80  Intelligence  and  Miscellaneous  Articles. 
By  such  experiments  we  can  ascertain  the  variations  which  humidity- 
induces  in  the  elasticity  of  hygrometric  substances,  such  as  paper. 
The  laws  of  vibrating  strings  are  verified  on  very  fine  wires,  except 
when  the  tension  of  the  wire  is  not  more  than  a  few  grammes. 
In  all  these  experiments,  whether  on  strings  or  rods,  the  position 
of  the  nodes  is  not  rigorously  fixed  ;  the  nodes,  especially  those  near 
the  diapason,  shift  during  the  motion  ;  their  distance  from  the  dia- 
pason increases  in  proportion  as  the  amplitude  of  the  vibrations  grows 
less. 
Free  rods,  or  wires  but  slightly  stretched,  present  another  anomaly. 
When  the  vibrations  have  very  little  amplitude,  the  wires  take  the 
mode  of  division  indicated  by  theory,  ^ind  the  point  of  attachment  is 
not  a  node :  but  if  the  diapason  is  made  to  vibrate  more  and  more 
forcibly,  the  number  of  the  nodes  decreases ;  thus  instead  of  four 
nodes,  only  three,  two,  or  one  is  observed,  or  even  none  at  all.  The 
point  of  attachment  of  the  wire  to  the  diapason  is  then  the  place  of 
a  node,  and  the  wire  is  divided  by  the  nodes  into  equal  parts.  Free 
rods,  therefore,  exhibit,  according  to  the  stroke,  a  variable  number 
of  nodes,  the  arrangement  of  which  follows  the  ordinary  laws. 
The  wire,  in  all  cases,  continues  to  vibrate  in  unison  with  the  dia- 
pason ;  or  at  least  no  sound  foreign  to  that  of  the  instrument  is 
heard.  Here  is  an  anomaly  which  the  theory  does  not  appear  to 
account  for  ;  perhaps  it  results  from  the  circumstance  that,  in  con- 
structing the  differential  equation  of  the*  motion  of  the  wire,  the 
amplitudes  of  the  vibrations  were  supposed  infinitely  small. — 
Comptes  Rendus  de  V  Acad,  des  Sciences,  1871,  Nov.  20,  pp.  1213— 
1215. 
ON  A  NEW  PHENOMENON  OF  PHOSPHORESCENCE  PRODUCED  BY 
FRICTIONAL  ELECTRICITY.       BY  M.  ALVERGNIAT. 
We  make  a  vacuum,  by  means  of  the  mercurial  air-pump,  in 
straight  tubes  of  glass  45  centims.  long;  we  then  introduce  a  small 
quantity  of  chloride  or  bromide  of  silicium,  and  continue  the  exhaus- 
tion till  the  pressure  is  reduced  to  12  or  15  millims.,  after  which  we 
close  the  tube  at  the  lamp. 
If  the  tube  thus  prepared  be  then  rubbed  between  the  fingers  or 
with  a  piece  of  silk,  a  bright  glimmer  within  the  tube  is  seen  to  fol- 
low the  movement  of  the  rubber  ;  it  is  rose-coloured  with  the  chloride, 
and  greenish  yellow  with  the  bromide  of  silicium.  It  recalls  that 
which  has  long  been  observed  in  the  barometer,  but  it  is  brighter. 
We  will  remark  that,  if  we  try  to  cause  the  spark  of  the  induction- 
coil  to  pass  in  these  tubes,  it  developes  no  light  there,  unless  the 
vacuum  be  more  perfect ;  but  then  the  phosphorescence  excited  by 
the  friction  disappears. 
We  owe  our  thanks  to  M.  Friedel  for  the  preparation,  in  a  state 
of  purity,  of  the  substances  which  have  given  this  result. — Comptes 
Rendus  de  V  Acad,  des  Sciences,  1871,  Nov.  20,  p.  1215. 
