156  Mr.  swift’s Account  of 
is  nearly  four  feet  and  a half,  and  is 
formed  with  materials  well  covered  with 
metal.  I place  three  houfes,  ftanding.in 
the  ftate  of  nature  (not  connected  with 
the  culhion)  at  a certain  diftance  from 
the  frame,  and  equally  diftant  from  each 
other,  as  may  be  feen  in  the  fketch  a, 
b,  c,  each  houfe  has  a condu&or,  and  is 
connected  with  magazines  of  powder,  a, 
c ; the  reafon  for  making  the  clouds  a 
femi- circle  is,  that  when  turned  back 
they  may  be  charged  from  the  machine, 
without  affecting,  or  being  affected  by, 
the  points  or  balls  on  the  tops  of  the 
houfes  a,  b,  and  c;  and,  by  means' of  their  motion  round 
their  own  axes,  I can  increafe  or  diminifii  at  pleafure  the 
velocity,  which  is  afcertained  by  the  graduated  edge  of 
the  frame.  I fix  an  electrometer  on  one  of  the  con- 
ductors of  the  machine,  and  put  points  for  the  upper 
terminations  of  the  conductors  of  the  houfes. 
Having  thus  prepared  the  machine,  the  femi-circular 
cloud  being  turned  back,  that  is,  within;  the  machine  is 
charged  till  the  index  of  the  electrometer  lifts  upwards 
01  90  ; the  cloud  being  then  put  in  motion,  as  it  Aides 
along  the  frame,  revolves  over  the  houfe  a,  with  its. 
length  of  41  feet : in  its  paifage  it  empties  itfelf,  the  elec 
3v 
trometer 
