Mr.  J.  E.  Stone  on  the  Velocity  of  Sound.  153 
any  one  metal  &c.  which  can  suggest  any  mechanical  explanation  of 
their  origin. 
Nov.  23. — General  Sir  Edward  Sabine,  K.C.B.,  President,  followed 
by  Mr.  Francis  Galton,  Vice-President,  in  the  Chair. 
The  following  communication  was  read  : — 
"  An  Experimental  Determination  of  the  Velocity  of  Sound."  By 
J.  E.  Stone,  M.A.,  F.R.S.,  Astronomer  Royal  at  the  Cape  of  Good 
Hope. 
A  galvanic  current  passes  from  the  batteries  at  the  Royal  Obser- 
vatory, Cape  Town,  at  1  o'clock,  and  discharges  a  gun  at  the  Castle, 
and  through  relays  drops  a  time-ball  at  Port  Elizabeth.  It  appeared 
to  the  author  that  a  valuable  determination  of  the  velocity  of  sound 
might  be  obtained  by  measuring  upon  the  chronograph  of  the  Ob- 
servatory the  interval  between  the  time  of  the  sound  reaching  some 
point  near  the  gun  and  that  of  its  arrival  at  the  Observatory.  As  there 
is  only  a  single  wire  between  the  Observatory  and  Cape  Town,  some 
little  difficulty  was  experienced  in  making  the  necessary  arrange- 
ments, without  any  interference  with  the  1  o'clock  current  to  Port 
Elizabeth;  but  this  difficulty  was  overcome  by  a  plan  which  the  author 
describes,  and  which  was  brought  into  successful  operation  on  Feb. 
27,  1871.  The  experiments  could  not  have  been  carried  out,  on 
account  of  the  encroachment  they  would  have  made  on  the  time  of 
the  Observatory  staff,  had  it  not  been  for  the  assistance  of  J.  Den, 
Esq.,  the  acting  manager  of  the  Cape  Telegraph  Company,  to  whom 
the  author  is  indebted  for  the  preparation  of  a  good  earth-connexion 
near  the  gun,  for  permission  to  Mr.  Kirby,  a  gentleman  attached 
to  the  telegraph  office,  to  assist  in  the  experiments,  and  for  a  general 
superintendence  of  the  arrangements  at  Cape  Town. 
The  observed  times  of  hearing  the  sound  were  recorded  on  the 
chronograph  by  two  observers,  situated  one  (Mr.  Kirby)  at  a  dis- 
tance of  641  feet  from  the  gun,  the  other  (Mr.  Mann)  at  the  Ob- 
servatory, at  a  distance  of  15,449  feet  from  the  gun.  The  former 
distance  was  sufficient  to  allow  the  connexion  of  the  main  wire  to 
be  broken  at  the  telegraph  office  after  the  gun  had  been  fired,  but 
before  the  sound  reached  the  first  observer. 
As  there  were  no  reciprocal  signals,  a  correction  was  made  by  cal- 
culation for  the  effect  of  the  wind,  its  velocity  being  measured  by  a 
set  of  Robinson's  cups.  The  personal  equation,  under  the  circum- 
stances of  the  observations,  was  found  as  follows  : — A  gun  was  fired 
at  such  a  distance  from  the  Observatory  as  to  be  heard  with  about 
the  same  degree  of  distinctness  as  the  time-gun  at  the  Castle.  This 
distance  was  found  to  be  1483  feet.  The  registrations  on  the  chro- 
nograph were  made  by  Mr.  Kirby  at  the  distance  of  162  feet  from 
the  gun,  and  Mr.  Mann  at  the  Observatory.  For  this  comparatively 
small  distance,  the  time  of  transit  calculated  from  the  velocity  de- 
duced from  the  time  taken  to  travel  over  the  larger  distance  may 
be  deemed  exact.  The  observed  time  for  the  smaller  difference  of 
distance  was  found  to  be  too  great  by  0S,09,  which  correction  has  been 
applied  to  all  the  observations.     It  depends  more  on  want  of  sensi- 
