30 ECONOMIC ESSAYS IN HONOR OF JOHN BATES CLARK 
gigs. 
2 a 
plantations of Cuba were effectively controlled with slight effort 
by introducing the Egyptian mongoose. A moderate expenditure 
of effort on a drainage canal may change the drainage system of 
a continent, transferring billions of tons of water, without further 
effort, from one ocean to another. The entire course of human 
history may likewise be changed by a shrewd diplomat who 
knows how to disturb the balance of power in the right way, and 
at the right time and place. However, it is not necessary to 
multiply illustrations, though thousands are available. 
Professor Marshall made a less general but more pointed use 
of the concept of a static state in his elaboration of the concept 
of an equilibrium of supply and demand, with the concept of an 
equilibrium price both as a result and a cause. The equilibrium 
price may be regarded as a cause in so far as it is a means of 
preserving the equilibrium of supply and demand, or in so far 
as the equilibrium may be disturbed by artificially changing the 
price. But the equilibrium, when thus disturbed, has a way of 
reasserting itself or, if it is to be continually disturbed, of requir- 
ing increasing effort, and the necessary effort increases in geo- 
metric ratio. If, for example, by some government decree or 
trade union rule, the price of a given commodity,—say a given 
kind of labor,—is raised above the equilibrium level (that is, 
above the level which will induce just as many men to seek 
employment as employers are willing to hire), the equilibrium is, 
of course, disturbed. But it tends to reassert itself, first, by 
tending to reduce the number of men whom employers are will- 
ing or able to hire, and, at the same time, tending to increase the 
number of laborers seeking employment in that particular kind 
of work. One of the first results of this disturbed equilibrium is 
unemployment,—more laborers seeking work in this kind of 
employment than can find it. This mass of unemployed laborers 
creates a long train of consequences which require increasingly 
drastic action on the part of the government or the trade union 
to overcome. Rather than remain unemployed, some of them 
1 A somewhat diverting but impractical illustration could be made out 
of Darwin’s famous correlation between the number of cats and the price 
of clover seed. If the number of cats could be decreased in any one of 
several easy ways, say by starting a fad for fox terriers, or by marrying 
off spinsters, the resulting increase of field mice would thin out bumble 
bees and this would prevent the spread of pollen and reduce the supply 
of clover seed, which in turn would raise its price. Thus one problem 
in agricultural price fixing would be solved without congressional action.