"While magneti=!m I* in the state of change above described,
it will produce the oth r forces but t may be sa d whJe
magnetism is thi a i o" es ve some othe fo ce is a t ng on
it, and therefore t does not mit ate tb s a t ti hut the
same may be sail of all the other foices they havo no com-
mencement that we can trac We m st ever lefet them
back to some antece lent force equal m amount (o that p >
duced, aad therefo e tl e woi 1 t at ou cannot n strictness
apply, but must nly he taken a'^ s "u fym the for e lele ted
as the flrit : this is another reason why the idea of abstract
causation is inapplicable to physical production. To this
point I shall again advert.
Electricity may thus be produced directly by magnetism,
either when the magnet as a mass is in motion, or when its
magnetism is commencing, increasing, decreasing, or ceasing ;
and heat may similarly be directly produced by magnetism,
I have, since the first edition of this Essay was published,
communicated tr the Eoyal Society a paper by which I tliinb



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lis COKKELATION OF PHYSICAL FORCES.
