Observations  on  the  Corona  seen  during  the  late  Eclipse,     191 
according  as  we  wish  to  measure  in  terms  of  a  volt  or  of  our 
standard  ordinary  cell.  We  then  bring  the  needle-point  of  the 
frame  to  the  first  of  the  lines  and  adjust  the  resistance  until  the 
index  coincides  with  the  line  and  cross  wires  ;  we  next  shift  the 
frame  until  the  needle-point  is  at  the  second  position,  and  re- 
sistance is  added  to  the  circuit  until  the  index  agrees  a  second 
time  with  the  line  and  cross  wires.  The  amount  of  resistance 
added  is  a  measure  of  the  electromotive  force.  If  the  y9^ 
shunts  are  used,  each,  unit  of  the  added  resistance  represents 
one  tenth  of  the  force  of  the  standard  cell  or  the  volt/ as 
the  case  may  be.  If  the  -f§$$  shunts  are  used,  each  unit  re- 
presents the  force  of  one  cell  or  volt.  If  the  -f$  shunts  are 
used,  each  unit  represents  the  one  hundredth  of  the  force  of 
the  standard  cell  or  volt  ;  and,  finally,  if  no  shunt  at  all  is 
used,  each  unit  represents  one  thousandth  of  the  force  of  the 
standard  cell  or  volt.  These  measurements  are  quite  suffici- 
ently accurate  for  ordinary  use  in  testing  telegraph-batteries, 
and  are  quickly  and  easily  taken. 
Arconum,  January  10,  1872. 
XXI.  Observations  on  the  Corona  seen  during  the  Eclipse  of  Be- 
cember  Wth  and  12th,  1871.  By  G.  K.  Winter,  Telegraph 
Engineer,  Madras  Railway*. 
[With  a  Plate.] 
MY  letter  referring  to  the  radial  polarization  of  the  corona, 
published  in  the  Number  for  January  1870,  will  doubt- 
less be  remembered. 
I  was  again  the  polariscope-observer  in  Mr.  Pogson's  party  on 
behalf  of  the  Madras  Government  at  the  eclipse  of  the  11th  and 
12th  of  December  last ;  and  as  I  fear  there  may  be  some  un- 
avoidable delay  in  the  publication  of  the  official  report,  I  hope 
the  following  remarks  upon  the  additional  results  obtained  by 
myself  and  others  may  not  be  found  without  value  during  the 
discussion  of  the  question. 
The  instrument  I  used  consisted  of  a  small  telescope  of 
2"*75  aperture  and  about  30"  focal  length,  mounted  equato- 
rially.  In  front  of  the  eyepiece  was  a  polarimeter,  consisting 
of  four  plates  of  thin  glass  mounted  in  a  frame  moveable  on 
an  axis  at  right  angles  to  the  direction  of  the  bands  in  a 
Savart's  polariscope,  which  was  fixed  in  front  of  the  frame; 
so  that  the  rays  from  the  object-glass  passed  first  through 
the  eyepiece,  next  through  the  four  plates  of  glass,  and  lastly 
*  Communicated  by  the  Author. 
