216         INVISIBLE  RADIATION  OP  THE  ELECTRIC  LIGHT. 
With  an  infusion  of  commercial  tobacco,  a  great  part  of  the 
nicotina  comes  over  without  the  addition  of  an  alkali,  and  nearly 
the  whole  quantity  is  obtained  by  adding  a  considerable  excess 
of  ammonia.    This  form  is  likewise  free  from  trimethylina. 
There  is  no  perceptible  difference  in  this  respect  between  a 
decoction  of  the  seed,  and  one  of  the  fresh  plant.  The  distillate 
contains  only  ammonia  [intentionally]  and  nicotina. 
From  the  watery  distillate  of  ordinary  tobacco,  which  had  a 
milky  appearance,  but  gave  no  deposit,  and  contained  both  am- 
monia and  nicotina  in  solution,  after  acidulating  with  sulphuric 
acid,  ether  extracted  a  small  quantity  of  a  substanee,  which  I 
believe  to  be  identical  with  the  soft  resin  described  before. 
Though  the  experiments  delineated  so  far  are  evidently  yet 
incomplete,  they  still  serve  to  answer  the  question  proposed  as 
completely  as  was  possible  at  this  season  of  the  year. 
The  conclusions  which  I  beg  to  submit  are — 
1.  That  nicotina  is  the  active  principal  in  all  parts  of  the 
plant  before  and  after  curing. 
2.  That  there  is  in  all  probability  no  increase,  but  rather  a 
loss  of  nicotina  during  the  drying  and  curing,  partly  or  wholly 
caused  by  volatilization  ;  and 
3.  That  the  plant  or  its  parts  contain  no  trimethylina,  nor 
any  ammonia  while  fresh.  — Proe.  Amer.  Pharm%  Asso.  1865. 
ON  THE  INVISIBLE  RADIATION  OP  THE  ELECTRIC  LIGHT. 
By  John  Tyndall,  F.  K.  S. 
Pending  the  preparation  of  my  complete  memoir,  which  may 
occupy  me  for  some  time  to  come,  I  would  ask  permission  of 
the  Royal  Society  to  lay  before  the  fellows  a  brief  and  partial 
summary  of  the  results  of  my  experiments  on  the  invisible 
radiation  of  the  electric  light. 
The  distribution  of  heat  in  the  spectrum  of  the  electric  light 
was  examined  by  means  of  the  linear  thermo-electric  pile,  ap- 
plied to  the  solar  spectrum  by  Melloni,  Franz,  Miiller,  and 
others.  The  electric  spectrum  was  formed  by  lenses  and  prisms 
of  pure  rock-salt,  its  width  being  equal  to  the  length  of  the 
row  of  elements  forming  the  pile.  The  latter,  standing  at  right 
angles  to  the  length  of  the  spectrum,  was  caused  to  pass  through 
