　all　very　well；　but　you　see　it　is
  contrary　to　all　experience　of　the　way　tea…pots　and　spoons　are
  abstracted；　so　that；　at　any　rate；　your　hypothesis　is　less　probable　than
  mine。〃　　While　you　are　talking　the　thing　over　in　this　way；　another　friend
  arrives；　one　of　that　good　kind　of　people　that　I　was　talking　of　a　little
  while　ago。　　And　he　might　say；　〃Oh；　my　dear　sir；　you　are　certainly　going
  on　a　great　deal　too　fast。　　You　are　most　presumptuous。　　You　admit　that
  all　these　occurrences　took　place　when　you　were　fast　asleep；　at　a　time
  when　you　could　not　possibly　have　known　anything　about　what　was　taking
  place。　　How　do　you　know　that　the　laws　of　Nature　are　not　suspended
  during　the　night？　　It　may　be　that　there　has　been　some　kind　of
  supernatural　interference　in　this　case。〃　　In　point　of　fact；　he　declares
  that　your　hypothesis　is　one　of　which　you　cannot　at　all　demonstrate　the
  truth；　and　that　you　are　by　no　means　sure　that　the　laws　of　Nature　are
  the　same　when　you　are　asleep　as　when　you　are　awake。
  Well；　now；　you　cannot　at　the　moment　answer　that　kind　of　reasoning。　　You
  feel　that　your　worthy　friend　has　you　somewhat　at　a　disadvantage。　　You
  will　feel　perfectly　convinced　in　your　own　mind；　however；　that　you　are
  quite　right；　and　you　say　to　him；　〃My　good　friend；　I　can　only　be　guided
  by　the　natural　probabilities　of　the　case；　and　if　you　will　be　kind　enough
  to　stand　aside　and　permit　me　to　pass；　I　will　go　and　fetch　the　police。〃
  Well；　we　will　suppose　that　your　journey　is　successful；　and　that　by　good
  luck　you　meet　with　a　policeman；　that　eventually　the　burglar　is　found
  with　your　property　on　his　person；　and　the　marks　correspond　to　his　hand
  and　to　his　boots。　　Probably　any　jury　would　consider　those　facts　a　very
  good　experimental　verification　of　your　hypothesis；　touching　the　cause
  of　the　abnormal　phenomena　observed　in　your　parlour；　and　would　act
  accordingly。
  Now；　in　this　suppositious　case；　I　have　taken　phenomena　of　a　very　common
  kind；　in　order　that　you　might　see　what　are　the　different　steps　in　an
  ordinary　process　of　reasoning；　if　you　will　only　take　the　trouble　to
  analyse　it　carefully。　　All　the　operations　I　have　described；　you　will
  see；　are　involved　in　the　mind　of　any　man　of　sense　in　leading　him　to　a
  conclusion　as　to　the　course　he　should　take　in　order　to　make　good　a
  robbery　and　punish　the　offender。　　I　say　that　you　are　led；　in　that　case；
  to　your　conclusion　by　exactly　the　same　train　of　reasoning　as　that　which
  a　man　of　science　pursues　when　he　is　endeavouring　to　discover　the　origin
  and　laws　of　the　most　occult　phenomena。　　The　process　is；　and　always　must
  be；　the　same；　and　precisely　the　same　mode　of　reasoning　was　employed　by
  Newton　and　Laplace　in　their　endeavours　to　discover　and　define　the
  causes　of　the　movements　of　the　heavenly　bodies；　as　you；　with　your　own
  common　sense；　would　employ　to　detect　a　burglar。　　The　only　difference
  is；　that　the　nature　of　the　inquiry　being　more　abstruse；　every　step　has
  to　be　most　carefully　watched；　so　that　there　may　not　be　a　single　crack
  or　flaw　in　your　hypothesis。　　A　flaw　or　crack　in　many　of　the　hypotheses
  of　daily　life　may　be　of　little　or　no　moment　as　affecting　the　general
  correctness　of　the　conclusions　at　which　we　may　arrive；　but；　in　a
  scientific　inquiry；　a　fallacy；　great　or　small；　is　always　of　importance；
  and　is　sure　to　be　constantly　productive　of　mischievous；　if　not　fatal
  results。
  Do　not　allow　yourselves　to　be　misled　by　the　common　notion　that　an
  hypothesis　is　untrustworthy　simply　because　it　is　an　hypothesis。　　It　is
  often　urged；　in　respect　to　some　scientific　conclusion；　that；　after　all；
  it　is　only　an　hypothesis。　　But　what　more　have　we　to　guide　us　in
  nine…tenths　of　the　most　important　affairs　of　daily　life　than　hypotheses；
  and　often　very　ill…based　ones？　　So　that　in　science；　where　the　evidence
  of　an　hypothesis　is　subjected　to　the　most　rigid　examination；　we　may
  rightly　pursue　the　same　course。　　You　may　have　hypotheses　and
  hypotheses。　　A　man　may　say；　if　he　likes；　that　the　moon　is　made　of　green
  cheese：　that　is　an　hypothesis。　　But　another　man；　who　has　devoted　a
  great　deal　of　time　and　attention　to　the　subject；　and　availed　himself　of
  the　most　powerful　telescopes　and　the　results　of　the　observations　of
  others；　declares　that　in　his　opinion　it　is　probably　composed　of
