178 ECONOMIC ESSAYS IN HONOR OF JOHN BATES CLARK 
3 to 4. The equation implies simply that the subjective desire for 
a dollar, or a dollar’s worth of food, will also be as 3 to 4. 
Equilibrium of Dollars Variously Spent 
I have used alternatively “a dollar or a dollar’s worth of food.” 
But this implies another assumption which must be explicitly 
specified, namely, that the want-for-one-more dollar is the same 
as the want-for-one-more dollar’s worth of food, and likewise as 
to one more dollar’s worth of housing, or of anything else. 
This is a familiar theorem in theoretical economics, resting on 
the idea that if, temporarily, there is any inequality between 
dollars in different uses, the family will speedily rectify it by 
spending more money in the direction where a dollar will bring 
more satisfaction than in other directions, until perfect equi- 
librium is established, whereupon one more dollar spent in any 
direction will bring exactly the same satisfaction as if spent in 
any other direction. Without such assumption of equilibrium, we 
would have not merely one uniform W; in Case 1, but many 
diverse W’s which we should have to distinguish as, say Wy, for 
a dollar’s worth of bread, W,” for a dollar’s worth of sugar, W," 
for a dollar’s worth of potatoes, etc., all differing slightly from 
each other. 
Strictly speaking such differences always do exist in some 
degree. But while there is never absolute equilibrium in this 
world, yet, for all practical purposes, I think we are safe in 
pinning our faith to this assumption of an approximate equi- 
librium of the want-for-one-more dollar’s worth of all com- 
modities and services, at least for all which are easily sub- 
divisible. 
The only exception to substantial equilibrium which is at all 
likely to trouble us in this statistical quest, is in respect to 
housing accommodation. Here the adjustments are so slow, that, 
with a rapid change in incomes or unequal changes in prices of 
foods, rents, ete., several months at least may be required before 
the tenants have had time to get their best money’s worth. It 
takes time to find the best bargains which the new situation has 
created, time to move into new quarters, time to get free of lease 
See my Mathematical Investigations, also Auspitz und Lieben, 
Untersuchungen iiber die Theorie des Preises, Leipzig (Dunkler & 
Humblot). 1889.