A  neglect  of  this  obvious  consequence  of  Ohm*s  law  of  resistanc
appears  to  have  been  the  cause  of  failure  very  recently,  in  an  attempt  t
ignite  a  number  of  mines  of  demolition  simultaneously,  at  Chatham.  Frori
the  great  magnitude  of  the  charges  frequently  fired  at  Holyhead,  and  th
very  serious  consequences  that  failure  of  ignition  would  involve,  the  batter
power  habitually  employed  is  wisely  of  superabundant  power.  It  consist
of  a  Grove's  battery  of  thirty-two  cells,  each  exposing  ninety-six  squa/i
inches  of  platinum  element.  It  is  but  justice  to  my  friend  Mr.  R.  L.  Coi^
sens,  C.E.,  to  whose  assistance  in  these  experiments  I  am  so  much  indebted
to  add,  that  during  the  several  years  he  has  controlled  these  vast  blasting
operations  a  single  failure  of  ignition  has  never  occurred.
