VARIETIES, 
165 
perpendicular  to  the  axis,  we  shall  observe  the  phenomena  of  elliptic  polari- 
zation, when  the  gold  leaf  and  the  analyzer  are  turned  to  an  angle  of 
45°  with  the  planes  of  polarization,  The  colored  rings  are  narrower  in  the 
nrst  and  third  quadrants  than  in  the  second  and  fourth,  the  cross  is  converted 
into  two  hyperbolas,  whose  branches  do  not  meet  When  in  the  above  ex- 
periment, we  leave  everything  else  unchanged,  and  examine  the  calcspar 
with  the  analyser,  by  means  of  the  light  reflected  from  the  gold  leaf  in  place 
of  that  transmitted,  we  observe  the  complementary  figure  such  a3  we  obtain 
it  when  we  employ  the  transmitted  light,  and  tourmaline  is  turned  through 
90°.  The  tourmaline  must  be  green  in  order  to  transmit  the  light  well. 
Brewster's  discovery  of  the  elliptic  polarization  by  metallic  reflection  is  thus 
extended  and  completed, — Ibid,  from  Pogg,  Ann.,  xc,  188. 
Vitrification  of  Photographic  Pictures. — The  author  of  this  process,  M« 
Piaut  first  procured  a  photograph  on  glass  covered  with  albumen,  and  sub- 
jected it  gradually  to  a  strong  heat  so  as  to  redden  the  glass.  The  albumen 
was  destroyed,  and  the  photograph,  if  negative,  became  positive  by  reflec- 
tion. The  picture  was  made  of  pure  silver  which  adheres  quite  strongly  to 
the  glass,  so  that  it  may  be  polished  without  alteration. 
On  exposing  this  glass  to  the  action  of  hydrofluoric  acid  in  vapor,  an 
engraving  of  the  design  is  obtained  over  parts  not  covered  by  the  image 
formed  of  the  silver.  It  may  also  be  possible  to  strengthen  the  image  by  a 
galvanic  deposit,  and  make  a  kind  of  plate  from  which  engravings  could  be 
taken. 
If,  in  place  of  arresting  the  process  at  a  red  heat,  it  is  continued  until  the 
glass  enters  into  fusion,  the  image  sinks  into  the  interior  of  the  glass  with- 
out being  altered,  and  covers  itself  with  a  vitreous  varnish.  It  appears  like 
a  design  of  .great  delicacy,  enclosed  between  two  plates  cf  glass  ;  and  if 
positive  proofs  are  employed,  the  method  may  be  used  for  making  pictured 
gi?.ss  which  may  without  doubt  be  colored  by  the  ordinary  processes. — Ibid. 
Photographic  Portraits  on  linen  cloth. — The  Revue  Eneyclopedique  of  the 
Abbe  Moigno.  from  which  we  have  taken  the  preceding  note,  states  that 
the  problem  of  making  protographs  on  linen  has  been  resolved.  The  Abbe 
Moigno  has  assisted  at  the  operations  of  M*  Wulff,  the  inventor  ;.  he  say? 
nothing  of  the  processes,  and  we  only  know  that  the  photographs  were  taken 
on  linen  covered  with  collodion, — lb uh 
Artificial  magnets, — For  some  time,  permanent  magnets  have  been  made 
from  cast  iron  by  the  aid  of  an  electric  current.  The  only  difficulty  con- 
sists in  tempering  the  metal.  M.  Florimond,  Professor  of  Physics  at 
Louvain  has  recently  given  the  results  of  some  investigations  on  this  subject 
to  the  Academy  of  Sciences  of  Brussels,  detailing  the  effects  from  using 
magnets  of  this  kind  in  the  construction  of  magneto  electric  machines,  these 
magnets  being  much  more  economical  on  account  of  the  difference  in  value 
of  cast  iron  and  steel.    The  following  are  some  of  his  conclusions  : 
