2 
ME.  GASSIOT  ON  THE  STEATIFICATIONS  AND  DAEK  BAND  IN 
electricians,  who  all  describe  the  intense  white  light  loithout  stratification  produced  in 
the  barometrical  vacuum*. 
5.  The  Rev.  Dr.  Robinson,  who  has  made  a series  of  beautiful  experiments  "uith  the 
inductive  coilf , says,  “ Nothing  satisfactory  has  yet  been  ascertained  as  to  the  cause  of  the 
stratification  of  light.  Mr.  Grove  appears  to  think  that  it  arises  from  some  vibration 
in  the  metal  of  the  contact  breaker,  which  produces  a fluctuation  in  the  inducing 
current ; he  flnds  that  it  is  not  always  visible  in  the  light  caused  by  a single  discharge,  ' 
and  that  it  is  influenced  by  the  nature  of  the  metals  between  w'hich  the  inteiTuption 
spark  occurs.”  Dr.  Robinson,  in  a prexious  communication  to  the  Royal  Irish  Aca- 
demyj,  considered  that  the  fact  of  their  being  produced  by  a single  discharge,  shows 
that  they  do  not  depend  on  the  discontinuity  of  the  current ; and  in  a note  to  his  paper 
of  December  1856,  he  adds,  “as  the  rarefaction  proceeds,  the  intensity  of  the  spark  at 
the  contact  breaker  decreases,  and  also  we  should  suppose  the  xibration  there,  yet  the 
stratiflcation  becomes  more  decided ; this  seems  against  Mr.  Grove’s  hypothesis.”  AMien 
the  discharge  from  the  terminals  of  Ruhmkorff’s  coil  is  taken  in  the  ah’  or  in  vacuo  from 
thin  platinum  wires,  the  negative  terminal  becomes  heated,  and  if  the  discharges  are 
continued  it  is  fused ; in  the  voltaic  battery  it  is  the  positive  terminal  that  is  heated 
by  the  discharge.  In  vacuo  Dr.  Robinson  describes  “ the  negative  terminal  as  wuapt  in 
a coat  of  bright  blue  light,  through  which,  by  an  optical  delusion,  the  platinum  seems 
red-hot.”  Under  some  conditions  the  intense  blue  round  the  negatixe  xvire  xxfiR  appear 
xvithout  the  red  (43.),  in  other  conditions  it  will  appear  red  as  if  intensely  heated,  and 
in  other  instances  white. 
6.  In  Mons.  Du  Moncel’s  work  on  the  Inductive  Coil,  the  stratiflcations  are  flgiu'ed 
as  concave  towards  the  positive  end,  the  concavity  decreasing  as  the  bands  extend  toxvards 
the  negative ; at  the  centre  they  become  straight,  and  then  gradually  concave  toxvards  the 
negative  terminal  until  they  arrive  at  the  dark  space  which  separates  the  bands  from  the 
negative  discharge.  Dr.  Robinson,  in  the  paper  of  January  1856,  already  alluded  to, 
has  given  a drawing  of  the  beautiful  stratiflcations  obtained  by  him  in  the  xacuum  of 
an  air-pump  prepared  with  great  care  over  sulphuric  acid  (34.). 
7.  In  Dr.  Robinson’s  flgure  the  bands  are  all  concave  toxvards  the  positive  terminal, 
this  being  a globe,  while  the  negative  is  a point.  I can  bear  xvitness  to  the  correctness  of 
both  representations ; for  although  I have  not  had  the  pleasure  of  seeing  Dr.  Robinson’s 
experiments,  I have  seen  and  obtained  a somewhat  similar  figure  to  that  xvhich  he  has 
represented  by  using  Mr.  Grove’s  method  xvith  phosphorus  vapour,  xvhile  in  the  vapour 
of  naphtha  I have  on  other  occasions  observed  the  discharge  as  figured  by  Du  Moncel  ; 
these  different  effects  do  not  however  in  any  way  arise,  as  might  be  assumed,  from  the 
difference  of  vapour,  but  from  other  causes,  which  will  be  explained  in  this  paper. 
* In  the  Torricellian  vacuum  the  inductive  spark  is  white,  filling  the  whole  tube. — Noad’s  ‘ Electricity,’ 
4th  edition,  p.  742. 
t Proceedings  of  the  Eoyal  Irish  Academy,  8th  December,  1856. 
J Procedings  of  the  Eoyal  Irish  Academy,  January  14,  1856. 
