24

Irving Fishet—Mathematical investigations

( 6 )

S ^ ~ ^ ota ^ utility.

== Utility-value.

( 7 )

dA-A

dJJ‘ dAdXJdA

= Gain.

Assumption:

= Function of A only.

Corfollaries: From (1) and (2) and postulate, when B is ex-changed for A

dU _ JUd& • ° ~ dA •

From (3) and assumption, in the equation : ut. of

dA/at. of dB=n, the value of n is independentof the particular commodity and of its quantityM used in the definition.

CHAPTER II.

MECHANISM.

§ 1 -

Scarcely a writer on economics omits to make some comparisonbetween economics and mechanics. One speaks of a “ rough cor-respondence” between the play of “economic forces” and mechan-ical equilibrium. Another compares uniformity of price to the level-seeking of water. Another (Jevons) compares his law of exchangeto that of the lever. Another (Edgeworth) figures his economic“system” as that of connected lakes of various levels. Anothercompares society to a plastic mass such that a “ pressure ” in oneregion is dissipated in all “ directions.” In fact the economist bor-rows much of his vocabulary from mechanics. Instances are : Equi-librium, stability, elasticity, expansion, inflation, contraction, flow,efflux, force, pressure, resistance, reaction, distribution (price), levels,movement, friction.

The student of economics thinks in terms of mechanics far morethan geometry, and a mechanical illustration corresponds more fullyto his antecedent notions than a graphical one. Ye.t so far as I know,no one has undertaken a systematic representation in terms of me-chanical interaction of that beautiful and intricate equilibrium whichmanifests itself on the “ exchanges ” of a great city but of which thecauses and effects lie far outside.