On  the  Cost  of  Agricultural  Buildings. 
569 
useful  to  receive  and  to  equalize  the  thrust  from  the  ends  of 
butting  timbers ; the  first  particularly,  where  they  are  employed 
as  a connecting  surface  between  the  butting  ends  of  timbers, 
which  from  shrinkage,  defect  of  workmanship,  or  otherwise,  may 
come  to  bear  upon  opposite  angles,  instead  of  the  whole  area  of 
their  intended  connecting  surfaces.  A most  reprehensible  prac- 
tice is  that  of  hammering  and  twisting  straps  and  stirrups  after 
they  are  cold  ; this  should  never  be  permitted,  as  it  cannot  be 
done  without  injuring  wrought-iron. 
The  duties  of  king-posts,  queen-posts,  &c.  being  suspension, 
they  may  be  efficiently,  and  with  advantage,  replaced  by  wrought- 
iron  rods,  as  may  be  all  timber  ties ; from  § of  an  inch  to  inch 
diameter,  will  in  almost  any  case  be  sufficient.  They  should 
pass  through  the  timbers,  and  be  secured  by  nuts  outwardly,  of 
three  times  the  diameter  of  the  bolt ; when  in  connexion  with 
struts,  they  may  pass  through  the  cast-iron  shoe  receiving  the 
strut.  By  these  means  the  tie-beam  may  be  suspended  from  any 
number  of  points,  and  a truss  of  great  span,  with  little  weight, 
constructed. 
The  methods  of  joining  timbers  are  various,  and  require  par- 
ticular attention  from  the  constructor,  as  they  should  always  be 
effected  according  to  the  position  and  strain  on  the  connected 
timbers  at  the  joints;  tenon  and  mortice,  joggle,  notching,  or 
cocking  down,  butting  joints,  scarfing  and  building,  or  modi- 
fications of  these,  are  the  principal  combinations  of  timbers  in 
trusses. 
In  tenon  and  mortice  the  tenon  is  cut  on  the  end  of  one 
timber,  and  the  mortice  is  cut  in  the  face  of  another  to  receive 
the  tenon.  In  the  square  tenon  and  mortice  the  thickness  of 
the  tenon  is  made  one-third  of  that  of  the  timber  in  which  it  is 
cut ; the  shoulders  should  be  in  exactly  one  plane,  and  perpen- 
dicular to  the  axis  of  the  timber  in  which  the  tenon  is  cut.  By 
these  means,  after  shrinkage,  an  equal  bearing  will  be  obtained, 
which  is  most  desirable  in  case  of  weight  on  the  shoulders,  one  of 
which  would  otherwise  have  a tendency  to  split  from  the  main 
timber.  The  cheeks  of  the  tenon  should  also  be  perfectly  parallel 
to  the  axis  of  the  timber ; the  size,  or  sectional  area  of  the  mor- 
tice, should  be  exactly  equal  to  that  of  the  tenon,  but  the  depth  of 
the  mortice  should  rather  exceed  that  of  the  tenon,  that  the  weight 
may  bear  on  the  shoulders,  and  not  on  the  head  of  the  tenon  itself, 
the  area  of  which  is  only  one-half  of  that  of  the  shoulders.  The 
cheeks  of  the  mortice  must  be  quite  parallel  to  the  axis  of  the 
timber  in  which  it  is  cut.  When  acting  by  suspension,  but  little 
depth  is  required,  if  secured  by  a strap.  An  oak  trenail  should 
be  driven  through  mortice  and  tenon,  the  hole  being  pierced  after 
