13、Archimedes  and  the  Gold  Crown
Archimedes  was  a  famous  Greek  scientist.
He  is  regarded  as  one  of  the  leading  scientists  in  classical  era.
He  was  also  a  great  inventor
and  is  given  credit  for  many  inventions  and  discoveries.
One  of  his  best-known  contributions  to  science  is  Archimedes ’principle.
There ’s  an  interesting  story  behind  it.
The  tale  goes  as  follows.
Over  two  thousand  years  ago,
on  the  island  of  Sicily  lived  a  rich  king  called  Heron.
The  king  had  a  golden  crown  which  was  supposed  to  be  made  of  pure  gold.
But  the  king  had  a  suspicion  that  the  crown  contained  some  cheaper  metals  like  silver.
To  prove  his  suspicion,
the  king  asked  Archimedes  to  check  the  golden  crown  to  see
if  it  was  really  made  of  pure  gold,
but  the  crown  could  not  be  harmed  or  damaged  in  any  way.
As  Archimedes  contemplated  this  difficult  problem  in  his  house,
his  servant  prepared  a  bath  for  him.
The  bathtub  was  filled  with  water  to  the  very  brim
and  Archimedes  stepped  into  his  bath.
As  he  sat  down  into  the  tub  fully,
he  noticed  water  spilling  over  the  edge  of  the  tub.
He  suddenly  discovered  the  relation  between  the  water
that  fallen  out  and  the  weight  of  his  body,
and  knew  the  method  to  solve  the  crown  problem.
Archimedes  was  so  excited  with  his  discovery
that  he  jumped  out  of  bath  and  ran  naked  into  the  street,
yelling “Eureka!”（Greek  word  for “I ’ve  found  it!”）
Archimedes  realized  that
his  body  occupying  space  in  the  tub  had  displaced  its  own  weight  of  water  from  the  bath.
All  he  had  to  do  is  put  the  gold  crown  into  a  vessel  with  water  to  the  very  brim.
If  the  overflow  of  water  was  equal  to  the  volume  of  an  equal  mass  of  pure  gold,
the  crown  would  be  made  of  pure  gold.
If  not,the  crown  might  contain  some  cheaper,materials.
And  after  the  experiment,
it  was  clear  that  the  crown  contained  some  cheaper  metals.
This  is  where  Archimedes ’Principle  comes  from.