96 
POLITICAL ECONOMY 
the data from which he calculates at what 
output maximum gains can be reaped ; 
but, according to the exposition above, the 
comparisons which determine his action are 
comparisons of aggregates—of total gains at 
different outputs—not of margins, or, in other 
words, of the differences made to gains by 
small variations of output. This, however, 
is not an altogether correct account of the 
matter. The monopolist aims at an aggregate, 
a maximised revenue, but in order to attain 
it he can be guided, and is not unlikely to 
be guided, by the marginal effects of varia 
tions of his output on his net gains. He 
need not make his supply leap about 
bewilderingly in the hope of fortuitously 
hitting upon the one most favourable to his 
interests. On the contrary, if he is wise, 
he will decide on some output which seems 
to offer reasonable prospects of yielding a 
high monopoly revenue and then proceed 
scientifically by making small variations in it 
and watching their effect on his profits. When 
an effect is favourable he will naturally 
make another variation in the same direction 
and so on, but when it is otherwise he 
will retrace his steps. When monopoly 
revenue is the greatest possible, marginal 
costs equal what might be termed differential