I iss  3 
IX.  An  Account  of  Jome  EleBrical  Experiments,  by  Mr. 
William  Swift,  in  a Letter 'to  John  Glen  King,  D.  D. 
F.  R.  S. 
REV.  SIR, 
Greenwich, 
Jan.  26,  1778. 
Read  Jan.  29.  T BEG  leave  to  lay  before  yon  an  account  of 
1 777"  an  electrical  apparatus,  which  I have  con- 
trived, to  fhew  the  different  effeCts  of  points  and  balls  at 
the  upper  terminations  of  conductors,  to  fecure  houfes 
and  magazines  of  powder  from  damage  by  lightning.  I 
have  reprefented  the  clouds,  which  are  added  to  my  ma- 
chine, by  interpofing  three  feet  of  water  infulated,  in- 
Itead  of  continuing  the  metal  from  the  prime  conductor ; 
this  I apprehend  to  be  analogous  to  the  natural  clouds, 
though  it  is  not  in  the  leaft  neceffary  for  the  experiments 
I am  firft  going  to  mention,  the  refults  of  which  are  not 
affeCted  by  one  method  more  than  the  other. 
The  clouds  being  charged  flide  on  a frame  with  a 
graduated  edge;  and,  as  they  pafs  the  length  of  the 
frame,  they  make  five  revolutions  round  their  own  axis ; 
for  they  are  reprefented  by  a femi-circle,  the  radius  of 
which  is  eighteen  inches,  confequently  the  extent  of  it 
Vo  l.  LXVIII.  X is 
