240  Intelligence  and  Miscellaneous  Articles. 
With  my  flint-glass  prism  of  60°  I  measured  the  displacements  of 
the  double  line  of  sodium ;  but  the  measurements  were  within  a 
small  interval  of  temperature.  To  give  you  an  idea  of  our  climate, 
I  may  mention  that  for  six  weeks,  during  which  I  chose  the  most 
favourable  hours  of  the  day  and  of  the  night,  I  could  obtain  no  greater 
interval  than  at  most  5^°.  But  by  using  an  excellent  theodolite- 
spectrometer  of  Starke  in  Vienna,  by  which  measurements  to  a  second 
could  be  effected,  I  could  observe  that  the  line  Df  was  displaced  3'  for 
1°  Centigrade.  This  displacement  is  considerable  ;  for  the  distance 
between  D  and  D'  amounts,  in  my  apparatus,  to  12'.  From  this 
it  follows  that  a  change  of  4°  C.  is  sufficient  to  remove  D  to  the 
place  of  D'.  This  source  of  error  is  the  more  important  because  it 
easily  occurs — if,  for  instance,  an  observation  made  in  full  sunshine 
be  compared  with  one  made  in  the  shade,  or  one  made  at  midday 
be  compared  with  one  in  the  night  or  one  in  the  morning. 
There  is  thus  only  one  good  method  of  spectroscopic  comparison, 
namely  the  superposition  of  the  spectra.  In  other  cases  the  spec- 
troscope must  be  graduated  and  the  temperature  frequently  deter- 
mined, which  is  difficult  when,  for  instance,  the  sun  is  observed.  For 
this  reason  more  than  one  spectroscopic  measurement  needs  repeat- 
ing.— BibliotKeque  Universelle,  August  1871. 
COLOURED  GELATINE  PLATES  AS  OBJECTS  FOR  THE  SPEC- 
TROSCOPE.      BY  E.  LOMMEL. 
In  order  to  avoid  the  inconvenience  of  using  solutions  in  glass  vessels 
in  demonstrating  the  phenomena  of  absorption  of  soluble  colouring- 
matters,  I  use  gelatine  lamince  which  are  coloured  with  the  matters  in 
question.  To  protect  them  from  wearing  out,  from  air  and  dust, 
they  are  enclosed  between  two  colourless  glass  plates  ;  and  even  with 
delicate  colouringmatters  they  keep  perfectly.  A  compendious  collec- 
tion of  the  most  varied  colouring-matters  may  thus  be  made,  which  are 
always  handy  for  demonstration,  whether  for  the  objective  projection 
of  absorption-spectra,  or  for  subjective  observation  by  the  spectroscope. 
We  can,  for  instance,  at  any  time  exhibit  the  changes  which  the  spec- 
trum of  the  colouring-matter  of  the  blood  undergoes  by  various  agents 
without  needing  to  perform  the  lengthy  operations  with  fresh  blood. 
The  changes  of  the  absorption- spectra  for  continually  thicker 
layers  of  the  colouring  medium  may  be  quickly  and  conveniently 
effected  by  superposing  on  each  other  a  continually  larger  number 
of  gelatine  plates  of  the  same  thickness  and  the  same  intensity  of 
colour.  The  phenomena  of  a  wedge-shaped  layer  may  be  imitated 
by  superposing  a  large  number  of  feebly  coloured  laminae. 
The  production  of  perfectly  homogeneous  and  transparent  laminae 
can  be  effected  even  with  colouring-matters  which  are  soluble  in 
alcohol  but  not  in  water,  as,  for  instance,  aniline  colours  and  chlo- 
rophyl.  Chlorophyl  gelatine,  however,  does  not  give  the  spectrum 
of  the  alcoholic  chlorophyl  solution  which  was  used  for  colouring 
the  aqueous  gelatine  solution,  but  that  of  solid  chlorophyl  as  shown 
by  leaves  in  transmitted  light.  I  have  not  been  able  to  observe  any 
such  difference  between  the  spectrum  of  the  solidified  colouring- 
matter  in  the  gelatine  as  compared  with  that  of  its  solution. — Pog- 
gendorff's  Annalen,  October  1871.  [Thin  plates  of  mica  might  be 
even  more  suitable  for  this  purpose. — Ed.  Phil.  Mag  .J 
