104 POLITICAL ECONOMY 
might pay to sell a small quantity at a high 
price. 
It can be proved that differential charges 
can be arranged so as to benefit the public. 
Without them much less use would be got 
out of railways and there would be an immense 
loss of consumers’ surplus. Coal can be 
carried cheaply just because certain other 
things are carried only at high freight rates. 
Some services, indeed, could not be provided 
at all were differential charges not permitted. 
However, we must be careful to observe 
that the adoption with reference to anything 
of the discriminative system of fixing prices 
is by no means bound to prove beneficial to 
the community, and that public interests 
must consequently be watched with a jealous 
eye when it is introduced or revised. 
We must not run away with the idea that 
a monopolist has a perfectly free hand to 
fix any price or scale of prices that suits him 
best. He is ultimately dependent upon the 
goodwill of the public—or, at least, on the 
absence of an intense degree of ill-will. 
People can find more or less satisfactory 
substitutes for most things, and will be 
moved to do so if they think they are being 
robbed by extortionate charges. Moreover, 
the modern State has to make a legitimate