12 
ME.  GASSIOT  ON  THE  STEATIFICATIONS  AND  DAEK  BAND  IN 
fig.  9 the  discharges  were  parallel  to  each  other;  in  fig.  10  one  discharge  was  made  in 
the  centre  of  the  other. 
Whether  the  discharges  were  made  in  the  same  direction  or  opposed  to  each  other, 
there  were  not  any  signs  of  interference,  the  separate  stratifications  from  the  discharge 
of  each  coil  remaining  visible,  although  producing  a degree  of  confusion  from  their 
interposition. 
These  two  experiments  will  probably  be  considered  strong  e\idence  to  show  that  the 
stratifications  in  the  positive  discharge  do  not  arise  from  interference,  but  from  a succes- 
sion of  impulses  or  pulsations  from  the  force  meeting  a resistiug  medium.  The  positive 
division  of  the  discharge  is  of  a greater  intensity,  and  consequently  much  greater  length 
than  the  negative ; indeed,  as  yet,  we  do  not  know  the  limit : I have  obtained  the  strati- 
fications in  a tube  of  5 feet  3 inches  length,  in  which  as  in  that  of  18  inches  they  are 
beautifully  shown. 
42.  The  dark  discharge  between  the  positive  and  the  negative  I venture  to  assume 
arises  from  interference.  When  the  discharge  is  taken,  in  the  apparatus,  Plate  I.  fig.  7, 
it  is  curious  to  observe  the  stratifications  retreating  from  the  negative  as  the  mercuiT 
ascends  the  tube,  or  following  them  as  they  descend  when  the  vessel  is  being  exhausted, 
the  dark  line  of  discharge  being  compressed  or  expanded  in  proportion  as  the  length  of 
the  stratifications  is  increased  or  decreased. 
Mr.  Geove,  in  his  note  to  his  paper,  to  which  I have  already  referred,  says,  “ ha-ving 
in  my  mind  the  analogy  of  interference,  it  seemed  to  me  that  this  dark  space  might  be 
due  to  the  crossing  of  the  lines  of  discharge  from  successive  points  of  the  needle,  the 
knob,  or  plate  from  which  the  negative  discharge  issues*. 
43.  I made  several  experiments  in  order  to  ascertain  the  cause  of  the  red  strata  on  the 
negative  mercury  (12.  16.  23.  25.),  which  was  evidently  identical  with  the  red  glow  of 
the  platinum,  described  by  Dr.  Robinson  (5.)  as  giving  the  wire,  by  an  optical  delusion, 
the  appearance  of  being  red-hot ; in  one  of  the  apparatus  (Plate  I.  fig.  1)  the  negative 
terminal,  lower  wire  in  a short  time  became,  for  about  half  its  length  inside  the  tube, 
coated  with  mercury,  while  the  remaining  half  presented  the  corroded  black  appearance 
already  referred  to  (25.) ; in  this  state,  when  the  discharge  was  made,  the  red  gloAv  was 
very  brilliant  on  the  black  portion  of  the  wire ; but  the  other,  which  was  the  fui'thest  from 
the  glass,  was  enveloped  with  white  phosphorescence. 
The  pear-shaped  apparatus  (23.),  Plate  I.  fig.  5,  is  filled  with  new  mercury;  in  this 
there  is  now  not  any  sign  of  red  glow,  while  in  the  long  tube  (fig.  7)  it  is  most  brilhant, 
giving  the  lower  portion  of  the  negative  discharge  a beautiful  rose-coloured  tint,  gradually 
shading  off  through  pale  blue  into  the  dark  space ; the  glow  was  also  seen  in  apparatus, 
Plate  I.  fig.  1.  I have  not  any  note  whether  the  mercury  inserted  in  this  apparatus  was 
new,  but  that  in  the  long  tube  (fig.  7)  had  been  previously  used  and  cleaned  in  the  usual 
manner,  first  with  dilute  nitric  acid,  then  with  water,  the  mercury  being  subsequently  dried. 
The  red  glow  on  the  surface  may  be  due  to  some  impurity  in  the  mercury ; it  is  always 
* Philosophical  Magazine,  December  1852,  p.  514. 
