Am.  Jour.  Pharm.  ) 
December,  1920.  ) 
Isotopy. 
849 
which  modern  chemists  define  their  views  of  combination.  The 
ancient  Greeks  must  have  reached  their  opinion  by  reasoning  alcne, 
for  we  have  no  indication  that  they  carried  out  any  experiments, 
and  as  they  were  substantiahy  unfamihar  with  the  exact  ph3'Sical 
and  chemical  properties  of  gases,  it  does  not  seem  possible  that  they 
could  have  applied  inductive  methods. 
The  atomic  theory  remained  for  many  centuries  unfruitful  and 
merely  a  philosophic  postulate.  That  it  did  not  lead  in  Greece  to  a 
development  of  more  definite  data  is  probably,  in  part  due  to  the 
idealism  that  overwhelmed  the  materialism  of  the  early  thinkers, 
but  at  any  rate  for  many  centuries  the  theory  is  not  active  in  de- 
termining the  course  of  investigation  or  thought.  - 
In  the  early  part  of  the  nineteenth  century,  John  Dalton  pro- 
pounded the  theory  in  a  definite  form,  and  gave  to  the  atom  a 
quantitative  relation  that  made  it  almost  immediately  a  fundamental 
datum  of  chemistry  and  physics,  a  position  which  it  has  held  with- 
out material  modification  until  recent  years.  Dalton 's  claim  to 
priority  in  the  formulation  of  the  modern  atomic  theory  has  been 
lately  challenged  by 'A.  N.  Meldrum,  a  Fellow  of  Bombay  Uni- 
versity, who,  in  a  paper  on  "The  Development  of  the  Atomic 
Theory,"  asserts  that  William  Higgins  published  substantially  the 
same  views  about  fourteen  years  before  Dalton.  This  is  not  the 
place  to  discuss  the  question,  but  it  is  to  be  noted  that  the  modern 
theory  differs  from  the  ancient  one  in  the  distinct  quantitative 
relations  that  the  several  atoms  bear  to  each  other.  In  the  same 
way  the  modern  system  of  symbols  differs  from  the  earlier  ones. 
The  Greek  alchemists  of  the  early  Christian  centuries,  had  symbols 
for  all  the  elements  they  knew,  and  methods  of  expressing  certain 
classes  of  compounds,  especially  alloys,  by  associating  the  symbols, 
but  Berzelius  de^dsed  the  system  in  which  each  symbol  is  not  simply 
an  abbreviation  of  the  name  of  the  element  or  derived  from  fanciful 
associations  of  it,  but  represents  a  definite  weight  in  relation  to  a 
standard.  A  combination  of  the  alchemistic  signs  for  mercury  and 
copper  represents  any  proportion  of  those  substances,  but  CuAg 
represents  a  definite  proportion  by  weight. 
The  theory  of  the  indivisibility  and  practical  inalterability  of 
the  atom  dominated  the  physical  sciences  for  nearly  a  century,  l)ut 
is  now  materially  modified,  this  modification  having  been  brought 
about  principally  by  the  study  of  the  phenomena  of  radio-activity. 
vSpace  does  not  ])ermit  of  (lescri])ti()n  of  the  details  of  the  metliods  ol 
