RESEARCHES  ON  EVAPORATION. 
261 
through  the  wire  might  be  recalled  before  it  arrived  at  America. 
Professor  Faraday  concluded  by  exhibiting  a  beautiful  experiment 
illustrative  of  the  identity  of  voltaic  and  frictional  electricity. 
The  terminal  wires  of  a  powerful  secondary-coil  apparatus  were 
placed  seven  inches  apart  within  the  receiver  of  an  air  pump,  and 
when  the  receiver  was  exhausted,  a  stream  of  purple  colored  light 
passed  between  the  wires,  resembling,  though  more  continuous 
and  brilliant,  the  imitation  of  the  aurora  borealis  produced  when 
an  electric  spark  is  passed  through  an  exhausted  glass  tube.  The 
voltaic  power  employed  to  produce  this  effect  of  static  electricity 
was  only  three  cells  of  a  Grove's  battery. — Frank.  Inst.  Jour. 
April,  1854. 
RESEARCHES  ON  EVAPORATION. 
By  Professor  Marcet,  of  Geneva. 
The  following  experiments  were  instituted  with  the  view  of 
throwing  some  light  on  the  tendency  of  certain  circumstances  to 
promote  or  diminish  the  evaporation  of  liquids.  Water  and  alco- 
hol were  the  liquids  chiefly  used.  The  results  obtained  by  the 
author  may  be  recapitulated  as  follows  : — 
1.  The  temperature  of  a  liquid,  allowed  to  evaporate  freely  in 
an  open  vessel,  is  always  inferior  to  that  of  the  surrounding 
atmosphere.  The  higher  the  temperature  of  the  atmosphere,  the 
greater  is  the  difference  between  its  temperature  and  that  of  the 
liquid  exposed  to  evaporation,  Between  40Q  and  50°  Centigrade, 
the  difference  was  found  to  vary  from  5°  to  7° ;  between  20° 
and  25°  it  varied  from  1  J°  to  1J°  ;  at  12°  it  was  0-8°  only,  and 
between  3°  and  zero  about  0-2°.  The  explanation  of  this  result 
is  obvious.  The  evaporation  of  a  liquid  diminishing  with  the 
external  temperature,  the  cold,  which  is  the  consequence  of  this 
evaporation,  must  diminish  in  the  same  proportion  ;  and  if  it  were 
possible  to  prevent  evaporation  altogether,  the  author  presumes 
that  there  would  be  no  difference  whatever  between  the  tempera- 
ture of  a  liquid  and  that  of  a  surrounding  medium. 
2.  The  temperature  of  liquids,  such  as  water  and  alcohol,  as 
well  as  the  rapidity  with  which  they  evaporate,  varies,  all  other 
circumstances  remaining  the  same,  according  to  the  nature  of  the 
vessel  in  which  these  liquids  are  contained.  For  instance,  the 
temperature  of  the  surrounding  atmosphere  being  from  15°  to 
