exert  an  appreciable  influence  upon  it;  hence  observations  made  witli
such  an  instrument  would  be  alike  in  all  parts  of  the  globe.  Tlie  vertical
galvanometer  is,  however,  more  expensive,  provided  it  is  accurateh'  cali-
brated, than  the  horizontal,  and  the  bearings  upon  which  of  necessity
the  needle  rests  are  liable  to  cause  more  or  less  friction.  At  my  request,
Messrs.  Waite  &  Bartlett,  of  New  York  Cit}',  have  lately  graduated
some  horizontal  milliampei-e-meters  with  great  accurac}-  (Fig.  162).      I


ATTACHMENTS   TO   A   COMPLETE   BATTERY.
C31


ean  recommend  them  as  reliable  and  comparatively  inexpensive.  They
will  not,  however,  accurately  measure  currents  of  over  titty  milliamperes.
Before  3'ou  purchase  this  important  attachment  to  a  battery,  test  it,  if
possible,  by  one  whose  accuracy  can  be  relied  upon.  I  would  far  rather
have  none  than  a  poor  one.  At  i)resent  I  am  using  the  so-called  "dead-
Ijeat "  milliampere-meter,  made  after  a  late  design.*  Hirschmann's
vertical  galvanometer  with  astatic  needles,  called  the  "  absolute  galva-
nometer," has  been  highly  recommended  of  late.  I  have  not  yet  pur-
chased one,  as  I  lind  my  own  to  be  perfectly  reliable.
The  instrument  represented  on  opposite  page  measures  from  one-
tenth  of  one  milliampere  to  five  hun-
dred milliamperes.  It  is  contained  in
an  all-metal  case  and  carefully  cali-
brated. It  contains  the  Siemens'  bell-
magnet,  and  is  dampened  in  its  vibra-
tions by  the  induced  currents  set  up
during  the  deflections  of  the  needle,
Avhereas  in  most  instruments  of  the
better  class  the  oscillations  of  the
needle  average  at  least  twenty-five
before  it  comes  to  rest.  In  this  in-
strument the  vibrations  seldom  ex-
ceed from  five  to  six.  Shunts  are  pro-
vided in  order  to  measure  very  high
currents.  I  regard  this  instrument
as  fully  equal,  if  not  superior,  to
Hirschmann's  expensive  instrument.
