346 
NEW  ELECTRICAL  MACHINE. 
only  much  denser  and  heavier,  was  also  heated,  and  which  was 
the  only  one  that  was  characterized  by  its  cracking  and  splitting 
in  all  directions.  White  deal  would,  perhaps,  form  the  best  wood 
for  the  purpose,  could  it  only  be  obtained  wide  enough,  because 
I  find  it  possible  to  get  sparks  from  it  with  amalgam,  no  doubt 
on  account  of  its  hard  smooth  surface,  which,  however,  speedily 
becomes  coated  with  metal,  and  so  cannot  vie  with  ebonite  on 
account  of  polish.  Were  it  not  for  this,  I  believe  wood  would 
be  found  equal  to  it,  as  under  similar  circumstances,  (as  when 
catskin  is  used,)  the  power  of  each  appears  equal. 
The  pieces  of  wood  I  speak  of  were  exposed  between  wire 
work  secured  by  wire  to  the  influence  of  a  good  fire,  at  from  six 
inches'  to  a  foot's  distance  from  the  bars  for  from  one  to  two 
hours — during  this  operation,  English  walnut  and  mahogany  are 
very  apt  to  ignite — and,  in  this  way,  ten  or  a  dozen  pieces  may 
readily  be  heated  at  a  time,  the  pieces  of  wood  measuring  8 
inches  by  4  or  —  32,  and  \  in.  thick. 
From  this  mode  of  operating,  it  will  be  seen  that  the  "  com- 
parisons "  must  necessarily  be  rather  rough  and  only  approxi- 
mate, though  the  pieces  were  so  arranged  as  to  be  heated  both 
sides  as  nearly  equally  as  possible.  Of  course,  had  I  possessed 
at  the  moment  required  the  necessary  conveniences,  an  oil  bath 
would  have  given  more  reliable  results ;  but  still  I  consider  the 
comparison  sufficiently  near  the  truth  to  prove  useful.  I  have 
already  dwelt  upon  the  necessity  of  heating  the  woods  a  suffi- 
cient time,  &c,  because  such  directions  are  necessary  to  success, 
and  without  them  it  often  comes  to  pass  that  in  the  hands  of 
another  statements  and  results  can  no  more  be  reconciled  in 
truth  than  can  those  of  "  Geology "  and  "  Religion."  But  to 
return  to  the  woods.  The  first  batch  were  examined  after  three 
weeks  or  more,  and  the  second  after  one — a  mere  matter  of 
accident.  Of  the  whole  list,  but  a  very  limited  number  retained 
anything  like  all  their  pristine  vigor.  Among  these  may  be  men- 
tioned rosewood,  satinwood,  kingwood,  and  perhaps  cedar  and 
tulipwood,  mahogany  not  doing  so  well.  Oak  was  the  only  wood 
in  which  the  sparks  mostly  ran  along  the  surface  before  dis- 
charge could  take  place,  as  if  it  contained  metals  ;  while  ash 
vEnglish,  if  not  foreign,)  had  by  this  time  lost  all  perceptible 
