of  the  Rotation  of  the  Sun.  49 
upon  the  region  near  P.  I  see  the  fine0line  behind  F  (distance 
1*5  ten-millionth  of  a  millimetre;  see  Angstrom's  Atlas)  about 
half  as  far  from  the  line  F  as  the  distance  between  the  sodium- 
lines  amounts  to  in  your  spectroscope.  If  necessary,  one  twen- 
tieth of  this  distance  can  be  estimated.  All  the  estimates  by 
Dr.  Lohse  and  myself  give  not  quite  0*1  of  a  ten-millionth  of  a 
millimetre,  which  would  correspond  to  a  difference  of  velocity  of 
the  equatorial  limbs  of  about  0'7  of  a  mile,  while  in  reality  the 
rotation  amounts  to  2  x  0-27,  therefore  0*54  mile.  When  the 
telescope  was  directed  to  the  north  or  the  south  point  of  the  sun, 
there  was  no  displacement,  therefore  no  flexure  of  the  individual 
parts  of  the  apparatus  during  the  observation.  Accordingly  the 
proof  of  the  rotation  of  the  sun  by  means  of  the  spectroscope  is 
to  be  considered  certain.  I  will,  besides,  repeat  the  experiments 
with  still  higher  magnify  ing-power. 
"Further,  a  second,  not  less  interesting  fact.  In  the  spectra 
of  some  nebuke  (planetary),  which  according^  to  other  observers 
show  only  three  lines,  I  have  been  able  to  find  some  additional 
lines;  of  these  it  is  in  the  highest  degree  probable  that  one, 
quite  distinctly  seen  by  Lohse  and  myself,  is  coincident  with  the 
brightest  line  of  the  aurora  borealis.  This  would  give  rise  to 
remarkable  conclusions." 
A  more  detailed  description  of  these  and  subsequent  observa- 
tions is  given  by  Dr.  Vogel  in  the  following: — 
Observations. 
u  1871,  June  9.  With  the  aid  of  your  reversion-spectroscope 
the  displacement  of  the  lines  by  the  rotation  of  the  sun  was  de- 
cidedly seen  by  Dr.  Lohse  and  myself.  The  experiments  were 
made  in  the  following  manner : — 
"  While  the  spectroscope,  with  the  aid  of  the  clockwork,  was 
directed  to  one  (the  preceding)  limb  of  the  sun,  the  coincidence 
of  the  D  lines  in  the  two  spectra  lying  one  over  the  other  was 
effected  with  the  utmost  sharpness  possible ;  the  clockwork  was 
then  stopped  and  the  moment  of  the  egress  of  the  second  (fol- 
lowing) limb  observed.  The  non-coincidence  of  the  D  lines  at 
the  second  limb  of  the  sun  was  distinctly  perceptible  in  all  the 
very  often  repeated  observations. 
"June  10.  Wre  repeated  the  experiments  with  our  very 
strongly  dispersing  spectroscope  by  Schroder,  which  consists 
of  five  direct-vision  prisms  and  as  many  prisms  of  very  heavy 
glass  arranged  in  a  circle.  The  observing-telescope  magnified 
nine  times.  In  the  focus  was  a  fine  steel  point,  which  was  put 
to  the  line  F,  or  to  a  very  finejine  a  little  more  refrangible  than 
F  (wave-length,  according  to  Angstrom,  4859*17),  while  the 
spectroscope  was  directed  to  one  limb  of  the  sun.     The  point  no 
Phil  Mag.  S.  4.  Vol.  43.  No.  283.  Jan.  1872.  E 
