Gray's  work  in  this  field  was  well  known  to  his  telegraphic
contemporaries,  whilst  Bell  was  comparatively  unknown.  It  is  not
surprising  that  the  surface  indications  of  Gray's  caveat,  together
with  his  recognised  standing  in  the  electrical  world,  should  have
produced  an  impression  that  served  to  influence  the  judgment  of
his  friends.  But  going  beneath  the  surface  and  examining  the
specification  of  Bell  and  the  caveat  of  Gray,  it  is  easy  to  see  that  Gray
showed  the  externals  without  the  essentials,  and  Bell  exactly  and
specifically  defined  the  essentials,  but  was  content  with  a  very
general  indication  of  some  of  the  means.
Gray's  words  indicate  that  makes  and  breaks  will  not  produce


104    THE  TELEPHONE  AND  TELEPHONE  EXCHANGES

the  required  result,  but  that  a  single  rod  will  permit  the  transmission
of  the  vibrations  of  the  diaphragm,  which  is  suggestive  of  a  recog-
nition of  the  need  of  an  undulatory  current.  But  the  practical
feature  of  this  suggestion  is  destroyed  when  he  goes  on  to  contemplate
the  use  of  several  diaphragms,  which  were  apparently  intended  to
respond  to  different  vibrations,  and  by  co-operation  were  to  send
to  the  line  a  composite  result.
Bell,  on  the  contrary,  emphasised  the  fact  that  in  order  to  trans-
mit speech  it  was  necessary  to  put  on  to  the  line  a  current  of  a
character  that  had  not  hitherto  been  used.  He  denned  those  which
had  been  used  and  the  kind  of  current  that  needed  to  be  employed.
He  said  in  effect :  You  must  have  an  undulatory  current.  If  you


B.
-a

g

'•;_

D

FIG.  29. — Gray's  Liquid  Transmitter.
