Hysteresis,  Magnetic A  variety  of

molecular  friction  produced  in  the  molecules
of  a  magnetizable  substance  during  changes
of  magnetic  stress.
According  to  Steinmetz,  the  loss  occasioned  by
magnetic  hysteresis  is  proportional  to  the  fre-
quency and  to  the  1. 6th  power  of  the  magnetic
variation.
According  to  Steinmetz,  for  a  magnetic  cycle
performed  between  the  limits  of  magnetic  induc-
tion Bx  and  B»,  the  loss  in  ergs  per  cubic  cm.  is

,1.6


•—(B*7Bf)1


where  n,  the  coefficient  of  hysteresis,  averages
.0033  in  average  good  sheet  iron,  .013  in  cast
iron,  .003  to  .03  in  cast  steel,  and  reaches  as  high
as  .08  in  hardened  steel.
With  alternating  magnetism  the  formula  can
be  written

L=nB1'6

The  actual  existence  of  magnetic  hysteresis  is
denied  by  some  able  electricians.
7. — A  symbol
current.
proposed    for  intensity  of


E


The  defining  equation  is  I  =  =r-

3 A  symbol  used  in  France  and

Germany  for  intensity  of  magnetization.
_m

The  defining  equation  is  c) y—


Idiostatic  Electrometer. — (See  Appendix
— Electrometer,  Idiostatic!)

Idle  Wire  of  Armature. — (See  Appendix
—  Wire,  Idle,  of  Armature!)

Idle  Wire  of  Armature  of  Motor.— (See
Wire,  Idle,  of  Armature  of  Motor!)

Idle  Wire  of  Dynamo.— (See  Appendix—
Wire,  Idle,  of  Armature  of  Dynamo!)


IdL]


615


[Ind.
Idle  Wire  of  Motor.— (See  Appendix —
Wire,  Idle,  of  Armature  of  Motor.)

Illumination,  Cosine  Law  of The

intensity  of  the  illumination  emitted  from  or
received  by  any  element  of  surface  is  propor-
tional to  the  cosine  of  the  angle  between  its
normal,  and  the  direction  of  the  radiation.
Illumination,  Glow A  term  pro-
posed for  an  illumination  similar  to  that  of
the  glow-worm  ;  that  is,  illumination  without
sensible  heat.
