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spectramore about spectra

spectra

 

  1  definition  found 
 
  From  Webster's  Revised  Unabridged  Dictionary  (1913)  [web1913]: 
 
  Spectrum  \Spec"trum\,  n.;  pl  {Spectra}.  [L.  See  {Specter}.] 
  1.  An  apparition;  a  specter.  [Obs.] 
 
  2.  (Opt.) 
  a  The  several  colored  and  other  rays  of  which  light  is 
  composed,  separated  by  the  refraction  of  a  prism  or 
  other  means  and  observed  or  studied  either  as  spread 
  out  on  a  screen,  by  direct  vision,  by  photography,  or 
  otherwise.  See  Illust.  of  {Light},  and  {Spectroscope}. 
  b  A  luminous  appearance,  or  an  image  seen  after  the  eye 
  has  been  exposed  to  an  intense  light  or  a  strongly 
  illuminated  object.  When  the  object  is  colored,  the 
  image  appears  of  the  complementary  color,  as  a  green 
  image  seen  after  viewing  a  red  wafer  lying  on  white 
  paper.  Called  also  {ocular  spectrum}. 
 
  {Absorption  spectrum},  the  spectrum  of  light  which  has  passed 
  through  a  medium  capable  of  absorbing  a  portion  of  the 
  rays.  It  is  characterized  by  dark  spaces,  bands,  or  lines. 
 
 
  {Chemical  spectrum},  a  spectrum  of  rays  considered  solely 
  with  reference  to  their  chemical  effects,  as  in 
  photography.  These  in  the  usual  photogrophic  methods, 
  have  their  maximum  influence  at  and  beyond  the  violet 
  rays,  but  are  not  limited  to  this  region. 
 
  {Chromatic  spectrum},  the  visible  colored  rays  of  the  solar 
  spectrum,  exhibiting  the  seven  principal  colors  in  their 
  order  and  covering  the  central  and  larger  portion  of  the 
  space  of  the  whole  spectrum. 
 
  {Continous  spectrum},  a  spectrum  not  broken  by  bands  or 
  lines,  but  having  the  colors  shaded  into  each  other 
  continously,  as  that  from  an  incandescent  solid  or  liquid, 
  or  a  gas  under  high  pressure. 
 
  {Diffraction  spectrum},  a  spectrum  produced  by  diffraction, 
  as  by  a  grating. 
 
  {Gaseous  spectrum},  the  spectrum  of  an  incandesoent  gas  or 
  vapor,  under  moderate,  or  especially  under  very  low 
  pressure.  It  is  characterized  by  bright  bands  or  lines. 
 
  {Normal  spectrum},  a  representation  of  a  spectrum  arranged 
  upon  conventional  plan  adopted  as  standard,  especially  a 
  spectrum  in  which  the  colors  are  spaced  proportionally  to 
  their  wave  lengths,  as  when  formed  by  a  diffraction 
  grating. 
 
  {Ocular  spectrum}.  See  {Spectrum},  2 
  (b),  above. 
 
  {Prismatic  spectrum},  a  spectrum  produced  by  means  of  a 
  prism. 
 
  {Solar  spectrum},  the  spectrum  of  solar  light,  especially  as 
  thrown  upon  a  screen  in  a  darkened  room  It  is 
  characterized  by  numerous  dark  lines  called  Fraunhofer 
  lines. 
 
  {Spectrum  analysis},  chemical  analysis  effected  by  comparison 
  of  the  different  relative  positions  and  qualities  of  the 
  fixed  lines  of  spectra  produced  by  flames  in  which 
  different  substances  are  burned  or  evaporated,  each 
  substance  having  its  own  characteristic  system  of  lines. 
 
 
  {Thermal  spectrum},  a  spectrum  of  rays  considered  solely  with 
  reference  to  their  heating  effect,  especially  of  those 
  rays  which  produce  no  luminous  phenomena.




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