480  Intelligence  and  Miscellaneous  Articles. 
has  been  rounded  for  heating  flasks  ;  it  contained  about  28  meshes 
to  the  inch. 
The  tube  chiefly  determines  the  pitch  of  the  note,  shorter  or  longer 
ones  producing,  of  course,  higher  or  lower  tones  respectively.  I  have 
most  frequently  used  either  a  glass  tube  twelve  inches  long  and  one 
and  a  quarter  inch  in  diameter,  or  a  brass  one  of  the  same  dimen- 
sions. Out  of  several  rough  pieces  of  common  gas-pipe  no  one 
failed  to  give  a  more  or  less  agreeable  sound.  Among  these  gas- 
pipes  was  one  as  short  as  seven  inches,  with  a  diameter  of  one  inch, 
while  another  was  two  feet  long  and  one  and  a  quarter  inch  in  dia- 
meter. A  third  gas-pipe,  fifteen  inches  long  and  three  quarters 
of  an  inch  in  diameter,  gave,  when  set  for  a  continuous  sound,  quite  a 
low  and  mellow  tone.  If  the  jet  be  moved  slightly  aside,  so  that 
the  flame  just  grazes  the  side  of  the  tube,  a  note  somewhat  lower 
than  the  fundamental  one  of  the  tube  is  produced.  This  sound  is 
stopped  by  external  noises,  but  it  goes  on  again  when  left  undis- 
turbed. AIL  these  experiments  can  be  made  under  the  ordinary 
pressure  of  street  gas,  three  fourths  of  an  inch  of  water  being 
sufficient. — Silliman's  American  Journal  for  May  1872. 
ON  THE  BEST  RESISTANCE  OF  THE  COILS  OF  ANY  DIFFERENTIAL 
GALVANOMETER.       BY  LOUIS  SCHWENDLER,  ESQ.* 
Mr.  Schwendler  gave  a  short  outline  of  his  investigations,  stating 
that  it  would  be  impossible  for  him  to  read  the  paper  in  full,  on  ac- 
count of  its  intricate  and  purely  mathematical  character  ;  he  would 
give,  however,  the  general  results  obtained  and  show  their  advan- 
tages when  applied,  illustrating  his  explanations  on  the  black  board 
andjby  a  differential  galvanometer  placed  on  the  table.  The  paper 
itself  would  be  published  in  Part  II.  of  the  Journal. 
In  that  most  common  form  of  the  differential  galvanometer,  when 
the  two  coils  are  fixed  and  of  equal  resistances  and  equal  magnetic 
moments,  Mr.  Schwendler  found  that  the  following  interesting  and 
most  simple  relation  should  exist  between  the  resistance  of  the  gal- 
vanometer-coil and  the  resistance  to  be  measured,  in  order  to  have 
the  greatest  possible  sensibility — namely,  that 
The  resistance  of  the  galvanometer'- coil  should  be  one  third  of  the 
resistance  under  measurement,  supposing  that  the  resistance  of  the 
testing-battery  common  to  both  the  coils  can  be  neglected  against 
the  resistance  to  be  measured. 
Mr.  Schwendler  remarked  that  the  differential  galvanometers  at 
present  employed  in  the  Government  Telegraph  Department  of  India 
have  a  far  too  low  resistance,  and  that  this,  to  a  certain  extent,  ex- 
plained the  great  want  of  sensitiveness  of  these  instruments  when 
used  for  measuring  resistances  higher  than  GOO  units. 
If  the  coils  had  a  resistance  of  about  2500  units  each,  instead  of 
200  only,  the  sensitiveness  of  these  instruments  would  at  once  be 
nearly  trebled — a  fact  which  shows  the  great  advantage  to  be  derived 
from  the  application  of  Mr.  Schwendler's  results  in  the  construction 
of  differential  galvanometers. 
*  Abstract  from  the  Proceedings  of  the  Asiatic  Society  of  Bengal,  March 
1872.     Communicated  by  the  Author. 
