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XXXIII.   On  the  Heat- Spectrum  of  the  Sun  and  the  Lime-Light. 
By  M.  S.  Lamansky  of  St.  Petersburg*. 
}N  these  investigations,  which  I  carried  out  in  Geh.  Rath 
HelmhohVs  laboratory  at  Heidelberg,  I  endeavoured  to 
analyze  by  means  of  a  prism  as  large  a  cone  of  light  as  possible. 
For  this  purpose  the  following  arrangement  was  hit  upon. 
Solar  rays,  reflected  from  the  mirror  of  a  heliostat,  were  col- 
lected by  means  of  a  lens  of  3  inches  aperture  and  25  inches 
focal  distance.  Into  the  focus  of  the  lens  a  slit  was  brought, 
the  length  of  which  was  exactly  equal  to  the  diameter  of  the 
sun's  image.  The  issuing  luminous  pencil  was  analyzed  by  a 
flint-glass  prism  of  2  inches  aperture  and  a  refracting  angle  of 
.60°.  The  separated  rays  were  collected  by  an  achromatic  lens. 
This  lens  was  placed  at  twice  its  focal  distance  both  from  the 
slit  and  from  the  linear  thermo-apparatus.  The  latter  consisted 
of  12  pairs  of  bismuth-antimony  elements,  and  was  connected 
with  a  thermo-multiplier  after  Magnus.  With  this  arrangement 
the  luminous  rays  covered  the  entire  face  of  the  prism ;  and  in 
the  investigation  of  the  ultra-red  rays  the  prism  was  placed  at 
the  minimum  of  deflection  for  the  red. 
Hence  resulted  a  very  pure  spectrum,  the  investigation  of 
which  was  conducted  in  the  following  manner.  First  the  double 
slit  of  the  thermo-apparatus,  of  only  half  a  millim.  breadth,  was 
placed  upon  the  line  D ;  the  thermo-apparatus,  enclosed  in  a 
tin-plate  box  containing  hot  water  for  compensation  of  the  tem- 
perature, was  then  moved  along  a  scale  of  millimetres  in  order 
to  trace,  step  by  step,  the  distribution  of  heat  in  the  entire  spec- 
trum. In  subsequent  experiments,  which  I  executed  in  the  past 
summer  with  rock-salt  apparatus,  a  micrometer-screw  was  added, 
suitable  for  shifting  the  thermo-apparatus,  which,  moreover,  stood 
behind  the  slit  of  a  thick  plate  of  brass.  Before  each  observation 
the  solar  image  was  first  thrown  upon  the  slit  by  the  mirror  of 
the  heliostat ;  the  screen  between  the  slit  and  the  prism  was 
then  removed,  and  the  deflection  of  the  magnet  read  off  with 
telescope  and  scale.  I  usually  made  two  observations  for  each 
position  of  the  thermo-apparatus  in  the  spectrum,  and  took  their 
mean.  Finally,  however,  I  came  back  again  to  the  line  D ;  in 
this  way  I  was  able  to  ascertain  the  variation  of  intensity  of  the 
heat-effect  during  the  experiment. 
I.  Distribution  of  the  Heat  in  the  Solar  Spectrum. 
In  the  above- described   manner  I  investigated  the  thermic 
effects  of  the  solar  spectrum  with  flint-glass  prisms,  with  prisms 
*  Translated  from  a  separate  copy,  communicated  by  the  Author,  from 
the  Monatsberichte  der  Konigl.  Akademie  der  Wissenschaften  xu  Berlin, 
Dec.  7,  1871. 
