tbe  device  covered  by  the  patent  has  been  in  public  use,  or  on  sale,
for  more  than  two  yeans  prior  to  the  appli'cation  for  th«  patent,
assumes  the  burden  of  proof,  and  is  bound  to  sustain  ttiis  defense
by  clear  and  convincing  testimony.  Proof  resting  wholly  in  the
recollection  of  persons  who  filaim  to  .have  seen  or  rased  such  prior
iJevices  twenty  years  bef®re  they  testified,  wher«  none  of  such
devices  is  produced,  and  it  does  not  appear  that  more  than  one  of
each  kind  was  ever  made,  is  too  unreliable  to  f oi-m  a  safe  basis  for
judicial  action.  Adams  A  Westlake  Manuf.  G©.  v.  Rathbone,  26
Md.  JSep'r,  262.
The  decision  of  tbe  patent-offi«e  is  not  conclusive  upon  the
court  where  priority  of  invention  between  interfering  patents  is  in
question,  but  is  of  sufficient  'weight  to  east  the  burden  of  proof
upon  the  party  against  whom  it  was  Tendered.  Wire  Book  Sewing
Machine  Co.  v.  Stevenson,  11  Md,  Eep'r,  165  ;  13  Hep'r,  422.
285.  General  Bules  of  Evidence  as  io  the  Construction  and

Validity  of  the  Patent,  and  Eoctent  of  the  JUght  it

Confers.
