on  Air,  See.  2 1 1 
imagine  her  ways  to  be  infcrutable ; it  was  merely 
through  ignorance  that  the  ancient  Egyptians  covered 
Ifis  with  a veil,  making  her  declare  that  no  mortal  could 
lift  it  up. 
exp.  xvi.  The  air  over  the  river  Ouze  was  conftantly 
purer  than  that  of  my  garden  by  two  or  three  degrees. 
exp.  xvii.  The  fame  was  obfervable  in  the  air  over 
the  fofs.  This  was  at  a time  when,  in  confequence  of 
floods,  the  current  was  pretty  rapid,  all  the  mud  and 
marfhy  ground  being  covered  to  a confiderable  height 
with  water. 
I next  tried  what  effect  the  fame  waters  might  have  upon 
air,  when  confined  together.  Two  ounces  of  the  water 
was  put  into  an  eight-ounce  phial,  fo  that  there  were  fix 
ounces  of  air;  being  corked  up,  they  were  fuffered  to 
ftand  together  fixteen  hours. 
exp.  xvin.  The  air  from  the  Ouze  water  was  equally 
good  as  at  firft;  and  this  in  feveral  experiments. 
exp.  xix.  The  fame  was  the  refult  in  the  fofs  water. 
It  was  perfectly  free  from  mud,  yet  not  fo  clear  as  the 
river  water,  and  had  fome  of  the  lens  palujlris  fwimming 
in  it. 
Hence  we  find,  that  the  air  was  not  any  way  polluted 
by  ftanding  over  the  furface  of  water.  Perhaps  if  longer 
time  had  been  allowed  in  the  nineteenth  experiment, 
Vol.  LXVIII.  Ee  the 
