Royal  Society.  529 
backed  up,  as  it  is,  by  the  direct  experiment  on  the  action  of 
alkaline  permanganate  on  picric  acid,  in  which  there  was  no  pro- 
duction of  ammonia,  and  by  the  general  observation  that  sam- 
ples of  water  sometimes  contain  very  little  organic  nitrogenous 
matter  and  very  much  nitrates — is  decisive  against  there  being 
any  risk  of  confounding  nitrates  with  albumen. 
In  making  a  resume  of  the  main  results  of  an  extended  appli- 
cation of  the  new  method  of  analysis,  I  have  to  note  the  fact  of 
the  extraordinary  purity  of  natural  water.  Instead  of  about  a 
grain  per  gallon  of  organic  nitrogenous  matter  (as  indeed  seemed 
not  unlikely  from  the  older  results  obtained  by  incinerating 
water-residues),  the  usual  proportion  of  nitrogenous  organic 
matter  does  not  amount  to  so  much  as  T\  grain  per  gallon,  the 
"  albuminoid  ammonia  "  being  some  0*06  or  007  parts  per  mil- 
lion. By  filtration,  either  through  a  filter  of  sand  and  charcoal 
or  naturally  through  porous  strata,  water  attains  to  exquisite 
purity. 
The  following  results  illustrate  these  facts.     In  one  litre  : — 
Milligrammes  of  albu- 
minoid ammonia. 
New  River,  London 0"05 
Thames,  West  Middlesex  Co.,  London  006 
Woodhead  water,  Manchester  .  .  0*07 
Edinburgh  water-supply  ....  0*07 
Glasgow,  from  Loch  Katrine  .     .     .     0'08 
Chester,  from  Dee 0*06 
Scarborough 0*06 
Spring,  from  Greensand     ....  000 
Caterham,  Kent 0"00 
Kent  Water  Co 002 
Somersetshire 0*01 
Guildford,  Surrey 0*01 
Carefullv  filtered  water       ....  O'Ol 
LXVII.  Proceedings  of  Learned  Societies. 
ROYAL  SOCIETY. 
[Continued  from  p.  473.] 
Feb.  15,  1S72. — George  Biddell  Airy,  C.B.,  President,  succeeded 
by  Mr.  C.  B.  Yignoles  (as  Deputy  appointed  by  the  President),  in 
the  Chair. 
fPHE  following  communication  was  read : — 
-*-      "On  the  Induction  of  Electric  Currents  in  an  Infinite  Plane 
Sheet  of  uniform  conductivity."  By  Prof.  J.  Clerk  Maxwell,  F.R.S. 
1.  When,  on  account  of  the  motion  or  the  change  of  strength 
Phil.  May.  S.  4.  No.  289.  Snppl.  Vol.  43.  2  M 
