from  Lightning  at  Purfleet.  293 
the  air  furrounding  it,  the  leaft  violence  exerted  muft 
necefiarily  difturb  it. 
And  although  experience  hath  taught  us  how  to  vary 
the  natural  quantity  of  this  fluid  in  many  fubftances,  in 
confeqlience  of  violence ; yet  the  fame  experience  hath 
likewife  taught  us,  that  we  cannot  increafe  that  quantity 
in  any  particular  fubftance,  without  taking  it  from  the 
general  flock  contained  in  the  earth  or  air  furrounding  it : 
and  therefore,  when  this  fluid  is  fo  increafed,  it  may  be 
properly  faid  to  be  in  an  unnatural  ftate ; and  whilft  it 
remains  fo,  muft  (from  its  elaftic  principle)  be  always 
endeavouring  to  recover  its  natural  one. 
But  experience  hath  alfo  taught  us,  that  metal,  for 
example,  hath  a property  of  receiving  the  fluid  more 
readily,  whenever  it  is  difturbed,  than  moft  other  fub- 
ftances : for  which  reafon  a notion  hath  prevailed  with 
many,  that  this  property  of  metal  arifes  from  a power  of 
attraction,  which  they  fuppofe  it  poflefles  in  a greater 
degree  than  any  other  fubftance. 
If  this  philofophy  were  true,  it  would  follow,  that  the 
fame  power  which  attracted  the  fluid  into  the  metal 
ought  to  keep  it  there : for  it  cannot  be  fuppofed  to  attract 
the  fluid  at  one  time,  and  then  let  it  go  at  another;  this 
would  be  abfurd,  and  contrary  to  experience.  We  muft 
therefore  try  to  find  a better  reafon  why  metal  is  poflefled 
P p a with 
