In  the  case  of  a  luminous  body  the  energy  is
transferred  from  the  body  to  the  luminiferous
ether.  For  example,  if  the  wire  is  heated  to
luminosity  by  a  certain  amount  of  energy  im-
parted to  it,  the  surrounding  ether  is  now  set
into  waves  of  both  light  and  heat,  which  differ
from  one  another  only  in  their  wave  length,  and
the  luminous  body  will  continue  to  radiate  light
and  heat  until  it  imparts  to  the  surrounding
ether  an  amount  of  energy  exactly  equal  to  that
originally  imparted  to  it.
So,  too,  in  the  case  of  a  body  charged  with
electricity.  If  disruptively  discharged,  the  im-
pulsive rush  of  electricity,  so  produced,  causes  the
energy  charged  on  it  to  be  radiated  as  electro-
magnetic waves  into  the  surrounding  ether.  The
discharging  body  is,  to  all  intents  and  purposes,  in
the  same  condition  as  the  vibrating  elastic  wire,
and  dissipates  or  radiates  its  energy  in  much  the
same  manner.
Radiation,    Electro-Magnetic
The  sending  out  in  all  directions  from  a  con-


Had.]


431


[Rad.
ductor,  through  which  an  oscillating  discharge
is  passing,  of  electro-magnetic  waves  in  all
respects  similar  to  those  of  light  except  that
they  are  of  much  greater  length.  (See  Elec-
tricity, Hertz's  Theory  of  Electro-Magnetic
Radiations  or  Waves.)

Radiation  of  Electricity. — (See  Electri-
city, Radiation  of.)

Radiation  of  Lines  of  Force.— (See  Force,
Lines  of,  Radiation  of.)

Radical,  Compound  — A  group  of

unsaturated  atoms.
A  group  of  elementary  atoms,  some  of  the
bonds  of  which  are  open,  or  not  connected
or  joined  with  the  bonds  of  other  atoms.
(See  Atomicity?)

For  example,  hydroxyl,  HO,  is  a  compound
radical,  with  one  of  the  two  bonds  of  the  diad
oxygen  atom,  open  or  unsaturated.
Radical,  Simple  •  — An  unsaturated

atom  with  its  bond  or  bonds  free.
