8 
ME.  GASSIOT  ON  THE  STEATIFICATIONS  AND  DAEK  BAND  IN 
and  sometimes  a third  and  fourth,  each  separated  by  the  dark  striae ; ’ they  were  beauti- 
fully drawn  out  by  approaching  to  them  a magnet. 
27.  When  the  upper  ball  is  positive  and  the  mercmy  is  permitted  to  rise  so  as  to 
cover  the  lower  or  negative  ball,  the  stratifications  instantly  disappear,  as  in  the  pre^ious 
experiment  (26.);  the  tube  is  then  filled  with  beautiful  phosphorescent  light. 
The  difference  in  the  stratification  from  vdres  and  balls  in  this  experiment  probably 
arose  from  the  latter  having  received  a coating  of  liquid  mercury,  and  the  greater 
mobility  of  that  metal  which  thus  formed  the  terminals.  In  this  apparatus  there  was  not 
any  fixed  deposit  on  the  glass ; near  the  negative  ball,  during  the  discharge,  mercurial 
vapour  condensed  on  the  tube  in  a considerable  quantity,  but  this  came  off  when  the 
mercury  ascended  the  tube  and  came  into  contact  with  it ; there  was  not  any  sign  of 
deposit  near  the  positive  ball,  or  on  any  other  portion  of  the  tube. 
28.  Plate  I.  fig.  7 represents  a tube  28  inches  long  and  of  about  l-ths  of  an  inch 
internal  diameter ; it  is  cemented  into  a brass  plate,  a,  and  when  carefully  filled  with  mer- 
cuiy,  was  placed  on  the  open  mouth  of  a receiver  on  the  air-pump,  the  lower  part  of  the 
tube  being  at  the  same  time  immersed  into  a tumbler  of  mercury ; platinum  wires  were 
sealed  in  as  before,  only  in  this  instance  they  were  18  inches  apart;  by  this  arrangement 
I could  Avith  facility  regulate  the  length  of  the  discharge  from  the  i^th  of  an  inch  to  18 
inches,  either  suddenly  or  very  gradually,  by  allowing  the  air  to  enter  into  the  receiver, 
or  by  exhausting  it  with  the  pump ; the  vacuum  was  not  so  good  as  I could  have  desii'ed, 
a very  minute  bubble  of  air  always  remaining ; but  the  stratifications  were  very  distinct 
w’'hen  the  discharge  traversed  the  full  length  of  18  inches. 
If  the  mercury  is  permitted  to  ascend  the  tube,  immediately  it  covers  the  lower  wire, 
the  upper  being  positive,  a dark  discharge,  3 inches  in  length,  appears ; immediately  con- 
tiguous to  this  dark  discharge  there  are  about  four  stratifications  to  the  inch;  towards 
the  upper  part  of  the  tube  they  appear  as  compressed ; about  9 inches  from  the  positive 
terminal  they  are  six  or  seven  to  the  inch,  but  above  this  they  are  very  close ; when  the 
mercury  ascends  to  within  from  7 to  5 inches  of  the  positive  termmal,  all  appearance  of 
stratifications  ceases,  and  in  lieu  thereof  we  have  the  white  phosphorescent  hght  of  the 
barometrical  discharge  (4.).  If,  instead  of  one  or  two  cells,  the  coil  is  excited  by  four  or 
five,  and  care  is  taken  to  manipulate  with  the  contact  breaker  so  as  to  give  sudden  dis- 
charges, the  lower  portions  of  the  striae  assume  a form  as  Plate  I.  fig.  8,  W'hich  repre- 
sents the  diameter  of  the  tube  and  the  striae  as  they  appear  in  the  apparatus. 
29.  If  the  hammer  of  Puhmkoeff’s  contact  breaker  is  removed,  or  the  contact  breaker 
of  Bentley’s  or  of  Heardee’s  is  separated,  the  primary  cu’cuit  can  be  completed  by 
wares  attached  to  the  screws  usually  used  for  the  condenser,  wdiich  in  the  follorving 
experiments  is  used. 
Ha\ing  fixed  two  fiexible  wires  (those  I use  are  made  of  wu’e-rope  covered  with  the 
India-rubber  tubing)  in  the  screws  as  above,  turn  the  commutator  so  as  to  allow"  the 
current  to  pass  through  it : the  primary  circuit  can  now'  be  completed  and  the  secondary 
charged,  by  means  of  tne  flexible  wires  attached  to  the  screw's. 