  materials　very　similar　to　those　of　which　our　own　earth　is　made　up：　and
  that　is　also　only　an　hypothesis。　　But　I　need　not　tell　you　that　there　is
  an　enormous　difference　in　the　value　of　the　two　hypotheses。　　That　one
  which　is　based　on　sound　scientific　knowledge　is　sure　to　have　a
  corresponding　value；　and　that　which　is　a　mere　hasty　random　guess　is
  likely　to　have　but　little　value。　　Every　great　step　in　our　progress　in
  discovering　causes　has　been　made　in　exactly　the　same　way　as　that　which　I
  have　detailed　to　you。　　A　person　observing　the　occurrence　of　certain
  facts　and　phenomena　asks；　naturally　enough；　what　process；　what　kind　of
  operation　known　to　occur　in　nature　applied　to　the　particular　case；　will
  unravel　and　explain　the　mystery？　　Hence　you　have　the　scientific
  hypothesis；　and　its　value　will　be　proportionate　to　the　care　and
  completeness　with　which　its　basis　had　been　tested　and　verified。　　It　is
  in　these　matters　as　in　the　commonest　affairs　of　practical　life：　the
  guess　of　the　fool　will　be　folly；　while　the　guess　of　the　wise　man　will
  contain　wisdom。　　In　all　cases；　you　see　that　the　value　of　the　result
  depends　on　the　patience　and　faithfulness　with　which　the　investigator
  applies　to　his　hypothesis　every　possible　kind　of　verification。
  I　dare　say　I　may　have　to　return　to　this　point　by…and…by；　but　having
  dealt　thus　far　with　our　logical　methods；　I　must　now　turn　to　something
  which；　perhaps；　you　may　consider　more　interesting；　or；　at　any　rate；
  more　tangible。　　But　in　reality　there　are　but　few　things　that　can　be
  more　important　for　you　to　understand　than　the　mental　processes　and　the
  means　by　which　we　obtain　scientific　conclusions　and　theories。1　　Having
  granted　that　the　inquiry　is　a　proper　one；　and　having　determined　on　the
  nature　of　the　methods　we　are　to　pursue　and　which　only　can　lead　to
  success；　I　must　now　turn　to　the　consideration　of　our　knowledge　of　the
  nature　of　the　processes　which　have　resulted　in　the　present　condition　of
  organic　nature。
  Here；　let　me　say　at　once；　lest　some　of　you　misunderstand　me；　that　I　have
  extremely　little　to　report。　　The　question　of　how　the　present　condition
  of　organic　nature　came　about；　resolves　itself　into　two　questions。　　The
  first　is：　How　has　organic　or　living　matter　commenced　its　existence？　And
  the　second　is：　How　has　it　been　perpetuated？　　On　the　second　question　I
  shall　have　more　to　say　hereafter。　　But　on　the　first　one；　what　I　now
  have　to　say　will　be　for　the　most　part　of　a　negative　character。
  If　you　consider　what　kind　of　evidence　we　can　have　upon　this　matter；　it
  will　resolve　itself　into　two　kinds。　　We　may　have　historical　evidence
  and　we　may　have　experimental　evidence。　　It　is；　for　example；
  conceivable；　that　inasmuch　as　the　hardened　mud　which　forms　a
  considerable　portion　of　the　thickness　of　the　earth's　crust　contains
  faithful　records　of　the　past　forms　of　life；　and　inasmuch　as　these
  differ　more　and　more　as　we　go　further　down；it　is　possible　and
  conceivable　that　we　might　come　to　some　particular　bed　or　stratum　which
  should　contain　the　remains　of　those　creatures　with　which　organic　life
  began　upon　the　earth。　　And　if　we　did　so；　and　if　such　forms　of　organic
  life　were　preservable；　we　should　have　what　I　would　call　historical
  evidence　of　the　mode　in　which　organic　life　began　upon　this　planet。　　Many
  persons　will　tell　you；　and　indeed　you　will　find　it　stated　in　many　works
  on　geology；　that　this　has　been　done；　and　that　we　really　possess　such　a
  record；　there　are　some　who　imagine　that　the　earliest　forms　of　life　of
  which　we　have　as　yet　discovered　any　record；　are　in　truth　the　forms　in
  which　animal　life　began　upon　the　globe。　　The　grounds　on　which　they　base
  that　supposition　are　these：That　if　you　go　through　the　enormous
  thickness　of　the　earth's　crust　and　get　down　to　the　older　rocks；　the
  higher　vertebrate　animalsthe　quadrupeds；　birds；　and　fishescease　to
  be　found；　beneath　them　you　find　only　the　invertebrate　animals；　and　in
  the　deepest　and　lowest　rocks　those　remains　become　scantier　and
  scantier；　not　in　any　very　gradual　progression；　however；　until；　at
  length；　in　what　are　supposed　to　be　the　oldest　rocks；　the　animal　remains
  which　are　found　are　almost　always　confined　to　four　forms'Oldhamia'；
  whose　precise　nature　is　not　known；　whether　p