or  TEMPEEATUEE  ON  THE  EEEEACTION  OF  LIGHT. 
893 
The  principal  fixed  lines  were  found  to  have  the  following  refractive  indices  at  13°  C. : — 
A. 
B. 
C. 
D. 
E. 
F. 
G. 
H. 
1-5377 
1-5416 
1-5433 
1-5488 
1*5564 
1-5639 
1-5763 
1-5886 
Hydrate  of  Oresyl. — portion  of  creasote,  which  after  repeated  distillations  boiled  at 
201°  to  205°  C.,  was  submitted  to  examination.  It  consisted  mainly,  no  doubt,  of  the 
higher  homologue  of  hydrate  of  phenyl,  which  has  been  designated  hydrate  of  cresyl, 
differing  from  it  by  one  increment  of  C2H2;  yet  the  liquid  could  scarcely  be  considered 
a pure  specimen  of  that  substance.  It  gave  results  almost  identical  with  those  obtained 
with  hydrate  of  phenyl,  in  the  amount  of  refraction,  dispersion,  and  sensitiveness. 
Phosphorus. — As  phosphorus  is  one  of  the  most  refractive  substances  known,  and  an 
element,  it  was  thought  desirable  to  determine  the  change  produced  in  its  relation  to 
light  by  change  of  temperature.  The  fixed  lines  of  the  spectrum,  however,  could  not  be 
recognized  through  melted  or  solid  phosphorus ; and  when  of  the  ordinary  pale  yellow 
colour,  it  absorbed  the  extreme  red  about  A.  By  employing  a red  glass  as  an  absorbent 
medium,  the  following  determinations  of  the  position  of  the  orange-red  ray  about  C were 
obtained : — 
Temperature. 
Refractive  index 
of  C (about) 
Sensitiveness 
per  5°  C. 
30°  C. 
35 
40 
45 
50 
55 
60 
65 
70 
000000000 
0-0032 
0-0032 
0-0037 
0-0037 
0-0046 
0-0042 
0-0042 
0-0051 
The  extreme  violet  ray  at  40°  had,  as  nearly  as  could  be  determined,  a refractive  index 
of  2‘2356,  giving  the  enormous  length  of  the  spectrum  0T679,  from  C to  H. 
Solid  phosphorus,  at  35°  C.,  was  found  to  give  the  index  2T168  for  the  orange-red 
ray.  On  solidifying,  this  substance  also  experiences  a great  increase  of  density. 
Oil  of  Cassia. — As  this  oil  is  reputed  to  be  one  of  the  most  dispersive  substances 
known,  and  highly  refractive  too,  it  presents  points  of  great  interest ; but  unfortunately 
it  is  no  definite  chemical  compound ; and  the  specimen  examined  by  us,  and  which  was 
said  to  be  very  pure,  was  far  less  dispersive  than  that  employed  by  the  Rev.  Baden 
Powell.  It  had  also  a slight  yellow  tint,  arising  from  the  partial  absorption  of  the  most 
refrangible  rays.  The  following  determinations  were  made,  the  line  G being  necessarily 
measured  instead  of  H : — 
