88  Dr.  W.  E.  Sumpner  on  the 
between  power-factors  0*9  and  1*0,  and  are  close  together 
for  the  values  most  wanted,  for  power-factors  between  0"6 
and  0.8,  the  values  of  <f>  for  which  only  differ  by  16  degrees. 
The  result  is  to  produce  an  instrument  having  a  scale  the 
greater  portion  of  which  is  hardly  ever  used,  while  the 
portion  which  is  most  used  is  small,  and  the  readings  un- 
desirably crowded.  Assuming  bilateral  symmetry  in  the 
moving  coils,  a  change  in  x  of  180  degrees  must  necessarily 
correspond  with  a  reversal  of  the  currents,  or  with  a  change 
in  <f>  of  180  degrees,  but  there  is  no  need  for  the  range  of  x 
for  leading  currents  to  be  as  great  as  that  for  lagging 
currents,  and  it  is  advantageous  to  get  a  large  range  of  x  for 
the  values  of  cos  <£  most  needed. 
Tests  on  Phasemeters  having  Iron  Cores. 
The  foregoing  theory  has  been  fully  tested  by  the  writer 
in  reference  to  three  new  instruments  each  provided  with 
Fisr.  2. 
P 
iron-cored  magnetic  circuits.  The  structure  of  one  of  these 
is  sufficiently  indicated  in  fig.  2.  The  iron  parts  are  built 
up  of  thin  circular  stampings  arranged  in  two  fixed  cylindrical 
coaxial  blocks  S0  and  S*.  The  outer  ones  S0  are  provided 
with  twelve  slots  on  their  inner  periphery  arranged  sym- 
metrically at  angular  intervals  of  30°.  In  each  pair  of 
diametrically  opposite  slots  a  coil  of  8  turns  is  wound,  and 
adjoining  coils  are  series  connected  in  pairs  to  form  the  three 
fixed  coils  Al5  A2,  A3.  When  positive  currents  are  sent 
through  the  coils  the  currents  flow  downwards  through  the 
slots  1,  2,  5,  6,  9,  and  10,  and  upwards  through  the  remaining 
slots.  This  is  indicated  in  the  figure  by  the  use  of  full  signs 
and  corresponding  outline  signs.  The  moving  coil  is  rect- 
angular in  shape  and  turns  with  its  sides  in  the  circular 
air-gap   about   the    common   axis    of  the   system.     To  this 
