ELASTICITY OF SUPPLY AS A DETERMINANT OF DISTRIBUTION 93 
marginal productivity of X would rise greatly above the amount 
P; while that of Y would fall. But while this rise in the 
marginal productivity of X to, let us say, P» would cause a 
still further contraction in 
the supply of X, the fall 
in the productivity of Y 
would cause an equal de- 
crease in its quantity. The 
differences in marginal 
productivity would not, 
therefore, be further ac- 
centuated from what they 
were as the result of the 
initial change in quanti- 
ties arising from the ex- 
pansion of production. An 
equilibrium would result 
in which the return to X 
would be greater than P, 
and that of Y would be less; and the amount of the differences 
of the return of X and Y from P; would be greater than in Figure 
9, where we assumed 
elasticities of 0 and 1.0 
respectively. 
What would happen, 
however, were the nega- 
tive elasticity of X to be 
greater than the positive 
elasticity, namely —1.0 
as compared with 4.5 as 
is illustrated in Figure 12. 
Then the initial increase 
in effectiveness and in unit 
return to each would cause 
the supply of X to de- 
crease twice as fast rela- 
tively as that of Y in- 
creased. Its marginal productivity would consequently rise 
and that of Y would fall, but this would lead to twice as great 
a relative decrease in the quantity of X as it would in that 
y