from  Lightning  at  Pur  fleet.  275 
the  ftroke  happened,  when  he  received  a blow,  uncom- 
monly violent,  infomuch  that  he  thought  it  exceeded 
greatly  what  he  had  ever  experienced  from  the  great 
cylinder  only. 
exp.  xx.  I now  repeated  the  eighteenth  experiment; 
and  attending  only  to  the  two  cramps  at  the  corner,  there 
appeared,  at  the  inftant  when  the  point  was  ftruck,  a 
fmall  fpark  or  explofion  between  them : which  clearly 
flie wed,  that  the  ftream-like  explofion,  obferved  in  the 
feventeenth  experiment,  was  only  this  fmall  fpark  ac- 
companied with  the  circumftance  of  the  motion  of  the 
model. 
tenth  observation.  From  what  we  have  now  ex- 
perienced it  appears,  that  thunder-clouds,  even  at  reft, 
and  that  ftrike  each  other  at  a given  diftance  with  the 
matter  of  lightning,  occafion  the  fame  phaenomena 
nearly  which  a fingle  cloud  produces  when  motion  is 
introduced. 
exp.  xxi.  When  the  diftance  between  the  two  fub- 
ftitutes  was  made  lefs  in  any  degree  than  the  greateft 
ftriking  diftance  (in  proportion  to  its  diminution  the  cir- 
cumftances  were  lefs  fimilar  to  thofe  in  nature)  it  made  a 
con fider able  difference  in  the  effects ; becaufe  the  fluid 
in  thefe  cafes  palTed  more  freely  from  the  greater  to  the 
lefs  fubftitute : and  the  freer  it  paired  into  the  latter, 
Vol.  LX VIII.  N n the 
