202 
The  Chemical  Elements. 
Km.  Jour.  Pharm^ 
April,  1879. 
of  temperature,  or  dissociating  power,  bodies  were  separated  from  each  other.  In 
this  way  Priestly,  from  his  "plomb  rouge,"  separated  oxygen,  and  Davy  separated 
potassium  ;  and  as  a  final  result  of  the  labor  of  generations  of  chemists,  the  million- 
fold  chemical  complexity  of  natural  bodies  in  the  three  kingdoms  of  nature  has  been 
reduced  by  separations  till  only  some  seventy  so  called  elements  are  left. 
Now  this  magnificent  simplification  has  been  brought  about  by  the  employment 
of  moderate  temperatures — moderate,  that  is  to  say,  in  comparison  with  the  trans- 
cendental dissociating  energies  of  electricity  as  employed  in  our  modern  voltaic  arc* 
and  electric  sparks. 
But,  in  the  observations  made  during  the  last  thirty  years  on  the  spectra  of  bodies 
rendered  incandescent  by  electricity,  -zve  have  actually,  though  yet  scarcely  consciously 
been  employing  these  transcendental  temperatures,  and,  if  it  be  that  this  higher  grade  of 
heat  does  what  all  other  lower  grades  have  done,  then  the  spectrum  we  have  observed 
in  each  case  is  not  the  record  of  the  vibrations  of  the  particular  substance  with  which 
we  have  imagined  ourselves  to  be  working  only,  but  of  all  the  simpler  substances 
produced  by  the  series,  whether  short  or  long,  of  the  "  separations  "  effected. 
The  question  then,  it  will  be  seen,  is  an  appeal  to  the  law  of  continuity^ 
nothing  more  and  nothing  less.  Is  a  temperature  higher  than  any  yet  applied  to 
act  in  the  same  way  as  each  higher  temperature,  which  has  been  applied,  has  done  r 
Or  is  there  to  be  some  unexplained  break  in  the  uniformity  of  nature's  processes1' 
The  definite  reason  for  my  asking  the  question  at  the  present  time  has  been  this  ; 
The  final  reduction  of  four  years'  work  at  a  special  branch  of  the  subject  to  which  I 
will  refer  presently,  on  the  assumption  that  at  the  temperature  of  the  electric  arc  we 
do  not  get  such  "  simplifications/'  has  landed  me  in  the  most  helpless  confusion,  and 
if  I  do  not  succeed  in  finding  a  higher  law  than  that  on  which  I  have  been  working,, 
my  four  year's  work,  in  this  direction  at  all  events,  will  have  been  thrown  away. 
This  and  other  reasons  compel  me  to  hold  that  the  answer  to  the  question  put  is, 
that  what  has  been  taken  for  granted  is,  in  all  probability  not  true.  But  before  I 
proceed  to  give  the  reasons  for  the  faith  that  is  in  me  I  must,  at  the  risk  of  being 
both  technical  and  tedious  when  I  should  wish  to  be  neither,  lead  up  to  the  under- 
standing of  them. 
The  spectioscope,  however  simple  or  complex  it  may  be,  is  an  instrument  whicb 
allows  us  to  observe  the  image  of  the  &lit  through  which  the  light  enters  it,  in  the- 
most  perfect  manner.  If  the  light  contains  rays  of  every  wave-length,  then  the 
images  formed  by  each  will  be  so  close  together  that  the  spectrum  will  be  contin- 
uous, that  is,  without  break.  If  the  light  contains  only  certain  wave- lengths,  then 
we  shall  get  certain,  and  not  all,  of  the  possible  images  of  the  slit,  and  the  spectrum 
will  be  discontinuous. 
Again,  if  we  have  an  extremely  complex  light-source,  let  us  say  a  solid  and  a 
mixture  of  gases  giving  us  light,  and  we  allow  the  light  to  enter,  so  to  speak,  Indis- 
criminately into  the  spectroscope,  then  in  each  part  of  the  spectrum  we  shall  get  a 
summation — a  complex  record — of  the  light  of  the  same  wave-length  proceeding 
from  all  the  different  light-waves.  But  if  by  means  of  a  lens  we  form  an  image  of 
the  light-source,  so  that  each  particular  part  shall  be  impressed  in  its  proper  place  on, 
the  slit-plate,  then  in  the  spectrum  the  different  kinds  of  light  will  be  sorted  out. 
