M.  0.  E.  Meyer  on  Anomalous  Dispersion  of  Light.      295 
ceteris  paribus,  to  the  square  of  the  earth's  velocity,  because  the 
motion  of  the  aether  which  it  generates  is  propagated  in  space 
with  that  velocity,  inasmuch  as  it  travels  with  the  earth.  But 
besides  this,  such  impressed  force  evidently  vanishes  if  p,  =  l. 
Therefore,  putting  V  for  the  earth's  velocity,  let  us  assume  that 
this  force  acting  in  the  direction  0  Oj  (figs.  I  and  2)  is  measured 
by  Vs  (l )  .     Then  on  the  same  scale  the  elastic  force  in 
a'* 
OWj  is  measured  by  -^.     The  former  force  would  give  rise  to 
a  velocity  of  propagation  equal  to  V  (  1 J    in  the  direction 
a!  . 
0  0^  and  the  latter  to  a  velocity  of  propagation  —  in  the  direc- 
tion  OW,.  Consequently,  if  the  angle  Wj  0W2  be  equal  to  the 
/        1\       a'         V 
ratio  of  V  (  1 J  to  — ,  or  —  (p,— 1),  the  resulting  direction 
of  propagation  will  be  in  0  W2.  This  in  fact  is  the  value  of  that 
angle  which,  as  already  shown,  satisfies  the  phenomena  of  aber- 
ration. Hence  the  dragging  of  the  ray  assumed  in  the  theory 
of  aberration  is  in  this  manner  accounted  for  on  the  Undulatory 
Theory  of  Light. 
Independently  of  the  truth  of  the  foregoing  theoretical  expla- 
nation, it  may  safely  be  asserted  to  be  a  consequence  of  the  an- 
tecedent argument  respecting  aberration,  that  whatever  accounts 
for  the  displacement  of  the  ray  in  M.  Hoek's  experiment  accounts 
for  it  also  in  the  Greenwich  experiment,  and  that  the  fact  that 
no  aberration  beyond  the  usual  amount  was  obtained  by  the 
letter  necessarily  results  from  the  non-existence  of  aberration 
established  by  the  other. 
Cambridge,  March  16,  18/2. 
XXXV.  An  Attempt  to  Account  for  Anomalous  Dispersion  of 
Light.     By  Oscar  Emil  Meyer*. 
IN  this  memoir  I  communicate  a  theory  which  I  projected  in 
the  year  1863,  to  account  for  the  anomalous  dispersion 
which  was  then  known  only  in  the  case  of  the  metals  and  the 
vapour  of  iodine.  I  have  hitherto  refrained  from  publishing  it, 
because  it  did  not  appear  to  me  quite  satisfactory.  But  I  think 
that  I  ought  no  longer  to  withhold  it,  now  that  the  discovery  of 
*  Translated  from  a  separate  copy,  communicated  by  the  Author,  from 
Poggendorff's  Annalen,  vol.  cxlv.  pp.  80-86. 
